College Street Green Stormwater Infrastructure (GSI) Retrofit Project

Project At A Glance:
When the City of Burlington, VT wanted to analyze and model the complex stormwater runoff in its urban core for Green Stormwater Infrastructure (GSI) implementation, they chose Watershed for the task.

Client: City of Burlington, VT

Partners: Lakeside Environmental Group (LEG), Waite-Heindel Environmental Management (WHEM), SMM Engineering, Urban Rain|Design

Location: Burlington, VT

Description:
The City of Burlington, VT, is a small city located on the shores of Lake Champlain. While most of Burlington’s downtown area is served by a combined sewer system, a 23 acre area drains to a separate stormwater outfall—the “College St. Outfall”—which discharges to the vibrant Burlington Waterfront. Over the past decade several end-of-pipe and gray solutions have been proposed but never implemented due to cost, lack of overall effectiveness, and, more recently, because they would provide only singular stormwater benefit vs. the co-benefits available with GSI and smaller-scale solutions.

The City of Burlington contracted with Watershed to complete a catchment-scale green stormwater infrastructure (GSI) implementation assessment to address the water quality issues at the outfall as well as improve streetscape level aesthetics. A GSI tool box specifically adapted for the College St watershed was developed.

A watershed-wide Stormwater Management Model (SWMM) model was selected as the best modeling approach to assess the watershed-wide benefit of various BMP implementation scenarios. The final proposed design solutions included a collection of curb bump outs with infiltrative bioretention, terraced planter boxes, green gutters, and a large underground infiltration storage unit located beneath a park area.

The full build-out scenario predicted a greater than 50% decrease in the water quality storm event and substantial reductions in sediment and phosphorus loading at the outfall. Final engineering of these practices is planned for 2014, with Phase 1 implementation likely by 2015.

UNIQUE GSI PLANNING APPROACH:
The College St. Project is an example of a unique GSI implementation approach ideal for the urban environment where above ground storage is not an option, infiltration is ideal, and a collection of small-scale GSI BMPs is the optimal approach to manage stormwater throughout the watershed. Moreover, the College St. retrofit plan demonstrates how GSI can aesthetically enhance the urban streetscape in synch with municipal landscape planning goals, and help ‘calm traffic,’ while also providing significant stormwater benefit, a co-benefit that is becoming increasingly important to communities with limited resources.