College Gardens: Synthesis of Stream Restoration and Stormwater Management for an Urban Park Renewal

Unusual is the case where both stream restoration (SR) and stormwater management (SM) aims can be achieved jointly and rare is the case where the effects of both fields are measured discretely. The renovation of the College Gardens Park in Rockville, Maryland is one example.The City of Rockville was charged with rejuvenating an aging park in concert with providing SM (flood control and water quality improvement) and SR work to protect the 640-m (2,100-ft) downstream receiving water, known as the College Gardens Tributary. This heavily impaired stream drains a 64-ha (158-ac), 42% impervious catchment. The drainage area is a mixture of residential and light commercial use with little SM control. Consequently the Tributary is deeply incised and enlarged. Bank erosion was ubiquitous and was estimated at 0.27 tonne/m/yr (0.09 ton/ft/yr).Four goals for rehabilitation work included:1) Cost-efficient renovation of the park to provide SM2) Reduction of bank erosion along the Tributary3) Protection and enhancement of natural resources4) Increased park patronage and aesthetic improvementThe City contracted with Charles P. Johnson and Associates, Incorporated (CPJ) to determine options. CPJ evaluated alternatives including SR along the entire length, on-site pond creation, and off-site SM. The option chosen involved the construction of an on-site extended detention wetland pond. The design included a sediment forebay, aquatic wetland bench and a direct feed of stormflow via a flow splitter from an adjacent 137-cm (54-in) storm sewer. The design provided 50% of the water quality volume and 100% of the channel protection goals at the park based on State of Maryland criteria.Specific goals for this project included a 42% reduction of sediment being generated by streambank erosion along with an 80% removal of total suspended solids (TSS). The streamwork was completed in February 2009 ahead of the park renovation which was completed in December 2009; the project is currently being monitored to determine project success.