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Coastal Processes Analysis of Lake Tashmoo Inlet

Similar to many small estuaries and coastal ponds along the Massachusetts coast, Lake Tashmoo requires frequent maintenance dredging to ensure safe navigation. To provide an understanding of the major factors causing shoaling within the Lake Tashmoo entrance channel, a study of coastal processes governing the movement of nearshore sediments is necessary. This understanding is performed by developing numerical models of waves and longshore sediment transport. Waves provide the primary driving forces governing erosion and the observed accretion/erosion of the shoreline in the study area. The overall purpose of the coastal processes analysis in the vicinity of the Lake Tashmoo entrance channel was to assess conditions responsible for frequent maintenance dredging requirements, evaluate the integrity of the existing jetty system, and develop sand management options that both reduce maintenance dredging frequency and enhance local shore protection. Since the inlet has a slightly larger cross-section than optimal, the inlet does not ?self-scour? and deposition occurs within the portion of the channel between the jetties, as well as within Lake Tashmoo. To maintain safe navigation through the entrance channel, the width of the channel should be maintained to its present permitted dimensions. Several alternatives to maintenance dredging were also considered. Allowing the channel to shoal naturally would diminish the capacity for safe navigation as well as impact the health of the estuarine water quality. As a second alternative to frequent maintenance dredging, an assessment of different sand management scenarios were evaluated both qualitatively and quantitatively. The shoreline change model also was utilized to assess potential beach nourishment options to the east of the Lake Tashmoo entrance. The volumes assessed in the analysis represent maximum excavation volumes to provide effective sand management without potential adverse impacts to adjacent properties. Smaller volumes of the updrift beach could be excavated; however, this would lead to more frequent dredging of the inlet system. In addition, larger volumes of material could be excavated from the offshore ?over-dredging? area; however, dredging beyond the 10 ft depth contour would prevent effective infilling and likely not improve the long-term performance of this option.

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