JWSS - Journal of Water and Soil Science

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Stage – discharge relationship is mainly developed from measured data in any hydrometry station. Measured data usually obtain in low to medium flow discharge, because in most cases it is very difficult to measure the flow discharge during flood. Therefore, the stage–discharge is extrapolated beyond the measured data to compute the flood which may estimate low or higher value. This is because during the high flow, the bed form is developed which causes the flow resistance to change. In order to establish a better stage – discharge relation, it is important to apply methods which consider the bed form resistance. In this study an attempt has been made to determine the best method for developing such relationship. To reach the goal, the required data such as river cross section, discharge and related stage and bed material gradation from Ghorbaghestan hydrometry station were measured for two years. Then a computer program was developed. Using this program and applying the measured data, the stage – discharge relationships were computed by five different methods. From the statistical comparison of the results of these methods with measured data, it was found that Shen, Brownlie, Engelund and White’s method overestimate the flow discharge. The best method was found to be the Einstein – Barbarossa’s method that provided the minimum absolute mean errors 0.31 and 1.468 m3/s and minimum root mean square error 0.112 and 0.466 m3/s for the two study years, respectively

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Reduction of quality and soil productivity due to organic carbon losses is one of the most important consequences of land use changes, that creates irreparable effects on the soil. To evaluate the land use effect on the amount of soil organic carbon in Vertisols, Sartip Abad series with extent of 1850 hectare in south of Bilehvar area in Kermanshah province was studied by using the completely randomized block design in factorial experiment with 10 repeats in farmland and grassland, some soil physical and chemical properties in two Lands compared with each other. The results showed that the soil organic carbon in surface horizons of grassland has been more than farmland and accordingly increase the amount of sequestrated carbon in grassland. No significant differences were found in the amount of soil organic carbon in lower horizons of two lands. Due to land use change from grassland to farmland, noticeably increase in Bulk density, Nitrogen, Acidity, soil Electrical Conductivity and decrease the organic carbon percent and the soil organic material. Pedutorbation, clay amount (higher of 50%), numerous small subsoil, and stable structure are the important factors in saving the organic carbon of vertisols that can reduce the effects of land use changes on organic carbon amount. Generally, it can be conclude that: the land use changes not only can create the severe damage on soil physical and chemical properties but with the carbon losses and more release of greenhouse gases exacerbate the pollution of environment which endangers the life in a earth planet.