Noor H., Fazli S., Alibakhshi S.M. (2013) Suspended sediment (SS) resulted from distributed soil erosions facilitates soil organic matter and phosphorus (P) transportation and influences soil depletion and water quality. Organic matter (OM) in soil is the most important indicator of soil quality and productivity. P is one of the major nutrients controlling eutrophication of surface water. Irregular contaminant load pulsed by heavy rainfall may damage the ecological quality of downstream waters. Evaluation of OM and P, depleted by erosion processes in watershed scale, is necessary for better understanding the watershed system and should lead to appropriate management approaches. On the other hand, different behaviours of soil erosion as well as the necessity of regional studies have been proved. The present study was conducted in the Kojour watershed, Iran in order to (1) get some ideas about the storm-wise OM and P load in river, (2) evaluate the relationship between the peak of OM and P concentration and discharge during individual rainfall events, and (3) assess the applicability of rainfall and runoff variables of ten storm events in the prediction of storm-wise OM and P loss. The results showed that most of the OM and P peaks preceded the peak discharge, following a clockwise hysteretic loop that exhibited hysteresis with a greater OM and P concentration for a given discharge occurring on the rising limb rather than on the falling limb. The results also showed that regression models had good efficiency in estimation of storm-wise OM and P loss with coefficient of determination of 0.96 and 0.93, respectively.
The effort to control sediment yield at watershed scale is an ongoing challenge that needs to take into account trade-offs between two conflicting objective functions, i.e. economic and hydrologic criteria. Therefore, researchers have coupled hydrologic and multi-objective optimization models to find Pareto-optimal solutions. However, very limited studies have been conducted to analyse the cost-effectiveness (C/E) of scenarios obtained in the Pareto-front optimal. This could provide new information leading to effective watershed management. Therefore, in the present study, the Soil and Water Assessment Tool (SWAT) was used to simulate sediment yield under different combinations of best management practices (BMPs) and was coupled with the Non-dominated Sorting Genetic Algorithm (NSGA-II). The model attends to providing the Pareto-optimal solutions by minimizing the costs of BMPs and maximizing sediment reduction. The results of the application of the cost-effective optimization model in Mehran watershed, Iran, showed that the solutions in the Pareto-optimal front reduce sediment yield between 2% and 40.5% from baseline at costs of between $6,500 and $72,100, respectively. Finally, comparison of four sediment reduction solutions (i.e. 10%, 20%, 30%, and 40%) showed that the total cost and C/E ratio of solutions increased as the sediment reduction criteria increased.
Evaluation of soil erosion by existing models is needed as an important tool for managerial purposes in designation of proper water and soil conservation techniques. The present study aimed to assess the applicability of hillslope erosion model (HEM) as one of the newest erosion models for prediction of storm-wise sediment yield in Khosbijan rangeland with 20% slope steepness by using soil erosion standard plots. In order to run the model, runoff depth, land surface cover, soil texture, slope steepness and length were determined for 16 storm events. The results showed that the uncalibrated HEM did not simulate the observed sediment yields properly. Calibration of soil erodibility parameter and developing regression between observed and estimated data indicated that the model was capable of predicting sediment yield in plots by applying soil erodibility parameter of 0.15 with determination coefficient of 0.64 and estimate error of 40%.
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