cwp.orgE:\ONE.PDFwater_ch2.pdfcwp.orgC:\MyFiles\Backup\wp{wp}.PDF_____________________________________________________________Chapter 1A Stream Protection StrategyIntroduction Urban streams are arguably the mostextensively degraded and disturbed aquaticsystem in North America. Research over thelast two decades has revealed that urbandevelopment has a profound impact on thehydrology, morphology, water quality andbiodiversity of urban streams (Table 1). Thequality of an urban stream depends on theinteraction of many different physical andbiological processes, each of which is stronglyinfluenced by the degree of impervious coverpresent in its contributing watershed (Fig. 1). Urban stream degradation is a classic exampleof the difficulty in addressing long–termenvironmental change at the local level.Development is a gradual process that spansdecades and occurs over a wide region of thelandscape. It is, however, composed ofhundreds of individual development projectscompleted over a much shorter time–span,which transform just a few acres at a time.Consequently, the true scope of streamdegradation may not be fully manifested at thewatershed scale for many years. The challengefor local planners is that they must review andmitigate the impact of each individualdevelopment proposal over the long termwithin a watershed context. When viewed from the air, headwater streamsdominate the landscape (Fig. 2). Their scale,proximity, and vulnerability to changes inland use make them an excellent choice forlocal water resources management. Indeed, thepreferred geographic unit for local planning isthe subwatershed, which drains a smallnetwork of individual streams. The stream protection strategy outlined in thischapter attempts to provide a coherentframework for effective environmentalregulation at the local level throughout thedevelopment process. The approach focuses onthe comprehensive protection of headwaterstream quality throughout the entiredevelopment cycle, utilizing an integratedreview process. Seven Elements of an Effective StreamProtection StrategyCommunities have tried to deal with thecomplex range of impacts on streams byadopting an equally complex series ofregulations and criteria to govern thedevelopment process. However, thesemeasures have often been less effective thananticipated. A major reason for this failure hasbeen the tendency to regulate a single impact atonly one stage of development. Until recently,few communities have tried to craft acomprehensive stream protection strategy overthe entire development cycle, fromwatershed–based zoning to its ultimaterealization in the construction of individualdevelopment projects.Site Planning for Urban Stream Protection_____________________________________________________________10TABLE 1: SUMMARY OF IMPACTS ASSOCIATED WITH URBAN STREAMSChanges in stream hydrologyIncreased magnitude/frequency of severe floodsIncreased frequency of erosive bankfull andsub–bankfull floodsReduced groundwater rechargeHigher flow velocities during storm eventsChanges in stream morphologyChannel widening and downcuttingStreambank erosionChannel scourShifting bars of coarse sedimentsImbedding of stream substrateLoss of pool/riffle structureStream enclosure or channelizationChanges in stream water qualitySediment pulse during constructionNutrient loads promote stream and lake algalgrowthBacterial contamination during dry and wetweatherHigher loads of organic matterHigher concentrations of metals,hydrocarbons, and priority pollutants Stream warming Trash and debris jamsChanges in stream ecology Shift from external production to internalproduction.Reduced diversity of aquatic insectsReduced diversity of fishCreation of barriers to fish migration Degradation of wetlands, riparian zones andspringsDecline in amphibian populationsChapter 1: A Stream Protection Strategy _____________________________________________________________11FIGURE 1: KEY PROCESSES THAT CONTRIBUTE TO URBAN STREAM QUALITYA stream is more than the water flowing between the banks. Many physical and biological factors interact toproduce stream quality.FIGURE 2: HEADWATER STREAMS IN THE URBAN LANDSCAPESite Planning for Urban Stream Protection_____________________________________________________________12The seven elements of an effective local stream protection strategy roughly follow each stage of the development cycle -from zoning, planning, site design, construction, stabilization, and final occupancy.One such approach is described below. Thelocal stream protection strategy has sevenprimary components that roughly correspondto normal stages of the development cycle (Fig.3).1. Watershed-based zoningThe future quality of an urban stream isfundamentally determined by the broad landuse decisions made by a community. It isFIGURE 3: THE STREAM PROTECTION STRATEGY AND THE LOCAL DEVELOPMENTCYCLEChapter 1: A Stream Protection Strategy _____________________________________________________________13therefore essential that the impact of futuredevelopment on streams be seriously assessedduring the zoning or master planning process.The most appropriate planning unit for thisassessment is the watershed or subwatershed.On the basis of the forecasted level of impervious cover, it is possible to deviseeffective and achievable strategies for streamprotection (Chapter 3). 2. Protect sensitive areas from developmentThe second component of a local streamprotection strategy involves the adoption andenforcement of ordinances that preventdevelopment from occurring in key naturalareas, such as streams, wetlands, floodplains,steep slopes, mature forests, critical habitatareas and shorelines. The ordinance describeshow these sensitive areas will be delineated ateach site and outlines how they are to beprotected during the site planning, constructionand post–construction stages. Some guidanceon effective performance criteria to protectsensitive areas can also be found in Schueler(1994). 3.Establish stream buffer networkTo fully protect urban streams, it is necessaryto establish a wide forested buffer adjacent tothe stream channel. The buffer network can beregarded as the right–of–way for a stream, andis an integral element of the stream itself. Aforested buffer provides shade, woody debris,leaf litter, streambank protection, pollutantremoval, and a multitude of other functions andservices to the stream. Given its keyimportance, extensive guidance is providedlater in this manual on how stream buffers