RiverSmart Washington – A Low-Impact Development Demonstration Project

The Challenge

DOEE needed to investigate ways to reduce its volume of stormwater wet weather runoff to ease the burden on existing storm sewer infrastructure, reduce streambank erosion in urban streams, and improve water quality. DOEE wanted to consider green infrastructure practices to help achieve these goals. However, before making a significant investment, the District needed to understand the extent of the potential benefits, opportunities for implementation, and real-world performance of green infrastructure and LID.

The Solution & Outcome

LimnoTech worked with DOEE to assess the benefits of green infrastructure and LID practices at a neighborhood scale. This work included evaluating and recommending potential demonstration locations for LID retrofits, developing and implementing a monitoring program to evaluate LID retrofit performance, assisting with design, conducting practice-level monitoring, helping to coordinate practice rehabilitation activities, analyzing pre-and post-rehabilitation monitoring data, and modeling at both site and city-wide scales.

LimnoTech collaborated with DOEE and project partners and stakeholders, including the District Department of Transportation (DDOT), DC Water, and several nonprofit organizations, to evaluate potential demonstration locations where LID retrofits could be installed and monitored in public spaces. This involved identifying and performing preliminary analyses of physical constraints and opportunities (proximity to other infrastructure, existing planned construction projects, etc.); educational and political opportunities (land ownership, educational access, etc.); and monitoring constraints (sewer access and network complexity). Based on these considerations, two demonstration sites and a control site were selected.

The next step was to develop full designs for the LID retrofits. As part of the design team, LimnoTech identified the appropriate placement of practices in alleys, within the streetscape, and on school properties and developed conceptual designs for each site. As part of this effort, LimnoTech further characterized the study areas with detailed hydrologic modeling and GIS analyses to better understand the benefits of various design alternatives.

To evaluate LID retrofit performance, LimnoTech conducted pre/post-construction and pre/post-rehabilitation monitoring and modeling. The monitoring program included the deployment of custom-configured data loggers, water level and soil moisture sensors, and rainfall stations and was specific to a LID practice (e.g., permeable surfaces, bioretention cells) to provide practice-level monitoring data. LimnoTech’s application of practice-level monitoring helped to quantify decreased LID performance over time due to inlet design issues, deficiencies in construction, and deferred maintenance, emphasizing the value of maintenance and rehabilitation activities.

As part of this effort, LimnoTech worked with DOEE to update its city-wide “Green Build Out Model” (GBOM) to reflect LID practice performance based on the practice-level rehabilitation monitoring and neighborhood-scale and site-specific stormwater management SWMM modeling (US EPA’s Storm Water Management Model). The GBOM update resulted in a model that provides a more realistic estimate of the volumetric water benefits of green infrastructure and enhances its utility as a stormwater management planning tool that reflects the real-world performance of LID retrofit practices in urban environments.

The assessment of the LID demonstration sites has bridged the gap between ideal design-specification performance estimates of green infrastructure and the real-world performance of retrofit practices in urban residential environments. The overall findings from this work, in support of the RiverSmart Program, demonstrate the benefit of LID and green infrastructure practices applied on a city-wide scale and the value of including LID and green infrastructure in the District’s long-term water management plans.