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A comparison of two editions of l:50,000-scale NOS charts covering 344 km of coastline provides the basis for a detailed study of coastal erosion occurring over a 30-year period. This study also determines patterns in coastline evolution and their probable causes, and sediment yields from erosion. Excluding the large Colville Delta, advancing on average +0.4 m/yr, the average erosion rate is -2.5 m/yr. Extremes for the long-term average rates range up to -18 m/yr. The coastal plain deposits in one third of the study area are fine-grained mud, with an average erosion rate of -5.4 m/yr. The remaining region is composed of coarser sandy deposits, which erode on average -1.4 m/yr. Thus grain size of bluff material exerts the dominant control on coastal retreat rates. Other important factors include bluff height, ice content and thaw settling, bluff orientation, and degree of exposure to the marine environment. Vertical crustal motion has not played an important role during Holocene time. In calculating sediment yield we treat not only the materials above sea level, but consider that the marine profile to 2m depths is in dynamic equilibrium, and therefore contributes to the sediment yield. The upper part of the eroded section contains up to 75% ice, and the sediment yield is reduced accordingly. The annual yield from coastal retreat thus calculated is 2.5 x 106m3, with the offshore contribution slightly higher than the onshore contribution. We estimate the annual sediment yield from the adjacent drainage areas is slightly less at 2 x 106m3 .
Reimnitz et al. (Tue,) studied this question.