1.4 EROSION AND SEDIMENT CONTROL PLAN PREPARATION

Transcription

1 1.4 EROSION AND SEDIMENT CONTROL PLAN PREPARATION This chapter is a guide fr the preparatin f an ersin and sediment cntrl plan fr a cnstructin prject. The plan describes the ptential fr ersin and sedimentatin prblems n a cnstructin prject. The plan als identifies and explains the measures that are t be taken t cntrl thse prblems. The ersin and sediment cntrl plan must cntain sufficient infrmatin t ensure that ersin and sedimentatin have been adequately addressed fr the prpsed prject. The cntrl plans fr a single huse develpment will be far less cmplicated than a large develpment n steep slpes r rugh terrain. This plan shuld have tw parts: the written prtin r narrative and the map r site plan. The narrative explains the ersin and sediment cntrl decisins fr a particular prject and the justificatins fr thse decisins. It is imprtant that adequate infrmatin is prvided in the narrative. The wner r lessee f the land being develped is respnsible fr the plan preparatin. The wner r lessee may engage an engineer r ther qualified persn t prepare the plan; hwever, the wner r lessee still has the respnsibility fr ensuring develpment f an acceptable plan. Plan Preparatin Five steps are needed fr adequate develpment f an ersin and sediment cntrl plan: 1. Data inventry 2. Data analysis 3. Site plan develpment 4. Ersin and sediment cntrl plan 5. Plan preparatin Step 1. Data Inventry Gather infrmatin that will help develp the mst effective ersin and sediment cntrl plan. The infrmatin btained shuld be pltted n a map and explained in the narrative prtin f the plan. Such a narrative shuld include the fllwing tpics: Aerial pht f site. An aerial pht f the site and adjacent lands shuld be btained and used t identify imprtant site characteristics, as well as features f adjacent lands that shuld be cnsidered in develping the ersin and sediment cntrl plan. A clr infrared map and a sils map f a site can be btained frm the fllwing website: Tpgraphy. A tpgraphic map f the site shuld be prepared t shw the existing cntur elevatins at intervals f 1 5 feet, depending n the slpe f the grund. Drainage patterns. All existing drainage ditches and swales must be lcated and indicated n the tpgraphic map. Sils. Majr sil types shuld be shwn n the tpgraphic map r n an verlay f the same scale fr ease f interpretatin. Iwa Cnstructin Site Ersin Cntrl Manual 13

2 Grund cver. The existing vegetatin n the site shuld be shwn. Features such as trees, shrubs, grassy areas, native grasses, and existing denuded r expsed sil and rck utcrps shuld be indicated. Adjacent areas (upstream and dwnstream). Areas adjacent t the prpsed develpment site shuld be indicated n the tpgraphic map, including features such as streams, rads, buildings, and wded areas. Anticipated runff velcities and vlumes frm thse areas shuld be calculated t determine the types f ersin cntrl r flw diversin techniques that shuld be emplyed n the cnstructin site. Streams that will receive runff frm the site shuld be surveyed t determine their carrying capacity and ways t cntrl sedimentatin prir t water leaving the site. Step 2. Data Analysis When the infrmatin in Step 1 is cmpiled, a picture f the site pssibilities begins t emerge. The imprtant pints t cnsider in site analysis are as fllws: Tpgraphy. The primary cnsideratins are slpe length and steepness. Lnger and steeper slpes will increase the runff flw and the ersin ptential. When the percent f slpe has been determined, areas f similar steepness shuld be gruped tgether. Slpe gradients shuld be gruped int three general ranges f sil erdibility: 0% 3% lw ersin ptential 3% 8% medium ersin ptential ver 8% high ersin ptential Within these slpe ranges, the greater the slpe length, the greater the ersin ptential. Generally the ersin ptential becmes mre serius if the slpe lengths exceed the fllwing distances: 0% 3% 300 feet 3% 8% 150 feet ver 8% 75 feet Drainage patterns: Natural drainage patterns exist n the land. These patterns, which cnsist f verland flw, swales and depressins, and natural waterways, need t be identified s that critical areas can be lcated where water will cncentrate. The natural waterways shuld be used wherever pssible rather than incurring the expense f cnstructing and maintaining an artificial waterway. Care shuld be taken ensure that any increase in runff frm the site will nt erde r fld the existing drainage system r cause dwnstream damage. Such a lcatin may require a retentin pnd. Sils. Sil characteristics need t be identified t determine permeability, shrink-swell ptential, texture, erdibility, and water table depth and depth t bedrck. This infrmatin can be btained frm the lcal SWCD ffice r frm the fllwing website: Grund cver. A dense grass grund cver is the mst imprtant feature fr preventing ersin. All existing vegetatin that can be saved will help prevent ersin. This includes trees, shrubs, and ther vegetative cver. Cnstructin that can be staged, which invlves stabilizing ne part f the site befre disturbing anther, will reduce the ersin ptential as well as the amunt f temprary seeding and mulching required. 14 Iwa Cnstructin Site Ersin Cntrl Manual

