[From the U.S. Government Printing Office, www.gpo.gov]
LANOD0N~~~L ~~~~~~~~~~~~~~~~~~~~~~NU ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~'Il f PIOeYD LAfl b1eid0 a guidance publication of the Waccamaw Regional Planning and Development Council EiiTMEN? OF COMMERCE NOAA " B 'SAL SERVICES CENTER /234 SOUTH HOBSON AVENUE ,so hAFl'ESTON SC 29405-2413 5-, � Property of CSC Library I~ - Waccamaw Regional Planning and Development Council Georgetown, South Carolina Leslie Mclver, Chairman Kenneth C. "Ken" Thompson, Executive Director William J. "Bill" Schwartzkopf, Director of Planning Larry Schwartz, Project Director Georgetown County Alfred B. "Al" Schooler, County Administrator Horry County John Hatchell, County Administrator Williamsburg County Alex Chatman, County Supervisor Roy Mann Associates, Inc. Landscape Architects and Environmental Planners Museum Wharf, Boston, Massachusetts The preparation of this report was made possible through a grant from the U.S. Environmental Protection, Agency under Section 208 of the Federal Water Pollution Control Act of 1972, as Amended (Public Law 92- 500) and with the support of George- town, Horry, and Williamsburg Counties April, 4982 contens Introduction 2 The region and its problems in brief What the handbook covers Objectives that can be reached by using this handbook From Rain to Run-off to the Sea 5 The landscape and its natural processes Development and its effects on natural drainage Problems and Solutions 13 Principles for improved drainage Agricultural lands Residential areas Shopping centers and other large developments Shore areas Conclusions 42 Glossary 44 For Further Assistance 44 Suggested Reading 45 Acknowledgments 45 and credits introdusction Farmers, developers, homeowners, roadbuilders, and county officials are all concerned with the problems of how land drains. Because the topography of the region is flat the region and its problems in brief and low, and because soils in many areas do not readily absorb rainfall, rainwater often remains ponded on the surface or overflows drainageways, causing crop and property damage and health and safety hazards to the region's people. * On the farm, practices that lead to erosion of field soil and poor ditch design can also worsen existing drainage conditions by silting in drainage systems and causing them to back up and overflow. * Within residential areas ditching has long been used to help speed rainfall away from homesites, as is the case with farmland, but most standard ditches ' L--i-- _---�assr~r_ cannot cure the problems of flat homesites on .... poorly drained soils, especially where high water tables exist. * At shopping centers and other large develop- Drainage problems in Georgetown, Horry, and Williams- ments, parking and other hard surfaces force the burg Counties present many constraints to farming, home shedding of water too quickly into municipal drain- building, and commercial development. Results from the age systems or onto streets, overloading them as Waccamaw Regional Planning and Development Coun- well. cil's Section 208 Nationwide Urban Runoff Program have shown overland water drainage from farm fields, residen- tial areas, and commercial development carries pollu- * In shore areas, too, the natural capabilities of the tants into downstream wetlands, estuaries, and ocean land to absorb rainfall are often ignored with pave- beach surf. Problems of drainage, flooding, erosion, and ments and roofs funnelling runoff onto beaches, water pollution affect both the inland areas of the three- eroding the beach and beauty of the Grand county region and the shoreline of the Grand Strand. Strand's shoreline. 2 To dispose of excess water and improve soil drainage so and gradient conditions. The techniques proposed can be that the land surface can be developed, swales, ditches, effective in dealing with pollution problems and the fre- and canals have been excavated in order to channel pre- quently occurring rainfalls of low and moderate intensity. cipitation more rapidly away from farm, residential, or Of course, wetlands and high water table lands on which other desirable lands. In some cases, ditches are dug development cannot occur without environmental deep enough to artificially lower the water table and thus damage should be left alone. And too, good basic land render the soil above the table better drained and more design cannot cure all drainage problems. usable. Fortunately, there are techniques available to help im- But more rapid removal of surface runoff at the local level prove drainage for many lands within the region, tech- and he geate quntites o watr rmove thrughprove drainage for many lands within the region, tech- and the greater quantities of water removed through niques that may also help reduce flow impacts on down- water table lowering mean a greater flow intensity and stream areas as well as improve drainage characteristics impact on downstream ditches, canals, drainage systems, on flat lands in various conditions. and elsewhere in the area or county. The faster it is that water flows from high elevations, the more intense are the flow impacts on downstream points within areawide drainage systems. When more water objectives that can be attained by reaches an outlet point at the downstream edge of any using this handbook drainage area than can be accommodated by the outlet drainage area than can be accommodated by the outlet The targets that can be reached through use of this handi- within a given time period, the drainageways upstream of book to benefit homeowne rs, developers, farmers, com- the outlet will back up and overflow, causing surface m eria property owners, and the general public are: flooding on low-lying lands. ~~mercial property owners, and the general public are: flooding on low-lying lands. �Improvement of water quality Because of the flatness of the land, many a resident of Improvement of water quality towns, subdivisions, and other communities of the region � Better management of on-site drainage has experienced flooded floors, lawns, streets, and farm- a Reduction of erosion and sedimentation lands year in and year out, where drainage systems are in- Reduction of downstream floding capable of overcoming the deficiencies of topography and soils. � Enhancement of aesthetic appearance * Reduction of private and public expenditures on drainage and water quality improvements * Protection of wildlife habitat and the environment what the handbook covers in general The techniques proposed in this handbook will not solve the next few pages... most flooding problems caused by severe storm runoff. Nor An understanding of the natural processes at work in the are they intended to salvage lands that, due to poor soils, region is an important first step towards learning to high water table, or insufficient gradient, are inherently un- manage storm drainage through improved land design. suitable for development. But they can help improve drain- age conditions for many sites of average soils, water table, A turn of the page is all you need to start I ] , , I 1-1 . RI I 11 .1 II 1 , from rain to runoff to the sea landscape and its natural processes .... :! E . An understanding of the processes by which precipitation moves across and through the land to the sea helps reveal many answers to better storm water management. The drawings on the next two pages show how area-wide drainage patterns occur in coastal Carolina. topography (landform) experienced where the landform is too flat, soils are imper- meable or heavy, a high water table prevails, and drain- Unlike the Piedmont region below which it lies, the coastal meable or havy, a h igh water table prevails, and drain- plain is characterized by low flatlands interrupted only oc- age systems have insufficient capacities. casionally by shallow rolling landforms