    [From the U.S. Government Printing Office, www.gpo.gov]

                                       A METHOD AND   SELECTED APPLICATION FOR
                                        USING AERIAL PHOTOS IN DELINEATING
                                        HISTORIC PATTERNS OF BEACH ACCRETION
                                        AND RETREAT

                                                                  SEP 1979

                      GB
                      458.8
                      .H83
                      1979

                                 A Method and Selected A pplicati n f    ng Aerial Photos
                              in Delineating Historic -Patterns of Beac!@@@tion and Retreat

                                                      Dennis H
                                            Coastal Zone Man      ekjt Project
                                           Urban and Region      nn i@Trograrn
            so                                     Universi     F74'

                                            This do           prepared for the
                                                            f Hawaii
                                    Departm       Plan      nd Economic Development

                                                           y the

                                            rb         gional Planning Program
                                                   University of Hawaii

                                    The preparation of this report was financed in part
                            through a Coastal Zone Management Program Implementation Grant
                                     from the United States Department of Commerce

                                                     September 1979

                                                      TABLE OF CONTENTS

                     INTRODUCTION  ..................................             ....................    I

                           General Problems Addressed    ..............        ......................     1

                           The Use of Aerial Photos in Monitorl                    Shoreline Changes.     3

                     METHODOLOGY

                           Determining Scale on a Photo..
                                                                                                          6
                                                                                  ...........
                           Beach  Index Lines  .............               ..........................    11
                           Calculating Beach Change    .....        @,& . ..........................     12

                     MEASURING SHORELINE CHANGES: ACCURACY        LI       IONS  ......................  13
                           Relief Displacement..:..                    .............................     13
                           Measurement Errors   ...               ...........................     : .... 16
                           Tilt ...................   o                                                . 16
                           Error in Computing Photog                                                     16
                           Summary of Error Analysis..          ..............................      .... 18

                     DISCUSSION .........                          ................................      22

                     RESULTS ........                 ............................................       28

                     CONCLUSION-               .. ............  o....... o  .........................    33

                     BIBLIOGR      ......       ....................   o.............  -    ............ 34

                     APPENDIX              ...........  o............  0-    ........................    39
                             4@

                                    A Method and Selected Application for Using Aerial Photos
                                  in Delineating Historic Patterns of Beach Accretion and Retreat

                                                           Dennis Hwang
                                                        University of Hawaii
                       INTRODUCTION                 General Problems Add

                             In Hawaii.' there is no single geomorphic        e which is more unstable than
                       the beach zone. Over periods of time rangin                y years to a f ew days, the
                       beach may be m        arkedly altered in i                    e, volume and other
                       characteristics. These changes may be ca          y nu         factors such as storms,
                       seasonal and long term variations in wave.       itions, re ctions in the rate of sand
                       production, increases in exposure d !          si@@
                                                             ue            of protecting headlands or reefs,
                       and human activity.

                             The constantly shifting sands_               have posed some    serious problems
                       with regard to coastal zone managern              problems are summarized below:

                                    Siting of New Beach Structures

                             1)     On some beach                      built on what were once
                                    back beach ar          isr     ing the potential for beach
                                    erosion.    Subseq            h retreat has      resulted in
                                    undermining of t            ructures. The houses built an
                                    Lanikai Beach on           are an example of this problem.
                                    Obviously         pot         for beach 'retreat must be
                                    co sider             tr   ures of any kind are built. The
                                    ro t o                   nt problem is determining how far
                                    in          sh          ures must be placed to be safe from
                                    na

                                    Re              ures to Save Present Structures from Beach

                                          a

                                                e of   'beach retreat relative to now-existing
                             2)
                                 _@ ME! u c t   the correci remedial policies are dependent on
                                    t h e s. c  f the problem. For example, if a well developed
                                    beac       i many buildings is threatened by erosion, then
                                      0      e  works or artificial beach maintenance may be
                                           d.   However, for a slowly retreating shoreline
                                          ning  a few old houses, no governmental action may-
                                    be -quired. In determining the best management policy, it
                                    should be realized that some remedial measures may make
                                    it unlikely that the beach will grow back, even if the
                                    conditions that led to its retreat are changed. Therefore,
                                    it would be useful to know if a particular beach has a
                                    historic record of continuous erosioni or cyclic accretion
                                          at

                                    and retreat.

                      A Method and Selected A pplication for Using Aerial Photos
                      in Delineating Historic Patterns of Beach Accretion and Retreat

                                                               -2-

                                   Regulation of Sand Mining

                            3)     The removal of sand from backbeach areas within the reach
                                   of uncommon storm waves or tsunamis should be prohibited
                                   because beach retreat may result if sand from the littoral
                                   cell is transferred to the removal sitg,      In defining the
                                   boundaries to which sand mining              prohibited, the
                                   possibility of beach erosion must            ecognized. The
                                   problem in this policy area is deter        the inland extent
                                   of prohibitive sand removal.

                                   Acquisition of Land for Public B       ar

                            4)     In acquiring beach front and           lands for public beach
                                   parks. the potential for be       r      must be considered.
                                   For example, if a plot of       e      ing 100 feet from the
                                   shoreline is needed, it w             ttle use to acquire just
                                   the 100 feet if the shor              retreating 10 feet per
                                   year especially if the plot             ed by private lands
                                   subject to future development          permanent structures
                                   within the next few        @1-111P     ).
                                   Extent-of Private      r s i 001@11-5

                            5)     M any of the boundar         een public and private portions
                                   of the beach are               defined by the debris line,
                                   vegetation 1*        iff      sea-level lines. Since beaches
                                   are so uns           use     any of these boundaries means
                                   that the                    private property is constantly
                                   changin                   assess land values for taxation
                                   purl:              e    cessary to periodically resurvey an
                                   area.       a      riate time interval for resurvey would
                                   depe             tability of the beach in question.

                           In any            iv       agement problems mentioned, the best effective
                     decisions m                on  the magnitude of beach instability. Therefore, it is--
                     extremely         tan       ave information on beach areas likely to prograde or
                     retreat a       I as       about the trends, ranges and rates of long term beach
                     change.

                            Al               ave been several studies in the past dealing with the beaches
                     of Hawaii,'           actually very little information concerning long term beach
                     variations. M o       and Chamberlain (1964) describe characteristics of 112 beach
                     sites for the seven major Hawaiian islands. This comprehensive report is the major
                     source of information concerning seasonal beach changes. However, the short
                     period of field work conducted in this study precluded a description of long term
                     beach trends.

                          A Method and Selected Application for Using Aerial Photos
                          in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                         -3-

                                  Campbell (1972) provided additional information on beach erosion for 33
                          selected beach sites. Resurveys were conducted to compare with the data of
                          Moberly and Chamberlain. While- most study sites showed insignificant changes in
                          the volume of beach sand, a few areas did display net accretion or erosion. For
                          Hawaiian beaches, this work provides the most information on the magnitude of
                          long term changes. However, the ten year observation period may have been
                          insuf f icient to define the ranges and trends in past S          *ne positions. .

                                  The Army Corps of Engineers in 1971 co                    available information from
                          previous studies to define 54 circum-Hawaila                        hich are critically eroding.
                          In the report the     description of beach chan                          qualitative and served
                          mainly to identify existing erosion hazard                               ntitative data can be
                          found in many of       the Army Corps of En              S indivi       case reports on beach
                          erosion. A recent study by the Corps in I               ckdes survey data from 1967 to 1970
                          for Barking Sands.'   Hanalei Bay and Kek                    i; Haleiwa. Kailua and Sunset on
                          Oahu,- Kaanapali on Maui and Papoha                        kai. In this study surveys were
                          conducted over 6 month intervals at                        original LM oberly and Chamberlain
                          survey ranges.

                                  No study has yet- provided concise info            on on the magnitude of long term
                          beach change for more than a f                         Ir-urvey methods are very accurate in
                          determining short term beac                             use in monitoring historic shoreline
                          movements repeatedly encou                 on         us problem: a lack of- past surveys
                          through which beach changes        .       e,     pared. Past measurements of the beach
                          may be scarce because the need              01'lzl@them was not recognized at the time.

                                  Accurate surveys            me         ian beaches may exist for only a ten-year
                          span. Extrapolating d                5 of     ch change beyond this time interval can be
                          difficult. For exam           u             e in 1962,: 1963 and 1972 may indicate that a
                          particular beach is          ve              Does this mean that beach structures with a
                          30 year life span           ea      ay e built free from the threat of beach retreat?

