استفاده از يك مدل تجربي ويژه در برآورد توليد رسوب حوزه ي آبخيز سد كوه برد در شهرستان كهگيلويه

Using a special empirical model to estimate sediment yield of Koohbord dam watershed in Kohgilouyeh County

ررسي دستور العمل هاي طراحي سدهاي كوتاه نشان مي دهد كه معمولا موضوع توليد رسوب و اثر رسوب گذاري آينده بر عمر سد و ذخيره ي آب در آن قابل توجه نيست و اغلب بر طراحي مهندسي عمران و جنبه هاي سازه اي آن توجه مي شود. عمليات احداث سد مخزني در خروجي حوزه ي آبخيز كوه برد با مساحت 29/38 كيلومتر مربع در استان كهگيلويه و بويراحمد، از سال 1390 شروع شده است. حوزه ي آبخيز كوه برد يكي از حوزه هاي آبخيز بدون آمار رسوب است كه استفاده از مدل هاي تجربي برآورد رسوب در آن الزامي به نظر مي رسد تا داده هاي حاصل شده، مبنايي براي برنامه ريزي هاي مديريتي در حوضه ي سد باشد. هدف از تحقيق حاضر، برآورد توليد رسوب حوزه ي آبخيز كوه برد با استفاده از يك مدل تجربي ويژه، همچنين ارزيابي فني سد در حال احداث در خروجي حوضه با استفاده از يك سري شاخص هاي ساده است كه در مناطق مختلف دنيا توسعه يافته اند. در اين تحقيق با استفاده از نقشه هاي پايه و اطلاعات بررسي هاي صحرايي، امتياز 3 عامل موثر بر ميزان توليد رسوب در مدل تجربي مذكور در قسمت هاي همگن حوضه تعيين و كل حوضه ميانگين گيري وزني شد. سپس با قرار دادن امتيازهاي به دست آمده در رابطه ي مدل، ميزان توليد رسوب برآورد شد. نتايج نشان داد ميزان رسوب توليدي در حوضه ي سد كوه برد 13/8 تن بر هكتار در سال است كه با احتساب نسبت تحويل رسوب 18/0، ميزان فرسايش خاك حوضه معادل 16/45 تن بر هكتار در سال است. پيش بيني مي شود كه بعد از 20 سال (عمر مفيد سد) ، حدود 27 درصد از ظرفيت ذخيره ي اوليه ي سد از دست برود. نتايج اين تحقيق براي برنامه ريزي اقدامات اصلاحي در زمينه ي حفاظت خاك در سطح حوزه ي آبخيز و كاهش حجم رسوبات ورودي به مخزن سد و در نتيجه افزايش عمر آن مفيد خواهد بود.

Koohbord dam watershed with a total area of 38.29 square kilometers in Kohgiluyeh and Boyerahmad province is one of the watersheds without sedimentation data, which requires the use of empirical models to estimate the sediment for estimating sediment, so the results obtained through data is the basis of the management plans of dam watershed. In this research, using base maps and field data, the score three factors affecting the amount of sediment yield were determined using a special empirical model of the dam watershed in the homogeneous parts of the watershed and weighed for the whole watershed and by estimating the obtained scores in the model relationship, sediment yield was estimated. The results showed that the amount of sediment yield in the Koohbord dam watershed is 13.8 tons per hectare per year, taking into the account of sediment delivery proportion of 0.18, which is equivalent to 45.16 tons per hectare per year for soil erosion. It is estimated that after 20 years lifetime of the dam, about 27% of the initial capacity of dam’s storage is lost. Meanwhile, due to the evaporation, about 32% of dam’s volume is lost too. Introduction: There are strong links between the availability of water for agricultures and livestock productions, and the incomes for poor rural nation. Rainfall variations, particularly droughts, effect on their living as well One meaning of increasing people’s resilience to these shocks is to store water in dams – so that crops can be irrigated and cattle watered during dry seasons. Many of the small dams are constructed in semi-arid regions of Africa which is rapidly filled with sediments and sometimes only after a few years. When dams silt up the rural areas that is relied on them for cattle watering or small-scale irrigations that deprived of the water and food security that dams provide them, and their source of income is seriously affected too. Predicting soil erosions, sediment yields and dam sedimentation rates can be a complex task, it requires professional experts, and in generally it has poorly covered in small dam design manuals. These results in many small dams constructed with little or no consideration of the impact of future siltation of a dam’s life or on water yields. This issue is poorly covered in most small dam design manuals, which mostly focuses on civil engineering designing and construction aspects. A capability to estimate future siltation rates in small dams is essential to ensure that: dams are not constructed in catchments with excessively high sediment yields; dams are sized correctly; catchments where the rapid introduction of soil and water conservation or other measures will be essential if a reasonable dam life is being obtained, are identified early enough for remedial activities to have a significant impact on dam siltation.