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HomeMy WebLinkAboutControlling Erosion on Construction Sitescontrolli.ng e.rosioo. on constrL~on sdes CONSERVATION SERVICE SOIL 127 E MAIN ST. ROOM lOi. RIVERHF. AD, N.Y. 11901 U.S. DEPARTMENT OF AGRICULTURE · 5Oll CONSERVATION SERVICE ' AGRICULTURE INFORMAT]ON BULLETIN 347 contrcdli .ng .erpsbn.. on constCzscbon s tes Each year more than a million acres of land in the United States are converted from agricultural use to urban use. These changing acres are the sites for the new houses, shopping centers, schools, indus- trial parks, highways, and airports needed by our growing population. These changing acres also are the source of much of the sediment that pol- lutes streams and rivers and fills lakes and reservoirs. Studies show that erosion on land going into use for highways, houses, or shopping centers is about 10 times greater than on land in cultivated row crops, 200 times greater than on land in pasture, and 2,000 times greater than on land in timber. The amount of erosion that occurs is determined by the kind of soil, the slope, the intensity of rainfall, and the construc- tion methods. Much of the erosion occurs during the construction period, but areas below a construction site may erode more after construction is completed because of the rapid runoff from impervious pave- ment, parking lots, or compacted soil. Improvements in earth-moving equip- ment have made reshaping of land easier and have brought steeper and rougher land into use. Also, the trend toward large subdivisions and developments to meet housing needs has left large cleared and graded areas exposed to erosion for long periods. Because of these factors, an ever- increasing amount of land is undergoing development each year and erosion is be- coming a more serious problem in urban areas than ever before. Damage to the land does not come from erosion alone. The increased runoff erodes stream banks and channels and causes flooding below the construction site. And the sediment pollutes streams, lakes, and reservoirs and damages the area where it comes to rest. damage to the construction site Erosion damage to the construction site includes rilled and gullied slopes, gullied waterways and channels, washed-out roads and streets, undercut pavements and pipelines, clogged storm sewers, flooded basements, and debris-laden work areas. Damage of this kind must be re- paired. It increases the cost of construc- tion and causes delays in work schedules. A construction site also can lose fertile topsoil through erosion. This loss could mean that lawns and gardens will be dif- ficult to establish. Left, Uncontrolled runoff damages the con- struction site and carries the sediment that damages a~-eas downstream, Right. Grading more land than needed for immediate construction can result in severe erosion and sedimentation. Cutting, filling, excavating, and grading leave a site highly susceptible to erosion. damage to stream channels Stream chaonels below a construction site can become filled with sedimeot nod then flood when the volume of runoff creases during heavy rains. A sediment- filled stream chaonel can cause stream- bank erosion and can f{~rce the stream to meander. Land along the stream may be damaged by sediment, floodh~g, and sion, and the esthetic wdue of the stream may be seriously impaired. Clearing removes trees and other plant cover that protects the soil. damage to water Sediment is the greatest single pollutant of streams, lakes, ponds, and reservoirs. Sediment lowers the quality of water for municipal and industrial uses and for boating, fishing, swimming, and other water-based recreation; it increases the wear on equipment, such as turbines, pumps, and sprinkler irrigation systems. Sediment carries with it pesticides, phos- phates, and other chercfical pollutants. damage to property, public and private Sediment almost always damages the areas where it is deposited. It buries lawns, fills ditches, and clogs storm sew- ers, culverts, and drains. It can make an area unsuitable for use as a park or play- ground. Sediment reduces the storage capacity of reservoirs and may fill small ponds and lakes. It is injurious to both game fish and shell fish. The sediment that reaches major waterways blocks naviga- tion channels, fills harbors, and silts estuaries. The nationwide damage caused annu- ally by sediment has been estimated at more than $500 rrdllion. Much sediment comes from agricultural land, but the amount contributed by land undergoing urban development is high in proportion to the acreage. Some areas may be getting sediment from construction sites only, and the damage may be catastrophic. public concern People today want better houses, bet- ter shopping centers, and better roads. But they also want pure water, clean air, more open space, and other improvements in the environment that make for pleasant living. People are demanding that natural resources be developed, protected, and improved for use now and in the future. If our population doubles in the next 50 years as predicted, the acreage of land needed for urban use will increase. And the hazards of erosion and sedimentation will be greater if effective and practical measures for controlling erosion are not adopted and used widely. the solution: self-help and Many organizations and federal, state, and local agencies can provide leadership and assistance in a program for erosion control. The Soil Conservation Service (SCS) of the Department of Agriculture gives technical help through conservation districts and in cooperation with many other agencies. But programs for erosion control need to be initiated by developers, builders, engineers, planners, architects, public officials--the people responsible This storm sewer proved too small, and the overflow undercut the pipeline. Sediment from hisher lying construction sites is de- stroying the lake. cooperation for controlling erosion in their com- nmnity. Today's conservation problems on /and undergoing development for urban use follow