                                  The Use       e              raphs, in Monitoring Historic Shoreline Changes

                                  On                    t  e survey method, which forms the basis of this report,
                          lies in          lizati        aerial photographs. By crosstime comparison of aerial
                          photos.'         st an       sent shoreline positions can be defined and perhaps future
                          change        icted. -

                                  T                of  photo comparison to monitor shoreline changes has been
                          successf ully         yed for many sections of the United States. In the earliest
                          studies,' descri     ns of beach change were mostly qualitative and utilized oblique
                          as well as vertical photographs (Howard, 1939; Dietz. 1947; Shepard, 1950). The
                          emphasis on vertical photographs gradually increased as their versatility allowed
                          qualitative and quantitative. descriptions of coastal morphologic changes (Tanner,
                          196111 Athearn.' 19630, El Ashry and Wanless. 1965; Cameron. 1965a; Cameron, 1965b;
                          El Ashry and Wanless, 1967; El Ashry and Wanless,@ 1968).

                    A Method and Selected Application for Using Aerial Photos
                    in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                -4-

                          In t.he last ten years, aerial photographs have been extensively used to collect
                    precise measurements on historic shoreline changes. Moffitt (1969) studied beach
                    erosion in Monterey Bay, California. by orienting reference points and shoreline
                    points on the photo into the State Plane Coordinate System. While this procedure
                    may give accurate results, its use is not required unless the absolute position of the
                    shoreline is needed.

                          Langfelder et. al. (1970) used aerial phot   ogr       to document beach changes
                    over a 30 year period for the North Carolina co             n this study, transects were
                    established every 1,000 feet and distances fr                   reference points to the
                    shoreline were measured.

                          Beach erosion of the Georgia barrier            system w     documented over a 30
                    year period using methods similar to L      n       r   ertel, 1973). Shoreline changes
                    at Sargent Beach, Texas, were reveale             5      of topographic maps and aerial
                    photographs (Seelig and Sorensen, 197            u     on beach instability in Pamlico
                    Sound, North Carolinai were based on                  aerial photographs over a 33 year
                    period (Stirewalt and Ingram, 1974).    FIS           eegan define procedures for using
                    transects, on photographs for a study of    b e         ion on Rhode Island (in Tanner.
                    1978). For the state of Hawaii, an air photo           ey on past shoreline movements
                    was conducted for Kailua Beach P

                          Past studies indicate t           ri      otographs are an excellent tool to
                    document historic shoreline                    ir use in the coastal zone is especially
                    advantageous for several re ons.             eral., imagery of the Hawaiian coastline
                    has been obtained more fr uent               he past 30 years than maps, charts on
                    surveys have been ma                0,         photographs provide an efficient and
                    economical means of c                   s ce information can be obtained without the
                    expense of costly sur         r           Ily. an aerial photograph records an almost
                    infinite amount of                       opposed to maps and charts which contain
                    selected detail subj       h       interpretation (Stafford and Langfelder, 1970).

                          The use of ae              raphs to collect beach instability data is not without
                    its drawbacks.                       photograph may record conditions which are not
                    typical of me             ons.   or example, strong winds may cause unusually high
                    waves giving                 arrow   appearance. This problem is somewhat. alleviated
                    by the f a        at p       raphs   are obtained only on clear days suitable           for
                    photograp        nother      lern is distinguishing on a photograph between long term
                    beach c          and         term changes due to seasonal fluctuations and storms.
                    Ideally,'         to      s  taken at the same time of the year should be used.
                    Unf ortuna               not always possible as the quality, quantity and periods of
                    photo covera           or each beach. Problems also exist in the photo resolution as
                    well as erro s inh    nt in the image itself. It is clear that these problems must be
                    resolved before the  photographs can be effectively used in this study. The methods
                    used to reduce or    eliminate these problems and to estimate their magnitude are
                    outlined in later sections of this report.

                          A M ethod and Selected A p      .plication for Using Aerial Photos
                          in Delineating Historic Patterns of Beach Accretion and Retreat
       1b                                                                  -5-

                          METHODOLOGY

                                 The first phase of this project was determining the aerial photographs which
                          were available for study. This was an important part of the project because the
                          periods of time coverage and the type of imagery available are sometimes
                          determined by what exists.

                                 Photographic inventories were conducted for                  iles of the R.M. Towill Co.,
                          Air Survey Hawaii, Hawad Institute of Geophysi                     d Army Corps of Engineers.
                          An investigation of potentially useful aerial ph                   hs Was made for the United
                          States Geological Survey, United States Air                            ct and Geodetic Survey,
                          National Ocean, Survey,* Bishop Museum, Stat                 i            brary Hawaii.
                                 Once the inventory of the available               og  aphS Was completed, flight lines
                          of a particular beach were ordered for d*              e       ars. When possible, photographs
                          taken at the same time of the year we                le       to minimize the affects of short
                          term seasonal changes.

                                 In the first prototype study of K                       flight lines for 1949, 1963, 197L
                          1975'  and 1978 were provided by the                         ent of Planning and          Economic
                          Development. These photogra                        used     ong with a 1957 Army Corps of
                          Engineers flight line. The set                            ed in scale f rom about        1:2,400 to
                          1:4.800 and were used to es                             racies involved in measurements at
                          different scales.

                                 An important part of     Ithis s         ncerned determining the best time interval
                          between photographic fli          lines.        ously, increasing the number of monitoring
                          flight lines would docu               ch       ges more accurately. Beaches which have a
                          history of reversing                          etion or erosion require more continuous
                          monitoring than a               W            e undergone stable unidirectional change.
                          Unfortunately, the             rs'         each types and their processes precludes a
                          predetermination            e         um   monitoring interval (Morton: in Tanner, 1978).
                          The optimum m                      rval would be the point when the value in labor and
                          money equals the v                  mation obtained from additional flight lines.

                                 I , t is              og    hs 'Were selected at roughly five year time            intervals.
                          The    x t                        depended on the imagery available. A f ive. year
                          obser ati        riod   s        allow documentation of significant long term beach
                          changes        e red            the affects of short term variability due to seasonal
                          change          a f          aches on Oahu. the observation period will have to be
                          increas                   ck of photo coverage.

                                 After sui        image@y was obtained. points along the beach were selected on
                          each photograph.       These points, which will be referred to as stable reference
                          points, must satisfy three requirements. First, stable reference points must have a
                          fixed ground position over the beach monitoring period. These points can then
                          serve as a marker by which beach changes can be measured against. Secondly, the

                       A Method -and Selected A pplication for Using Aerial Photos
                       in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                    -6-

                       points selected must be located as close to the beach as                    possible. Since
                       photographic scales are determined between stable reference points within close
                       proximity of the beach.: the variation of scale within a photograph due to tilt
                       becomes a significantly less important factor. Finally, the stable reference points
                       must have a minimum of ground elevation in order to reduce relief displacement
                       problems.

                             In general, the corners of single level.hous             re  used as stable reference
                       points. These structures tend to have clear disti             undaries which can be easily
                       distinguished on a photograph. After suitable                   es had been selected,: the
                       points on the photograph were sequentially num

                                                      Determining SC          kPhoto
                                                                              @L<Irequired because of the variable
                             A scale determination for each ph            p
                       flying height of an airplane along the               I'*,-- The scale of -each photograph is
                       determined by use of the following for

                             Photo Scale = Photo Distance       Photo Di          X Map Scale
                                             Ground Distan

                             Orthophoto maps produ                               Towill Company      were used to
                       determine the photographic sc            or,     lua Beach. These maps        are controlled
                       photo mosaics which have been                  d for tilt and scale variations along the
                       flight line. Orthophoto maps all               y accurate measurements of the ground
                       distance between stable           ence.        s. An example is given to illustrate this
                       point.

                             It is generally           t          stric-el limit -in accuracy to which the human
                       eye can consisteAl           te      in  on a photo oi map is .01 inch (Tanner 1978).
                       Since measuring              C       res locating two points,: an error of up to b2 inch
                       can be expecte                     y using precise measuring scales and a ten times
                       magnifying glass,' t                  measuring error     is about .005 of--aft-inch-(-T-able
                       #1). This figur          e u        a working number      throughout the remainder of this
                       report.

