This bulletin is preparedmonthly as an informationresource on storm waterquality issues relatedto the planning anddesign of transportationinfrastructure.Direct address changes tohuttondl @cdm.com or to:Storm Water QualityControl BulletinCamp Dresser & McKee2920 Inland Empire Blvd.Suite 108Ontario, CA 91764Project Developmentquestions or commentsmay be directed toThomas Fung, Caltrans(916) 653-2115or Dan Hutton,Camp Dresser & McKee(909) 945-3000Erosion Controlquestions or commentsmay be directed toKen Keaton, Caltrans(916) 653-4947or Erika Kegel, Caltrans(916) 653-8369then it is necessaryto determine if thealignment and/or geometriccross section canbe changed based onthe following priorities:1.Completely avoidimpacts to existingslopes.2.Reduce the area ofimpact to existingslopes.3.Create new slopes that minimize the potentialerosion impact. Typically, impacts toexisting slopes and creation of new slopescannot be completely avoided. Therefore, adetailed design of the slopes that includesselection and design of permanent soil stabilizationBMPs for slope protection of bothdisturbed existing slopes and newly createdslopes is required.Erosion can be minimized by reducing theimpact of rainfall on the surface and runoff downthe slope, preventing the initiation of erosion andchannelization of runoff into erosive rills andgullies. Appropriate design strategies for slopeprotection measures include scheduling finalstabilization measure before the winter season,covering slopes with vegetation or other materialsto control splash erosion, minimizing slopesteepness/length, preventing runoff from concentrating,and/or collecting runoff in stabilizedchannels/drains. This can be accomplishedthrough these BMPs and SSP:

n Permanent Seeding and Planting CD24A(1)n Mulching CD25n Rounded/Terraced/Stepped Slopes CD35(1)n Top, Toe and Mid-Slope Diversion Ditches/Berms CD32B(1)n Slope/Subsurface Drains CD32A(1)n Scheduling PD20(1)n Order of Work SSP 05-0101Regardless of the control selected, a strategyfor permanently restablizing all disturbed areasof each project site must be developed andincorporated into the project.Any soil disturbed as the result of constructing anew project has the potential to erode, butslopes are of critical concern due to their potentialfor highly accelerated erosion. Sedimentresulting from erosion can impact waterquality, and erosion and sediment control can bemaintenance intensive. Some projects containslopes steep enough and long enough that,unless adequately designed and stabilized, wouldallow run-off to channelize, erode rills or gullies,and release significant sediment from the project.In other cases, the project may require constructionof a cut or fill slope that will erode unlessproperly stabilized.Caltrans has implemented procedures forreview and approval of slope designs and hasidentified Best Management Practices (BMPs)for use in preparing a design. The .CaltransStorm Water Quality Handbook, Planning andDesign Staff Guide. (Handbook) provides thefollowing guidance:The general strategy for minimizing erosion ofslopes is to only disturb existing slopes or createnew slopes if necessary. If the preliminary geometricaldesign of the project would potentiallyimpact the existing slopes or create new slopesVol. 1/Issue 2February 26, 1999Selection andDesign ofPermanent SoilStabilizationPracticesThe Handbook definesa slope as an areawith a grade changeof more than 1.2m(4 ft) in height andsteeper than 1:20(V:H). For existingslopes, this refersto the portion thatwould be disturbed

by construction.A slope-specific stabilization design approved by theDistrict Landscape Architect and written concurrencefrom the District Maintenance DivisionA slope-specific stabilization design with approvalby the District ArchitectDesign based upon appropriate BMPs listed below