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This essay traces the historical relationship between the construction of the Nile River and the prevalence of disease in Egypt in the long twentieth century, with an eye to the relevance of this history to other regions on the African continent impacted by the construction of large dams. Beginning in the second decade of the nineteenth century and stretching through the 1970s, the Nile River underwent a dramatic process of transformation. Two large dams–the 1902 Khazan Aswan and the Aswan High Dam–were constructed on the river. Networks of perennial irrigation canals facilitated the practice of year-round agricultural production and the High Dam provided electricity. The remaking of Egypt’s riparian ecologies also had important implications for the health of Egypt’s population as these ecologies were associated with new landscapes of disease and approaches to biomedical treatment.
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Estimating the timescale of fluvial response to anthropogenic disturbance using two generations of dams on the South River, Massachusetts, USA
Abstract Centuries‐long intensive land‐use change in the north‐eastern United States provides the opportunity to study the timescale of geomorphic response to anthropogenic disturbances. In this region, forest‐clearing and agricultural practices following EuroAmerican settlement led to deposition of legacy sediment along valley bottoms, including behind mill dams. The South River in western Massachusetts experienced two generations of damming, beginning with mill dams up to 6‐m high in the eighteenth–nineteenth century, and followed by construction of the Conway Electric Dam (CED), a 17‐m‐tall hydroelectric dam near the watershed outlet in 1906. We use the mercury (Hg) concentration in upstream deposits along the South River to constrain the magnitude, source, and timing of inputs to the CED impoundment. Based on cesium‐137 (137Cs) chronology and results from a sediment mixing model, remobilized legacy sediment comprised% of the sediment load in the South River prior to 1954; thereafter, from 1954 to 1980s, erosion from glacial deposits likely dominated (63 ± 14%), but with legacy sediments still a substantial source (37 ± 14%). We also use the CED reservoir deposits to estimate sediment yield through time, and find it decreased after 1952. These results are consistent with high rates of mobilization of legacy sediment as historic dams breached in the early twentieth century, and suggest rapid initial response to channel incision, followed by a long decay in the second half of the century, that is likely dependent on large flood events to access legacy sediment stored in banks. Identifying sources of sediment in a watershed and quantifying erosion rates can help to guide river restoration practices. Our findings suggest a short fluvial recovery time from the eighteenth–nineteenth century to perturbation during the first half of the twentieth century, with subsequent return to a dominant long‐term signal from erosion of glacial deposits, with anthropogenic sediment persisting as a secondary source. © 2020 John Wiley & Sons, Ltd.
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- Award ID(s):
- 1654462
- PAR ID:
- 10456178
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Earth Surface Processes and Landforms
- Volume:
- 45
- Issue:
- 10
- ISSN:
- 0197-9337
- Format(s):
- Medium: X Size: p. 2380-2393
- Size(s):
- p. 2380-2393
- Sponsoring Org:
- National Science Foundation
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