by nearly three decades the initia~ tion of soil and water conservation work on farmland. Most of what we know about erosion and sediment control has been learned from research, demonstra- tion, and action programs on farmland. This wealth of information and experi- ence can serve urban areas equally well if properly interpreted. The basic prin- ciples of soil and water conservation and resource development can be applied any- where. principles of erosion and Erosion is a process of detachment and transportation of soil particles. Rain fall- ing oll bare soil or on soil with sparse cover detaches soil particles, and the run- off carries the detached particles down the slope. Rills and g,allies are cut by tile force of the moving water. The soil parti- cles are deposited as the water slows down and spreads out. Water moving over the land and in downstream channels carries soil material in proportion to the volume and velocity of the water. Top. The sediment in this storm drain, which is less than a year old, is more than 2 feet deep in places. The sediment came from a nearby construction site. Right, The capacity of this culvert is no 8 longer adequate because of sediment. sediment control Erosion and sedimentation can be con- trolled effectively, and at reasonable cost, if certain principles are followed in the use and treatment of land. These prin- ciples are: (1) using soils that are suited for development, (2) leaving the soil bare for the shortest time possible, (3) reduc- ing the velocity and controlling the flow of runoff, (4) detaining runoff on the site to trap sediment, and (5) releasing run- off safely to downstream areas. In applying these principles various combinations of the following practices have proved effective: 1. Selecting land where drainage pat- terns, topography, and soils are favorable for the intended use. 2. Fitting the development to the site and providing for erosion control in the site development plan. 3. Using for open space and recrea- tion those areas not well suited for urban development. 4. Developing large tracts in small workable units on which construction can be completed rapidly so that large areas are not left bare and exposed for long periods. 5. Grading at a minimum and re- moving only undesirable trees wherever possible. 6. Controlling runoff and conveying it to storm sewers or other outlets so it will not erode the land or cause offsite damage. 7. Protecting critical areas during construction with mulch or temporary cover crops and with mechanical mea- sures such as diversions and prepared outlets. 8. Constructing sediment basins to detain runoff and trap sediment during construction. Sediment from construction sites in the watershed has almost filled this lake. Choked to death by sediment. 10 9. Providing for safe offsite disposal of runoff, including the increased runoff resulting from construction. 10. Establishing permanent vegeta- tion and installing erosion control struc- tures as soon as possible. select the right land Builders and developers can minimize erosion, sedimentation, and other conser- vation problems by selecting the best site for an intended use. Tracts of land vary in suitability for different uses, so knowing the kind of soil, the topography, and the drainage pattern of the area will help in identifying and evaluating potential prob- lems. Regional and community planning is guiding land development in much of the rapidly urbanizing areas. Community planners, using information about the soils and about the geology, hydrology, and topography of the area, determine how the different kinds of land in a com- munity can best be used. They make studies to determine future land needs for urban, agricultural, recreational, and other purposes. Other studies project pop- ulation growth and trends and determine the land needs for schools, transporta- A pond or reservoir in the right place can bring many benefits to the landowner or the community. tion, utilities, and other public services. The studies are based on community ob- jectives to meet all necessary needs for land in ways that can protect natural re- sources, enhance the environment, and provide for both efficient and pleasant communities. soil surveys can help Soil surveys can be used iri community planning to determine land use suitability. Soil surveys include soil maps, soil de- scriptions, and soil interpretations. The interpretations serve to point out the haz- ards and ]imitations in nsing the soils for different pnrposes. With this kind of in- formation developers and builders can select sites that have the fewest limitations for a certain use and know that their se- lection will be compatible with the com- munity's plans and interests. Left. The soil data that a soil surveyor re- cords can help bring about better land-use planning and urban development. Right. Planning results in orderly develop- ment of land. More and more developers and build- ers are making use of soil and other resource data in selecting land for devel- opment and in preparing site development plans. Soil surveys were first used by farmers and agricultural scientists. They have guided the use and treatment of farmland and rangeland for years. Highway engi- neers have found soil surveys useful as an aid in designing highways as well as in determining the best routes. Sometimes adjustments in locating the right-of-way to avoid highly erodible soils or steep topography can reduce erosion problems greatly. Bankers are using soil surveys in land appraisal for making loans. Land as- sessors are using them as one criterion in determining a fair tax base. And land- planning agencies in increasing numbers are using them. The same soil survey can serve many different uses. To date soil surveys have been completed for more than 2,000 counties or other areas and additional surveys are being completed each year. In making a soil map, the boundaries of the different kinds of soil occurring on a tract of land are delineated on an aerial photograph. The delineations show the