Stonnwater and Sediment 



Thermal Impacts 



Organisms adapted to coldwater fresh or marine environments may be seriously affected 

 by an increase in water temperature of a few degrees above ambient conditions. Thermal 

 enrichment problems may be critical for tributary streams as well as for coves or enclosed 

 embayments exhibiting well-defined thermal regimes. Several factors influence 

 summertime water temperatures in these areas, and of these, certain factors may act 

 synergistically to increase water temperature. 



A heated urban landscape significandy warms any runoff passing over it Unless 

 streambanks or channels are shaded, runoff enters receiving waters at elevated 

 temperatures. The Vermont Upland Stream Smdy found shoreline shading highly 

 significant in maintaining temperature and light penetration regimes necessary for protection 

 of native fish populations (Moreland, 1985). In addition, runoff stored in shallow wet 

 ponds or other impoundments is heated between storms, and may release pulses of warmed 

 water following storm events. 



ISSUES OF CONCERN IN NARRAGANSETT BAY 



EROSION AND SEDIMENTATION 



Rhode Island's AWQMP concluded that erosion and sediment control would be 

 necessary in order for the Narragansett Basin's waters to meet applicable water quality 

 standards. Unacceptable erosion and sedimentation problems exist in many urbanizing 

 areas and agricultural areas. (See Chapter 2.2 on Agricultural non-point sources.) 



Erosion attributable to urbanization or urban sources in the Bay Basin totals roughly 

 178,000 tons per year (USDA SCS, 1984). Of this total, die majority occurs at 

 construction sites where removal of vegetation has exposed underlying soil for most or all 

 of the construction period SCS estimates that erosion rates of 30 to 40 tons per acre per 

 year can be expeaed on construction sites, and that at least 4500 acres are disturbed 

 annually in the Bay Basin as a consequence of development (USDA SCS, 1984). 



In inland portions of the Basin, much of the sediment delivered to waterways is 

 deposited in stream channels or in wetlands, ponds, reservoirs, or other impoundments 

 along the drainage system. Sediment has accumulated in numerous such impoundments, 

 reducing storage capacity by as much as 50 percent and significandy affecting flooding 

 potential in certain watersheds (SCS, 1984). 



In the Providence River, sediment accumulation has severely limited use of commercial 

 and recreational ports, and has created a major dredged spoil disposal problem. Pickan and 

 Boothroyd (1987), in studies of the physical stratigraphy of the river, determined that 

 sediment accumulation in channels was 5 cm/yr, while Pawtuxet Cove accumulation ranged 

 from 2 cm to 5 cm per year. The audiors acknowledge that riverine accumulation rates 

 exceed values reported for the upper and lower Bay by 1.5 to 4.5 cm/yr. Although 

 calculated sedimentation rates for the Bay as a whole show great variability and 

 inconsistency. King, et al. (1987) are undertaking a detailed stratigraphic analysis of a 

 network of sediment cores which should improve understanding of conditions and 

 processes throughout the Bay. 



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