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A multi basin SWAT model analysis of runoff and sedimentation in the Blue Nile, Ethiopia

机译：埃塞俄比亚青尼罗河地区径流与泥沙的多流域SWAT模型分析

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A multi basin analysis of runoff and erosion in the Blue Nile Basin,Ethiopia was conducted to elucidate sources of runoff and sediment. Erosionis arguably the most critical problem in the Blue Nile Basin, as it limitsagricultural productivity in Ethiopia, degrades benthos in the Nile, andresults in sedimentation of dams in downstream countries. A modified versionof the Soil and Water Assessment Tool (SWAT) model was developed to predictrunoff and sediment losses from the Ethiopian Blue Nile Basin. The modelsimulates saturation excess runoff from the landscape using a simple dailywater balance coupled to a topographic wetness index in ways that areconsistent with observed runoff processes in the basin. The spatialdistribution of landscape erosion is thus simulated more correctly. Themodel was parameterized in a nested design for flow at eight and sediment atthree locations in the basin. Subbasins ranged in size from 1.3 to174 000 km2, and interestingly, the partitioning of runoff and infiltratingflow could be predicted by topographic information. Model predictions showedreasonable accuracy (Nash Sutcliffe Efficiencies ranged from 0.53–0.92) withmeasured data across all sites except Kessie, where the water budget couldnot be closed; however, the timing of flow was well captured. Runoff lossesincreased with rainfall during the monsoonal season and were greatest fromareas with shallow soils and large contributing areas. Analysis of modelresults indicate that upland landscape erosion dominated sediment deliveryto the main stem of the Blue Nile in the early part of the growing seasonwhen tillage occurs and before the soil was wetted up and plant cover wasestablished. Once plant cover was established in mid August landscapeerosion was negligible and sediment export was dominated by channelprocesses and re-suspension of landscape sediment deposited early in thegrowing season. These results imply that targeting small areas of thelandscape where runoff is produced can be the most effective at controllingerosion and protecting water resources. However, it is not clear what can bedone to manage channel erosion, particularly in first order streams in thebasin.
机译：对埃塞俄比亚青尼罗河盆地的径流和侵蚀进行了多盆地分析，以阐明径流和沉积物的来源。侵蚀可以说是青尼罗河盆地中最关键的问题，因为它限制了埃塞俄比亚的农业生产力，使尼罗河的底栖生物退化，并导致下游国家的大坝沉降。开发了土壤和水评估工具（SWAT）模型的修改版本，以预测埃塞俄比亚青尼罗河盆地的径流和沉积物损失。该模型使用简单的每日水平衡和地形湿度指数，以与盆地中观测到的径流过程相一致的方式，模拟了景观中的饱和过量径流。因此，可以更正确地模拟景观侵蚀的空间分布。在嵌套设计中对模型进行了参数化，以实现盆地中八个位置和三个位置的沉积物流动。子流域的大小从1.3到17.4万公里 2 不等，有趣的是，可以通过地形信息预测径流和渗流的分配。模型预测表明，除凯西（Kessie）无法关闭水预算外，所有地点的测量数据均具有合理的准确性（纳什苏特克利夫效率在0.53–0.92之间）。然而，流动的时机被很好地捕捉了。在季风季节，径流损失随降雨增加而增加，在土壤浅，贡献面积大的地区尤为严重。对模型结果的分析表明，在生长季节的初期，当耕作发生时，在土壤被润湿并建立植物覆盖之前，山地景观侵蚀主导着沉积物向青尼罗河主要茎的输送。一旦在8月中旬建立了植物覆盖物，景观侵蚀就可以忽略不计，而沉积物的出口则主要由河道过程和生长季节初期沉积的景观沉积物的再悬浮所决定。这些结果表明，针对产生径流的小面积景观，最有效地控制侵蚀和保护水资源。但是，尚不清楚可以用什么方法来管理河道侵蚀，特别是在盆地中的一阶流中。

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