location and extent of the different kinds of soil in relation to streams, roads, build- ings, and other features of the landscape. Soil surveys describe the characteristics and properties of each kind of soil-its texture, slope, depth, erodibility, perme- ability, degree of wetness, presence of im- pervious or porous layers, and other information useful in construction. The soil descriptions are the basis for inter- preting soil suitability for different uses. Many soils are well suited to many uses; others, because of limitations, are suited to only a few uses. Soil limitations are expressed as slight, moderate, and severe. A severe limitation does not mean that the soil cannot be used for a specific purpose, but rather that the cost of overcoming the limitation for that purpose may be prohibitive. Soils vary in permeability and in their suitability for use as septic-tank absorp- tion fields. Some soils have impervious layers that cause them to slip when satu- rated. Wide shrink-swell ratios, flood hazards, and seepage problems impose limitations on other soils for use as con- struction sites. Soil surveys published in recent years are useful in urban planning and construc- tion. Older surveys have interpretations only for farming uses of the land. But the soil descriptions in the older surveys con- tain basic information from which inter- pretations for urban use can be made. Anyone needing such interpretations usu- ally can get help from the local conserva- tion district or the Agricultural Extension Service. Soil surveys do not lessen the need for onsite investigation. include erosion control in the development plan If a program for erosion control is worked out during the planning and de- sign stages, before plans become fixed and construction begins, the problems brought on by soil erosion, runoff, and sedimenta- tion can usually be avoided or lessened. Detailed information on the soils, topog- raphy, and geologic and hydrologic con- ditions should be obtained during field ex- amination of the site. Particular attention should be given to identifying and evaluat- ing problems that may cause serious ero- sion during construction. For example, will disposing of runoff be a problem? Runoff originating on the site and runoff 13 14 A well-planned site will include open-space areas. This one is used as an outdoor laboratory. from the watershed above must be con- trolled and disposed of safely. Considera- tion should also be given to offsite measures that may be needed to prevent damage to downstream land and property by either erosion or sediment. Special consideration should be given to fitting developments to the site and the landscape. Street, lot, and building layout can minimize or encourage erosion during construction and complement or detract from the natural environment. Steep slopes and areas of highly erodible soils can be protected or left exposed; clearing and grading can save or destroy trees and can result in limited or excessive soil dis- turbance; cut-and-fill slopes can be stable or unstable, protected by cover or left bare for long periods. These are the kinds of considerations that need to be weighed and resolved during planning and design to get erosion control into the site devel- opment plan. On sites where the cost of controlling erosion may be high because of the mea- sures needed to overcome the site limita- tions, alternative uses or a layout that is more compatible with the land should be considered. The cluster method of devel- oping residential areas, for example, fits the buildings and streets to the natural characteristics of the land. In using tfie cluster method on sloping land, houses can be built only on the more level areas and the steep, more erodible land is left undisturbed. Erosion hazards have been minimized and costs have not been in- creased. The problems presented by small areas where erodible soils or steep slopes im- pose severe limitations may be solved best by using these areas as open space. Per- haps they can be added to public parks or to areas managed by community associa- tions. In some places, schools make good use of them as nature areas or outdoor laboratories for class study. There are always alternative ways of effectively controlling erosion and sedi- ment production on most sites. The final plan generally is based on such factors as the time of year that construction will take place, the extent of grading, the amount of cover on the land, and the builder's preferences. On most sites a combination of fitting the development to the land, limiting grading, limiting the exposure of bare soil, and applying appropriate ero- sion control practices will prove the most practical. erosion and sediment control measures ]'here are two kinds of erosion and sediment control measures--mechanical and vegetative. The most widely used of these measures are discnssed here from the standpoint of their general use and pur- pose. Detailed information and standards and specifications developed for local conditions can be obtained from the local office of the Soil Conservation Service or from conservation districts. SCS can also give technical advice. Erosion control measures must be properly designed, in- stalled, and maintained if they are to accomplish their intended purpose. mechanical measures Mechanical measures are used to re- shape the land to intercept, divert, con- vey, retard, or otherwise control runoff. land grading Grading only those areas going into immediate construction, as opposed to grading the entire site, helps immensely in controlling erosion. On large tracts, to avoid leaving a large area bare and un- protected, milts of workable size can be graded one at a time--as construction is completed on one, grading proceeds to another. On some sites, until storm sewers are installed, only the street rights-of-way are graded. This leaves only linfited areas ex- posed to erosion and usually the adjacent undistnrbed areas can be used as tempo- rary outlets for diversions, or berms, built to protect the graded street rights-of-way. After the storm sewers are installed, other areas can be graded and the runoff can be directed to the streets and storm sewers. As a general rule, grading should be held to the minimum that makes the site suitable for its intended purpose without appreciably increasing runoff. Only unde- sirable trees should be removed wherever possible. In some areas heavy cutting, filling, or reshaping of the natural topography is needed to increase the percentage of us- able land. Heavy grading almost always increases erosion hazards and should be accompanied by the maximum use of ap- propriate erosion control measures. 