Advantages of Stream Corridor Restoration as a BMP in the Chesapeake Bay Watershed MS4 Program

Elaine Langone Center, Gallery Theater

Stream Restoration (SR) is among the structural Best Management Practices (BMPs) acceptable for pollution reduction credits under the Municipal Separate Storm Sewer System (MS4) permit program. An important advantage of SR over other, infiltration-based MS4 BMPs, such as rain gardens and permeable pavement (here termed Green Stormwater Infrastructure, or GSI), is that SR directly reduces channel erosion, the principal source of fine sediment pollution in anthropogenic streams. Even when widely deployed, GSI cannot prevent the largest, most intense rainstorms (≥2 inch per hour) from generating high peak flows in channels because runoff from such storms tends to exceed the infiltration capacity of GSI facilities, causing much of this runoff to overflow and quickly drain to receiving streams. Peak flows from such heavy rainstorms are the main cause of channel erosion and the incidence of such storms is increasing in the USA. Acquiring MS4 credit via SR can also piggyback on essential projects addressing failing municipal infrastructure, such as sanitary sewer line exposure due to stream erosion. In such cases, MS4 program benefits are acquired as streamside property owners realize the tangible benefits of continued sewer operation and land preservation. Stream restorations are also a proven way to enhance community livability in public open spaces such as parks and downtowns. People are naturally attracted to flowing water within accessible green spaces and SR in such areas can make these key locations for urban revitalization and economic re-development. SR can also provide an economic advantage with respect to long-term maintenance, which is required with all MS4 BMPs. While many SRs can be allowed to re-naturalize and become largely self-maintaining, upland GSI landscaping must be maintained to accommodate societal norms of tidiness and attractiveness in the built landscape. Also, these facilities must not only be maintained for appearance but for continued function (e.g. infiltration capacity). Many upland GSI BMPs such as rain gardens will therefore require renewal of the soil media and replanting after a limited number of years of receiving pollutant-laden runoff from grimy impervious surfaces. Permeable pavements likewise have known long-term maintenance costs and a limited effective lifespan.