ارزيابي مدل WEPP در برآورد ميزان فرسايش و رسوب در اراضي مارني منطقه خواجه

Prediction of Erosion and Sediment, Using WEPP Model in Marly Lands, Khajeh Region

نقش فرسايش خاك، در توليد رسوب و پُر شدن مخازن سدها، از اهميت جهاني برخوردار است. از آنجا كه بسياري از حوضه هاي آبخيز در اكثر كشورها ، ازجمله ايران، فاقد ايستگاه هاي رسوب‎سنجي هستند، بنابراين بايد در چنين مناطقي براي برآورد فرسايش و رسوب از مدل‎سازي استفاده شود. منطقه مورد مطالعه، ايستگاه هاي حفاظت خاك مركز تحقيقات كشاورزي آذربايجان شرقي است كه از سازندهاي مارني تشكيل شده است. براي برآورد فرسايش و رسوب، منطقه مورد مطالعه به سه زيرحوضه تقسيم شد و هر زيرحوضه تحت مديريت متفاوت حفاظت خاك قرار گرفت و در خروجي آنها، ميزان فرسايش و رسوب به‎صورت مستقيم اندازه‎گيري شد. براي ارايه تصوير مناسبي از توزيع مكاني مقادير تلفات خاك در سطح منطقه و همچنين بررسي تاثير روش هاي مختلف مديريتي در كاهش هدررفت خاك و نهشته گذاري آن، از مدل ويپ با به‎كارگيري برنامه ژيوويپ استفاده شده است. نتايج اين مدل در قالب نقشه‎هاي تلفات خاك و مكان‎هاي ترسيب در محيط GIS ارايه شده است. ارزيابي كارايي مدل مذكور از طريق مقايسه مقادير كمي رسوب مشاهداتي با مقادير برآوردي صورت گرفته است. نتايج شبيه سازي مدل در محل خروجي هر زيرحوضه، به‎ترتيب مقادير 2/23، 3/21 و 5/6 تن در هكتار گزارش شده است؛ در حالي‎كه مقادير مشاهداتي در اين مناطق، به‎ترتيب 2/20، 7/18 و 8/4 تن در هكتار بوده است. از سوي ديگر مكان‎هاي نهشته‎گذاري در سطح حوضه، مطابقت كاملاًً مناسبي با محل هاي سازه هاي مكانيكي (كنتور باند و كنتور ترنج ها) نشان داد. نتايج اين پژوهش نشان داد كه مدل WEPP كارايي خوبي در شبيه سازي فرسايش و رسوب دارد؛ به‎طوري كه مقايسه آماري نتايج به‎دست‎آمده از اين روش با نتايج آزمون t نرم‎افزار STATGRAPHICS بين داده هاي مشاهده اي، در سطح احتمال 5 درصد اختلاف معنا داري ديده نشد.

Introduction Nowadays, soil erosion and its outcomes are considered as one of the important environmental problems (Ikwan et al., 2009). Soil erosion is a global problem which seriously threaten soil and water resources, also in cultivated lands, it is known an environmental problem ( Gyanq denj et al , 2008). The role of soil erosion, in sediment yield and reservoirs filling has global importance. Because in most countries many watersheds such as Iran, there are lack of hydrometric stations, so for these areas erosion and sediment modeling should be used. Soil conservation in watershed management is necessary and it is important that how think about ways to conserve natural resources. Regarding this matter, the purpose of the erosion and sediment modeling using a process simulation model; WEPP at marly land accomplished. Marly land of Khajeh, as the sub-catchments of Aji Chay watershed is composed of marl formations and is particularly susceptible to water erosion. Also due to Shahid Madani dam construction in this watershed, an accurate estimation of erosion and sediment in this area is necessary. Therefore, due to the ability of model in simulation in comparison to empirical models, this model was applied in this area. Methodology The studied area as one of the East Azerbaijan Agricultural Research Center soil conservation station is composed of marl formations. The studied area was divided into three sub-basins and each sub-basin was under different management of soil conservation. At output of basins, erosion and sediment has been measured directly. For presentation of spatial distribution of soil loss and studying of management systems in soil conservation, GeoWEPP model was applied. The results of this model as the soil maps and precipitation areas are presented using GIS. Evaluation of model efficiency accomplished the performance of the model by comparing the observations with estimated values. Results and Discussion The results of model in the form of soil maps and precipitation areas in are presented in GIS. Evaluation of model efficiency by comparing the observations with sediment estimated values was accomplished. The model simulation results 23.2, 21.3 and 6.5 tons per hectare have been predicted, respectively. Whereas the observed values in these regions 20.2, 18.7 and 4.8 tons per hectare have been reported, respectively. On the other hand, deposits places had convenient accordance with mechanical conservation practices (countorbands and contourtrenches). Statistical comparison using STATGRAPHICS is indicated there is no significantly difference between estimated and observed data at 5 percent level. Conclusion Since the studied area is a soil conservation and watershed management station which its major surface the marl erosive susceptible formations is located upstream of the Shahidmadani dam. So the necessity of accurate estimations soil losses associated with the useful life of the dam was considered. Sediment data in the three -point area as the desired output of each sub-basin scale through Parshal flume and runoff measurements were available; therefore the comparison of the observed and predicted data for evaluating of WEPP model was possible. The results showed that the model performance in terms of presenting the spatial distribution of soil loss and estimated soil loss values with the critical points has acceptable level (95 percent). Also this model has the ability of accumulation places simulating for watershed. In this research, deposits places had convenient accordance with mechanical conservation practices, so effects of such conservative practices are indicated ability and efficiency of WEPP model.