                             on           ophot       p@: at a scale of I  in.   200 fut a measurement error        of
                       .005 of           repr         a ground distance    error of I foot. The. average distance
                       betw n            refe       points used 1n@this -study   is approximately 5 inches on the
                       orth    0                  0 feet on   the gr  'ound. T   'aking the rneasuring errors into
                       consideratio            und  distance  between the    two stable reference points is 1,    '000
                       + I foot.

                             Therefore,' using the orthophoto ---maps        as ground control allows a          very
                       accurate scale determination f o*r each photograph. Unfortunately,; orthophoto           maps
                       -have not been compiled for all sections of the Oahu coastline and for some beachesi
                       the coverage is'partial or non-existent.

                          A M etho'd and Selected A pplication f or Using A erial- Photos
                          in Delineating Historic Patterns of- Beach Accretion and Retreat

                                                                            -7-

                                 For beaches with partial       orthophoto coverage, ground control can be extended
                          by using the 60% overlap of the photos. In this procedure; a flight line is selected
                          with the least amount of tilt and scale variations. This is determined by comparing
                          the relative positions of selected points on adjacent overlapping photos (Fig. #1).
                          After a suitable flight line is selected, ground control is extended by successive
                          measurements on adjacent photographs (Fig. #2). In this method,: the errors
                          accumulate for each photograph in which cont I                          en
                                                                                      ro         t ded. However@ in later
                          sections of this report it is -shown that this proce                   ields more than acceptable
                          error levels.

                                               Table #I-An Evaluation of M_              em

                                 Five students measured the dista                     between well defined points, To
                          prevent biasing,' none of the measurem                   b   "*,en the same,points were made
                          consecutively. All results were conceal                         students.

                                 Student-#                        Distance                            Distance #2

                                 #1                                                                   2.407 in.
                                                                                                      2.405 in.

                                 #2                                                                   2.412 in.
                                                                                                      2.412 in.

                                 #3                               2.6                                 2.408 in.
                                                                  2.68                                .2.410 in.
                                 #4                                      in.                          2.4,12'in'
                                                                  2.   7 in.                          2.410 in.

                                 #5                               2.689 in.                           2.410 in.
                                                                  2.688 in.                           2.410 in.

                                                                  X    2.687                          X    2.410

                                As        9 that,         mean    value of   the   measurements       approaches the correct
                          distan            ma             error  between    any   of the twenty measurements is .005
                          inch.                      ative estimate, this value is established as the limit' in
                          measureme                cy@
                                On beach           ithobt orthophoto -coverage, the 'only alternative for: ground
                          control would b    'e field measurements. In,this case,t a few. ground distances could be
                          measured and the control extended to all sections of the beach by photographic
                          measurements. This method             Nould yield    accurate results      and reduce the time of
                          field work considerably..

                                      A Method and Selected Applications for Using Aerial Photos
                                      in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                                                                                                                                                                                      4-3

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                           Fig. #2-0  On beaches with partial     orthophoto coverage, the ground.control can be
                                                            ween  pt. 3 and..pt. 4 is   known,-then scales can be de
                                      If the distance bet
                                      for photos B and C. This will allow the distances between pts. 2 and 3
                                      pts. 4 and 5 to be determined. Scales for photos A and D can then be c

                      A M ethod and Selec" ted A pplication f or Using A erial Photos
                      in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                 _10-

                                                          Beach Index Lines

                          After the photographic scales have been calculated, the distance between
                      stable reference points and a beach index line is measured for all photographs.
                      There are three index lines on the beach which can be used to represent actual
                      beach location (Fig. #3). Previous aerial photographni studies of beach areas have
                      used the vegetation line,' high water line and watE;*         . Each has its advantages
                          -disadvantages.
                      and

                          The vegetation line., marked by the se                      it of existing perennial
                      vegetation,' is an indicator of the highest annua                   ox, 19.78). This index
                      line is especially useful because of its. clear          on         tograph. In addition,
                      the position of the vegetation line would ref         ong ter     each changes while th;
                      affects of seasonal variations would be mini

                          The use of the vegetation line is no          0     s problems. The position of this
                      line on eroding beaches would chang                    dily than on accreting beaches.
                      However* a five year monitoring inter                 flow the vegetation to reach some
                      degree @f equilibrium with an accretin                   Another problem in using the
                      vegetation line is that human activity or wl             n sand may after its position.
                      Generally,'. these modifications                        on a photograph by 'the highly
                      irregular appearance of the ve                       e  beaches, the vegetation may be
                      located on the top of a berm            ay          lief displacement problems. In some
                      limited areas,' the vegetation lin             exist because of manmade structures or
                      unusual beach features.

                          The high water mark           tingu       on the photograph as a line separating dry
                      sand from moist sand. I             e po     n of the high water line is not af fected by
                      tidal f luctuations beca.                 ords the extent of highest wave runup during
                      high tide. However,          0            s sands, the high water line may not exist
                      (Rib' 1957). If the         w       in is present: its position is highly variable and
                      dei;ndent on the           n      tors: 1) the ex@ent of wave runup; 2) atmospheric
                      conditions related               ion; 4) the location of the ground water table; 5) the
                      elevation of the     re            water level (Weber- 1969). Probably the greatest
                      problem in usi           ig       r mark is distinguis@ing between wet and dry sands
                      on a photogra

                          The t        ndex         which may be used to document beach change             is the
                      water lin        a pho      ph the position of this line depends on the degree of light
                      penetra           he         the extent of wave runup, and the tide level at the time
                      of the p                  beaches which have high tidal ranges and gentle slopes, the
                      Water line rn           laced significantly between high. and low, tides.

                          Using the prototype. study of Kallua Beach as an example, the displacement of
                      the water line caused by tidal changes can be calculated. For Oahu, an average of
                      eight different tide stations yields a mean diurnal tide range of about 1.9 feet'(Tide
                      Tables,* U.S.  Dept.    of Commerce;     1973).  The diurnal range is defined as -the

                 710% Ift M                  M No M M M                                                            M M M M

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                                              77

                                                                                                         Fig. 3. Beach Index Lines
                                                                                                                   (Adapted from, Weber, 1970)

                      A Method and Selected Application for Using Aerial Photos--
                      in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                  -12-

                      elevation difference between mean higher high water and mean lower low water.
                      For some. sections of Kailua Beach,' the slope is approximately 1:15 (Noda,:* 1977).
                      Using these figures,' a displacement of the water line of up to 28.5 feet may result
                      from tidal changes alone. For thi's reason,@ some aerial photographic studies have
                      made tidal corrections when using the water line (Moffitt, 1969). However; the use
                      of any constant tidal correction factor for a beach with varying slopes introduces
                      further inaccuracies (Langfelder et. al., 1968). In        tIA: tudy; no tidal corrections
                      were made.

                           Another problem in using the water mar                     tinguishing the line on a
                      photograph. Poor contrasts exists between                           nd land'. because the
                      wavelengths of the light spectrum that black                           r9matic film record
                      are characteristically reflected by land and w            eber.

                           For this , study,@ two beach index li            r     ed. It is believed that the
                      vegetation line provides the most inform            c      ning long term beach changes.
                      Distinguishing the vegetation line on a           9      is easier and thus more accurate
                      than any of the other two lines. The                      the water line is    also used to
                      collect beach instability data. In order                  line ef f ectively@ : it is important
                      to know how tidal, fluctuations may affect i               on. The position   -of the  ' water
                      line is also sensitive to long term           rt term     anges, in the beach profile. This
                      must be fully realized in order t                        long term changes which are in
                      reality only short term changes.                       beach where the vegetation line is
                      missing or the water line is unde         a       gap will be left in the data.

                                                        alcu a        ach Change

                           On each photogra                    C - between stable reference points and the
                      beach index lines is m         d.           tographic distance multiplied by the scale of
                      the photograph gives         ro,          ce between the reference point and the index
                      lines at the time o         to      y. The change in ground position for beach index
                      lines can then be                  successive monitoring intervals. The net change in
                      position for each o                 riod,- divided by the monitoring time interval gives
                      an incremental r         C           the beach location.

