Advisor

Paula L. Sturdevant-Rees

Publication Date

2-2007

Abstract

The Blackstone River watershed covers an area of 475 me in central Massachusetts and northern Rhode Island. The Blackstone flows from its headwaters in the hills above Worcester, MA, through Woonsocket, RI and finally joins the Seekonk River in Pawtucket, RI. The Seekonk then flows into the Providence River on its way into Narragansett Bay. The historical significance of the Blackstone River has been recognized at the federal, state and local levels. Furthermore, the Blackstone is known to playa significant role on the hydrology and ecology of Narragansett Bay. This study is part of a larger study designed to evaluate the cost-benefit effectiveness of past remediation efforts and, in a modeling framework, potential future, traditional and progressive abatement strategies at the local and watershed scales. A driving theme of this portion of the study is the development of a detailed understanding of point and nonpoint source contributions within both the headwaters of the Blackstone and the watershed as a whole. Understanding the source, fate and transport of contaminants along the mainstem of the Blackstone River is essential for setting reasonable management strategies in order to achieve the desired water quality goals in both the river and the bay. Initial investigations into the relative magnitudes of point source and nonpoint source nutrient loadings under current and future loading regimes were conducted to allow a better understanding of the impacts of current regulations and the need if any for future regulatory action. Relationships between water quality and surrounding land use characteristics were analyzed to determine if correlations between the two exist and to predict the impact on water quality that may be caused by future changes in land use in the basin. Analyses on monthly and annual point and nonpoint source loadings dynamics between the Blackstone and Narragansett Bay were conducted as well. The relative nutrient loadings under wet and dry weather loading regimes were determined, with particular attention being placed on the impacts of the numerous impoundments along the mainstem of the Blackstone River. Based on the work contained herein, it has been concluded that there is a positive correlation between the amount of urbanized area and the amount of water quality degradation in the Blackstone watershed and its sub-basins. Furthermore, increasing amounts of urbanization wi11lead to increased peak flow values seen in the river, allowing for increased resuspension of pollutant laden sediment from behind the impoundments along the mainstem of the river, especially during wet weather events. Also, due to the complex hydraulics and loading dynamics ofthe Blackstone River, its tributaries and the bay as a whole, further regulation of point source pollution alone may not be an adequate or cost effective method for reducing nutrient loadings into the Blackstone River and Narragansett Bay. The loading dynamics have been shown to be highly variable on a monthly timescale, a variability that is likely to increase if more refined water quality and quantity data is collected for the river. Finally, the lack of available wet weather data also points to the need for additional, more refined data collection to be undertaken in order to better assess the loadings into the Blackstone River and their propagation downstream into Narragansett Bay. The need for additional data is supported by the highly variable loadings seen in the river as well as the changes in both the land use and the hydrology in the watershed that have occurred since the BRI was conducted.

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