never exceeding Infiltration, or percolation, is the process by which precipi- 75 feet above mean sea level. Along the coastline lowation moves downward through the upper soil layers. tation moves downward through the upper soil layers. When water reaches the zone of water saturation (the hydrology er rns) "water table") or an impermeable layer of hardpan, it moves toward ditches, streams, or other drainageways Swamps and marshes edge the lower river reaches and which lie at lower elevations. When the entire upper soil estuarine waters of the region, while the water table found layers become saturated, as during flood, or where pav- beneath even the better drained lands does not exceed ing or other impervious layers cover the land, rainfall will four to five feet in most areas. Many areas are shallower run off the surface as overland flow ("storm runoff"). During than these. Near the coast, the influences of high tide and the initial moments of intense rainfalls, also, water carrying surging sea levels during storms act to worsen inland flood- pollutants will shed over land surfaces without infiltrating, ing as river and stream flows are impeded and the drain- particularly where soils are bare of restraining vegetation, ageways that feed into them are backed up. Even when and transport pollutants to rivers, downstream wetlands, sea levels are low, flooding and standing water are often and to the beach surf. 6C F12<09~T g aA'raL 9L.,4 PpUL4srzlhE N1UeIK4SO 6 soils Well drained soils yield better building, roadway, and Soils within the Wccmw region are generally sandy in drainageway sites because of better percolation and nature, varying from poorly drained to well-drained drainage. However, where both poorly and well drained nature, varying from poorly drained to well-drained, depending on elevation and amounts of clay. One type of soils exist in proximity, it may be preferable to locate build- depending on elevation and amounts of clay. One type of igrawyaddangwy vrtepol clay commonly found in the region is gumbo. Within the ings, roadways, and drainageways over the poorly drained soils, if foundation conditions allow, and to allow poorly drained lowlying marsh and riverine areas, erodeddriesolffuntonodtosalwndoalw poorly drained lowlying marsh and riverine areas, eroded for a larger infiltration area where the soils are better silts, clays, and fine organic matter are found carried by drained. water flow from elsewhere within the region. Percolation is often poor where clay is abundant in soil. Standing water is Appropriate measures should be taken when considering common where a saturated layer of clay (claypan) exists use of on-site sewage disposal units near less permeable beneath surface soils. Within the higher elevated and agri- soils or over a high water table. cultural areas, sandy loams exist that contain concentra- Because drainage ditches and adjacent areas are sus- tions of clay and fertile organic matter. Along the dune ceptible to erosion, proper side slopes, spoil disposal, and and beach areas coarser, highly permeable and well drainageway gradients must be designed to minimize soil ~~~drained sands exist. ~erosion, maximize infiltration, and decrease runoff and siltation. C ( & i </' ~ a : ' !:!:!::::~~.:.:..-..':'......'."....'. ^,<21L$7~~~~~~~ ~~~~~~ ........A~ . .. ... . . . . . . . . . . . . A ~L~~~~~~~~~~~~~~~...........~.[:I,"-I-r1lM:4' Z_...--� PlFt~-.4r ~T,.... ~~~~~?.A..r.,..., (...l Slelels v N>LL \g\ - onu.s ~1~ ~ �~ 11,,41�11..TI~-4~TiO N4~~~~~~~~~~~~~~~~~~~~~~~....... G64S9Jb7119 V10\/M 1>1E41 ZOZ4- 0r: '~;4TL1 1TL* 2ATUa~olc Hpl;fiS�4 H0A'eF~.;Fq I4/K3C ~-~i' Afa, r,~ ~V >wo",~I H~.r ale'~-F~~- vegetation Vegetation impedes surface flow. Where soils can accept infiltration, vegetation can cut down the quantity and velocity of surface runoff and diminish erosion resulting from rain impact. Debris from vegetation can also clog ditches and reduce effective drainageway capacities, but fine-textured growth, such as mown lawn grasses and other ground-hugging covers, can preserve high drain- ageway capacities while moderately increasing friction in the ditch, swale, or ground surface, resulting in a degree of moderation in the rate of runoff and on impact on down- stream flooding. ~~~~~~~~~~~/ / ~ / 8 development and its effect on natural drainage Residential development laid out in gridiron patterns with flat homesites and straightline ditching causes the rapid Changing land use within Horry, Williamsburg, and Georgewn cundthi Hoverretyea h ams anad- flow of runoff from rooftops, homesites, and impervious Georgetown counties over recent years has had an ad- paved surfaces to surcharge downstream drainageways. verse effect on drainage within the region. Farm fields, Residential development imposed on the land without areas developed for housing, shopping centers, commer- respect to natural drainage patterns causes flooding, cial properties, and industrial areas have been developed erosion, sedimentation, and destruction to private, public, in many instances without due regard to off-site drainage and ecolo call imeortant natural areas. impacts, or even to drainage effects on the site itself. g y Commercial land uses, such as shopping centers and in- Parking areas, paved roads, rooftops, and compaction of Cmeca aduesc ssopn etr n n Parking areas, paved roads, rooftops, and compaction of dustrial properties, also contribute to a speeding up of the soil coupled with raised water tables resulting from septic rates of runoff that would exist in the natural landscape. tank drain field installation, clearing of vegetation from This is so because these areas are surfaced with imper- larg arasand limnaton o drinaeway duingde-This is so because these areas are surfaced with imper- large areas, and elimination of drainageways during de- vious paving designed to carry water quickly and effec- velopment all have created highly increased runoff. If tively away from customer access, parking, loading, and these effects continue, existing drainage facilities will oter aes, a lading, and other areas, as well as the buildings, other structures, and become increasingly overburdened and unable to becomhinrasndgl overburdunablefo valuable open lands on the property. In achieving this legi- ~~~~~~handle runoff. ~timate drainage objective, however, large volumes are In order to improve drainage throughout the three-county carried rapidly into public ditches and streams. region, the U.S. Soil Conservation Service (SCS) has pro- Shoreline development is the major cause of dune de- posed a regional drainage network consisting of main struction and beach erosion along the Grand Strand. Sand canals and lateral drainageways that would be dug dunes and the natural areas directly inland that absorb along natural drainage paths to improve the flow of runoff and retain stormwater help protect inland areas from the in each watershed. brunt of major storms. These natural features, however, Improvement of local drainage techniques, however, have been replaced by seawalls and other hard vertical guided by better land design, needs to be adopted by in- surfaces that cause erosion and narrowing of the beach dividual property owners and users, step by step with any face. The rapid flow of runoff from impervious surfaces of improvements in area-wide or county drainage systems, if pool decks, roadways, parking lots, rooftops, and other im- the latter systems are to work effectively. pervious surfaces, and drainpipes causes extensive erosion to the beach face, embankments, and pavement edges. Agricultural land drainage is one system that alters natural runoff for legitimate reasons, but increases the rate of runoff and volumes in public ditches and canals. Where The following diagrams show how "not so good" and poor farming practices are allowed, however, the runoff "good" local land design can affect area-wide drainage problem is compounded with field erosion - carrying in agricultural, residential, and commercial situations. away soil, pesticides, and fertilizers - which can pollute and silt in drainageways, estuarine marshes, and boating channels. 