Hamzeh Noor; Mahmood Arabkhedri; yahya parvizi
Abstract
IntroductionImplementation of watershed management measures in Iran to reduce the damage caused by the misuse of natural resources has begun many years ago and is still ongoing. Evaluating the performance of previous remedial work is essential for better planning of future watershed management projects. ...
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IntroductionImplementation of watershed management measures in Iran to reduce the damage caused by the misuse of natural resources has begun many years ago and is still ongoing. Evaluating the performance of previous remedial work is essential for better planning of future watershed management projects. In this regard, due to the monitoring of soil loss, runoff and sedimentation at slope and watershed scales, a suitable platform has been provided to assess the effects of watershed management measures. Material and methodsThe Kakhk paired watershed with an area of 217 ha is located at a distance of 300 km from Mashhad City and 35 km southwest of Gonabad City.The Kakhk paired watershed consists of two sub-watershds, the control and the treatment. A series of biological and structural watershed management measures have been implemented in the treatment sub-watershed. While the control sub-watershed is exploited according to the custom of the region. In this research, the impact of different watershed management measures on the soil loss, sediment yield and hydrology in the Kakhk paired watershed were evaluated. For this purpose, the recorded data of suspended sediment and discharge at the watershed scale, as well as the data of soil loss (by standard plots and erosion pins) and runoff (standard plots) were analyzed at the hillslope scale. Results and discussionThe results at plot scale showed that the average annual soil loss of the two treatment and control sub-watersheds is 0.05 and 0.27 ton.ha-1.y-1, respectively. These results indicate that the soil loss in the control sub-watershed is 536% higher than the treatment sub-watershed. The amount of runoff yield in the control sub-watershed was calculated to be 138% more than the treatment sub-watershed. At watershed scale, the results showed that the total amount of suspended sediment output from the control and treatment watersheds is 379 and 85 tons, respectively, which indicates the average specific sediment of 0.4 and 0.1 ton.ha-1 in the control and treatment watersheds, respectively. The volume of runoff in the control sub-watershed is 1.3 times more than treatment sub-watershed. On the other hand, despite the difference between the treatment and control sub-watersheds in soil loss, run-off production and sediment yield, the role of maximum events in soil erosion and runoff production in both sub-watersheds is very significant. So that one to three erosive events in both studied sub-watershes are responsible for more than 80% of the soil loss in the slopes and the production of runoff and sediment yield of watersheds. ConclusionThe results showed that a total of 136,000 m3 of runoff storage and 294 ton of suspended sediment control were achieved as a result of watershed operations in the treatment sub-watershed. Therefore, it can be stated that the watershed management measures carried out in the treatment sub-watershed on the one hand have reduced soil erosion and runoff production on the slopes compared to the control sub-watershed. This action has been done through increasing the vegetation, increasing the roughness of the land surface, reducing the carrying capacity of the flow and settling the materials being transported. Further, the flow from the slopes enters the waterway and is kept by watershed management structures, and as a result, the sediment yield and volume of runoff in the treatment sub-watershed is less than the control sub-watershed.
Arash Zare Garizi; Ali Talebi; Monireh Faramarzi
Abstract
In this study, SWAT model was used for simulating soil erosion and sediment transport in Gharesou Watershed, Golestan Province and for identifying and prioritizing critical areas of soil erosion. After model calibration, validation and uncertainty analysis using semi-automatic SUFI-2 method, the outputs ...
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In this study, SWAT model was used for simulating soil erosion and sediment transport in Gharesou Watershed, Golestan Province and for identifying and prioritizing critical areas of soil erosion. After model calibration, validation and uncertainty analysis using semi-automatic SUFI-2 method, the outputs of the calibrated model were used for assessing spatial pattern of soil erosion and sediment. For this purpose, four indices including: load per unit area index, concentration index, load index and total index were defined and analyzed based on the model outputs. The results indicated that, despite lack and uncertainty of available data, SWAT model performance in simulating soil erosion and sediment transport in Gharesou watershed is quite acceptable. During calibration, the simulated monthly sediment loads matched the observed values with a Nash-Sutcliffe coefficient of 0.24 and PBIAS of -17%. The values for validation period were 0.2 and -12.1% respectively, indicating the model’s weakness in simulating sediment dynamics and its capability in predicting average sediment load. Assessing spatial pattern of erosion and sediment indices showed that, in general, critical sub-watersheds based on load per unit area index are located in upstream areas of watershed while sensitive sub-watersheds in terms of sediment concentration are situated in the middle part of the watershed, and sensitive sub-watersheds with respect to sediment load are in downstream. Suitable conservation practices were recommended for each zone based on their ecohydrological conditions. The outputs of this study can help experts and managers in planning of management practices for the watershed.