                           The incr                 of change computed for any observation period assume
                      that the tr        nd  ra      f change were constant, for the beach section under
                      study. If        r of         assumptions is incorrect,@. then the calculated rates of
                      change wj        d to        derestimated. For.example,@ Suppose ten feet of beach
                      erosion                      two photographs over a five year time lapse. Then the
                      incremental               the beach position would be -2 ft./year. However,* if the
                      beach accreted           the first three years 12 ft. anderoded in the next two years
                      22 f t.' then the tru  rat6s  of change are +4.0   ,fi./year for'the first three years and
                      -11 ft./year for the   next two years. Thus., the estimated rate of change has been
                      underestimated by assuming the beach underwent constant unidirectional change.

                     A Method and Selected Application for Using Aerial Photos
                     in Delineating Historic Patterns of Beach Accretion and Retreat

                                                               -13-

                          The five year monitoring interval selected in this study should be sufficiently
                     frequent to determine long term beach trends; to calculate rates of change, and
                     perhaps for predicting future rates of change. However,: the limitations inherent in
                     calculating rates of change from net shoreline movements should be realized
                     (Morton: in Tanner,' 1978).

                     MEASURING SHORELINE CHANGES: ACCURACY                          ATIONS

                          Whenever data on shoreline changes is prese                measurements should be
                     accompanied with a statement on the probable                        racy.  In this report;
                     the magnitude of these limits is estimated              e t          ferent situations in
                     which ground control may be obtained:                    orthop     o coverage; partial
                     orthophoto coverage@ and field measurem               Zh                                  w
                                                                              e computations which follo
                                                                             fikhe prototype study for Kailua.
                     employ the specifications of the photogra           e
                     Beach.

                          According to Scherz (1974), th                    nd ranges of errors in using
                     photogrammetic materials are listed in decre                r:

                                       1) Relief Dis lac                      terrain)

                                       2) M easure en         rs          ith technique)

                                       3) Paper Shrinkag                         0 to .5%

                                       4) Tilt      :                            0 to .3%

                                       5) Fil                                    0 to .1

                                       6) L       is     n                       0 to.1%

                                       7)              al Plane Flatness         0 to .-01%

                                                re       ilm Shrinkage           0 to .005%

                           For t         udy,       th item should be added to the list. The error in
                     determini           cale      photograph may be an important factor in limiting the
                     accuracy            t       gy.

                           Of  the n         rs  listed" only relief displacement; tilt,; measurement errors
                     and photog   a. hic    ale  erro@ are Included -    'in the 'accuracy analysis.      Paper
                     shrinkage and film shrinkage are not important factors since a scale is determined
                     for each photograph. Lens distortion, differential film shrinkage and       lack  of  focal
                     plane flatness are insignificant when compared to other possible errors..
                                                   m P

                         A Method and Selected Application for Using Aerial Photos
                         in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                          -14-

                                                                 Relief Displacement

                               The displacement of an objett on a photograph due to its relief is shown on
                         Fig. A. At sea level there is no relief' so one might think that relief displacement
                         problems are not a factor in measurin@ shoreline changes. However, the position of
                         a beach index line is usually measured relative to tructures having elevations
                         considerably greater than sea level (Tanner, 1978).

                               The magnitude of relief displacement is give                    e following formula:

                                     m = rh                               M Off itt

                               where m           the displacement on the                graph o        e top relative to the
                                                 base
                                     h           height of the object
                                     H           altitude of the plane
                                     r           radial distance fro                    nter to the image        of the ground
                                                 point

                               The value of the parameters used in the fo                ing computations are:

                                  H    5.'000 ft.           (Th                        the 1949 f light line f or
                                                            Kai         ac

                                  r    10 in.               (The               f the photographs allowed all
                                                            stable!          ence points to be selected
                                                                  in 10       es of the photo center. The
                                                                   f-the     otographs are 27 x 27 inches)

                                  h    25 ft.                              the    estimated       dif f erence     in
                                                                  ation between the stable reference
                                                                 nts and the water line)

                                          T        le             ment of the object is then;
                                                           M     (10 inJ (25 ft.) .05 in.
                                                                  5. 000 ft.

                               The         graph*         le for   the 1949 flight      line is approximately I in.            200
                         feet. T              'in      nd distance    due to relief     displacement on the photo would
                         then.be    t                is horizontal.    displacement     may be misinterpreted as beach
                         erosion or acc

                              Relief displacements, on a          photograph     are'the    most serious photogrammetric
                         error in this study. Even by selecting single level buildings and staying as close to
                         the photographic centeras possible,' an error of up to ten feet may still result when
                         measuring distances to the water line. Fortunately,: relief distortion problems                       are
                         less serious     for measurements to          the   vegetation       line.  On   Kailua Beachi        the

                A Method and Selected -A@pplicatio'ns for' UsingIAerial Photos
                 in Delineating Historic. Patterns of Beach Accretion and Retreat

                                                         -15-

                                                  Relief Displacement       m   r--- r'

       Ib

                                                          P,
                                                                                             Sec, It-el

                      @,@igr     @,.Relief displacement 6n''.-a'@hotograp@,-@t4offitt,1967).-

                      A Method and Selected Application for Using Aerial Photos
                      in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                  -16-

                      elevation 'difference,' parameter h,; is about 15 feet between stable reference points
                      and the vegetation line. This elevation would result in a relief displacement. error
                      of 6 f eet.

                           One additional factor may alleviate the problems of -relief distortion. Any
                      relief displacement on a photograph can be divided * to components parallel and
                      perpendicular to the shoreline. When measuring dis              s to a particular part of
                      the beach.: the perpendicular components are the               detrimental. On the 1949
                      photographs for Kailua Beach,' the maximum          rn        perpendicular to the beach
                      is 9 inches. Substituting 'this value into para                 ts in a distance error to
                      the vegetation line of 5 feet.

                           The component of relief displacemen               Bel. to       shoreline is a more
                      serious problem when computing photogra              c,! e
                                                                            ,krs. This factor is considered in
                                            0
                      section #4 of the err r analysis.                    @@M@
                                                        M easure        E

                              The distance between any two                 the photograph can be measured to
                      an accuracy of about .005 of an inch ab              On'the 1949 flight line of Kailua'
                      Beach,: at a scale of I in. = 200     ft., this me      ment error represents a ground
                      distance error of -I foot.

                              Generally. tilts on a ph                of up to 30 may result from weather
                      conditionsi pilot errors.' etc. (Sche         4). Figure #5 shows the geometry of a
                      vertical photograph and             gra       h a 30 tilt. The ground distance between
                      AB measured from the                 otog, p is .3% off compared with          the correct
                      distance computed fro                     otograph.

                         For the 1949 fli        ne,      ailua Beach, the average distance between stable
                      reference points                  ation line is about one inch. The effect of a .3% tilt
                      error on the compu                istance is:

                                                           -F Orn tilt     X       .3%
                                                                         .1.00 in.
                                                    distance
                                     N

                                                              X   .003 in

                         At              a       cale of I   in. = 200 f t.,  the change in     ground distance
                      resulting                 on the photo is .6 feet. Thus,1 photographs     with a 30 tilt or
                      less may be us           curate measurements of the beach.

                         A f ew of    the  photographs used    in this study, were   excessivley tilted.  In   this
                      case,7 accurate     measurements are still possible             provided several scale
                      determinations are made perpendicula,    r to the beach for each photograph.

                         A Method and Selected Application for Using Aerial Photo5
                         in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                       -17-

                                                  Error in Computing Photographic Scales

                                 In order to convert photographic distances to ground distances,' an accurate
                         sale determination is needed for each photograph. The scale of a photograph can
                         be found by use of the following formula:

                                                         Scale = Photo Distance
                                                                 Ground Distance

                               The photo distance measured between an                        ints may be in error f rom
                         two major sources. The actual measurement                                  005 inch (Table #I).
                         This would be the only error if afl the points               e
                                                                                                I ph were at their true
                         ground positions. However. relief displace                f  stabl     derence points relative
                         to the vegetation line ma@ contribute an                Mal error of .03 inch (section #1).
                         This value is a maximum estimate for t                         (a) not all the components of
                         relief displacement is parallel to the               Ii     nd W the two stable reference
                         points selected for each scale determi                     located   'sufficiently close so that
                         in all cases the relief - dispiacements                  r negligable or compensating. The
                         combined effects of both. errors result       in             m error in the measured photo
                         distance of .035 inch.
                               In the section of this pa                         nation of Scaleill it was shown that
                         the ground distance could be              ure          accuracy of I foot from orthophoto
                         maps. The effect of this erro              t       ale accuracy can be computed using the
                         194 9 flight line of Kailua Beach                 ple.