9 a comparison of agricultural area roadside ditch systems s o, :typical layout improved design . Bare fields promote erosion of soil causing sedimen- Cover crops reduce runoff rate, erosion, and pollu- to the environment. drai nageways. ~~~ocaessAutn10� ypical layout Iimproved design t o the environment. drainageways. a comparison of residential land design layouts -~~~~~~~~~~~~~~~~~~~~~~,,4 , 0- " typical layout improved design * Ungraded flat land leaves homes and other � Land graded into mounds and swales allows buildingsclosetoelevationsofsurfaceflow. buildings to perch higher above the water table. * Straight-line swales and ditches carry water away Curving swales take more water and release it more from homes and farms but are limited in infiltration gradually to downstream drainageways. capacity. * Detention ponds release water more gradually over � Head drainageways often short-cut across weirs, setatcalculated heights. topography, resulting in too rapid a runoff rate, * Vegetation softens rain impact, decreases overland further surcharging downstream drainageways and flow, and allows for absorption. causing them to overflow. * Cleared vegetation does not allow for rainfall inter- ception, increases runoff rate, and does not allow for absorption of rainfall. a comparison of commercial land design layouts ______ H I&H ......__ --+r'IT yh _ _ f typical layout improved design * Impervious rooftops and paved surfaces shed runoff * Roof ponding, porous paving, and uncurbed off-site with high intensity. median strips help to reduce the rate and amount � Escaping runoff overloads municipal storm drains or of runoff. flows across street surfaces to damage other � Perimeter drainage retains runoff on-site while property or beaches. detention ponds slowly release water to an off-site outlet. 12 Impervios rooftopsand pavedsurfaces sed runoff Roof ponin~g, porou I~Epavng adunure off-ste wih hig intesitymedia strps el t rdue fthraendmot * Ecain rnof velodsmuicipal stor driso ouof f lowsacros stret surace odmg ohr*Prmee riaerean uof nst hl property ~ oril beces eenin od solyrlas atrt a ffst problems & solutions principles for improved drainage As we have seen, there are right and wrong ways of con- trolling drainage. The techniques proposed in this hand- book are based on simple principles that are by no means new. They have been and are being used in coastal Caro- lina, though not as widely as they ought to be. To properly control drainage the following principles should be applied to land design. problems and solutions : ~2 :. ~ provide curves in swales and other on-site drainageways so that runoff will travel longer and at a lower gradient � .&;*~. ...........:";~~ 7before reaching outlet points, following landforms wherever possible. design and modify landform to create high and low /~~~~~~~~~ points in advance of building construction to create higher an l ..... elevations for houses and other valuable property areas, and lower elevations for broad swales, ponds and other drainageways. maintain absorptive surfaces while planning develop- ment wisely by leaving as much of the absorbent surfaces as lawn, garden, or natural areas. 14 use porous paving instead of impervious paving particu- larly where parking areas are extensive, in conjunction with well-graded planted median strips. lit r I' /2' ~~~'' If these simple principles are followed by homeowners, site planners, designers and others, it is very likely that an im- provement in local drainage can be achieved. The tech- design and maintain ditches to last with a minimum of niques presented on the following pages are the specific ditch wall erosion and sedimentation. action steps that can be taken to reach this objective. 15 . . ''N* N N N V K' W N N " *' " ' N N N N' 'h"'" N**N *.'.'. N' *NN . N 'a N N Nj N-"' N N ' N agricultural lands Poor farm practices, lack of adequate ditch design, and improper ditch maintenance have caused erosion, sedi- mentation, and flooding to occur on farm fields, adjacent drainageways, and downstream points. To reduce these adverse effects and the impact of pollution on down- stream wetlands and estuaries, improved management measures need to be adopted. These can be found on the following pages. the problems ...., ""In agricultural areas, roadside ditches are sometimes silted in as the result of steep wall ditch design, which allows crumbling of erodible soils. Two other typical prob- lems are the mounding of ditch and canal excavation ~~blii' �a ~ spoil too close to the drainageways, a negligent practice which allows rainfall to wash the spoil right back into the B " ~channel, and farm equipment turns too close to roadside ditch edges, which can result in direct assault on the ditch ,,~,~4 ~'~' iff~ � ~~crest. Another contribution to the sedimentation of ditches has , ~been the practice of some of leaving farm fields bare of '~" ~.I !~ ~ cover between cash crops. Unprotected fields are easily > -; '~ ' ~'~ ~ ~". eroded by strong rainfalls since there is no foliage to absorb impact and decrease the flow rate of stormwater ~.~ �%,~,,~ ~-::runoff. Without the restraining action of crops or other '.~, ~ .~cover vegetation, great amounts of topsoil, fertilizer, and .~ . ~ :~.~;. - ~pesticides can be carried away and seriously impact stream, wetland, and coastal environments. ',' , : When ditches and drainageways fill in because of these " . 'poor practices, the potential for back-up and flooding of crops increases, often resulting in significant dollar losses. ,, -Filled in ditches also mean higher county, municipal, and private maintenance costs. ,,. : o i ~the solutions Many improvements to faulty drainage ditch design can be found. Many problems of poor design and mainten- ance can be overcome if the following procedures are followed. ditch design Drainageways should ensure efficient roadside flow by proper vertical placement of ditches, culverts, and pipe inverts. Elevations should be set by a qualified professional to avoid local blockages and overflow. 18 Proper ditch design will make sure that agricultural land is well drained. * Side slopes of sandy unstable soil should be cut at 45%. In areas where clayey soil exists, 60% is ac- 4 ,, , - ceptable. - * Equipment should be carefully selected - a V- bucket for ditches three feet or less in width and a , - - - ' dragline for larger ditches. � Grasses, such as tight-growing Bahia, Bermuda, and Common Lespedeza should be planted on ditch bottoms, slopes, and adjacent areas to stabilize , soil and restrict weed growth. spoil disposal drainage ditch design Material excavated from drainageways should be han- dled properly. If it cannot be spread over the land, it should be piled as far from the ditch as possible. ; D The location of spoil should be set back from ditch edges to prevent it from washing back into the ditch and reduce excess weight on the ditch wall, Open spacing should be provided between piles for drainage. * Mounds should be seeded with suitable grasses after excavation to provide spoil stabilization. _ improved field practices Ditch sedimentation can be reduced by eliminating soil ' ->" erosion resulting from poor field practices. . � Crops such as barley, oats, rye, or winter wheat should be planted during periods when fields are otherwise left without vegetative cover, . * A planted buffer between the ditch edge and turn- - ing border should be left undisturbed to prevent equipment damage to the ditch. spoil mound placement and seeding . Detention ponds should be excavated at suitable low points to detain and retard stormwater runoff and for livestock watering. : Weirs at pond outlets should be sized and located to ensure that outflow to downstream drainageways is managed at the lowest discharge rate possible with- out causing flooding from the pond. maintenance In order to maintain their runoff carrying capacity and reduce flooding, routine maintenance should be per- formed on all ditches. . Plant debris and other matter that can obstruct .,_.,/.