15 The conservation measures applied here have stabilized this critical area. The grading plan should show location, slope, and elevation of the areas to be graded and the measnres to be used for disposing of runoff and for erosion con- trol. Constructed slopes should be limited to a degree of steepness that will provide stability and allow easy maintenance. Re- taining walls may be required. Stumps and other decayable material should not be used in fills. Soft, mushy soil material is not suitable for fills that are to be nsed to support buildings nr other structures. bench terraces Bench terraces constructed across the slope of the land and fitted to the natural terrain are used to break long slopes and slow the flow of runoff. In some areas the terraces are constructed wide enough to be nsed as residential sites. The cut-and- fill slopes of the bench terraces are always steeper than the natural slope of the land, so land slides may be a threat. Engineer- ing studies should always be made to guide the design of the slopes and insure a reasonable degree of slope stability and safety. Small bench terraces are sometimes used on the face of cut-and-fill slopes to help control runoff and erosion and estab- lish vegetation. subsurface drains Subsurface drains are sometimes required at the base of fill slopes to remove excess gronnd water. In heavy grading, it may be necessary to fill natural drainage channels; subsurface drains may have to be installed below the newly filled areas to prevent accumulation of ground water. Subsurface drains may be needed in vegetated channels to lower a high water table that prevents establishing an effec- tive plant cover. diversions Diversions intercept and divert runoff so it will not cause damage; they consist of a channel and a ridge constructed across the slope. Diversions need a stable outlet to dispose of water safely. In many places diversions are placed above critical slopes to divert runoff. Run- off over such slopes would cause serious erosion. Diversions can be used in this same way to protect construction areas. Also, they can be used on long slopes, in a series if needed. 17 A diversion protects a steep cut slope by diverting runoff to a safe outlet. Permanent diversions should be seeded to the same grasses that cover the sur- rounding areas. If built to protect open spaces, they should blend into the land- scape for both better appearance and ease of maintenance. Berms are a type of diversion. They are compacted earth ridges on a slight grade and have no channels. They may be per- Berms can be used to protect newly constructed slopes until the slopes are stabilized with permanent vegetation. They can be constructed across graded rights-of-way in a series and at intervals needed to intercept runoff. The side slopes of the berms are made fiat enough to Berms too must have stable outlets. Well-stabilized ungraded areas adjacent to the street rights-of-way are often used as temporary outlets. In many places half- channel flumes, sod, or other material can be used to make temporary outlets. Storm sewers dispose of runoff from the streets and adjacent lots. Temporary dj- versions may be needed to control runoff on the lots and convey it safely to the streets and storm sewers. The use of storm sewers for runoff dis- posal does not prevent sediment from being deposited downstream. To reduce the sediment load carried by runoff through storm sewers during construction, some developers have improvised small sediment basins adjacent to sewer inlets. The sediment collected in the basins is removed following each runoff-producing rain. Storm sewers should discharge where the grade is stable. Generally an energy dissipator is needed to slow the force of the flow at the point of discharge. outlets Most outlets are grassed waterways, either natural or mamnade, and serve to dispose safely of water from diversions and from parking lots, highways, and other areas. Natural waterways, or swales, can be improved by grading, reshaping, and re- vegetating. Manmade outlets should have fiat side slopes and a wide bottom so they can be easily maintained. They should have adequate capacity. This concrete-lined channel will carry runoff from the road su~ace and road shoulders, The shoulders have been mulched and seeded. have preferred permanent basins that can be used later to protect downstream areas from accidentally released materials that would cause pollution. The location, design, and construction of a sediment basin should be such that serious damage to areas downstream would be avoided should the basin fail. If the minimum storage requirement can- not be met, excavation to enlarge the basin and periodic cleanout may be nec- essary. Sediment basins are constructed to dis- charge on stable ground below the dam. Emergency spillways should be added to increase safety. Exposed areas of the em- bankment and the emergency spillway should be protected by mulching and seeding. stream channel and bank stabilization The increased runoff from coestruction sites may make it necessary to stabilize the stream channel below. Stream channels can be stabilized by installing grade control structures or by paving. Undercutting of banks can be controlled by measures that withstand the flow, such as concrete structures or rock riprap built along the toe and lower facing of the bank, or by measures that dissi- pate the energy of the flow, such