                               Suppose the photo             ce          red is 5.00 � .035 inches and the ground
                         distance is 1,1000.1 1 f               ex      ed scale of the. photo. if no errors were
                         involved is.
                                       Scale            0           0 x 10-3 in./ft.   I in. or
                                                            f t.                     200 ft.

                                                                  I in. = 200 ft.,

                              The ef                  stimated errors on the       scale can be computed by. taking
                         partial der*      es o         cale formula.
                                                           V            .035         3.50 x 10-5 in./ft
                                                           G           1,:000 fto
                                   dS                   (1.-00 in.) G ft.)           5.0 x 10-6 in./f t.
                                   FG                     (1,:000 ft.),6

                                   Combining     the two error values     and adding them to the expected scale of
                         the photo results in the following change.
                                   (5.00 x 10 .3. in./f t. (4.00 x 10-5 in./ft.)   5oO4O X+ 10-3 in./f t.
                                                        I in./198 ft. or'I in.'= 198 ft.

                                                                                                                                                                  >
                   aJ/ If:.  f= 8.25   in.                                            b) For- a                     h a 30 ti I t:
                                                                                                 lotograph wit
                             Z= 5,000 ft.                                                   f- 8 5 in.                                                          (D Q
                                                                                            Z=5,000   @ft.
                             ap= pb   = 3.33in.
                                                                                                                                                                  0
                                                                                                21.9T
                        then;         tarf'. (3.33/8.25      21.98                                                                                                a
                                                                                                18.9e
                               AB=1 2        21.).98    i=5,000 ft.)                                                                                              M
                                  =403                                                     A    24.980                                                          orq
                                                                                           AN= (5000   ft.) (tan 18.99)=.      1.719.6   ft.
                                                                                                                                                                  (D
                                                                                           NB=' (5000  ft.) (tan 24.9T)=       2,329.4,ft.
                                                                                           AB= AN     NB= 4,049.0 ft.                                           0.,+

                                                                                                                                                                  >

                                                                                                                                                                0 0

                                                                                                                          b

                                                                                                                                                                >
                                                                                                                                                           00
                                             0C
                                                                                                                      Oro
                                                                                                                                                                  >
                                                                                                  Of

                                                                                                                                                                (D0

                             A
                                                                                                                          bL

                                          Fig. 5.  Tilt on a photograph.        For the vertical     photograph, the computed       distance between
                                            AB i's 4036.2 feet. - On a photograph with a 3"tilt, this distance is computed as 4,049.0
                                            feet.  The error 'is 02.8/4036.0 (100)= ..3%.
                                                                                (Adapted from Scherz,1974)

                      A Method and Selected Application for Using Aerial Photos
                      in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                  -19-

                                The range in scale resulting from the estimated errors is Lin.              200 4- 2
                      feet. Sifice the distance between stable reference points and the vegetation fine
                      averages I inch on the photo,: the scale error results in a ground distance error of 2
                      f eet.

                                                      Summary of Error An ly

                                Table #2 summarizes the estimated er                  ich may result from using
                      orthophoto maps as ground control for the                          1978 flight lines. The
                      procedures used for estimating the errors on                           aphs were similar to
                      those outlined in this report.

                                The total sum of errors for the             li   'lines appear at the bottom of
                      the table. These figures are most likel                    stimation because any of the
                      errors may be accumulating or compe                        may range f rom zero to their
                      maximum estimated limits. For this r                    robable error has been calculated
                      and appears below the total error figure

                                The probable error is estimat         by m      g three assumptions. -Firsti@ the
                      errors are assumed to follow a                            al error distribution. This is a
                      reasonable assumption because                          ve a f inite variance and seem,' to
                      the first approximation, to be              m      ts.  Secondly, it is assumed that the
                      maximum estimated errors are        t            d deviations away from the mean error
                      values. As a result; about 95%      of          errors are within the interval defined by
                      plus or minus the maximum estima               ror. This is believed to be a conservative
                      estimate. Finally, it is as          that      errors are uncorrelated or independent of
                      each other. This req                           sfied for relief displacemen      *t. tilt and
                      measurement errors bu                       raphic scale errors. In this study,: the total
                      probable error is ap            a          ssuming the photographic scale error is an
                      independent deviatio

                                Based on                 e assumptions.: the total probable error can be
                      computed to a 95       co            nterval by summing the squares of the individual
                      error compone                t       69). When comparing beach changes on the 1949
                      and 1978 f lig                 limit in accuracy can be computed by the procedures
                      shown at the        m 6           #2. In this case, the limit is about 11 feet.

                                S      the.  s@     or  the six f light lines used in     this. study varies from
                      1:2,400 A                    Cc'uracy in comparing any two         of the flight lines also
                      changes..                   otype study of Kailua Beack           the maximum error in
                      comparing any              the data points is about 12 feet. The procedures used in
                      estimating this fig     are similar to those outlined. on Table #2.

                                For beaches   which have partial orthophoto coveragei the ground control is
                      extended by successive measurements on adjacent overlapping photographs (Fig.
                      #2). In the first test study for Kail     'ua Beack   this procedure was used to        extend
                      ground control from    the  middle -portions. of. the beach to both ends.      Scales  for all

                            J,

                    A Method and Selected Application for Using Aerial Photos
                    in Delineating Historic Patterns of Beach Accretion and Retreat

                                                           -20-

                    photographs were then determined. Distances between selected points on the
                    photograohs were converted to ground distances and compared with field
                    measurements. This comparison was made only for points at opposite ends of the
                    beach. Since ground control was extended,-  the accuracy of measurements at the
                    end portions of the beach would be dependent on those in between.

                            Table #3 shows the results of the accura         t. The maximum error is
                    1.1% for all the measurements made. It is clear         extending control by this
                    method can yield very accurate results provided        raphs with the least amount
                    of tilt are used. As mentioned previously,- t              raphs are selected by
                    comparing the relative positions of common                    t over apping photos
                    (Fig. #1).

                            For this   study  of Kailua Bea        t.               involved in using
                    photographs with   extended ground co               photographs with orthophoto
                    coverage are assumed to be about equ        er    e, on photographs with extended
                    ground control.' the maximum error for            d beach change is about 12 feet.

                                           -z'

                       A Method and Selected Application for Using Aerial Photos
                       in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                 -21-

                                 TABLE #2 - Summary of Errors for the 1949 and 1978 F1ight Lines
                                                       Using Orthophoto Maps

                             The 1978 photographs were taken at a flying height of 6,000 feet with a 6 inch
                       focal length camera and enlarged to a scale of 1:4,800.

                                                                    1949        1978

                                    Relief displacement             5.4          8.0
                                    Measurement Errors              1.0          2.0
                                    Tilt                            0.6          0.6
                                    Photograph Scale Errors         2.0          3.1

                                         Total Error                9.0         13.7

                             Calculating the probable error to a 95 confidence interval by use of the
                       following formula:
                                             02 tot = 021 + 022 +023 + 024(Bevington, 1969)

                                             where o = the standard deviation of the errors involved.

                       Assume:

                                             2o1 = 5.4              2ol = 8.0
                                             2o2 = 1.0              2o2 = 2.0
                                             2o3 = 0.6              2o3 = 0.6
                                             2o4 = 2.0              204 = 3.1

                                                 otot = o21 + o22 + o23 + o24

                       Otot=  (2.7)2+(0.5)2+(0.3)2+(1.0)2  Otot= (4.0)2+(1.0)2+(0.3)2+(1.6)2

                                               otot = 2.9        otot = 4.4
                                              2otot = 5 8       2otot = 8.8

                             The limit in accuracy for comparing beach change is:

                                          2o/1949-1978/=        (5.8)2 + (8.8)2
                                          2o/1949-1978/= 10.5

                           A Method and Selected Application for Using Aerial Photos
                           in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                                -22-

                                                  TABLE #3- A Comparison of Field Measurements
                                            With Ground Distances Computed from Aerial Photographs

                                 Measurements #1 and #2 were taken near Kailua Beach Park. Measurements
                           #3 and #4 were taken at the north end of the beach. The maximum error is 1.1% for'
                           all measurements made
                                                                                                Z@,? mb@,

                                 M easurement                 Aerial Photograph                                  % Error

                                       #1                              159 ft.                  158                0.6%

                                       #2                              538 ft.                    4 4 ft.          1.1

                                       #3                              78 f t.                   78 f t.           0.0%

                                       #4                              537 f t.                 542 f t.           0.9%

                       A M ethod and Selected A pplication f or Using A erial Photos
                       in Delineating Historic Pattern, of Beach Accretion and Retreat

                                                                     -23-

                       DISCUSSION

                             Fifteen transects were established perpendicular to Kailua Beach at
                       approximately 4000 ft. intervals. The exact spacing was dependent on the stable
                       reference points available. The location of these transects is shown on a map for
                       Kailua Beach (Fig. #6).