~,~.~:: , ., ,.,, ,~,,~, water flow should be cleaned from ditches and disposed of so that they will not re-enter the drainageway. * The stability of ditch walls and spoil mounds should Adequate setback of turnarounds from ditch edges is essential. A buffer of be checked. thick grasses can reduce erosion. poil should be seeded with recoin- ~~~~ 0~~~~~~ Exposed spolsol esee ihrcm mended grasses. � " farm pond, Williamsburg County 20 residential areas Poor site conditions on flat lands and poorly designed stormwater control methods in residential areas have led to flooding of on-site housing as well as lands in down- stream areas. Early in the site planning process, problems of excessively flat topography and stormwater control need to be addressed and appropriate land design measures selected to improve drainage, reduce flood- ing, and enhance land values. Solutions for achieving these goals through improved land design can be found on the following pages. the problems poor site design Residential areas and subdivisions have often been laid out in gridiron patterns with flat homesites and straightline ditching. Even though straightline ditching allows for rapid on-site drainage, such design may allow runoff to accumu- late and surcharge downstream drainageways, with little help to the homes they serve. Instead, flooding to proper- ties, roadways, and natural areas results in times of heavy or moderately heavy rainfall. For disposal of stormwater, landowners and developers have relied on poorly designed drainageways, inherited from the past, that connect and discharge into the larger county system. Often, these inadequately designed local and county drainageways which lack proper outlets flood because of sedimentation from rapid runoff caused by new residential development. Eroded sediments accumu- late in wetlands and estuaries, upsetting nutrient flows and smothering habitats valuable to fish, shellfish, and wildlife. Then, too, surface shedding from parking lots, driveways, walkways, rooftops, and other impervious surfaces accel- � .; erates the arrival of runoff at outlet points and increases flooding potential downstream. On flat land, in the ab- sence of a raised homesite, there is little recourse for the .,... '~. ~ v �,~ ~ , . . � -.-- '-homeowner during a heavy rain except to hope for clear- ~~~~~~~~~~~~,- . ... ,m ...... ing skies. 22 the solutions Runoff in residential areas developed on basically flat land can be better managed if the land can be graded into landforms of a more rolling character. On the one hand, the curving, meandering swales that carry runoff will allow somewhat more time, as well as space, for runoff to move across and off the site than is allowed in straight-line ditching, providing greater opportunity for water infiltration .~ into the soil (through the swale shoulders) and a less intense outflow into the main ditch system. On the other hand, the higher ground formed with the soil excavated from the swales supports homes at higher elevations and protects them from wet foundations and flooding to a better degree than existed on the original lay of the land. . Because all soil types and depth to groundwater play such an important role in controlling drainage, it is essential that information about the topography and groundwater of the land be obtained before a site plan is drawn. The Soil Con- servation Service or County Agricultural Extension can pro- vide general information on soil characteristics such as ab- sorption and percolation capabilities as well as depth to water table. South Carolina Department of Health and Environmental regulations require avoidance of septic system develop- ment on unsuitable soil types and over shallow water tables. These criteria and minimum drainage requirements of local subdivision regulations, where they exist, should be met in any housing development. For specific investiga- ./ tions of site absorption, percolation, and water table depth, a competent consultant should be retained. Finally, mounding to provide raised elevations for home- ' sites, if accomplished through sensitive landscape design, can produce a quality image, improved property values, Map drainage patterns, determine soil suitabilities, and establish water and a more liveable environment. table depth. 23 POOFL- 0 a-D . NLe mounding mA-r F- 1AI-t- .f-$_ZI4-0ArH HOUL4'. Where individual lots are large enough, mounding can be /51mt PRal4NP .Bw 6412KA-Mi accomplished by building on earth fill. Mounds of sandy l lIMIP0E~ P cOsaPMIP ~soil help water drain into swales and away from structures and ensure a safe height above the water table for living areas and septic systems. ~4 Aj W6 *� Slopes should allow for ease of mowing and permit *00. -~~~s~~r a". ~cN,4 p a uniform, non-erosive rate of runoff flowing into ad- iU'i | Pf~P ~ C is akarjacent swales. -cniiI l~l11 .*1 � Landscaping of mounds will assist in runoff control while improving the aesthetic appearance of home- RW;~ By,~ I~~11~ sites and residential areas. � On-site sewage disposal units should be placed in porous soil away from less permeable soil, and away Both flood protection and groundwater protection are improved. from shallow water tables. HOU4,, Oj-C 04 PVL4':Ji 4,;14 Raised structures may appear unnatural on flat terrain, while buildings on raised earthforms can appear compatible with natural terrain. 24 swales Runoff from raised homesites and areas where imperme- able soils predominate should be slowed in its progress ---- toward the main drainageways by flowing toward and through gently sloped, grassed swales. * The location of swales should be along natural r-- ~p ..,. drainage paths in the lower and border areas of / '"''- - A, -- sites. � The grading of swales should be designed to assure / A, 4al@-' '_ the flow of runoff into roadside drainageways so that' - standing water does not occur. � Side Slopes should be designed to allow for a slow, even flow of runoff, enabling the swales to absorb 4 water and reduce downstream flooding. Where homesite lots are large enough to be modified from flatland to a o Grasses, such as tight growing Bahia and Bermuda, varied topography, a valuable flexibility becomes available to the home- among others, should be planted in swales to help owner or developer. For the home can now be set higher and drier, while slow runoff, stabilize soil, and slow weed growth. swales in new low points collect and lead water safely away. slow runoff, stabilize soil, and slow weed growth. roadside drainageways Roadside drainageways collect water from swales, home- sites, and roadways. Steps should be taken to ensure efficient roadside flow by properly locating ditches, culverts, and pipe inverts. Eleva- tions should be specified by a qualified professional to avoid local blockages and overflow. * The design of residential roadside drainageways should follow the guidelines described previously in the agricultural roadside ditch design section. E- natural vegetation and landscaping Vegetation improves the visual quality of homesites and enhances property values. A local landscape architect can best provide information on plant types, their avail- ability, design, and other pertinent landscaping in- Proper widths, slopes, and elevations of roadside drainageways are formation. essential as are adequate culverts. 