بررسی تاثیر سامانه‌های سطوح آبگیر باران در کنترل رواناب و رسوب (مطالعه موردی حوضه آبخیز دره‌مرید بافت)

آب منبع حیات و عامل رشد و توسعه‌ ی جوامع بشری است. با توجه به افزایش جمعیت و احتیاج بشر به غذا، نیاز به این منبع حیاتی روز به روز نمایان تر می شود. استفاده ‌ی بهینه از نزولات جوی به خصوص برف و باران، در مناطق خشک و نیمه خشک اهمیت ویژه‌ ای دارد. ایجاد سطوح آبگیر با ضریب رواناب بالا و ذخیره کردن رواناب حاصل از آن، می ‌تواند نیاز آبی گیاهان و درختان در فصول کم آب را فراهم سازد و شرایط پایداری را ایجاد کند. برای این منظور، سه تیمار شامل سامانه ‌ی غیر قابل نفوذ، سامانه ‌ی به طور طبیعی به همراه فیلتر و سامانه ‌ی طبیعی به صورت شاهد انتخاب شد. هر کدام از کرت ‌های آزمایش، 49 متر مربع مساحت داشت و به شکل مربع بود که در زمین شیب ‌دار با شیب متوسط 20 درصد احداث شد. در پایین دست هر سامانه، مخزنی برای جمع‌ آوری و ذخیره ‌ی نابه ‌جا تعبیه شد. اطلاعات بارش نیز از طریق باران ‌نگار و حجم آب جمع ‌آوری شده در داخل هر مخزن به دقت اندازه ‌گیری شد. نتایج محاسبه ‌ی ضریب رواناب نشان داد که میانگین این ضریب در تیمار غیر قابل نفوذ به طور متوسط 66.4 درصد و در تیمار طبیعی با فیلتر و تیمار طبیعی به صورت شاهد به ترتیب 9.3 و 2.8 درصد است. در نتیجه می‌ توان گفت در مناطق مستعد در اقلیم خشک و نیمه خشک، استفاده از پوشش غیر قابل نفوذ در سیستم‌ های سطوح آبگیر می‌ تواند در کاهش فرسایش رسوب، استحصال آب باران و جمع ‌آوری حجم آب کافی نقش مهمی داشته باشد تا رطوبت مورد نیاز درختان ثمردهنده را تامین کند.

The effect of rain‌water catchment systems on runoff and sediment control (Case study: Darehmorid Watershed, Baft)

Extended abstract1 IntroductionNatural hazards are naturally occurring phenomena that have disastrous effects on humans and have different categories, but the one that concerns us and has posed significant problems is ldquo;erosion rdquo;. Sedimentation in water resources and reservoirs of dams, loss of agricultural lands and loss of fertile soil are among the effects of erosion. As a result of the negative impacts of erosion, extensive research is being carried out in different parts of the world regarding different erosion protection methods and the use of insulated and semiinsulated surfaces.Water is a nonrenewable resource that is used for many different purposes (from agriculture to afforestation to domestic use), and unfortunately many countries are facing water shortage due to the decline in groundwater availability. As a result, a sustainable groundwater and rainwater management is required. One of the sustainable plans made, is rain water harvesting (RWH) and the purpose of this study is to investigate the performance of different levels of catchment in rainwater harvesting. Based on the results, the best level that creates the most runoff can be selected and introduced to produce runoff. In RWH system, rainwater is stored during wet periods and used efficiently during dry periods as a supplementary irrigation to eliminate water shortage of the plants. This issue is of great importance in Iran as the climate is arid and semiarid and the annual rainfall is very little.2 MethodologyIn this study, three types of catchment surfaces were selected to collect rain water and in return three replications were considered for each of them. The areas selected were all square in shape and 49 m2 in size and were all build on a slope of 20%. The three reservoir surface treatments included1) Impermeable surface2) Natural surface with filter3) Natural surface (control)A total of 9 plots were created, which were put together in a completely randomized statistical design. To measure rainfall runoff, a 200liter barrel was installed downstream of each plot and the runoff generated by the pipe was directed into the barrel. A rain gauge was installed on the site to measure the depth of rainfall. After each storm leading to runoff production, the height of the runoff and the volume of water collected inside each barrel were accurately measured.The surface runoff coefficient in each of the treatments used was determined by dividing the runoff volume to the system level. Statistical analysis of data including mean comparison test along with descriptive analysis of data and comparison of results was performed. Correlation coefficient and regression analysis were used to investigate between rainfall depth as an independent variable and runoff depth as a dependent variable.3 Results The results of the correlation between the amount and intensity of rainfall with the amount of runoff produced in the treatments shows that the reaction of all treatments to the storms was almost the same, although impermeable treatments were more correlated than the other two treatments. In each rainfall, the highest amount of runoff was collected in the impermeable treatment and the lowest in the natural land treatment.The results of this study show that with increasing the depth of daily precipitation in the region, their frequency decreases so that only 1% of the frequency of daily precipitation is related to precipitation of more than 25 mm. Rainfall of less than 5 mm, on the other hand, has only led to runoff production at impermeable surfaces. This shows the significant impact of impermeable surfaces on runoff from shallow rainfall. Occurrence of rainfall with shallow depth and intensity at natural levels is mainly absorbed by the soil and its runoff production is minimal. That is, the natural surfaces of the earth, depending on the texture of its soil, store part of the rainfall. Therefore, one of the advantages of using insulation surfaces can be considered in the production of runoff at minimum rainfall.4 Discussion ConclusionsIn conclusion, this study was conducted to investigate the effect of using different management methods in the context of catchment surface systems in reducing sediment erosion and increasing vegetation. The results of this study showed that by making the surface of water intake systems impermeable, sediment erosion would be reduced. In order to model the depth of extracted runoff in catchment areas in semiarid climatic conditions, the average runoff coefficient was calculated in different treatments of catchment surface systems. The results showed that the average runoff coefficient in the impermeable treatment during the studied rainfall was 66.4. In other words, 2125 cubic meters of water can be extracted from each hectare of impermeable surface in an area with an annual average of the research site (320 mm), which can provide the required water for 15 hectares of rainfed almond orchard with supplementary irrigation. Occurrence of rainfall with shallow depth and intensity at natural levels is mainly absorbed by the soil and its runoff production is minimized. Therefore, the advantage of using impermeable surfaces can be considered in the production of runoff at minimum rainfall. This issue, due to the frequency of rainfall events with amounts of less than 5 mm in semiarid regions of the country, necessitates the use of insulation surfaces.