Rivers Riparian buffer zones Determination by Combining USDA and Qualitative Vulnerability (Case study: Ab shirin River)

  Vulnerability of surface water resources to contamination in comparison with groundwater is often higher, and thus, their quality buffers determination is more important than groundwater. The aims of rivers quality buffers determination are mainly the reduction of water pollution, erosion control, and sometimes the creation of wildlife sanctuaries. According to the intended purpose and the importance of rivers, the different values of quality buffers can be considered around the river. The United States Agriculture Organization (USDA) considers various physiography factors of rivers such as topography, soil holding capacity and vegetation as effective factors for finding out rivers quality buffers. Due to consider only physical factors by USDA and aim to improve it, the USDA method was combined with rivers quality vulnerability as the first study. The case of this study was the Ab-Shirin river in Kohgiluyeh and Boyer Ahmad province, where its branches have been qualitatively analyzed. Sampling of the river was carried out at 9 stations in Esfand 1394 in order to determine the qualitative vulnerability of the river. This study presents a new method to determine the quality buffers of rivers by combining the USDA method with qualitative vulnerability based on sampling. The USDA method proposes an initial quality buffer for the Ab-Shirin river by integrating slope, soil type and vegetation layers of river banks. In the next step, sampling was done along the river to determine its qualitative vulnerability. Sampling analysis showed that the amount of Nitrate Concentration, BOD and Ec were higher than other qualitative parameters, especially at the upstream intersections of the river branches. Moreover, some studies were already conducted by other researchers to propose quality buffers. In other words, where the concentration of contamination exceeds their limitations, they could be reduced or eliminated by increasing the quality buffers of the river. These buffers should also be added to USDA suggested buffers. For instance, where the slope and the soil permeability of the river bank are low and also the vegetation is thick, USDA suggested a quality buffer about 21 m, but regarding the sampling and the other studies result, it considers increasing to 26 m. In other words, by increasing the buffer around 5 meters, according to other researchers’ studies, the concentration of contamination will be moderated due to increased distance and transport time. The results of the qualitative classification of Ab-Shirin showed that the biggest change in vulnerability belongs to branches come from the Dehdasht study area, at the intersection of branches in the Tilkeh-Kuh zone. Also, the quality buffers of the Yasouj River vary from 10 m to 55 m, and the parameters of Ec, Nitrate and BOD have the greatest effect on the increase in buffers.