                             On each transect,- the distance from stable r               ce points to the water line
                       and vegetation line was measured over the 3                     r observation period. For
                       transects #1 and #2,: data was available only for                  eight years due to a lack
                       of suitable reference points.

                             For the Ka     ilua Beach Park areW                 ct #13        the map, additional
                       photographs were provided by the Army Co               f                            0     1:
                                                                                Wineers for 1959,- 1961i 1962: 1966
                       and 1970. This historic data was combi                 ff e six flight lines used in this
                       study to draw cumulative movement cur                r      vegetation and water lines (Fig.
                       V). On the diagram       : the results are                ith a previous aerial photographic.
                       study for Kailua Beach Park (Noda.' 19 -                   ximum deviation between any of
                       the data points for the two curves on                         line is about 14 feet. These
                       deviations are. due to the errors inherent i                  methods involved as well as
                       different interpretations on the                          of  the land-water boundary on a
                       photograph. Even with the de                              the two curves show the same
                       historic trends in the position o           at      e.

                             The exact location of the      w            is dependent on seasonal and long         term
                       changes in the beach profile.        Th           a better indication of long term beach
                       trends is the position of t         etati        e. When the cumulative movement curve
                       for the vegetation line               red        the two water line curves, a very strong
                       coincidence is shown                         major differences (Fig. #7). For the period
                       f rom 1963 to 1966,- th        c             he water line was +45 feet while that for the
                       vegetation line       s       ee      e cumulative curves also deviate in the indicated
                       range in beach c                    he water line curve, the apparent long term range is
                       approximately 15                   he vegetation line indicates a historic range of about
                       134 f eet.
                             Genera                    line and vegetation, line can be used to determine past
                       long t r            prov       he seasonal   'fluctuations are small in relation to the 1ong
                       term               For          ailua Beach Park area, this requirement is satisfied.
                       However         some          ns of Kailua Beach where -the long term changes are
                       relative            t       parent trends from the water line and vegetation line are
                       quite dif f                ). From the diagram,: the vegetation line appears relatively
                       stable except             period from 1957 to 1963. Information obtained on the'water
                       line shows a cons       rbly different trend. the net changes in this line are greater
                       than 24 feet   for all  observation periods from 1949 to 1975. Only for the time from
                       1975 to 1978   does the position of the water line indicate any degree of stability.
                       Since the location of the water line is affected by seasonal fluctuations of the
                       beacN' the description of long term beach trends in this report is based           primarily on
                       vegetation line dala.

                      A Method and Selected Application for Using Aerial Photos
                      in Delineating Hi5toric Patterns of Beach Accretion and Retreat

                                                              -24-

                           Historic shoreline movement curves for     each transect are drawn from six
                      photogr@phic flight lines,*' except for the Kailua Beach Park area.: where eleven
                      flight lines are used. A comparison of cumulative movement curves based on six
                      and eleven data points reveals the problems in determining historic trends from
                      alimited time sample of the beach (Fig. #9). The curves for the eleven observation
                      points document beach changes more accurately. I this example; the total range
                      in shoreline movement has been underestimated            sing only six flight lines.
                      However,' the six monitoring points do define al         ificant trends in long term
                      beach change. Also, using eleven data points is         twice as expensive and time
                      consuming as six. When all factors are conside             ms that for Kailua Beach.'
                      an approximate five year monitoring inter                       a good compromise
                      between economy. and accuracy of results.

                                                                                                                                                    OAHU

                                                                                                                                                         13

                                                                                                                                                                14
                                                                                                               A

                       2

                                                                                                                                          12
                            3
                                                                        KAI LUA            BEACH

                                             4
                                                                                                                      10
                                                          5

                                                                                              8
                                                                                     7
                                                                                                                                      SCALE: 1 inch  950 feet

                                      Fig. #6. The location of the transects established at Kailua Beach.
                                                                                                                                                @O A H @U-

                                                           -'(i nfeet)
                                                    Change

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                                                                      Change (in          feet)

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                          A Method and Selected Application for Using              Aerial Photos
                          in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                            -28-

                          RESULTS

                                  Table #4 summarizes the historic changes in the                  position of th    e vegetation
                          line for the fifteen transects. From the data,                  t several interesting trends are
                          apparent. Within the total littoral cell known as Kailua Beach are three distinct
                          units or subcells. Although the sand transport processes in any of the subcells is
                          dependent on the oithers,t each unit seems to behave as'---parate entity.

                                  For the period from 1949 to 1957,i Kailua                       grew throughout its entire
                          length except for       'the middle portion between                      s #7 and #9. During the
                                                                                    i
                                                                                      0
                          monitoring interval from 1957 to 1963,i           accret                      evalent 'With especially
                                                                                   t- -
                          high growth in the middle section of the beach.

                                  It is not obvious why the middle port'                f Kailua Beach      changed the way it
                          did for these two observation periods. H                      r,@,,@en the two monitoring intervals
                          are combined,i and net changes compute                     m    _  to 1963,- all transects show the
                          beach growth to be more regular. Thi                          it
                                                                                        w, te an important clue to the beach
                          processes operating at that time. Sin                           photograph represents only a spot
                          observation,' it may be possible that                              photographs recorded unstable
                          conditions for the central part of the                             An examination. of the 1957
                          photographs does show the shore                               t  orientation abruptly -in this area.
                          During the monitoring interva4i                                   the middle portion of the beach
                          gre Iw about twice as much as                                 realign itself with other sections of
                          the shoreline.

                                  For. the next three observa                  eriods,1 from 1963 to 1978,, an interesting
                          pattern of beach change                early          from the data. While one end of Kailua
                          Beach is accreting,! the                  d is I    eating. The middle sections tend to remain
                          relatively stable. Thl                           also supported by the historic ranges in the
                          position of the veget                             es.

                                  During the              r        terval.  from 1963 to 1971,, the southeast of Kailua
                          Beach was in an a                      le while   the'opposite end retreated by as much as'40
                          feet. For the two o                       periods from 1971 to 1978,, the trend reversed,: and
                          resulted in si               er        at Kallua Beach Park while the Kaneohe end of the
                          littoral ce I                    ahl

                                  The        c tren          rosion and- accretion at opposite ends of Kailua Beach is
                          similar             seas          hanges on other Hawaiian beaches,; such as on Lumahi
                          Beach                (M        y  and Chamberlain,, 1963). This pattern indicates that sand
                          eroded   a                    he beach is transported to the opposite end. Therefore,i it
                          should   be re              at any structures designed to horde sand at one end of the
                          littoral cell may        rve all down drift sectionsof the beach.
                                  Any shifts in    the trend of beach change            reflect reversals in the      direction of
                          long term littoral transport.          Two    possibilities   are presented to account for these
                          reversals.

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                         A Method and Selected Application for Using Aerial Photo,
                         in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                         -30-

                                1) It has been suggested that the direction of littoral transport varies
                                seasonally for Kailua Beach (Noda; 1977). During the summer months,'
                                strong persistent trade wind waves tend to transport sand to the
                                northwest. In the winter,! sand transport may be to the northwest or
                                southeast depending on the interaction of trade wind waves with North
                                Pacific Swell. According to this concept,i the direction of long term
                                littoral transport would be to the south as -1@
                                                                                          A unusually strong or
                                persistent North Pacific Swell occurred ove                  i-yearly period.