3 Adjacent areas. Careful analysis f adjacent prperties, especially areas upslpe and dwnslpe frm the cnstructin prject is necessary. T prevent ersin frm ccurring in the cnstructin area, upstream prperty runff velcities and vlumes must be cntrlled as they enter the site r flws must be diverted. Special cnsideratin must be given t watercurses that will receive runff directly frm the cnstructin site. The ptential fr sediment pllutin f the watercurses needs t be cnsidered, as well as dwnstream ersin due t an increased vlume f runff. The ptential fr sediment depsitin n adjacent prperties due t sheet and rill ersin shuld als be cnsidered s apprpriate sediment trapping measures can be planned. Step 3. Site Plan Develpment After reviewing the data and nting the site limitatins, develpment f the site plan can begin. The planner shuld lcate the prpsed buildings, rads, and parking areas, and develp a landscape plan t explit the strengths and take int accunt the limitatins f the site. The fllwing items shuld help in the planning decisins: Fit the develpment t the site cnditins. Ding s will avid unnecessary land disturbance, minimize cut and fill, and reduce ersin ptential and develpment csts. Limit cnstructin activities t the least critical areas. Land disturbance f the mre erdible areas will require the installatin and maintenance f cstly cntrl measures. Cluster buildings tgether: this plan will reduce the amunt f disturbed area. Cncentrating utility lines and cnnectins in ne area will prvide mre natural pen space. The cluster cncept lessens the erdible area, reduces runff, and usually reduces develpment csts. Minimize paved areas. Keep paved areas such as rads, drives, and parking lts t a minimum. The mre land kept in vegetative cver, the mre water will infiltrate, thus minimizing runff and ersin. Use the natural drainage system. By retaining the natural drainage system, the ptential fr dwnstream damage due t increased runff can be minimized and strm water management made easier. Step 4. Ersin and Sediment Cntrl Plan Once the plan fr the site has been decided, a plan t cntrl ersin and sediment frm the disturbed areas must be prepared. The planner shuld refer t Sectin 1.6 f this manual, Implementatin Guidelines, Ersin Cntrl Measures, t help select the mst apprpriate cntrl measure. The fllwing prcedure is suggested fr ersin and sediment cntrl planning: Determine the limits f clearing and grading. Determine which areas must be disturbed fr the prpsed cnstructin. Nte critical areas that must be disturbed. Divide the site and adjacent runff-cntributing prperties int individual drainage areas. Determine hw the runff will travel ver the site. Determine hw ersin and sedimentatin can be cntrlled in each small drainage area befre reviewing the whle site. It is easier t cntrl ersin than t cntend with sediment after it has been carried dwnstream. Select ersin and sediment cntrl measures fr the cnstructin site and the runff cntributins f adjacent runff cntributing areas. Ersin and sediment Iwa Cnstructin Site Ersin Cntrl Manual 15

