Hurricane Flooding Nutrient Reduction Rooftop Reuse Airport Drainage 18 Path to resiliency 20 Innovative practices 25 Citizen science 29 Kraków expands Volume 6 / Issue 3 Autumn 2018 The Official Publication of the WEF Stormwater Institute MANAGEMENT Stream restoration Nutrient Reduction Nontraditional solutions GHOLYHUPXOWLSOHEHQHƮWV for municipalities Stream restoration and shoreline stabilization provide valuable results for municipalities required to meet assigned waste load allocations for phosphorus, nitrogen, and sediment. Ashley Hall, Daniel Proctor, Karen Hall, Josh Running, and Travis Crayosky RI6WDQWHF,QFH[SODLQWKHHQYLURQPHQWDOƮQDQFLDODQGSUDFWLFDOEHQHƮWVRIHPSOR\LQJWKHVH two nontraditional stormwater practices in the Commonwealth of Virginia, United States. Localities with Municipal Separate Many MS4s initially struggled Ideal projects would ideally have plants, etc.) and can be traded Storm Sewer System (MS4) Per- to find enough projects to meet easy support from all stakeholders as a nutrient credit among point mits in the state of Virginia, United the reductions and then quickly and have clear environmental sources and nutrient bankers. States (US), have been pushed fit them into long-term funding benefits with a low cost relative to The success of a project can hard to meet their assigned Waste plans to be approved by elected the amount of pollutants removed. be measured, to an extent, by the Load Allocations (WLAs) given officials who were surprised by In Virginia, phosphorus has tradi- pounds of phosphorus removed in Total Maximum Daily Loads the financial consequences of the tionally been marked as a unique along with the overall cost of the (TMDLs). MS4s are named in MS4 permits. As a result, a search type of currency for benchmarking project, providing a data point TMDLs that have been developed led by local government officials stormwater practices. In the most in terms of dollars per pound of for hundreds of impaired water- (with support from contracted general terms, the presence of removed phosphorus ($/lb-P). sheds. These local TMDLs have consultants) ensued for innovative phosphorus represents stormwater While this figure represents a challenging reductions, but the practices that would bring multiple pollution from multiple sources gross estimate, not accounting for current TMDL-related pressure visual benefits to the public. (construction sites, treatment maintenance costs, community point for Virginia MS4s is the Chesapeake Bay TMDL, which assigns WLAs for phosphorous, nitrogen, and sediment. The Chesapeake Bay has its own Special Condition in Vir- ginia’s MS4 permits, with a firm deadline to meet the WLAs for nutrient and sediment reductions by 2028, as detailed in the General Virginia Pollutant Discharge Elim- ination System Permit (VPDES) for Discharges of Stormwater from Small Municipal Separate Storm Sewer Systems, Section 1.C: Spe- cial condition for the Chesapeake Bay TMDL. This objective is also integrated into Virginia’s com- mitments to the Environmental Protection Agency (EPA) to clean up the Chesapeake Bay. The financials for meeting these goals started off dire as cost estimates returned were higher than anticipated and there were no dedicated funds for TMDL implementation at the time. The above image shows Dead Run before the stream restoration project began. Photo by Stantec 20 World Water: Stormwater Management Autumn 2018 Nutrient Reduction benefit, improved infrastructure, shear stresses that cause erosion, the stream restoration project may etc., it provides a tangible starting channel incision, and overall initially be undertaken for ero- point that allows for consistent FACED WITH THE degradation of the natural stream sion concerns, but then it may be tracking of results. INSURMOUNTABLE system. While upland stormwater further enhanced to endure future During the search for innovative CHALLENGE OF practices can alleviate some of considerations such as recurrent practices, Virginia MS4s col- INSTALLING SUCH these symptoms through flow flooding or upcoming development. lectively found that conventional controls, streams are still vulner- All aspects of the stream and stormwater structural practices A HIGH NUMBER able to impacts from urbanization its watershed are reviewed prior – detention basins, constructed OF PRACTICES IN A and stormwater discharges. to designing a stream restoration wetlands, bioretention, and SHORT TIMEFRAME, Stream channel erosion releases project. Key considerations include permeable pavement, for example sediment into waterways, along topography and geology, along – posed a challenge as far as cost MANY MS4S WERE with the associated nutrients with constraints such as bedrock. and scale was concerned. They CONSIDERING BUYING bonded to the soil