ROLE OF HISTORICAL HURRICANE DEPOSITS IN CONTROLLING SALT MARSHEROSION IN THE HOUSATONIC ESTUARY OF CONNECTICUT

摘要

The wetland complex in the lower-most Housatonic estuary is part of the State ofrnConnecticut’s Wheeler Wildlife Management Area and the U.S. Fish and Wildlife’s McKinneyrnWildlife Refuge and is significant both in terms of its ecology and its size. Presently, portions ofrnthe salt marsh complex are undergoing bank retreat at rates locally as high as 1 m/yr. The marshrncomplex has historically been characterized by rapid growth. Present day erosion patternsrnrepresent an impressive alteration of this historical trend. Bank retreat is predominantlyrnproduced via erosion of low-cohesion, sand-rich strata. The overlying marsh is progressivelyrnundercut until the weight of the undercut portion exceeds the tensile strength of the overlyingrnmaterial. Bank failure occurs by means of blockfall with typical blocks being approximately 2 mrnlong, 1 m high, and 0.5 m deep. Subsequent wave and current action disaggregates the blocksrnand removes the constituent sediments from the area. These low-cohesion, sand-rich stratarnappear to be storm deposits and have been correlated with historical hurricanes. Age-depthrnrelationships were estimated via existing 14C and 210Pb data obtained for the area by WesleyanrnUniversity researchers. Significant erosional strata correlate best with the hurricanes of 1783,rn1788, and 1821. Another erosion-prone horizon consists of glacial outwash sands that underliernthe marsh. This horizon is locally exposed during low tides. The overall spatial distribution ofrnthe sand-rich strata is somewhat patchy presumably reflecting variability in patterns ofrndeposition from one storm to the next. The principal controls on the acceleration of bank erosionrnappear to be exposure to high-energy wave action, particularly that produced by boat wakes withrnthe increase in pleasure boat traffic in the estuary, and presumably the interaction of tides and searnlevel change which determines the vertical distribution of energy against the bank.