Island Land Loss in the Chesapeake Bay: A Quantitative and Process Analysis

Abstract

The rates and processes of land loss were studied for seven islands in the Chesapeake Bay: Barren, Bloodsworth, Hooper, James, Poplar, Smith and South Marsh Islands. Rates and patterns of land loss were quantified for the years 1848 to 1987 with the Metric Mapping technique which utilizes digitized data from historical maps and vertical aerial photographs. Processes of land loss were determined through field surveys and correlated with environmental factors. Two distinct island types were identified which exhibited different, long-term patterns of land loss. Small, upland islands, termed the Northern Group, showed rapid land loss along the main stem of the Bay primarily due to wave action driven by the predominant westerly winds. Land loss appeared to accelerate during periods of high storm frequency. The long-term averaged land loss rate for Northern Group islands is 1.9 ha/yr. The averaged erosion rate on the western side of the islands is 4.9 m/yr, compared to 0.68 m/yr on the eastern side of the islands. In contrast, the large, marshy islands of the Southern Group experienced uniform marsh edge erosion and interior marsh degradation. The Southern Group islands lost land at an averaged rate of 5. 6 ha/yr, with an averaged rate of marsh edge erosion of 1.2 m/yr. Land loss appeared to be weakly correlated to storm frequency. Interior marsh loss was not quantified for this study, however, so this study provides an underestimation of total land loss of coastal wetlands.