                                2) It is also possible that a shift in the                   n of the trade winds
                                causes the reversals. Since the orienta                             Beach is almost
                                perpendicular to the northeast trade wi                e              f luctuations in
                                this wind system would have a pron                     af fe        the direction of
                                littoral drif t. If over a ten year       pe       the trade    winds blew from a
                                more easterly directon than us                   i      ay result   at'Kailua Beach
                                Park and accretion at the oppos*                       e littoral   cell. This trend
                                may be reversed if the trad                   d       w from a more northerly
                                direction i when averaged over a                    y period.
                                Accordin@ to Wentworth (1949),,                        winds shifted in       direction
                                from northeast to east and back         to no           over a period of - 40 years
                                (Fig. #10). If trade wind                             riodicity are the rule., then
                                beach changes at Kailua                              have a natural cycle of 40
                                years.

                                While the two hypothesis p                  have been mentioned separatelyl' they are
                         not mutually exclusive. For exam                 e long term direction of littoral drift may
                         be to the southeast for             e wi         ave activity accompanied with a northerly
                         shift in the trade winds

                                Since the litto         0               allua Beach are dependent on meteorological
                         factors,;* an accura         edki            beach changes would require a knowledge of
                         future weather c             n        He our ability to forecast trade wind directions or
                         North Pacific S                       is limited,: it should be realized that the historic
                         record for Kailua                     s a tendency towards cyclic erosion and accretion.
                         Therefore,' th            es         ccur in the future. This means that trees,, houses or
                         any other sr                   no   be placed on that portion of an accreting beach which
                         may retre           ny          later as part of the natural cycle. Unfortunately.: this
                         practice          t been        wed for several sections. of Kallua Beach. For example:

                                I           the       d  from 1949 to 1971 the vegetation in front of transect
                                                    128  feet. Within this time lnterval,i two rows of trees
                                were.             approximately 95 feet and 40. feet inland of the 1971
                                vegetati         e. Between 1971 and 1978,i the Vegetation retreated about
                                119 f eet to the position where the 1978 vegetation line was within ten
                                feet of its 1949 location. Needless to say,! many trees fell,in the water.

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                      A M ethod and Selected A pplication f or Using A erial:Photos
                      in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                -32-

                            2) From 1949 to' 1978,; the net change in the position of the vegetation
                            line for transect #8 was +44 feet. During this period a house was built
                            35 feet inland of the 1978 vegetation line. If the beach retreated to its
                            1949 positioni this house would be undermined.

                            3) Between transects #5 and #6,! the vegetation grew about 54 feet over
                            the 30 year observation period. Five houses            been built along this
                            stretch and are located from 47 to 40 f                ndward of the 1978
                            vegetation line.

                            4) Approximately 300 feet south of trans                   egetatio n grew 61
                            feet over the 30 year monitoring peri                        constructed at
                            this location about 32 feet inland of           8 veg      ion line. In fact
                            this.house is situated within-10 feet        he  1949 land-water boundary.
                            This is an especially precarious posj       S'    the house is located near
                            the end of the beach where changes        0      ter magnitude.
                            It cannot be predicted whether                n  of the -beach will retreat to its
                      1949  position. The cumulative movemen                or most of the transects show a
                      general increasing trend (Appendix A).                 1 the Kailua Beach Park area
                      showed a general increasing tre                   rs. until rapid erosion began without
                      any forewarning. Since our kn                       littoral cycles at Kailua Beach is
                      imperfect it would be wise to                      evelopment well inland of the most
                      withdrawn historic position o                  tation line,; as determined by aerial
                      photographs. If this practice     I          d,,, extensive property damage may be
                      avoided in the near future. For,;' t       oric record indicates that Kailua Beach is a
                      dynamic zone which will         inue        nge through natural cycles of erosion and
                      accretion.

                        A Method and Selected Application for Using Aerial Photos
                        in Delineating Historic Patterns of Beach Accretion and Retreat

                                                                      -33-

                        CONCLUSION

                              The use of aerial photographs to document historic shoreline changes is an
                        economical and time efficient method.1 Most of the work can be conducted in the
                        office,: except one field trip should be made to check or obtain ground control.
                        Even then,' the use of aerial photographs greatly reduces the amount of field
                        measurements because ground control can be accur                    extended by the methods
                        prescribed in this report. Another advantage in                    aerial photographs is that
                        imagery of the Haw aiiian coastline has been obtai              ore f requently in the past 30
                        years than maps.. charts or surveys have been c                      erhaps,: the lack of aerial
                        photographic studies for beaches on Hawaii                               d to the questionable
                        accuracy of the measurements made.

                              In this study,; a method is presented                 aximum estimated error of about
                        12 feet for measuring beach changes. Th               b       d to be an accurate estimate,-
                        as indicated by a comparison of field                        aphic measurements and by the
                        consistent distances obtained for ne                       of the beach in the Kailua pilot
                        study. While a 12 foot measUremen                        n may seem large, this f igure is
                        sufficiently accurate to meet the objedtiv                    project for two    reasons. First
                        any anomalous. measurements can. be checked                  se the almost infinite amount of
                        ground detail on a photo allows                           to be established. Secondly.' the
                        extreme ranges in long term                              ake any accuracy limitations less
                        critical. For examplei the min*             his        nge in the position of the vegetation
                        line for the Kailua Beach study                   while the maximum was 146 feet.

                              The methods described in       thi        rt were applied for a pilot study of Kailua
                        Beach. It was found that             tire         grew from 32 to 81 feet during the period
                        from 1949 to 1963. Due*                xt t   'e monitoring intervals, a pattern of erosion
                        at one end of the bea                         at the opposite end is clearly shown from the
                        data. From 1963 to I            e             of Kailua Beach grew by as much as 69 feet
                        while the Kaneo e            f        tor  I cell retreated up to 40 feet. The direction of
                        net littoral dr* t                  indicated from data for the next two observation
                        periodsi which s o                 t erosion at'Kailua Beach Park while the north end of
                        the beach grew         ide

                              Effecti                   t of the beach requires information about the long term
                        changes   to      x    c        this zone. To actually forecast beach changes may be
                        dif f icult          sibl       to a number of unpredictable variables such as storms or
                        long ter        ather         ions. However, by studying historic shoreline movements,:
                        a know              ai      f the trends; rates and ranges of change Which are possible
                        foe any   p               ach. These possible changes must be considered whenever
                        proper planni           isions are made.@ For example,- development on portions of
                        Kailua Beach in         process of an accreting cycle should be avoided because'.beach
                        retreat may result in the future as part of the 'normal sequence. This practice has
                        not been followed for several sections of the beach,, although the historic record
                        shows a definite cycle of erosion and accretion.

                    A Method and Selected Application for Using Aerial Photos
                    in Delineating Historic Patterns'of Beach Accretion and Retreat

                                                           -34-

                         When the time and cost of an aerial photographic study is weighed against the
                    wealth of information to be obtained,@ it is evident that this methc;d of beach
                    monitoring should be extended to ;ill sections of the coast. This report has shown
                    that aerial photographs may be used for a general reconnaissance as well as for
                    planning purposes and sedimentological studies.
                                                                         00
                    1.   Based on the Kallua Beach- Studyi: it has be       culated that each mile of
                         beach requires approximately 20 man hours a        .00 of photographs.

                                                        BIBLIOGRAPHY

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                     Bascom,W., 1960, "Beaches": Reprinted from Scientific American,     12p.

                     Bascom, W., 1964, Waves and Beaches: New York, Doubleday, 267 p.

                     Bevington, P.R., 1969, Data Reduction and Error Analysis for the Physical
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                     Cameron, H.L., 1965b, "Coastal Studies by Sequential Air Photography":
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                     Chamberlain, T., 1968, "The Littoral Sand  Budget, Hawaiian Islands":
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                     El-Ashry, M.T., and Wanlessq,H.R., 1968, "Photo 1nterpretation  of
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                        North Carolina State University, Raleigh, N.C.

                    Stafford, D.B. and Langfelder, J., 1970,"Air Photo Survey of Coastal
                        Erosion": Photogrammetric Engineering,. V. 37, No. 6, p.   565-575.

                    Stafford, D.B., 1972. "Coastal Engineering Applications of Aerial Remote
                        Sensing": In Proceedings of the 13th Coastal Engineering Conference.
                        American Society of Civil Engineers, Vancouver, B.C., p. 2045 - 2064.

                    Stafford D.B., Bruno, R.O., and Goldstein, H.M., 1973, "An Annotated
                        Bibliography of Aerial Remote Sensing in Coastal Engineering": U.S. Army
                        Corps of Engineers, misc. paper #2-73, 127 p.

