مجله مهندسی و مدیریت آبخیز
سال چهارم شماره 3 (پاییز 1391)

Due to vegetation cover importance in protecting soil and its important role in controlling erosion، this study was conducted to determine the effect of land use management on the Orumiyeh lake watershed erosion rate، using GIS and RS technologies and EPM model. Using ETM+ 2002 satellite imagery، field work and existing map، required layer of model prepared and soil erosion was estimated in the current situation. Management scenarios، with good and bad actions through changes hypothetically in land use rank (decreased and increased in steps of five to 50 percent)، the rate of soil erosion and changes in estimates were calculated. Results showed that maximum of erosion rates is belong to 3015 and 3054 sub-watershed with values of 768 and 749، minimum is belong to 3072 and 3056 sub-watershed with values of and 287 respectively and the mean for the watershed 485. 9. Trend of erosion rate change due to land use change was linearly and positive، meanwhile ultimate condition with 50% addition or reduction to land use rank، respectively caused 83. 7 and -64. 6 percent change in soil erosion.

Computation and estimation of flood discharge is necessary in hydraulic structure planning and flood control projects. The precise estimation of runoff and flood discharge needs comprehensive data of the amount and condition of rainfall and design precipitation. Rainfall Depth-Area-Duration curves (DAD) of each region، are used to estimate the optimal precipitation. In this research، these curves were provided for 1، 3، 6، 9، 12، 18 and 24 hours intervals and their relations were studied for Northern parts of Western Azerbaijan province. Eleven maximum and pervasive storms were selected to draw the cumulative rainfall graph. There are adequate recorded and non-recorded rain gauges in the region. Mass curves were prepared for non-recorded stations using relations between rainfall gradient and altitude in the isohyets maps. Results showed that the maximum rainfall for 1 km2 is related to 18 h rainfall with 42 mm and its minimum is related to 1 h rainfall with 4. 29 mm. Also، 9 and 12 h curves indicated no difference in different areas. Comparing 18 and 24 h curves indicated that the amount of precipitations are equal in small areas and 18 h curve is above 24 h curve in wast areas that could be related to the shortage of rainfalls with 24 h duration.

Investigation of effective factors on soil erosion and their variability analysis is essential for soil and water conservation projects. The present research was carried out to survey the role of two north and south facing slope plots on soil erosion on storm basis at Sanganeh watershed located in Khorasan Razavi province، Iran. The study was conducted using a pair of small plots with dimensions of 2×2 meters. The plots were be designed using metal sheets and their outlet was directed towards collecting tanks. These plots were established close to each other at two different aspects. The generated runoff and sediment from plots caused by 12 storm events during October 2006 and May 2007 were collected and sediment concentration was ultimately calculated. The results of sediment concentration analysis verified a significant difference (p<0. 01) between soil erosion study plots with very low quantities in plots installed in northern aspect. The difference was clearly associated with effect of slope aspects on vegetation cover.

Wind erosion is one of the aspects of land degradation resulting in some problems especially for arid and semi-arid regions. Recognition of Sediment size Distribution (PSD) as well as transport mechanisms is important in modelling of wind erosion. In the present study، this topic was investigated on two soils taken from cropland and sand dune with different PSD، using wind tunnel. Results showed that compared to the original soil، the collected sediment had finer sizes، indicating a selective mechanism in transporting detachable particles. It was found that for cropland soil، increasing wind speed from 2 to 18 m/s at the height of 20 cm، the PSD of sediment approached to the original soil. This trend was reverse for sandy soil so that، for higher wind velocities، the frequency of fine particles was more than the original soil. The result of transport mechanisms indicated that compared to saltation as well as suspension، creeping was the least important mechanism. The contributing percentage of creeping for cropland and sandy soils was determined less than 10 and 1 %، respectively. For the cropland soil at wind speed of 2 m/s، suspension was the most important mechanism of transport and depends on soil''s PSD، 61. 1- 68. 5 % of particles were transported. Increasing wind speed up to 18 m/s، saltation with 50. 4- 53. 8 % was found as the main transport mechanism. Reversely، in the sandy soil at low wind speed، most of sediment (59. 3 %) was transported through saltation، whereas increasing the speed، suspension with 55. 3 % became the dominant mechanism. The finding of this study brings up the important of soil PSD on the PSD of sediment as well as transport mechanisms.

Water deficiency in arid regions especially in Iran، generally reduces the cultivation and considered as a major limitation in green cover re-establishment process in deserted areas. This study aims to overcome on drought and to achieve a strategic way of increasing the water use efficiency and reduction of costs. This study is carried out in a wind-eroded part of Aran and Bidgol county of Isfahan province، Iran and two species of Haloxylon and Nitraria sp were cultivated in treated and check soils in mentioned area. The treatments were adding five of two kinds of polymer water absorbent to the soil of root environment. The check samples were irrigated every 14 days once and the treated ones every 14، 28، 35 and 42 days once. During two years of study، the moisture of root environment was measured in all samples. In third year the amount of live seedlings were also accounted. The statistical analysis showed that there is a significant difference between the treated and check samples in all irrigation periods in significance level of 5%. In other words، increasing of irrigation period in treated samples compared with check treatment hold more moisture in root environment. Mean comparison between treatments showed no differences in volumetric moisture of 21 compared with 28 and 28 compared with 42 irrigation periods. And also there was no difference between two absorbent in all treatments. The increasing rate of live seedlings، after 3 years، between treated and check samples represents that the polymers give a good establishing circumstance to young seedlings. In other words it is resulted that these water absorbents are capable of reducing the moisture stress in root area of irrigation periods and increase the rate of established seedlings. We assume that Aquasorb polymers and TC are successfully increasing the water holding capacity of soils in green cover re-establishing activities of deserted areas. With increasing the water holding capacity they also reduce also the costs by 50-70 percent.

The most of the soil erosion and sediment yield in the Talkheh Rood watershed are mainly related to marl formations. This study was conducted to evaluate physico- chemical properties of Talkheh Rood marl samples in rill، gully، mass and badland erosion types. For this purpose، marl samples were taken from marl sediment of homogenous work units. Twenty four samples were selected، in total. Some of main physic - chemical properties of these marls were measured in lab. These properties were pH، EC، CEC، Lime، gypsum and OC content، SAR، Na، K، Cl، Ca، Mg، clay، silt and sand percentage. These data were interpreted by ANOVA and mean comparisons analysis methods. Results showed that pH، gypsum content and sand percentage had statistically significant differences between four erosion types. Mean comparison showed that significant difference of pH، was between mass and badland erosions، sand between badland and gully ones، and gypsum، rill and gully، also badland and gully ones.