25 Natural vegetation should be retained and trees and shrubs planted on homesites. Low, dense grasses should be maintained on lawns to soften initial rain impact on soil and slow runoff. permeable paving In sites where sandy absorptive soils exist, the use of per- meable type pavings should be considered, since they allow infiltration of runoff into the soil and slow down the rapid flow of water to swales and ditches from hard sur- tltJ~l'``'trilsil "`"''"! i i~i!ll~ L'".'`'~i pop ,~1LT faces. Water moves through permeable paving into a r-~..~~'" , a .. t q' F"4IN ~" -6I.Eu F1-'ros4- layer of gravel and then filters naturally into the underlying W '- 7J ,l xX -'J GLV-HE soil. The Waccamaw Regional Planning and Development P;- di;~L; ;-6r, c-rrCouncil can provide advice on local sources, costs of per- meable paving, and conditions of use. -_ ~u~-~ �"; e Porous asphalt paving, commonly known as pop- corn paving, should be used on driveways, parking popcorn paving/porous asphalt areas, and road surfaces because of its ability to absorb runoff and reduce surface flow. Its strength and stability make it acceptable for a great range of access and parking conditions. i-,'X" �P~'H ~-0-E 0< � Lattice block pavers contain hollow voids and may be filled with sand, crushed stone, grass over porous /- aJT - 'r ~ore- ~L soil, and other porous material. Their use can be best applied to special parking areas where low speeds are suited to their masonry quality. d?.~ *: o~ ~ ~ ' K � Precast interlocking and brick pavers, set on sand "iFi g ! BROML for increased absorption, can provide a hard -IIi,'T-~ Meq. support surface for pedestrian use on patios and sidewalks and for vehicular parking. Precast pavers are somewhat more expensive than concrete, al- aggregate paving surface though they are more effective in reducing runoff and are visually pleasing. 26 * Aggregate paving, such as gravel, crushed stone, sand, or cinders can also be used in areas of pedes- trian and low-speed vehicular use. They provide / FO-rETE *-4, better infiltration than the popcorn paving and , pavers set in sand, although they do not possess their I. . - -. / stability and require greater maintenance. / ! . u-voTii- WA/>A&&6TES I at yapulI-, J/A1,.1'� infiltration structures ,> . / , - Infiltration pits, dry wells, Dutch drains, and French drains can receive runoff from roof eaves or downspouts, drive- ways, or large lawn areas, and allow it to be absorbed directly into the lower layers of the soil. Since soil will ac- cept less infiltration with continuing rainfall, pits, dry wells, I T fT and other stone-filled drains are most effective at the be- go . ginning of storms. I ' - _ ' ? -UH 0 - * Infiltration pits dug directly into the ground and filled with gravel or porous rubble that is separated from " the soil by a filter mat can be used to intercept and , 1�.~TIo4 absorb runoff. The filter mat will prevent soil from clogging the porous gravel and decreasing infiltra- tion. These pits can also be used to lower the water lattice block paving table in desired areas. Linear infiltration pits or trenches are commonly referred to as Dutch drains. / _ _ _ ___ E7e i T~i~F~; -IA'T 6 L62 Ad infiltration pititrench 27 5U li:PI l -.. * Dry wells, pits filled with gravel or stone rubble and I4,ALL.L surrounded by a mesh soil separator or by a verti- cally set perforated fiberglass, concrete, or metal cylinder, can be used to collect stormwater from roof gutter downspouts. The water will be absorbed into the ground provided the soil is sufficiently perme- able and unsaturated. a ||O|MUHiS>EATIO~-I� * French drains, perforated linear pipes set in a gravel 4,LL.L trench, should be used to collect excess stormwater HoIu | t z S A~e10l/ b A from the base of dry wells in areas where less perme- .i � able soils exist, and lead it into areas of greater soil '.,b-~onrf~: Gob , A permeability or to drainage outlets. SzEX- PlIk-1� o ,rOo11 1L ag G s . roof downspout drainage system 28 shopping centers and other large developments Planners and developers are often faced with the difficult question of how to control the large amounts of runoff generated from shopping centers and other large devel- opments and are often unaware of methods that can be used to increase on-site infiltration without cutting back on drainage efficiency. Improved methods of controlling runoff can be found on the following pages. the problems Some of the problems of flooding in shopping centers and PAPI~ 'toV �PA,4,~ other large developments are the result of the natural per- .-is~~i~a~e~ �- . meability of the original soil giving way to excessive r. ~ck~.�-!-rFo -.~ ,~ amounts of impervious paved and building surfaces that =. '.~~ I-IF�"Y1'S C~i$F E5 -are unable to absorb or retard the flow of stormwater. With the large amounts of runoff that occur in commercial parking lots, roadways, walkways, and rooftops, any open a~~~F ~~~~rE ~land that can be retained and landscaped in their vicinity F, U-. will help to balance runoff with positive infiltration. the solutions As with residential areas, the major objective of stormwater control for large developments is to allow for drainage away from the buildings and to hold some portion of runoff safely on-site until it can be absorbed by natural processes , .~.._._ D o or slowly released to other drainage systems. This can be accomplished by proper site grading, increasing absorp- tive capacities, and detaining stormwater on-site. The use .e ~ E Do < of porous paving, planted areas, detention ponds, and in- filtration pits along the edge of parking lots and at the -oiqL4 ,^JoII- ! base of building walls, can increase the total absorptive s lcGlin\ w A- Ad capacity of the site, These features can reduce flood damages while providing an attractive environment for shoppers and other users. improved grading To limit the amount of sheet runoff causing local and down- stream flooding, parking lots should be graded to direct Iasd~-~ k-IOFT Xrunoff at a reasonable rate toward areas that can detain l-frAII, IN1! - and either absorb or discharge rainwater slowly to other outlet points. 0 The gradient of parking surfaces should not exceed A- ~- ~ two percent where feasible, to slow runoff and in- crease infiltration through the pavement pores. Porous paving absorbs rainfall while runoff drains into planted medians, Where parking surfaces are forced into steeper perimeter swales, and detention ponds. slopes, flatter bands or landings should be graded 30 at no more than 1 1/2-2%, at suitable intervals, to in- j O tercept flow and increase infiltration through the porous paving or other permeable material used. 0 Runoff should be shed toward swales, perimeter ,! UE*g*,g ., g ditches, medians, and other detention areas by - e ' proper grading design. graded landings to increase infiltration in porous paving porous paving In order to allow water to seep into subsurface soils, porous , - -EE s s paving should be incorporated into existing sites and used / on hard surfaced areas. Its ability to absorb and allow Y . - ,.. - ~ . . stormwater to percolate through will help to slow and re- i T.o { -I.- 7 - duce the amount of runoff. * Popcorn paving may be used on roads and parking p/l -b AsO< surfaces especially where highly porous soils exist. Clogging of pores by silt and sand may occur over time, but may be reversed by vigorous hosing or by f*,9 frequent vacuuming and sweeping. Where less per- ,- -..... -_-.... mE p meable soil exists, borrowed porous fill from on- or off-site can be used in the grading process. CL- * Aggregate paving, such as crushed stone or sand, A may also be used on pedestrian and on some vehic- ular surfaces. , * Brick, interlocking, and lattice block pavers, set on sand, as defined in the preceding residential sec- tion, may be used on pedestrian and parking areas lattice block paving among others for better absorption of stormwater. tL- I--7 7 I`7' : 1.: popcor paing/o asHatge p avng sr--ac popcorn pavinglporous asphalt aggregate paving surface 31 perforated wheel stops /Afr.