City of Rockville, Montgomery County, MD Stream Restoration - Assessment/Design/Build

The incorporated City of Rockville is a highly urbanized township located in Montgomery County, Maryland. The City has experienced severe streambank erosion along its tributary streams resulting in the loss of private property, habitat, storm and sanitary sewer infrastructure. Excessive amounts of in-stream soil loss have generated heavy sediment loads through the catchments, indicative of the flashy nature of the streams.

ESA was retained to perform design/build remediation of the City's principal waterways that included Cabin John, Watts Branch and Rock Creek. ESA was responsible for all field methods of ecology to evaluate and prioritize stream restoration, preparation of design blueprints, regulatory permitting, public meetings and outreach, negotiations with individual landowners, preparation of bid documents for construction, construction oversight and post-implementation monitoring.

Our hydrologic/hydraulic analysis and ecological studies documented that the majority of stream erosion was occurring during frequent flooding events of a magnitude of less than the one-year, two-hour storm. For the streams studied, this flood event typically produced scouring bankfull conditions. Our restoration plans addressed research observations of channel down cutting, excessive channel widening and reduction of wetted perimeter, embedded riffle substrate and large, unstable point bars. We determined that all of the streams within the study confines were subject to flows of high volume and short duration, which significantly alter their appearance, stability and biological carrying capacity.

The resulting restoration measures that were employed included both a combination of bioengineering methods (vegetation), natural stabilization techniques (stream alignment, grade control), and traditional engineering solutions (hard structure). Measures utilized included rock vanes, notched and vortex weirs, revetments and deflectors, brush bundles, root wads, the re-grading of bank slopes, removal of excessive sediment bars, stream re-alignment to improve sinuosity (curvature), biolog toe-of-slope protection, riparian plantings, tree thinning, removal of in-stream debris complemented with numerous types of vegetative treatments. Because runoff quantity was documented as the principal cause of degradation, management recommendations included the retrofit of existing facilities where possible, with quantity controls managing runoff generated by the 1-year frequency storm event, and that all future facilities approved through the City be designed to a 1-year storm standard.

This highly visible stream bioengineering project has received high marks for accomplishing project goals with accolades coming from the regulatory community, municipal government and adjoining citizenry whose private properties were affected. The visible nature of the project has provided the opportunity to publicly demonstrate natural stream restoration techniques. The project has benefited indigenous fisheries (dace, chub, shiner, minnow), aquatic insects and wildlife by providing in-stream cover and riffle/pool complexity, expansion of riparian buffers, improved meander patterns and bank repose, sediment load reductions, increased channel roughness, stream temperature amelioration and improved water quality.