پديد آورندگان :
علوي نيا، مرتضي دانشگاه تربيت مدرس - دانشكده مهندسي عمران و محيط زيست , فرزين نصيري صالح دانشگاه تربيت مدرس - دانشكده مهندسي عمران و محيط زيست , اسدي، حسين دانشگاه تهران - دانشكده كشاورزي
كليدواژه :
پروفيل بارندگي , رواناب , رسوب , شبيه سازي باران , فرسايش بين شياري
چكيده فارسي :
انتقال رسوب ناشي از بارندگي يكي از اصلي ترين بخش هاي فرسايش بين شياري خاك در طبيعت است. در طي رگبارهاي طبيعي شدت بارندگي در نوسان است. نوسانات شدت بارندگي در طي رگبار را مي توان پروفيل رگبار ناميد. در اين تحقيق با شبيه سازي چهار رگبار با پروفيل هاي متفاوت و انرژي جنبشي يكسان بر روي دو نوع خاك متفاوت، اثر پروفيل رگبار بر رواناب و رسوب ناشي از فرسايش بين شياري مورد بررسي قرار گرفت. نتايج اين تحقيق نشان داد اگرچه در هر دو نوع خاك حجم رواناب ناشي از رگبارهايي با پروفيل هاي مختلف تفاوت معني داري ندارند اما اثر پذيري حداكثر نرخ رواناب از پروفيل رگبار به نوع خاك بستگي دارد. نتايج مربوط به رسوب نيز نشان داد معني دار بودن اثر پروفيل رگبار بر توليد رسوب به نوع خاك بستگي دارد. علاوه بر اين يافته هاي اين تحقيق نشان مي دهد در رگبارهاي شدت متغير استفاده از مدل هايي كه فرسايش بين شياري را با استفاده از شدت بارندگي برآورد مي كنند كارايي ندارد. از اين رو توسعه استفاده از شبيه سازي رگبارهاي شدت متغير در مطالعات فرسايش خاك و انتقال رسوب مي تواند باعث شناخت دقيق مكانيسم هاي موثر حاكم بر توليد رواناب و رسوب در فرسايش بين شياري گردد.
چكيده لاتين :
Soil erosion, as a complicated natural phenomenon, is a global challenge threatening soil and water resources. Therefore, accurate understanding of soil erosion, sediment transport processes and their interactions is necessary for prediction of soil erosion. To distinguish between the dominant processes involved in soil loss, soil erosion has been classified into rill and interrill erosion. Rainfall-induced detachment and transport of sediment have a fundamental contribution to interrill and sheet erosion. Instead of observation of natural rain showers, simulation of rainfall is widely used for better understanding of processes involved in soil erosion and their interactions. Rainfall intensity is variable during natural rain showers. Peak rainfall intensity in an event can exceed the mean event intensity by an order of magnitude. Variations of rainfall intensity during a rainfall event is called ‘event profile’. However, the available information is inadequate to understand its effects on runoff and soil loss processes. Thus, this study is aimed to quantify the effect of event profile on runoff and soil loss in rainfall-induced erosion. The experiments are defined based on the use of simulated rainfall on disturbed soils in a small laboratory detachment tray. The study is conducted in the rainfall simulation laboratory, Department of Hydraulic, Faculty of Civil and Environmental Engineering, Tarbiat ModaresUniversity, Iran. Since kinetic energy controls runoff and soil loss processes, the effects on the soil surface of rainfall events with the same average intensity may be different. Hence to study only the effects of event profile, four events with different temporal profiles of rainfall intensity, each with the same kinetic energy, were chosen; (a) constant intensity, (b) increasing intensity, (c) decreasing intensity and (d) increasing - decreasing intensity. The soil samples used in the experiments are from sandy soil (soil A) and sandy loam soil (soil B). Disturbed soil samples are collected, air dried, crushed to pass a 4.75-mm sieve, and thoroughly mixed. For each experiment, soil is packed into a drainable detachment tray to a specific bulk density. The test area of this tray is 15-cm width by 30-cm length and 15-cm depth. Eliminating the effects of soil moisture on results, soil is saturated from the bottom using drainage outlet tube connected to a water reservoir 24-hr before each experiment. The tray is setup at a slope of 0.5% and exposed to simulated rainfall events. Each treatment is tested in three replicates. For each simulation, runoff and sediment are sampled at regular intervals. Results show that while the peak runoff is affected by event profile for the two soil types, there is no significant difference in total runoff among rainfall events examined for both soil types. However, the soil type significantly affects the soil loss. In addition, it seems that the models which estimate interrill soil erosion directly from the rainfall intensity are expected to perform poorly in predicting soil erosion from varying intensity rainfall events. It may imply that various and complicated mechanisms might be activated in runoff and erosion under natural rainfall conditions. The results may indicate that negligence of the event profile may lead to inaccurate understanding of mechanisms involved in runoff and soil erosion.