as jetties, piling, and fencing built into or along the channel. Realining the channel may be desirable or necessary in many places, but it creates the risk of starting a new erosion cycle. Stabilizing stream channels and stream- banks is usually complex and costly. Con- trol measures should be undertaken only on the basis of thorough engineering studies and plans. If a stream runs along or through a flood plain that is to be de- veloped for parks and recreation, for ex- ample, esthetic values may determine the methods of improvemeet. vegetative measures Vegetative measures provide tempo- rary cover to help control erosion during construction and permanent cover to sta- bilize the site after construction is com- pleted. The measures include the use of mulches and temporary and permanent cover crops. Erosion can be controlled with less dif- ficulty on some sites than on others during construction, and permanent cover is easy This newly sodded channel will dispose of runoff safely. The slope has been planted to honeysuckle and mulched with tanbark. Note riprapping at critical points. Grass protects a channel against ero- sion by reducing the velocity of flow. The most suitable grass species are those that produce a dense uniform cover near tile soil surface, are long lived, tire able to withstand small amounts of sedimenta- tion, and provide protection during all seasons of the year. The species selected should be adapted to the locality and the site. Jute netting or fiber glass can be used as channeI liners to protect the channel from erosion until vegetation becomes established. Liners may not be needed if runoff can be diverted from the channel during the establishment period. waterway stabilization structures A waterway needs a stabilizing struc- ture if its slope is so steep that the velocity of runoff exceeds the limit of protection that the vegetation alone gives. Grade stabilization structures, special culverts, and various kinds of pipe can be used in combination with vegetation. Energy dis- sipaters may be required. The structures should be designed and constructed to provide permanent stabilization. lined channels The alternative to using vegetated wa- terways with grade stabilization structures is using lined channels. Such channels, paved ditches and valley gutters for ex- ample, have many uses in urban areas where slopes are too steep or soils too unstable for control by vegetation alone. Fiber-glass mats can be used as tempo- rary lining for ditches and channels. sediment basins The function of a sediment basin is to detain runoff and trap sediment, thus, pre- venting damage to areas downstream. By detaining runoff, sediment basins also duce peak flows. Basins can be excavated or formed by a combination of dam mid excavation. Earth dains can be con- structed across waterways to form basins. Under some conditions a highway em- bankment can serve as a dam. Sediment basins are almost always temporary struc- tures. They are graded into the surround- ing landscape after construction bas been completed and the :~rea has been stabilized. But they can be designed as permanent structures il' there is a perma- nent need for them. Some industrial firms 19 to establish on some sites and di¢icult on others. Establishing and maintaining good plant cover is easy in areas of fertile soil and moderate slopes. Usually such areas can be stabilized by using the plants and cultural methods that are common in the community. Sites that are difficult to stabilize, be- cause of exposed subsoil, steep slopes, a droughty exposure, and other conditions, require special treatment. Such sites are called critical areas because they erode This vegetated channel and drop structure dispose of runoff safely. severely and are the source of much sedi- ment if they are not well stabilized. mulch Straw mulch can be used to protect constructed slopes and other areas brought to final grade at an unfavorable time for seeding. The areas can be seeded when the time is favorable without moving the mulch. Mulch is essential in establishing good stands of grasses and legumes on steep cut-and-fill slopes and other areas where it is difficult to establish plants. By ducing runoff, mulch allows more water to infiltrate the soil. It also reduces the loss of soil moisture by evaporation; holds seed, lime, and fertilizer in place; and re- duces seedling damage from heaving of the soil caused by freezing and thawing. The materials most widely used in mulching are small-grain straw, hay, and certain processed materials. Grain straw is easily applied and generally is more readily available than hay, and it costs less. in some places, certain hays are pre- ferred because they are a source of seed of plants that can be used for stabilization. Straw and hay mulches are usually applied at the rate of I~A tons per acre. Paper netting helps secure straw mulch on a newly seeded waterway. A number of processed mulches are available, and some show promise of greater use under specific conditions. Hydromulching, in which seed, fertilizer, and mulch are applied as a slurry, is a fast, all-in-one operation that requires little labor. Hydromulching may not be successful if done during a period of high- intensity storms. Straw and hay mulches must be an- chored to keep them from blowing or washing away. Anchoring methods in- clude spraying the mulch with asphalt, tucking the mulch into the soil with a straight-blade disk, stapling netting over the mulch, and driving pegs into the mulched area at intervals of about 4 feet and interlacing them with twine. 