برآورد فرسایش و رسوب به روش ژئومرفولوژی جهت ارزیابی طرح‌های آبخیزداری (مطالعه موردی: حوزه آبخیز صفارود استان مازندران) مقالة

افزایش روبه رشد تخریب منابع‌ طبیعی در چند دهه‌ی اخیر به تشدید فرسایش و افزایش نرخ تولید رسوب منجر شده‌است. برای کنترل تخریب و کاهش اثرات آن، فعالیت‌های بسیاری در سطح حوزه‌های آبخیز اجرا می‌شود. این پژوهش با هدف ارزیابی طرح‌های آبخیزداری اجرا شده در حوزه‌ی آبخیز صفارود در استان مازندران، از طریق برآورد فرسایش به روش ژئومرفولوژی انجام شده‌است. بدین منظور نقشه‌ی شدت فرسایش منطقه با روش ژئومرفولوژی در دو پایه‌ی زمانی قبل از اجرای طرح (1373) و بعد از اجرای طرح (1393) تهیه و میزان رسوب خروجی از حوضه در این پایه‌های زمانی بررسی شد. با بررسی نقشه‌ی شدت فرسایش در هر واحدکاری در پایه‌های زمانی مورد مطالعه، نقشه‌ی روند شدت فرسایش منطقه تهیه شد. با انطباق نقشه‌ی روند شدت فرسایش با نقشه‌ی طرح‌های اجرا شده، میزان اثرگذاری طرح‌ها در هر واحدکاری مشخص شد. با استفاده از آزمون‌های آماری، رابطه‌ی بین شدت فرسایش و رسوب خروجی از حوضه در دو پایه‌ی زمانی قبل و بعد از اجرای طرح بررسی شد. بررسی‌ها نشان داد که در حدود 95/75 درصد از سطح منطقه، روند شدت فرسایش منفی دارد که تأثیر مثبت طرح‌ها را نشان می‌دهد. ولی نتایج حاصل از آنالیزهای آماری بیانگر این است که رابطه‌ی معنی‌داری بین شدت فرسایش و رسوب خروجی از حوضه در پایه‌های زمانی مورد مطالعه در سطح خطای 05/0 وجود ندارد. با تفسیر نتایج حاصل شده مشخص شد که واحدهای کاری به شماره‌های 14، 16 و 17 بیشترین نرخ افزایش روند شدت فرسایش را دارد. با حذف این سه واحد کاری از آنالیز آماری مقایسه‌ی شدت فرسایش در دو پایه‌ی زمانی مورد بررسی، مشخص شد که اختلاف بین شدت فرسایش در سطح خطای 05/0 معنی‌دار است.

Extended abstract 1- 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.