particles. Ad- Existing utilities – sewer mains and discovered that these traditional CREDITS AND WALKING ditionally, urbanization’s effects laterals, fiber optics, and electrical practices would have to number in on streams have caused discon- – are also frequent constraints the hundreds in order to meet their AWAY FROM THE nection from floodplains as well that must be considered and WLAs, would eventually become MAINTENANCE AND as decreased contact time and addressed as part of the design. a maintenance nightmare, and LOGISTICS. a reduced ability for nutrient Floodplain analysis is also a would have a very high dollar-per- uptake by streams and ripar- major consideration. The design pound removal rate. Faced with ian vegetation. These sediment of a stream restoration project the insurmountable challenge of and nutrient loads were noted has the ability to impact the installing such a high number of contributors to the degradation of mapped flood zones and thereby practices in a short timeframe, the Chesapeake Bay and its many influence Federal Emergency many MS4s were considering buy- tributaries. Sediment can impair Management Agency (FEMA) ing credits and walking away from benthic communities that rely on mapping, insurance rates, and the maintenance and logistics. stable stream cobble and gravel property values. Sourcing of However, Virginia’s MS4s substrates for habitat colonization. materials for these projects is soon identified two nontraditional Excess nutrients, coupled with also a key project consideration. practices that had the potential warm temperatures, create algae Local, state, and federal regulatory to achieve similar quantities of blooms and the resultant hypoxic agencies typically prefer to see pollutant reductions as numerous conditions currently found within onsite materials used where structural stormwater practices in parts of the Chesapeake Bay. possible such as root balls from one project at a more cost-effective for climate resiliency, reducing The practice of urban stream trees, native soils, and harvested removal rate: stream restoration flooding impacts, protecting exist- restoration seeks to reduce the loss streambed materials. Large and shoreline management. In ing infrastructure, and increasing of sediment and associated nutri- rock structures are typically both practices, sediment and public access to green spaces. ents from the stream channel while installed to help direct flows associated nutrients are directly stabilizing the stream channel to and provide for grade controls. prevented from entering waterbod- Stream restoration withstand new watershed condi- Visits to quarries to view boulder ies, with additional ecological Urbanization has significantly tions and other environmental choices are common, and hauling uplift added through natural affected waterways, with increases factors. A stream restoration project costs need to be considered. processes that can be designed in impervious areas spiking storm- can vary greatly depending on the Many MS4s have successfully into the project. Addressing the water discharges and peak flows. existing conditions and the desired restored stream channels and stream and shoreline erosion also These stormwater discharges outcome. In some instances, reported the amount of sediment improves other conditions for MS4 are conveyed to receiving chan- erosion reduction is all that is war- and nutrients (nitrogen and phos- permit holders, such as designing nels with high velocities and ranted for a project. In other cases, phorus) effectively removed from downstream receiving waters, and ultimately from the Chesapeake Bay. The amount of sediment and nutrients that is credited to the project for purposes of the Chesa- peake Bay TMDL is determined using the Chesapeake Bay Pro- gram’s assembled Expert Panel guidance document, which describes the practice, recomm- ends removal rates, and outlines qualifying criteria. Projects are credited using four primary protocols. The majority of a stream restoration project’s credit comes from the prevented mass of sediment and nutrients that is annually lost from erod- ing streambanks. This figure is estimated using a predictive model that considers susceptibility to erosion and dimensions of the stream, and it may be verified with bank pin measurements. Other The Dead Run stream restoration project, currently underway in Virginia, is protocols account for reductions expected to result in the environment depicted in the above rendering after achieved through nutrient process- restoration and stabilization are complete. Image by Stantec ing by denitrification and nutrient World Water: Stormwater Management Autumn 2018 21 Nutrient Reduction An aerial rendering of Jamaica Bay illustrates shoreline stabilization