EXPLORING WATERSHED URBANIZATION IN USE ATTAINABILITY ANALYSES OF URBAN WATERBODIES
Abstract:New York Harbor and its tributaries form a complex hydrologic network of open waters, embayments, rivers, estuaries, wetlands and riparian areas that are influenced by highly urbanized watersheds. The New York State classifications of many of these waterbodies may not be considered to meet the “fishable/swimmable” criteria of the Clean Water Act. Even so, current water quality standards, although lower than fishable/swimmable, are still not attained in many locations throughout the harbor and its tributaries. The New York City Department of Environmental Protection (DEP) is conducting a Use and Standards Attainment (USA) Project that was launched in August 1999 as part of its continuing efforts to maintain and improve water quality in the harbor. A watershed-based approach is being utilized to conduct an integrated evaluation of the interdependent factors affecting receiving water uses, including storm water, combined sewer overflows (CSO), wastewater treatment, upland uses, shoreline uses, habitats, sediment and water quality for twenty-six waterbodies throughout the harbor.
Presentations on the USA Project were given at the Water Environment Federation's Watershed 2000 and 2002 speciality conferences. The presentations described the overall project and a case study of an impacted urban tributary for which a waterbody/watershed plan was developed. The plan will significantly improve riparian and ambient water quality conditions but despite a cost exceeding 300 million, water quality standards associated with the current use designation and fishable/swimmable criteria will not be attained at all times. As such, a Use Attainability Analysis (UAA) was conducted to identify the physical, chemical and biological factors affecting use attainment using a watershed-based approach. In particular, the changes to the watershed affected by urbanization are a key component of the analysis that is now being applied on several ongoing assessments.
A major goal of the DEP is to develop plans to restore, enhance, and protect riparian and waterbody uses as they are affected by water quality. These uses include fish and aquatic life protection, fish and shellfish consumption, wildlife protection, shellfishing, bathing/recreation, aesthetics, and public access – all of which are protected by state water quality standards. However, these uses are directly affected by watershed influences – especially urbanization. For example, not only are the topographic characteristics of a watershed altered by urbanization, but its runoff characteristics are particularly altered. Percent impervious is typically altered from a 10 to 15 percent level for natural areas to 70 percent or more for urban areas. The literature demonstrates that few urban streams can support a diverse benthic habitat at imperviousness greater than 25 percent. The overall runoff yield may be increased from a moderate level of overland runoff to millions of gallons discharged by combined and stormwater sewer systems even in a moderately sized city. Urbanization also decreases the travel time to a waterbody, which would otherwise naturally degrade pollutants, and increases peak discharge rates.
Discharges are then made directly to a waterbody rather than being attenuated, filtered, and mitigated by adjoining wetlands that have also been eliminated by urbanization. This is one example of a physical factor affecting use attainability that can be applied in many urban watersheds that have been urbanized to a high degree of imperviousness. In many cases, predevelopment water quality and beneficial uses cannot be reasonably restored by implementing cost-effective and reasonable best management practices that do not sufficiently reduce watershed runoff and pollutant loads to meet designated uses. Such conditions represent human-caused conditions or sources of pollution that cannot be remedied or would cause more environmental damage to correct and represents a limit on complying with standards at all times.
In such cases, attaining fishable/swimmable uses is not feasible, therefore federal UAA criteria should apply.
Document Type: Research Article
Publication date: 2004-01-01
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