4 cntrl measures can be divided int three categries: vegetatin and sil stabilizatin measures, structural measures and special cnditins. Vegetatin and sil stabilizatin measures. The bjective is t prevent ersin and t prtect the sil frm the impact f raindrps and the verland flw f runff. The best way t prtect the sil is with a cver f grass. If disturbance is necessary, seed, mulch, and fertilize the area as sn as pssible. If the area will be disturbed again, then temprarily seed the area and mulch if necessary. The ersin and sediment cntrl plans must cntain prvisins fr permanent stabilizatin f the disturbed areas. Selectin f permanent vegetatin shuld include the fllwing cnsideratins: establishment requirements, adaptability t the site, aesthetics, and maintenance requirements. Structural measures. Structural measures are generally mre cstly and less efficient than vegetatin. Nevertheless, they are usually necessary, since nt all disturbed areas can be prtected with vegetatin. Hwever, it is very imprtant that the structural measures selected be designed and installed accrding t standard engineering practices. Imprper use r incrrect installatin can create larger prblems than thse the structure was designed t slve. Special cnditins. These measures are needed fr special situatins and may require a special design fr an installatin. Strm water permit requirements. Land-disturbing activities that will disturb an area f ne r mre acres are required t be cvered by an NPDES permit. The strmwater permits are managed by the Envirnmental Services Divisin f the Iwa DNR, Wallace State Office Building in Des Mines, Iwa. Step 5. Plan Preparatin The planning wrk has been dne in Steps 1 4. The final step cnsists f cnslidating the pertinent infrmatin and develping a specific ersin and sediment cntrl plan fr the prject. The plan cnsists f tw parts: a narrative and a site plan. The narrative explains the prblems and the slutins, alng with necessary dcumentatin. The site plan is ne r a series f maps r drawings shwing the lcatin f the varius cntrl measures. The fllwing checklist shuld be included in the plan: Descriptin. Describe the land, purpse, and the amunt f grading invlved. Site cnditins. Describe the existing tpgraphy, vegetatin, and drainage. Adjacent areas. Describe the neighbring areas, drainageways, buildings, streams, rads, land use, etc. Sils. Briefly explain the sils, sil names, sil depth, erdibility, and texture. Critical areas. Nte areas n the site that have ptentially serius ersin prblems. Ersin and sediment cntrl measures. The measures selected fr use n the site are listed and illustrated in Chapters 2 4 f this dcument. Permanent stabilizatin. Briefly describe hw the site will be stabilized after cnstructin is cmpleted. Strmwater permit requirements. Identify whether the develpment f the site will increase the runff and whether a discharge permit will be required. Maintenance. Prvide a schedule fr inspectin and repair f ersin and sediment cntrl measures. 16 Iwa Cnstructin Site Ersin Cntrl Manual

5 Calculatins. Calculatins fr the design f such items as sediment basins, diversins, waterways, and retentin basins shuld be included. Wetlands. Identify steps t be taken t cmply with all regulatins and include drainage patterns. The fllwing checklist shuld be included in the site plan: Lcatin map. Shw the lcatin f the prpsed cnstructin site in relatin t the surrunding area n the map. Identify wner and develper. Nrth pint. Indicate the nrth pint and the scale. Cnturs. Shw the existing cnturs f the site n a map. Existing vegetatin. Shw tree and shrub lines, grassy areas, r special vegetatin n a map. Sils. Shw the bundaries f different sil types n a map. Critical ersin areas. Indicate areas with the ptential fr serius ersin prblems n a map. Drainage patterns. Shw the dividing lines and the directin f flw fr the different drainage areas n the map. Final cnturs. Shw changes t the existing cnturs n a map. Clearing and grading. Outline areas t be cleared and graded n a map. Lcatin f cntrl measures. Indicate the lcatin f the varius ersin and sediment cntrl measures n a map. Drawings. As necessary, prvide detailed drawings and explanatins f structural cntrl measures, especially fr measures nt referenced in this manual. Iwa Cnstructin Site Ersin Cntrl Manual 17