~o6 r., HoL. Wheel stops are used to prevent vehicles from damaging median strips and other planted borders. They are a / I XI - v typically precast in concrete and should have horizontal mA9GIH~OP lMflc voids in their base for runoff flow. precast concrete wheelstops with runoff cuts perimeter ditches A principal drainage channel should be located around shopping centers and other large developments to ac- cept a portion of parking lot and roadway runoff while pro- viding an opportunity for natural absorption and evapora- -t l: i' t ;': , } .tion, and to carry excess runoff into an on-site detention pond where feasible. The design of perimeter ditches should follow that previously outlined in the agricultural land section. median strips Median strips should be designed to accept safe amounts of runoff from adjacent roadways and parking lots. Depending on their size they can incorporate plantings of species tolerant of temporary wet conditions and urban 1 Hpa~,1, ads~ Jo Istormwater runoff, along with linear infiltration pits. Not only VTg By N . i ; 4 w A k do median strips absorb stormwater runoff - passing ex- cessive amounts on to other on-site outlet points - but they .~:~ '"~-'~ 't~ ~ ~!t"~~S ~'also filter out pollutants collected by runoff. Provision OF ICUj.. , should be made through design to prevent vehicular leak- ages from reaching any sensitive plants in the median. * The size of median strips should vary depending on planning requirements and the overall dimensions E1.. v~r and requirements of each site. * Dutch drains, linear ditches of gravel, should be f3ac-~. iei ~dTeH AI~t-.J used along the perimeter of medians to help inter- cept runoff, store it, and allow it to percolate into sub- surface soils. Filter fabric should be used to separate median strips intercept and absorb runoff gravel from the bordering soil to prevent clogging. 32 � French drains, perforated pipe surrounded by gravel, should be used to carry excessive stormwater from Dutch drains to on-site outlet points. * Sweeping and vacuuming on roadways and park- ing lots should be performed on a regular basis to . . �Tm$. reduce clogging of pores caused by fine particles of soil and other debris. -Ai ,6: l M',r controlled roof drainage t1K : Large rooftops can be designed to temporarily detain stormwater, reduce the total amount of runoff on ground surfaces, and allow collected stormwater to be absorbed rooftop drain by subsurface soils or passed on to other on-site detention points. * Rooftop drains that utilize a strainer and detention ring to ensure a safe, moderated release of water into a drain pipe may be used. b..- PPr * Infiltration pits dug into the ground directly below a __ _ _ --- drain pipes and filled with gravel or porous rubble, _7 -.. should be installed to detain stormwater until it is ; :1 R 6' absorbed by soil. Filter fabric should be used around gravel to keep out soil particles and other debris. ..o. Shrubs or other ground covers can be planted around the edges of infiltration pits to soften their appearance. detention ponds .:*,...... Detention ponds are intended to store excess on-site runoff IPoIA ,VIH,- r N'i Ia .O., collected from Dutch drains, French drains, swales, and perimeter ditches. During periods of moderate and high rainfall, detention ponds release excess amounts of storm- water into natural water courses or man-made systems. At F-Ch other periods in time they allow for vegetative absorption, evaporation, and natural infiltration of detained water. rooftop drainage system 33 * The size and design of detention ponds should not be determined by their stormwater control function alone, but with consideration given to their use as recreation areas, groundwater resuppliers, and aesthetic resources, among other functions. * Weirs provide outlet of excess stormwater at pond edges and should be designed and set at a proper elevation by an engineer or other qualified profes- sional. Weirs may also be arranged to hold back a higher head of water during storms than during fair weather and thus aid in flood control. landscaping The use of native or ornamental trees, shrubs, and ground covers should be incorporated into shopping centers and other large developments not only for their visual benefits, as is oftentimes done, but to take advantage of their ability to control stormwater. A local landscape architect, nur- seryman, or agricultural extension expert can recommend , ' ' ''" V' plants best adapted to site conditions. � A perimeter planting of low grass should be used on gently sloping drainageway borders to stabilize bank soil. Grassing also helps to moderate fluctua- tions in ditch flow. * Dense vegetative ground covers and heavy P-H, ~ E ' .OZLI ' mulches, such as gravel, rocks, and shell hulls, may Fast _IrOlE<,>~v~s61 2cwt ~be used in planted median strips and areas where the soil is void of cover to prevent erosion. if-%!B! _, � Root zones of median plantings should be slightly '"i"I mTI A;~i-~,, , C 5> l '""elevated by berming where standing water is likely to occur. landscaping controls stormwater and improves aesthetic appearance. * Invasive vegetation, including types with intrusive root systems, should not be used in areas where they may cut down absorptive capabilities of French drains, infiltration pits, and other drainageways. 34 shore areas Development has taken place along the Grand Strand shoreline without respect to the sand dunes and their ad- jacent inland areas. Extensive erosion has occurred be- cause of the lack of planning or poor design, and only recently have questions been asked on ways to reduce these adverse effects. Modern methods for improving drainage by simulating natural processes can be found on the following pages. . / <~the problems the dynamic shoreline and the value of its dune system The beaches, dunes, sand ridges, and swales that com- pose the Grand Strand's coastal edge are a dynamic and easily damaged component of the South Carolina coastal zone. Formed by a constantly changing regime of wind and water, sand dunes act as barriers, protecting the beach and inland areas from the erosive power of wind and waves. Stabilized by native vegetation such as Sea Oats, dunes are the primary shoreline defense against severe storms, high wave action, and strong winds. A stable, undisturbed dune system shelters the area imme- diately behind it. In a natural environment, this buffer pro- tects the delicate ecological balances of the backshore and wetlands in their lee. Dunes and the natural areas that occur behind them absorb and retain stormwater. When these areas are re- placed with hard, impervious surfaces, such as parking lots, pool decks, patios, and rooftops, the stormwater that can no longer flow into the ground must be collected and �a' ~' ~disposed of. Often, as in Myrtle Beach, such drainage con- sists of stormwater pipes that discharge directly onto the beach. The result has been extensive erosion of the beach ~Pa ~.~face, embankments, and pavement edges, all of which tend to accelerate natural beach erosion where it may exist, or change a stable beach into one susceptible to ;~ ~erosion. Correction of these problems generally requires drastic and expensive remedial action. -*81 4 ~" ~'~urban development and dune destruction In developing areas, the dunes help buffer buildings, park- ing lots, lawns, and other site improvements against ero- de'9~ .1~~~ ~'~ ~sion and potentially destructive storms. If man is not careful in the planning, design, construction, and maintenance of "~~~6~~~~~ ~areas that affect the dune zone, serious problems, many of a-,~~ ".