برآورد فرسايش و رسوب به روش ژئومرفولوژي جهت ارزيابي طرح هاي آبخيزداري (مطالعه موردي: حوزه آبخيز صفارود استان مازندران)

Estimation of Erosion and Sediment by Geomorphology Method for Assessing Watershed Management projects: A Case of Safaroud Watershed in Mazandaran Province

افزايش روبه رشد تخريب منابع طبيعي در چند دهه ي اخير به تشديد فرسايش و افزايش نرخ توليد رسوب منجر شده است. براي كنترل تخريب و كاهش اثرات آن، فعاليت هاي بسياري در سطح حوزه هاي آبخيز اجرا مي شود. اين پژوهش با هدف ارزيابي طرح هاي آبخيزداري اجرا شده در حوزه ي آبخيز صفارود در استان مازندران، از طريق برآورد فرسايش به روش ژئومرفولوژي انجام شده است. بدين منظور نقشه ي شدت فرسايش منطقه با روش ژئومرفولوژي در دو پايه ي زماني قبل از اجراي طرح (1373) و بعد از اجراي طرح (1393) تهيه و ميزان رسوب خروجي از حوضه در اين پايه هاي زماني بررسي شد. با بررسي نقشه ي شدت فرسايش در هر واحدكاري در پايه هاي زماني مورد مطالعه، نقشه ي روند شدت فرسايش منطقه تهيه شد. با انطباق نقشه ي روند شدت فرسايش با نقشه ي طرح هاي اجرا شده، ميزان اثرگذاري طرح ها در هر واحدكاري مشخص شد. با استفاده از آزمون هاي آماري، رابطه ي بين شدت فرسايش و رسوب خروجي از حوضه در دو پايه ي زماني قبل و بعد از اجراي طرح بررسي شد. بررسي ها نشان داد كه در حدود 95/75 درصد از سطح منطقه، روند شدت فرسايش منفي دارد كه تاثير مثبت طرح ها را نشان مي دهد. ولي نتايج حاصل از آناليزهاي آماري بيانگر اين است كه رابطه ي معني داري بين شدت فرسايش و رسوب خروجي از حوضه در پايه هاي زماني مورد مطالعه در سطح خطاي 05/0 وجود ندارد. با تفسير نتايج حاصل شده مشخص شد كه واحدهاي كاري به شماره هاي 14، 16 و 17 بيشترين نرخ افزايش روند شدت فرسايش را دارد. با حذف اين سه واحد كاري از آناليز آماري مقايسه ي شدت فرسايش در دو پايه ي زماني مورد بررسي، مشخص شد كه اختلاف بين شدت فرسايش در سطح خطاي 05/0 معني دار است.

Introduction The degradation of natural resources in recent decades has led to increasing the erosion and an increase in the sediment production rates. Many activities are carried out at watershed level in order to control the destruction and decrease its effects. Assessment of watershed management projects is one of the most important issues performed today of implementation plans and natural resources management (Abbasi et al., 2010).Considering one of the most important goals of watershed management projects is the prevention of erosion and sedimentation and flood control, Therefore, using erosion estimation methods can be a good way to evaluate projects that are used in indigenous and regionally compatible methods. One of the methods for estimating the water erosion in Iran is Geomorphology (Ahmadi, 2006).This method has been examined and approved by various researchers including (Maleki, 2008, MohammadKhan, 2009, and Angebini, 2014) in different parts of the country. In this model, the erosion rate map can be prepared by determining the criteria and indicators affecting the erosion and the projects were evaluated by investigating the erosion map. In the present study, the effect of watershed management activities on erosion and sediment reduction in Safaroud watershed in Mazandaran province was evaluated using erosion intensity map through geomorphology model. 2- Materials and Methods Safaroud watershed is located in the west of Mazandaran province with a total area of ​​13551 hectares. In the present research, the implemented projects in the region were evaluated by geomorphologic method by providing the erosion intensity map. For this purpose, the erosion intensity map was prepared on two time bases before and after the implementation of the projects, the first time base was in 1994 and after the implementation of the projects, the second time base was in 2014, by Geomorphology method. AHP and GIS techniques were used to quantify the erosion intensity map. The erosion trend map in each homogeneous unit was prepared from the difference between the erosion intensity map at the second time base and the erosion intensity map at the first time base. The statistical analysis of the erosion and sediment data in two time bases studied was carried out by comparing the average values. 3- Results According to the erosion intensity map, it was determined that out of 39 homogeneous units, the erosion trend was negative in 24 homogeneous ones at the area of 10292 hectares. The erosion trend was positive for 15 homogeneous units at the area of 3259 hectares. The results of statistical analysis of the comparison between the specific erosion in the two time bases studied shows that with 95% accuracy level, that is to say, there is no significant difference between erosion in two bases before and after the implementation of the projects. The statistical analysis of the sediment output from the basin indicates, within the same 95%accuracy level, there was no significant difference between the sediment discharge from Safaroud watershed in the two time bases before and after the implementation of the projects. 4- Discussion & Conclusion The results of statistical analysis of the erosion indicate that the implementation of the plans has not been able to significantly change the intensity of erosion in the region. This result is obtained in a situation where in the 24 homogeneous units of the total 39 homogeneous units, i.e. at the area of 10292 hectares (75.95% of the total area), the erosion trend is negative and the erosion has increased in 15 units of 39homogeneous units totaled 3259 hectares (24.05% of the total area).By examining the histogram diagram of the erosion trend, it is found that the erosion in the three homogeneous units of No. 14, 16 and 17 were respectively 0.0357, 0.0209 and 0.0352 which were relatively high comparing to other units. Thus, these three units with a total area of ​​234.54 hectares (73.1 percent of the total area) were identified as very sensitive units. If we do not consider these three units in the statistical analysis and average comparison with 36 remaining units, the result of statistical analysis shows that there is a significant difference between the erosion in the two groups and the plans implemented in the region have been effective in reducing erosion. Therefore, these three units must first be investigated in terms of prioritization of homogeneous units for future planning. Homogeneous unit 14 due to road construction and, homogeneous units: No. 16 and 17 due to mass movements are also sensitive areas.