2I 22 temporar~ cover Temporary cover crops can be used where cover is needed for a few months or a year or two. If construction is delayed on a site that has been cleared and graded, temporary cover crops can be used to pro- tect the site against erosion. And they can be planted at a time of year that is unfa- vorable for seeding and establishing per- Rapidly growing plauts, such as annual rye grass, small grain, sudangrass, and millet, are most often used for temporary cover. Plants that are adapted to the lo- cality and the season of the year during which protection is needed should always be used. permanent cover Special care should be taken in select- ing plants for permanent cover. There are many grasses and legumes, trees, shrubs, vines, and ground covers from which to choose ill most humid areas of the country bat only a few in most dry regions. Final choice should be based on adaptafion of the plants to the soils and climate, ease of establishment, suitability for a specific use, longevity or ability to self-reseed, The asphalt-paved apron and drop chute will carry runoff into the sediment basin. maintenance requirements, esthetic val- ues, and other special qualities. The best plants are those that are well adapted to the site and to the purpose for which they are to be used. For example, grasses used for waterway stabilization must be able to withstand submergence and provide a dense cover to prevent scouring of the channel. In playgronnds, grasses must be able to withstand tram- piing. In some places, such as south-fac- lng cut-and-fill slopes, the plauts needed are those that are adapted to droughty areas. In olher places, plants must be able to tolerate shade. Some plants can beau- tify as well as stabilize an area. Maintenance may be the most inrpor- rant factor in selectiug plants for perma- nent stabilization. Most tame grasses and legumes require mnch maintenance, and they gradually give way to native grasses, shrubs, and weedy phmts if they are not mowed and fertilized regularly. In some areas native plants are preferred. On steep slopes and other inaccessible areas, it is preferable to select plants that require little or uo maintenance. Sericea lespe- deza, crownvetch, and honeysuckle, for example, are long lived and provide good erosion control with a minimnm of main- This temporary sediment basin has a per- forated riser to make easier the gradual drawdown of impounded runoff. tenance. Most native grasses, trees~ and shrubs grow well with little or no main- tenance. fibrous materials A number of fibrous materials have special uses in erosion control. Jute netting, a coarse, open-mesh, web- like material, can be applied directly on the soil to protect newly seeded channels until vegetation becomes established. It can also be used in repairing outlets and diversions where gullies have cut the channel. In some places it can be used to hold down straw mulch. Cotton netting and paper netting are both lightweight; they can hold straw mulch in place and prevent it from blow- ing or washing away. Solid heavy-duty fiber-glass matting can be used as a temporary channel liner where water velocity is too high for the use of vegetation or where vegetation is not wanted. Impregnating the mat with asphalt prolongs its life. Perforated fiber- glass matting can be used in the same way as jute netting to protect newly seeded channels. It can be used as a transition apron, lining the head of a channel to pro- tect it from runoff, especially that from road culverts, which tends to cut a gully down the channel. And used as erosion stops, perforated matting can check rilling. Fiber-glass erosion stops have certain advantages over rigid stops of masonry or wood. Soil often settles around rigid structures causing a turbulent and erosive flow. The fiber~glass stops are flexible and conform to the channel. Also, they are porous--water can seep through them-- so subsurface drainage is improved. stabilizing cut-and-fill slopes The first requirement in stabilizing cut- and-fill slopes is to prevent runoff from flowing over the face of the slopes. Tem- porary diversions, berms, shoulder dikes, or other measures should be used to inter- cept and divert the runoff. Permanent structures such as brow ditches and valley gutters are required where the areas con- tributing to runoff are large, for example, in areas of highway construction. 23 A temporary cover of annual ryegrass pro- tects this graded area against erosion until construction begins, The cultipacker seeder works exceptionally well on a well-prepared seedbed. Small benches, intercepter ditches, or other measures can be used to protect long slopes from runoff originating on the slope itself. Methods of establishing vegetation vary for different parts of the country, depend- ing on the plants used and on soil and climate. In selecting plants and in getting them established, it is best to be guided by the methods commonly used and recom- mended in the area. As a general rule, when seeding grasses and legumes it is advisable to prepare as good a seedbed as site conditions permit. Applications of lime and fertilizer should be based on local standards or on soil tests. Usually a good stand can be obtained by broadcasting, drilling, or hydroseeding if other conditions are met. Mulching after seeding and then anchoring the mulch are essential in most areas. Irriga- tion is oeeded in many places. Sodding is more costly than seeding, but it provides immediate protection. It should be ased where the concentration of runoff is such that other methods of stabi- lizatioo will not be effective. Sod can be laid anytime the soil is not frozen. Sod responds to a good seedbed and to lime and fertilizer. The strips of sod should always be laid across the slope, anchored to the soil, and watered. Some grasses can be established by sprigging and chunk sodding. If trees are used to stabilize steep slopes, they are usually planted in pure stands. Mulching is important. Vines are usually established by transplanting in- dividual plants or crowns. R~ght, top. Hydroseeding--spraying seed and fertilizer in a water solution is one way of establishing grass on a graded area. Right, bottom. The notched-disk machine is anchoring the mulch to the soil Below. This machine spreads a uniform cov, er of straw mulch to control erosion on the face of the dam. 26 apply measures during construction installation of erosion and sediment control measures should be planned and scheduled as a part of construction