In search of the Denny regrade: Fate of a Large Spoil bank in Elliott bay, Puget sound

Abstract

A large shoal located approximately 800 ft ( 2 5 0 m) off Seattle’s waterfront along the northeast shore of Elliott Bay in Puget Sound is attributed to offshore dunping of material from the Denny Hill Regrade, which occurred in two phases between 1898 and 1 9 3 1 . A compilation of hydrographic surveys dating from 1875 to 1 9 7 0 , together with recent marine geophysical data, 3 show the developnent of a bank and as ociated flank deposits whose v o l m ( 8 . 9 million yd / 6 . 8 million m ) canpares closely with that of estimates of the amount of materia3 removed durinfi the regrading operation ( 1 0 million yd / 7 . 6 million m ). Seismic records and available bottom samples suggest that the spoil bank is covered in places by a thin mantle of modern sediment, and that slunping of the steep flanks of the bank is contributing material to the central submarine valley in Elliott Bay. This spoil bank is being studied to determine its role and relationship to sediment distribution patterns and transport mechanisms in Elliott Bay. 5,