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navigation, andlor to re^uve <br /> more feasible if combined with a need for safe <br /> contai'ninated sediments (if any exist). <br /> Dredging the shoal at the mouth of Mashpce River and a channel in <br /> Mashpee River would have no significant impact on tidal flushing in other <br /> portions of the Popponesset Bay Estuary. <br /> The most efficient scenario for dredging Mashpee River (Scenario 2) way <br /> combined with maintenance dredging in popponesset Bay. The PoppOrusset Bay <br /> maintenance dredgingconsisted only of the channel at the r,outh of the bay, <br /> proposed by BSC (1996). This dredging was defined as Scenario 5, and the residence <br /> time,., are listed in Table 1. Residence times are unchanged compared to Scellaric 2; <br /> therefore, the small chonnel ma'.ntenance dredging at the mouth Or i oppUncgset <br /> Bay would have no significant impact or tidal *'lushix,g ir. the estuarine syStem. <br /> Sce—aria .5 was combined with a c.nynn2l, five feet deep at Pylean Low Water, <br /> connecting the Popponcsset Bay, Inlet with Mashpee Rizer. This dredging <br /> configuration, Scenario 6, was modeled to deter-mine if a chant:el in PopporLesset <br /> Bay would help promnie flaw into Mashpee River and improve tid:11 flushing in <br /> the river. Model result: indicated there wis a slight irs.rease in residence time for <br /> Mashpee Ri:'er, Qckway Bay, and Shcestring Bay. Rcsidencu tii:tes increased <br /> because the dredging increased the volume of Fater roquired to fill and flush <br /> Popponesset Bay. The significant increase in volume ii, Popponesset Bay prevented <br /> some water from flushing more remote portions of the system. <br /> Conclusion <br /> the shoal at the <br /> In. conclusion, the hydrady:eamic m^dei revealed dr8dging 0� <br /> mouth of Mashpce River, as well as a SMAIl channel extending approximately 1,000 <br /> ft upriver would improve tidal flushing of the riv2r by ten percent (ScenariO 2). <br /> Sidecasting the dredgod spoils on the sides of the river Would help improve tidal <br /> b Fa i <br /> � i to be flus':ted from the river would <br /> flushing because the volume of wa.er_ recd lir � <br /> not be increased by the dredpging. However, sid*eCasting the spoils may not improve <br /> water quality since the spoils are likely to be composed of fine sediments, which <br /> potentially sequester nutrients ani other pollutants. rield sarnpling and laboratory <br /> testing (tar grain size and chemicAl. composition) of the bottom sediments is <br /> recommended. Althovtgh a tell percent improvernent to tidal flushing of Mashpee <br /> River may help improve' water quality, a number of other factors must be <br /> considered, such as nutrient anti pollutant loading rates (septic systerns, fertilizers, <br /> waterfowl, etc.), as' well as 1 awral fnr he 1 estuary al and(ACI, 1 g6�;cm ylcal be appliedes, The <br /> tc� help , <br /> existing water quality mode y <br /> resolve water quality concerns in -Mashpee River. <br /> AGI appreciates the opportunity to work with the 1'ow:; of Mashpee to <br /> address issues rLlated to tidal fiu�hing and water quality in the PoppOnesset Bay <br />