Hydrology as a Surrogate Indicator in Restoring Urban Northeastern Watersheds

Habitat/aquatic impairments in an urban environment are often associated with multiple stressors, including known and unknown pollutants, storm water runoff, hydrologic modifications, riparian corridor encroachment, and channel alteration. These stressors may be acting either individually or cumulatively. In the absence of comprehensive physical, chemical, and biological data it is often difficult to determine each stressor's role and significance in contributing to the impairment. As a result, developing restoration plans or TMDLs and implementing improvements to address these impairments presents unique and complex challenges. This paper presents an approach to restoration plans or TMDL development and implementation planning for data-limited urban watersheds using a manageable watershed model and a flow analysis. Evaluation of data in many New England watersheds has shown that habitat/aquatic impairments are frequently related to excessive urban development and the accompanying increased storm water runoff. Not only does the storm water runoff regime (including changes in the peak and base flows) alone lead to problems, but increased runoff also generally leads to increased pollutant transport capacity and loading. Therefore, using storm water as an "umbrella" surrogate to address a suite of stressors contributing to aquatic life impairments is a plausible option in urban areas (where discrete local problems have not been identified). The use of surrogate indicators expressed as quantitative targets is an important tool for developing TMDLs. This paper demonstrates application of simple watershed models to support flow duration analysis and hydrologic target identification for TMDL development in Maine, Vermont, and Massachusetts. It also exemplifies how the approach can be extended to support storm water implementation planning.