opera- tions. Construction contracts should clearly outline the location, scope, and manner of performing or installing the measures. If possible, construction should be scheduled for that time of year when ero- sion is less of a hazard. This is particularly advisable for those sites where limitations for construction are severe because of steep slopes and erodible soils. Avoiding erosion hazards is an inexpensive way of controlling erosion and sedimentation. Structures for controlling erosion on newly graded areas should be written into the grading contract. All permanent struc- tures should be installed as early in the construction schedule as possible. Sedi- ment basins also, if they are needed, should be installed early. Newly con- structed slopes and other areas susceptible to erosion should be mulched or seeded to a temporary cover crop as soon as possible after grading. Finished grading leaves the soil extremely vulner- able to erosion. For this reason, it is advisable to schedule finished grading for the time of year that is favorable to estab- lishing vegetation; the site can be seeded and mulched or sodded immediately fol- lowing grading. During construct/on, equipment should be used in a manner that does not leave the site more susceptible to erosion. Leav- ing deep wheel tracks up and down the slope, for example, should be avoided. Cultivation and seeding should be across the slope where possible. Access and work roads should be located and built so as not to encourage erosion. If the construction site borders streams, lakes, or reservoirs, special measures may This severely eroded fill was the source of tons of sediment that were deposited on parkland below. The same area 2 years [ater is well stabi- lized. A shoutder dike prevents runoff from going over the face of the slope. be necessary to prevent damage to fish and wildlife, water supplies, and irrigation systems. Construction should conform to regulations of water resource and fish and wildlife agencies. Restoring borrow pits and spoil areas should help control runoff and sedimenta- tion. Such areas should be drained, graded, and revegetated so as to blend into the surrounding landscape~ Diver- sions, dikes, and sediment basins should be used where needed to keep sediment from entering streams or damaging land and structures. Responsibility for maintenance of the permanent structures and plantings should be clearly understood when ownership or management of property transfers from the developer or builder to a private own- er, a public land administering agency, or a community management association. Permanent structures should be spected soon after installation to locate and correct any deficiencies. They then should be inspected annually and after major storms. Plantings should be fertilized and mowed according to a plan if they are in- tended to be permanent. In some places a change in cover may be planned or needed. Reseeding or other appropriate measures may be necessary in places to improve the cover before erosion becomes serious. working together Interest in community and area-wide planning is increasing in both urban and rural sectors. People want to get the most beneficial use out of the land, and they want pure water and clean air. They un- derstand that these amenities come only as a result of good planning; welbadmin- istered ordinances, codes, and regulations; public understanding and support; team- work; and dedicated leadership. SCS through conservation districts can help engineers~ planners, zoning boards, builders, and others by providing them with soil, water, and plant data, interpre- tations, inventories, and other technical assistance. A few local governments have adopted erosion and sediment control programs along with appropriate ordinances, build- ing codes, and regulations to help carry out their conservation policy. Ordinances, codes, and regulations can be helpful in two ways. They establish public policy and criteria and guides for erosion and sediment control, and they protect the people, public property, and natural re- sources. Ordinances have sometimes failed to accomplish their intended purpose be- cause they were too complicated and vague. Those that seem to work tie certain controls into the local code by adding to or amending existing subdivision regula- tions. Builders and developers already complying with the code merely assume additional responsibilities. 27 Native trees, shrubs, and other plants have stabilized and beautified this roadside. In areas where an erosion and sediment control ordinance has been adopted, the local conservation district has usually ac~ cepted the responsibility of providing technical assistance to the local govern- ment agency that administers the code. A site development plan then is approved only if the developer or builder provides for a level of protection against erosion that meets the standards set by the con~ servation district. Some local governments have adopted ordinances to control flood-plain develop- ment or encroachment. Flood plains are the areas adjacent to streams that flood. This steep cut slope was stabilized with serioea ]espedeza, a Iow-maintenance cover. In recent years, some local govern- merits have modified their zoning and flood-plaio regulations to provide for planned unit development, whereby the upland and the flood plain are considered as a unit. This makes it possible to avoid problem areas and to preserve open space for scenic and recreation purposes. Esthetic values are beiog lost in many urban areas as parts of streams, creeks, and runs are replaced by underground water disposal or drainage systems. But the loss goes beyond esthetics. Such sys- tems are costly to install, and they in- crease the peak flows of runoff down- stream. Innovations in storm drainage systems are needed to reduce peak flows, lower costs, and preserve and enhance esthetic values. An alternative to an un~ derground water disposal system could be a stabilized natural stream with multipur- pose structures for flood