                    Stirewalt, G.L., and Ingram, R.L., 1974, Aerial Photographic Study of
                        Shoreline Erosion  and Deposition, Pamfica Sound, North Carolina:
                        UNC-SG-74-09, 68 p.

                    Tanner, W.F., 1961, "Mainland Beach Changes due to Hurricane Donna":
                        Journal of Geophysocal Research, V. 66, No. 7, p. 2265-2266.

                    Tanner, W.F., (ed.), 1978, Standards for Measuring Shoreline Changes: A
                        Report of a Workshop.  Published jointly by Coastal Research and Dept. of
                        Geology, Florida State Univ., Tallahassee, Florida, 87 p.

                    Thompson, M.M., Eller, R.L., Radinski, W.A., and Speert, J.L., 1966,
                        Manual of Photogrammetry, Third Edition:  Menasha, George Banta Co., .536 p.

                    U.S. Army-Engineer District, 1977, "Detailed Project Report and Beach
                        Erosion Control and Environmental Statement, Kualoa Regional Park, Oahu,
                        Hawaii."

                    U.S. Army Engineer Division, 1971. "Hawaii Regional Inventory of the
                        National Shoreline Study":  Corps of Engineers, 110 p.

                    U.S. Army Engineer Division, 1975. "Observations of Selected Hawaiian
                        Beaches". Unpublished report.  Corps of Engineers, 43 p. + Appx. A.

                    U.S. Department of Commerce, 1972. Tide Tables - High. and Low Water
                        Predictions-  1973 - Central and Western  Pacific Ocean and Indian Ocean:
                        National Oceanic and Atmospheric Administration, 386 p.

                    Weber J.D., 1969, "Photographic Monitoring of Shoreline Movement": Shore
                         and Beach, V. 38, No. 1, p. 36-39.

                    Wentworth, C., 1949, "Directional Shift of Trade Winds at Honolulu":
                         Oacif ic ScienSe, V. 3, p. 86-88.

                    Wyrtki, K. and Meyers, G., 1975, "The Trade Wind Field Over the Pacific
                         Ocean - Part 1. The Mean Field and The Mean Annual Variation": HIG Rept.
                         75-1, 63 p.

                                                                LN

                                          Transect #1

             150

             100

             50

                                         Transect #2
        F
         4a,  100-
        Fr
         4-)

         cu

             50
         4J

         M                               Transe
         4j

         M
         C                                      oric     ge in vegetation line- 67 ft.
         0
        C
         cc                                           range in water line- 68 ft.
         a)  300

         4)

             250

             200

                           1950         1955'       1960        1965        1970        1975        1980

                                                         x   based  on Jdne,' 1979, -field measurements
                                                           -@.`Tncludes June,. 1 �79'", field' measurements

                                  Transect #4

                                  historic range   in vegetation line- 63 ft.
                                 -historic range   in water  line- 63 ft.:
               @300

                 250

                                                                        S@

                                                            7
                 200

           4J    150

               350
                                  Transect  #5

                                  historic  ra     in ve      ion line- 57   ft.
           4J                     historic  r         wat     ine- 79 ft.

           0   300.

               250

               200

               150
                                1950        '1955:        '1960         19.65         1970         1975.        198(

                                     Transect #6'

                                     historic range   in vegetation  line-  56 ft.
                  250                historic  range. in water  I i-ne- .69.  ft.;

                  100
             4J
             u

             4J

             Cn

             0.

             Oj

             to
             4-1
             ILA
                                     Tr

                                     his           e  in vegetation  line- 4.0 ft.
                                         or           in water*line- 73 ft'.,

                 350

                 300

                 250
                                  1950         1955         1960          .1965        1970:         1975

                                 Transect #6"

                                 historic range  in vegetation line- 52 ft.
                                 historic range  in water'line= 57 ft.'

                250

                200

                150

                                                 41m
                100

                                 Transe

                                 his             in egetation line- 54 ft.
                                 hi              in water line- 56 ft.

              300

              250

              200

                              1950         1955        1960        1965        1970-       1975

                                                 ransect #10

                                                 I         ange in vegetation line-   50 ft.
                                                                in water
                                                                          line-,65 ft.

                            300,-                                                    ------

                            250-

                   4J
                   (A

                            200                                               . . . . ...

                                            .1950        1955         1960         1965         1970         1975          1980

                                   Distance   along -th-e..-,transect.,(in,feet)
                                                                    J

                                                Pa            N)

                    CD            CD            C)

                                                                                   N

                   ko

                                                                                   4h

                  .01
                                                              Sam          X 4<
                                                                           0) (D
                                                                           C+ (a
                                                                           (D CD
                                                                             C+
                   CA                                                        0)
                                                                             C+

                                                                             0

                                                                             C+

                   Ln

                           7

                   00

                                                                                                                                             ICA

                                                  Distance along the transe'ct                   in   feet)

                          4t*-              4t:-                                 ul
                          C)                C"                 CD                Cn,
                          C)                CD                -CD                Cx

                                                                                                            sz-

                        CD

                                                                                                                 0
                                                                                                                 C+

                                                                                                      C+ to

                                                                                                          C+

                                                                                                          C+
                        CD
                                                                                                          0

                                                                                                      C+  Co
                        CA                                                                                Co

                        @4
                        C)

                        14
                        Ln

                        00
                        C)

                                                                                                                                                                                                                            4F

                                                                                                                                                                                                A
                                                                             Distance                along,the                   trans'ect               (.in       f eet,)--.,,--.,

                                                                                                           cn                                                                Cn
                                          Cl                               CD                              C)

                                        Ln
                                        CD

                                                                                                                                                                                                     LA
                                                                                                                                                                                                     rt-
                                                                                                                                                                                                     0           Ln
                                                                                                                                                                                                     -1          m

                                                                                                                                                                                                     0           C+

                                        ko
                                        Cil

                                                                                                                                                                                             m       CID

                                                                                                                                                                                                     m
                          CL                                                                                                                                                                 C+      U3
                                                                                                                                                                                             fD      M
                                                                                                                                                                                                     C+
                                                                                                                                                                                                     0)
                                        CD                                                                                                                                                           C+

                                                                                                                                                                                             kO      M

                                                                                                                                                                                                     Co

                                                                                                                                                                                                     C+

                                        CD

                           CD

                                        kc

                                        Ul

                                        to
                                        00

                                              Distance     along    the   transect     (in    f.eet)

                                                             cm
                          U1               CD                                                   UI
                          CD               C)                C)                 C)              CD

                     U1                                                                                                =r =r
                     CD                                                                                                           -S

                                                                                                                       C+ C+
                                                                                                                       0 0        W               I
                                                                                                                           -S     CD
                                                                                                                                  0
                                                                                                                                  C+

                                                                                                                                  =4=

                                                                                                                                  4@b
                     Ln
                                                                                                                       (D CD

                                                                                                                       :E  <

                                                                                                                       C+ U3

                                                                                                                           C+
                     CYI                                                                                                   0) .   -
                                                                                                                           C+

                                                                                                                           0
                                                                                                                       CD  :3

                                                                                                                       14
                                                                                                                       CO  (D

                     %0
                     ON
                     U1                                                                                                    4:b
                                                                                                                           ON

                     Ln

                     to                                                       (D  0)
                     co                                                           :3
                     C)
                                                                              (D
                                                                              0
                                                                              C+
                                                                                  C+
                                                                              0   (D

                                                          :Distance          al6ng       the     transect          (in         (!t)

                                                                                                                                4-b
                                                        C>                       Ul                     C)                      Cn
                                .Cl                     C)                       C)                     C)                      C),

                           C>

                                                                                                                                                                   V)   tA
                                                                                                                                                                   C+   C+
                                                                                                                                                                   0    0

                                                                                                                                                                   0    0         Ct

                           Ul                                                                                                                                      Ao   m
                                                                                                                                                                   M    M

                                                                                                                                                                   M    CD
                           ON.
                           C)
                                                                                                                                                                        Ci.

                                                                                                                                                                   Co
                                                                                                                                                                   CO   CD

                                                                                                                                                                   C+

                                                                                                                                                                        CD

                           %0

                           CD

                           00                                                                                                                                         ------
                           C)

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