بررسی کمی میزان فرسایش و رسوب جاده‌های جنگلی شهرستان لردگان با استفاده از مدل sedmodl

یکی از بزرگ ترین مشکلات ناشی از جاده سازی های غیراصولی، وقوع اشکال مختلف فرسایش از قبیل فرسایش آبکندی و توده‌ای وتشدیدآن ها در اطراف جاده‌ها است. در پژوهش حاضر از مدل تحویل رسوب جاده (sedmodl) و سیستم اطلاعات جغرافیایی برای تخمین میزان و درصد رسوب‌دهی متوسط سالانه ناشی از شبکه جاده‌های جنگلی در جنگل‌های بلوط غرب کشور در استان چهار محال و بختیاری استفاده شد. در این تحقیق از جاده‌های جنگلی بیدله واقع در شهرستان لردگان به طول 5828 متر که به صورت خاکی و عمدتا جهت سهولت دسترسی به مناطق جنگلی، مسکونی (روستا) ، عشایری و تفریحی در مناطق جنگلی استان چهار محال و بختیاری احداث شده است به عنوان منطقه مطالعاتی استفاده شد. ابتدا نقشه‌های مورد نیاز شامل زمین‌شناسی، مسیرجاده، شیب، بارندگی و تراکم زهکشی تهیه و در محیط نرم افزار arc gis 10.8 رقومی شد و همچنین طی بازدید‌های میدانی جنس، سن و ترافیک جاده‌های مطالعاتی تعیین گردید. فرمول‌های به‌کارگرفته شده در sedmodl بر پایه روابط ریاضی و کمی بین عامل‌های فرسایش از قبیل نوع استفاده از جاده، ترافیک جاده، مواد مادری به کار گرفته شده در احداث جاده، وضعیت سطح جاده، شیب طولی جاده، پوشش گیاهی ترانشه خاک‌برداری، میزان بارش منطقه و میزان فاصله از آبراهه طراحی شده‌اند. همچنین در این تحقیق به منظور اندازه‌گیری میدانی میزان فرسایش و رسوب در قسمت‌های مختلف جاده‌های مطالعاتی 30 پیکه فرسایشی نصب و در طول یک سال میزان تغییرات آنها به کمک متر لیزری با دقت 0/02 میلیمتر اندازه‌گیری شد و میانگین فرسایش خاک بر اساس اندازه‌گیری صورت گرفته 4 میلیمتر در یک سال برآورد شد. میزان فرسایش بر اساس مدل sedmodl در جاده بیدله 2068 تن در سال و میزان رسوب دهی کل بر اساس مدل sedmodl 234 تن در سال است. همچنین آنالیز لکه‌های داغ نشان داد 39/8 درصد از جاده‌ها دارای تولید فرسایش بسیار زیاد می باشند.

quantitative investigation of erosion and sedimentation of forest roads in lordegan county using sedmodl

introduction the road sediment delivery model (sedmodl) and geographic information system were used to estimate the amount of average annual sedimentation caused by the forest roads network in the oak forests of the west of the country in chaharmahal and bakhtiari provinces. in this research, bideleh forest roads in lordegan county with a length of 5828 meters selected. the area maps including geology, road networks, slope, and rainfall and drainage density were prepared and digitized in the arc gis 10.8 software, and also during field visits, the type, age and traffic of the study roads were determined. the formules used in sedmodl are based on mathematical and quantitative relationships between erosion factors such as the type of road, road traffic, and parent materials used in road construction, road surface condition, road longitudinal slope, vegetation cover, excavation trench, the amount of rainfall in the area and the distance from the waterway. also, in this research, in order to measure the amount of erosion and sediment in the field, 30 erosion markers were installed in different parts of the study roads, and during one year, their changes were measured with the help of a laser meter with an accuracy of 0.02 mm. the average soil erosion was estimated 4 mm per year based on the measurements. according to the sedmodl model, the amount of erosion in bidleh road is 2068 tons per year and the amount of sedimentation is 234 tons per year according to the sedmodl model. also, the analysis of hot spots showed that 39.8% of bideleh forest roads have very high erosion.methodology sediment production from a road is usually influenced by three types of water flow on the road surface, soil removal trench and roadside waterways. in fact, the model used in this research (sedmodl) is based on these three factors (akay et al. 2008). therefore, the total precipitation in tons per year from each road section is calculated based on the equation 1.(equation 1) total sediment (t/year) = (ts+cs)*af in the above equation, ts is sediment production from road surface and roadside waterways, cs is sediment production caused by soil removal trench and af is the age factor of the road. according to equation 2, ts is also affected by road length (lr), road width (w), geological erosion rate (ger), road surface material (sf), traffic (tf), road slope (gf), rainfall. (pf) and sediment delivery factor (df).(equation 2) ts = lr* wr*ger* sf*tf* gf*pf*df also, sediment production caused by soil removal trench cs according to equation 3, a function of geological erosion rate factors (ger), vegetation and stone cover around the road (csf), soil removal trench height (csh), road length (lr) and the sediment delivery factor (df).  (equation 3) cs = ger*csf*csh* lr*df sediment production of the road during the first and secondry years of construction until the excavation trench and embankment pile is properly fixed by vegetation has its maximum amount. in sedmodl, the effect of the road age factor (af) is 10 in the first year of construction and 2 after two years. the values for other erosion factors was obtained from the provided tables of the model which were calculated based on previous researches (akay et al. 2008; naghdi et al. 2017).for field measurement of erosion on the forest road, 30 wooden rods were installed around the road. the wooden rods were installed in the sections perpendicular to the road in different conditions of geology, vegetation and the slope of the road and on both sides of the road at intervals of 5 meters, 15 meters and 25 meters. then, the height of each rod was measured using a laser meter with an accuracy of 0.02 mm. the height of each rod was measured in 5 times and the average of these values was determined as the height of the rod in each stage.