~ ~ ~which can be seen in Myrtle Beach, can develop. These 36 problems, outlined below, can impose high reconstruction and maintenance costs on private landowners and peren- nial expenses on municipalities and other public bodies. Three destructive mistakes are common along the sea edge of the Grand Strand: � removal of dunes * construction of seawalls and other built edges as replacements to the dunes * direct discharge of runoff via storm drains onto the beach face When dunes are removed, inland properties face a greater risk of danger from storm driven waves and winds unless a seawall or other vertical surface has replaced the IS i. dune. Seawalls and other vertical structures, however, can increase problems of beach erosion by reflecting wave energy that is normally absorbed by dunes, downward t onto the beach, causing the breaking waters to scour and erode the beach. This scouring erosive action of waves de- creases the beach width and leaves it more vulnerable to I : erosion. The removal of the dunes and narrowing of the beach area compromises the appearance and natural beauty of the shoreline, reducing the attractiveness of the beach to both residents and tourists., The direct discharge of runoff via storm drains onto the , ....,. .. beach causes deep eroded gullies to occur during d , :.. periods of moderate and heavy rainfall; afterwards, O standing water often occurs beneath these drain pipe outlets. Runoff from drain pipes and impervious hard sur- faces not only deposits pollutants on the beach, but it also causes extensive erosion to the beach face and pavement edges and makes possible a greater "bite" by wave ac- tion. Pollutants and runoff from inland and adjacent shore areas cause the beach to become both visually and phys- ically degraded and oftentimes requires costly repair and restoration efforts. 379 the solutions By proper site selection, site planning, and design aimed at controlling runoff and minimizing erosion, developers can protect and enhance their investments in the dune environment. Owners of existing development can enhance the value of their properties and improve. the ap- zone 3 postive dranage/absorptlon pearance of their environment by altering the pattern of zone 2 awale/ebsorDtion ' dJ ' runoff. Dunes, beaches, and all other elements of a coastline - whether natural or man-made - are subject to all the forces of the coastal environment. Before a municipality or a private landowner embarks on a dune reconstruction --{ti~rC~ ~ _' B project, modifies seawalls, or begins a beach nourishment program, the expertise of coastal experts and knowledge- ' .,iw park t able officials, as well as the appropriate permits for beach modification, should be obtained. beach access ,..realigned parking * ::& rehabitated dunes build be hind the dune zone Sand dunes play an important role within the coastal com- munity and provide protection to coastal development > w t inueased ndscaping Xfrom wind, waves, and high tides. * Where construction is yet to begin, new residential ;~ .~ |..=- -.I-,,.,,,,'-.., - vor commercial structures should be sited behind Ile--/ I-'-:--- -t- "� the dune and swale zones in the leeward protected area. e Structures should be located on the land so that dune stabilizing vegetation is left intact. In this way, the dunes can continue to act in their natural role as The beach (Zone 0 of the coastal edge) Is vulnerable to erosion from both protectors of lands to their lee, while leeward devel- the sea and stormwater runoff. The dune line (Zone 1]) can hold back and opment can be sited to take advantage of the absorb surface runoff unabsorbed by the swale. The swale (Zone 2) beauty and image of the dunes, as well as of views provides for Infiltration of runoff not absorbed by Zone 3 surfaces. Public of the beach and ocean beyond. and private parking areas, motels, street ends, and public walkways form the primary absorption zone (Zone 3). Existing surfaces in this zone should be redesigned to incorporate porous materials for parking, drives, and walks, along with extensive landscaping to provide for positive absorption of Iandform modification stormwater. In sand flats leeward of the backdunes, where well- drained soils lie sufficiently above the water table, a greater opportunity for landform modification exists than is formed closer to the sea. As new communities developed in recent years have demonstrated, residential layouts with landforms modified into mounds and swales achieve good drainage and attractive residentail environments at the same time. * Pond and swale excavation material should be graded into broad mounds or other natural appear- ing landforms to elevate houses and their adjacent grounds. * Mounds and swales should be laid out consistent with the overall drainage plan of the site, allowing water to move off the land at a restrained, non- erosive rate. * Suitable grasses should be planted over exposed sand surfaces after landform modifications have been completed. avoid obstruction to estuarine flow The construction of causeways or the placement of landfill in salt marshes or waters can adversely affect the subtle and varied circulation patterns that are critical to provid- ing nutrients to aquatic and intertidal organisms through , x: the food web to coastal fish and wildlife. By slowing the velocity of tidal flow, causeways and other fill typically cause increased sedimentation and yet further loss of ecological systems, not to speak of lost navigation capacity and increased dredging costs. * Pilings or other substructures should be used to ele- vate roadways in order to allow the continuity of natural tidal flow patterns. * Fill should never be placed in wetlands, which are among the most valuable biologically productive re- sources we possess. I~ ~ ~ '--* -~- - " "'' /;~.,~ k' *F1'":"" ~ ( .........- ........ dune reconstruction -~~~ B E @"I~ w ~~ _ .By limiting development to the leeward side of the dune /$U~~~~ ,{/,,;. \ Izone, seawalls and other beachfront protection structures :te~t, " s t / vpptt s , \~~ lmay not be necessary. Where dunes have been removed ,~, ., 1 \ or seawalls already exist, the remnant dune may be recon- structed to renaturalize the appearance of the beach and P>~~ F_ St/z?^z///AS A ,afford some storm protection. Sand can be bermed up 1/X.I\,g, - :v//.(6e { �t" aagainst a seawall, where one has been built, and may be sR4 ~ ~ ~ ~ ~ ~ ~ ~~~Sve -partially stabilized by native vegetation and dune fencing. -- /acidic In some areas, sand nourishment may be feasible as a /. 4 ~ / lmeans of restoring beaches. Where this is possible, recon- ,,~v~~~~~ ~structed dunes will be afforded added protection from grassed swale absorbs stormwater the sea. ro oF Pu ~ If beach conditions allow dune reconstruction, the follow- ~~--~~ -OF --SL,&T S411F_-I~4e ing steps can befollowed. _, X-/H'P �amU es Place sand to a height of three to four feet to estab- /L / r ~~OVa L<Vklish the dune base. ' v / � - ff '< O' 0Plant suitable vegetation such as Sea Oats (Uniola .... ,... v ,-- lt. ,W paniculata), Bitter Panicum (Panicum amarum), and --7a3~~~~~ ~other suitable species. Experts should be consulted before planting to determine site specific suitabilities for particular species. * Dune fencing should be installed just behind the dune fence beach toe of the dune to encourage the deposition of more sand by the wind. A line of dune fence should also be installed on the backside of the dune / zi.p 1% 2' to prevent trampling and erosion by beachgoers. /'~"~ /~~ IThis fence will also help trap windblown sand. (A /,4 ~ -/ ; 9?Ai fence is also typically set along the dune ridge ........... ~ ,~ rAlA f 6where the dune base is broader than fifty feet.) i * C ............a� Dune walkovers should be constructed to allow D;4 IX~~~~~ -F~~~~~~~~ :people access to the beach and minimize trampling of the reestablished dune. dune walkover conclusions Mync% 0g^ An l , *<IZ minimized erosion and sedimentation