storage and water-based recreation. Alternatives, of course, need to be tested. public understanding and support There is no substitute for a well-in- formed public. People must know about the resource potentials and problems in their area, aud they must know about the erosion and sediment control programs that can help them. Civic groups are helping in many ways to inform the public. Some, for example, make available to other groups speakers and slide shows on urban erosion and sedimentation problems. Builder associations publish technical material on erosion and sediment control practices and distribute it to their mem- bers. Some include conservation items in their newsletters; others join conservation districts or local government agencies in promoting erosion and sediment control. Conservation councils, watershed as- sociations, river-basin commissions, com- mittees for preservation of grcen space, for protection of stream valleys, or for acquisition of park land, and many others influence public opinion and provide forums for citizen reaction. Some builders and developers serve on their local conservation district governing board. Many builders and developers have been recognized by conservation districts for their outstanding conserva- tion work. policies need to be clearly stated The conservation policy that a com- munity or local government intends to fol- low must be clearly outlined and simply stated. Complexity or vagueness can lead to misunderstanding on the part of build- ers and developers, zoning boards, state or federal government agencies, or one of the many other groups that may have a function to perform or have simply an interest in conservation policy and pro- cedures. SCS conservationists working through conservation districts meet periodically with policy planning boards or other rep- resentatives of local government to re- view and evaluate conservation policy and operating procedures and to improve, if possible, coordination among individuals, groups, and organizations. conservation districts provide leadership Conservation districts are local public bodies responsible under state law to pro- mote the conservation of soil and water and related resources. Districts meet their objectives through citizen, group, and community participation. Crownvetch controls erosion and beautifies as well 3O Conservation districts across the coun- try have broadened their programs to give needed priority to urban conservation problems, particularly problems on land use. Several states have amended their district enabling legislation to include ur- ban areas within their district boundaries. in some states, the nriginal legislation limited district operations to rural areas, Many districts have strengthened their leadership in the community through the election or appointment of urban leaders to their governing body. Districts are managed by local citizens who know local prnblcms, and districts that take in sub- stantial areas of urban land or rural land being converted to urban use need strong urban leaders on their governing boards. Conservation tours, workshops, and seminars have been effectively used by districts to inform the public in urban areas about conservation problems. Dis- trict newsletters, leaflets, and films have also been effective. A few districts have employed a public relations specialist to give leadership to such activities. Districts are now looking beyond their own boundaries to form multidistrict re- source councils to help solve resource conservation problems affecting large areas, Left. The fibrous material will help protect this newly seeded streambank. Right, Retaining walls of concrete rubble have stabilized and improved this storm channel. Careful planning and construction have saved the trees. Below. The fiat slopes along this concrete- lined storm channel can be easily mowed. assistance is available SCS, through local conservation dis~ tricts, gives technical help to builders, developers, town and county officials, and others in working out land and water rem source problems. SCS can advise builders or developers concerning conservation problems, pro- vide technical information, and suggest alternative solutions~ The builders or de- velopers decide what they want to do after considering the alternatives and use their own planners aod engineers to carry out the decisions. Builders and developers are encour- aged to discuss erosion and other conser- vation problems with district conserva- fionists before starting a site development plan. Conservation in urban development means teamwork on the part of many agencies, organizations, groups, and in- dividoals. The hub of the program is the county, town, or other local government and the local conservation district. The Focal government establishes land- development policy and is responsible for community planning, zoning, approving site plans, issuing pernfits, and inspecting constroction. Local government is the developer when public land is used for schools, recreation, parks, highways, and other public purposes. Conservation districts and the Soil Con- servation Service are the technical arms of the team. Districts represent the public and promote the public interest. SCS pro- vides the technical information. It a/so makes soil snrveys and adminislers the small watershed program. Other agencies of the Department of Agriculture contribute to conservation with research on soil and water conserva- tion and with educational programs. The Department of Housing and Urban De- velopment insures loans for land develop- ment and through other programs helps communities and municipalities in many ways. Other departments and agencies provide assistance in the fields of hydrol- ogy and geology, health and sanitation, transportation, outdoor recreation, and preservation of scenic and historic areas. Stone, or rubble, side slopes provide added protection for this channel in open parkland. Open-space land for parks and recreation add beauty and enjoyment to everyday liv- ing. December 1970