مکان‌یابی بند اصلاحی به منظور کنترل فرسایش با کمک فرآیند تحلیل سلسله‌مراتبی

خاک یکی از مهم‌ترین عناصر منابع طبیعی در هر کشور است. در مناطقی که فرسایش کنترل نمی‌شود، خاک‌ها به ‌تدریج فرسایش می یابد و حاصلخیزی خود را از دست می‌دهد. یکی از پیامدهای کاهش حاصلخیزی خاک، عدم امکان تامین غذای کافی است. معمولاً برای حفاظت خاک و جلوگیری از فرسایش، دو روش مستقیم و غیرمستقیم وجود دارد. یکی از روش های مستقیم جلوگیری از فرسایش، احداث بندهای اصلاحی است. این سازه ها در بستر آبراهه‌ها و عمود بر جریان ساخته می‌شود تا سرعت آب و قدرت فرسایش رواناب در اثر کاهش شیب بستر را کاهش دهد. هدف پژوهش حاضر، اولویت‌بندی مکانی محل احداث بندهای سنگی ملاتی و گابیونی در حوزه‌ی آبخیز قورچای رامیان براساس روش‌های تصمیم‌گیری چند ‌معیاره است. اولویت بندی بر اساس معیارهای تاثیرگذار مانند فیزیوگرافی، هیدرواقلیم، زمین‌شناسی و خاک‌شناسی و عوامل اقتصادی اجتماعی با استفاده از مدل ahp و سیستم اطلاعات جغرافیایی (gis) انجام شد. وزن معیارهای اقتصادی اجتماعی، هیدرواقلیم، فیزیوگرافی، خاک و زمین‌شناسی به ترتیب برابر با 0.409، 0.124، 0.058 و 0.409 است که میزان تاثیر معیارها را بر مکان‌یابی محل احداث بند گابیونی و سنگی ملاتی نشان می دهد. بر اساس اولویت‌بندی که در بین وزن ها صورت گرفته ، اولویت‌های 1 تا 5 برای احداث بندهای سنگی ملاتی به‌ترتیب متعلق به زیرحوزه‌های 14، 10، 13، 6 و 9 است. زیرحوزه‌ی 14 با وزن 0.304 به‌عنوان اولویت اول و زیرحوزه ی شماره 1 با وزن 0.129 در اولویت آخر است. از بین زیرمعیارها، زیرمعیار حساسیت به فرسایش سازند با وزن 0.36 دارای بیشترین تاثیر و زیرمعیار ضریب سیل‌خیزی و درصد شیب با وزن 0.05 دارای کمترین تاثیر در انتخاب اولویت اول یعنی زیر حوزه ی 14 است. براساس اولویت‌بندی که در بین وزن های نهایی 62 زیرحوزه با آبراهه درجه 2 برای احداث بندهای گابیونی صورت گرفت، اولویت‌های 1 تا 5 به ترتیب به زیرحوزه‌های 36، 35، 34، 32 و 57 تعلق دارد. زیر حوزه‌ی شماره ی 36 با وزن 0.453 به‌عنوان اولویت اول و زیر حوزه‌ی شماره ی 1 با وزن 0.113 به عنوان اولویت آخر برای احداث بند گابیونی پیشنهاد شد.

Check dam suitable locations for erosion control using hierarchical analysis process

1 IntroductionWatershed describes an area of land that contains a common set of streams and rivers, which all drain into a single large body of water. For sustainable management of watersheds, soil erosion is a major factor, which accelerates the rate of land degradation and hence influences agricultural productivity, run off movement and sometimes leads flood in the lower basin. Soil is one of the most important elements of natural resources in each country. In areas where erosion is not controlled, soil gradually erodes and loses fertility. There are two methods to maintain soil and prevent erosion: direct method and indirect method. One of the direct methods to prevent erosion is the construction of checking dam. These structures are constructed in floodplains and perpendicular to the flow of reducing water velocity and run off erosion by reducing the bed slope. Check dams are constructed using materials such as wood, stone, rock, and mortar and gravel (gabion). The aim of the present research is to determine the suitable location of mortar and gabion check dam in Ghorchay Ramiyan watershed based on multicriteria decisionmaking methods.2 MethodologyGorkhay basin (one of the sub basins of Gorgan Rood basin) is located in the southern Gorgan Rood basin and in south of the city of Ramiyan, Golestan province. The hydrometric stations of Ramiyan and Nodeh were used for data analysis that located inside and in the neighbor of study area respectively. Criteria and indicators are chosen for evaluation of topic. The research criteria were also considered as factors influencing the location of check dam construction site in separate clusters for the second layer. The classes or options are classified in the third layer based on the risk classes in a separate cluster. In a hierarchy analysis, the normalization is performed using Saati method on the comparison matrix. In this research, the vector of the weight of the options is calculated using the geometric mean method. Prioritization was done using the AHP model and GIS based on effective criteria such as physiography, hydrology, geology , soil science and socioeconomic factors.3 Results The weight of socioeconomic, hydrological, physiographic, soil and geological criteria is equal to 0.409, 0.124, 0.0558 and 0.409 respectively, which indicates the impact of criteria on site selecting of gabion and stonemortar check dam. Based on weights prioritization, priorities 1 to 5 is selected for construction stonemortar check dam belongs to 14, 10, 13, 6 and 9 subbasin. Subbasin No. 14 with a weight of 0.304 is the first priority and subbasin No. 1 with weight of 0.129 is the last priority. Among the subcriteria, the sub criteria of sensitivity to erosion of geology formation with 0.36 weight has the greatest effect and the sub criteria of flooding coefficient and slop percent with weight 0.05 have the least effect on the selection of the first priority, that is, subbasin No. 14. On the basis of prioritization of 62 subbasins final weights with 2nd grade channel for construction of gobbins, the priorities 1 to 5 belong to the subbasins 3535343257, respectively. Subbasin No. 36 with a weight of 0.453 as the first priority and subbasin No. 1 with a weight of 0.113 was proposed as the last priority for construction of gabion.4 Discussion ConclusionsThe rapid growth of technology and economic has transformed human rsquo;s life in recent decades and has challenged modern societies with sophisticated decision making. The basic characteristic of such issues is the existence of nonhomogeneous and inappropriate criteria or objectives, such as cost, reliability, performance, safety and productivity. Subbasin No. 14 with weight 0.304 as the first priority (at the end of the basin, which has a slope and high erosion due to formations such as limestone and marn) and sub basin No. 1 is the last priority with weight 0.129 (Shale Formation, Sandstone and coal with high sensitivity to erosion and distance from residential areas and away from resources). Among the subcriteria, formation erosion sensitivity subcriteria with weight 0.36 has the greatest effect and the subcriterion of distance from the road with a weight of 0.01 has the least effect on the selection of the first priority, the subbasin No. 14. The purpose of this research is to assist managers and decision makers in the Watershed Management Department to select the most appropriate options and to rank the location of structures based on choosing the best decision options and emphasizing on effective decision making by introducing and applying scientific decisionmaking methods.