Proper ditch design, spoil handling, farm equipment turns, ditch slope grassing and maintenance, curved swale and mound design, detention pond development, replace- t > X: ' ;0- ;. ; f f 000 0 0000 ment of impervious surfaces with permeable paving, and retaining large areas of landscaping and other high-in- filtration surfaces can all go far to improve both on-site and off-site drainage. With improvement, houses and other structures set upon the higher ground of graded earth mounds will be better protected from stormwater. At the same time, there will be less erosion and sedimentation of drainageways and less flooding from filled ditches. improved water quality By building homes and septic systems on raised earth to secure satisfactory heights above groundwater, we may be able to decrease chances that septic leachate will The use of most land within the Waccamaw region is highly reach and pollute water supplies and recreational water dependent on adequate drainage. If land resources are dependent on adequate drainage. If land resources are bodies. The slowing down of rapid runoff can also improve to be more wisely managed, protected, or developed, im- water quality in rivers, ponds, and estuaries by reducing water quality in rivers, ponds, and estuaries by reducing proved measures to control flooding, erosion, and sedi- erosion and siltation. mentation must be put into practice. For much, if not all, development within the region there are ways to design the land, improve site drainage, enhance property value, reduce public and private expense, and decrease impact on natural areas. Through improved site and land design, together with local and county storm water runoff management, sup- By limiting erosion and sediment loads in drainageways, ported by both ordinances and voluntary cooperation at the problems of siltation and filling in of wetlands, water- both levels, improved drainage and runoff control are ways, and estuarine waters can be reduced. Proper drain- achievable. If the objectives can be achieved, George- age control can thus result in improved environmental town, Horry and Williamsburg Counties may enjoy new quality and help protect fragile ecosystems and the valu- benefits and lowered costs through the years to come. able fisheries and wildlife species they support. 4 minimized public and private costs By employing techniques outlined in this handbook, home and other property owners can limit the expense they incur from the costs associated with clean-up, repair, and re- .... ... placement of flood damaged features. Costs to muni- cipal, county, and state government for flood clean-up, ditch maintenance, and pipe and ditch installation can be reduced. The cost of dredging navigable waters to remove sediments can be lowered. Similarly, on agricul- tural lands, a reduction of back-up flooding will decrease crop damage and loss of revenue to the farmer. 5 improved appearance By molding landforms and carving meandering swales, mounds, retention ponds, and other landscape elements, we can make residential and commercial areas more at- tractive. The Waccamaw region is a good place to live, and its landscape can be not only protected, but en- hanced by the simple measures discussed in this hand- book. 6 enhanced property values The improved appearance and reduced potential for flooding and wet conditions can serve to increase property values and the marketability of new develop- ments. 43 glossary for further assistance berm low mound of earth used to alter runoff direction For further information on ways in which you can help minimize coastal plain the relatively flat coastal region that lies between the drainage problems, please contact: Piedmont and the ocean shore * Waccamaw Regional Planning and Development Council culvert drainageway extending beneath a roadway, driveway, or 1001 Front Street embankment Georgetown, S.C. 29440 erosion process by which rainfall or wind suspends and transports (803) 546-8502 soil particles In Georgetown County: groundwater subsurface water in a zone of permanently saturated e Soil Conservation Service soil beneath the water table P.O. Box 606 gumbo heavy, clayey soil with low permeability Georgetown, S.C. 29440 (803) 546-7808 hydrology circulation of water on the surface layers of the earth and * Clemson University Agricultural Extension Service through the atmosphere P.O. Box 1100 impervious not permitting the infiltration of water Georgetown, S.C. 29440 marsh wet, periodically flooded area mainly covered by grasses (803) 546-4481,546-6421 percolation movement of water downward through the upper soil In Horry County: surfaces to the water table * Soil Conservation Service permeable permitting the infiltration of water P.O. Box 500 Conway, S.C. 29526 sedimentation or siltation the deposition of fine soil or sand particles (803) 248-9118 by water * Clemson University Agricultural Extension Service spoil excavated soil or rock P.O. Box 967 surcharge a flow of water that exceeds the capacity of the channel Conway, S.C. 29526 carrying it (803) 248-2267 water table uppermost limit of water-saturated subsurface soils In Williamsburg County: weir a barrier in a drainageway or detention pond designed to * Soil Conservation Service maintain the water level at a specified height P.O. Box 30 Kingstree, S.C. 29556 (803) 354-9621 * Clemson University Agricultural Extension Service Courthouse Square Kingstree, S.C. 29556 (803) 354-6106 44 suggested reading acknowledgements Georgia Department of Natural Resources, Handbook: Building in the The following individuals provided valuable assistance during the Coastal Environment, 1975 course of the handbook study: Hayes, Miles O., Thomas F. Moslow, and Dennis K. Hubbard, Beach Waccamaw Regional Planning and Development Council Erosion in South Carolina, 1978 William J. "Bill" Schwartzkopf, Director of Planning Roy Mann Associates, Inc., Managing Storm Drainage Through Im- Larry Schwartz, Project Director proved Land Design (slide-tape). Waccamaw Regional Plan- Marshall Truluck, Recreation Planner ning and Development Council, 1981 Jimmy A. Williams, Recreation Planner Roy Mann Associates, Inc., Land Design for Stormwater Runoff Control County Administrators in Myrtle Beach. Waccamaw Regional Planning and Develop- Alfred B. "Al" Schooler, Georgetown County ment Council, 1981 William F. "Bill" Brown, Horry County Tourbier, Toby J., and Richard Westmocatt, A Handbook of Measures James Hugh McCutchen, Williamsburg County to Protect Water Resources in Land Development. Urban Land ~~~~~~~~~~Institute. ~Soil Conservation Service U.S. Soil Conservation Service, Water Runoff Study for Main Drainage- Georgetown County: Henry T. Moore ways and Outlets, Georgetown County, South Carolina. HorryCounty Robert L. Squires Georgetown Drainage Commission and Georgetown Soil and Williamsburg County: Alex W. Johnson Water Conservation District, June, 1979 U.S. Soil Conservation Service, Feasibility Study of Requirements for Main Drainage Canals, Horry County, South Carolina. Horry - County Board of Commissioners and Horry Soil and Water Con- credits servation District, 1975 Roy Mann Associates, Inc. U.S. Soil Conservation Service, Feasibility Study of Requirements for Roy Mann, Project Director Main Drainage Canals, Williamsburg County, South Carolina. Jeffrey C. Brandenburg, Publication Design and Coordination Williamsburg County Board of Commissioners and Williamsburg Robert C. Hanss, Drawings Soil and Water Conservation District, 1972 Arthur J. Neumann, Research and Text Untermann, Richard K., Grade Easy. American Society of Landscape Samuel Coplon, Research and Text Architects Foundation, 1717 N Street, NW, Washington, D.C. Jeffrey W. Piro, Technical Drawings Mark Sorensen, Technical Drawings associated consultants Moore, Gardner & Associates, Inc., Consulting Engineers Owen W. Bludau