مجله علوم و مهندسی آبخیزداری ایران
پیاپی 52 (بهار 1400)

Fire causes destructive effects on soil, water and components of wetland ecosystems. The aim of this study was to investigate the effects of fire on runoff amount and nutrient concentration of Zrebar Lake watershed between 2014 and 2017 and the return of burned areas to their natural conditions in the short, medium and long term. The results showed that in the fourth year after the fire, the amount of runoff and concentrations of dissolved calcium and ammonium in the burned areas compared to normal increased by 47, 5.9 and 23.5 percent, respectively, indicating that the conditions has not return to normal. Concentrations of dissolved total phosphorus and nitrate in the third year after the fire showed insignificant increases of 6.3 and 4.2 percent, respectively, indicating a return to normal conditions. The concentration of dissolved potassium and total nitrogen in the fourth year after the fire in the burned areas compared to the natural areas increased by 1.5 and 1.4 percent, respectively, which indicates a return to normal in the fourth year after the fire.  In general, it can be concluded that even in the long term, some of the destructive effects of the fire on water quantity and quality of the Zrebar Lake watershed will remain.

Zoning of gully erosion susceptibility and determining the factors controlling gully erosion is very important and vital. The aim of this study was to investigate the spatial distribution of gully erosion using two models of ANN and MaxEnt and to determine the factors affecting this type of erosion in Golestan Dam basin. Therefore, 14 factors in the form of three divisions, including topographic factors, other factors and combination of factors (14 factors) were considered as predictors of sensitivity. Out of 1042 gully erosion points, 30 and 70 percent were randomly classified as validation and test data, respectively. The results of Jackknife test showed that the parameters of height, rainfall and depth of valley are the most important variables affecting the prediction of gully erosion. The results of the modeling showed that the best accuracy of the model based on the ROC curve in the training model (0.923) and in the validation, stage (0.902) was the artificial neural network model, and this condition is achieved when all the factors in the modeling be involved. According to this model, about more than 20 percent of the domain (45633 ha) has a high sensitivity and is very susceptible to gully erosion.

The process of splash of soil particles by raindrops and their transport by splash or surface shallow flow is considered as interrill erosion, which can reduce soil fertility and cause pollution of surface water. This research was carried out to investigate the temporal variation of interrill erosion in different soils affected by surface slope. For this purpose, laboratory experiments were carried out on three soils with different texture on four slopes under simulated rainfall with a constant intensity of 30 mm.h-1 in three replications with a total of 36 test units. The results showed that there are significant differences between the slopes in terms of the threshold of occurrence of interrill erosion (P<0.0001). The threshold for the interrill erosion in the occurred speedy steeper slopes. The coarse textured soil (sandy clay loam) appended hither dependency on slope gradient witch was associated ti its more percentage of coarse particles. In lower slope gradients, the interrill erosion threshold was occurred with more delay after runoff appearance. Coarse- textured soil (sandy clay loam) showed hither dependency on slope gradient in interrill erosion that other to soils. This study revealed that slope gradients is an important factor controlling time threshold, pick time and rate of interrill erosion during rainfall in semi-arid soils.

Droughts affects on agriculture and water consumption management through LU/LC and water resources changes in western mountainous areas of Iran. The aim of this study was to investigate terrestrial and remote sensing drought indices and their effects on LU/LC and ground water level in Razan-Ghahavand watershed. Precipitation trend in two stations and water level trend in six piezometric well were studied using Man Kendaland modified Man Kendal and also SPI and SWI drought indices were computed in month, season and year scale during 71-94. LU/LC changes and relationship among SPI, SWI, VCI and TCI drought indices were computed during 2008-2013(two main drought year). The results showed that water level drop(more than 10m) was relate to SPI index with two-year delay significantly. There is a significant correlation with SPI index for VCI index than TCI index and season scale than month and year scales. The finding indicted that agriculture area, gardens and rangelands were decreased 10.96 percent, 13.57 percent and 0.23 percent respectively and also, salin lands was increased 9.51percent during the 2008-2013.

Gully erosion is one of the causes of land degradation, which causes a lot of damage with the loss of fertile soil. For this purpose, in the present study, using the Cochran relation, 40 gullies were selected for measurement in the Mazayjan watershed located in the southeast of Fars province. Factor analysis method was used to determine the factors affecting the classification of samples. Backward multivariate regression was used to determine the most effective factors in the formation, expansion and production of gutter sediment. The results showed that the creation area of ​​the gullies is a function of the variables of bare soil, organic matter and sand. So that with each percentage increase of bare soil, the amount of 0.379 is added to the creation area of ​​the watershed and at the rate of each unit, the percentage of soil organic matter and the percentage of sand are 0.349 and 0.363 units of the creation area are reduced respectively. Also, in determining the factors affecting the volume of gullies, the percentage of sand was the most important factor was reducing the volume of gullies. Therefore, in order to prevent the development of gullies and reduce the production of sediment, more attention should be paid to erosion control in the headcutchr('39')s gullies. It helped reduce gully erosion by increasing roughness and reducing runoff.

Nowdays, more than half of the worldchr(chr('39')39chr('39'))s population lives in urban areas, increasing land use change leads to an increase in impermeable land, which greatly reduces the possibility of rainwater infiltration into the land. In this study, Fooladshahr city of Isfahan province was selected as the study area to determine possible flooding points. Previous studies and experimental methods were used to calculate focus time. The SWMM model was used to identify flood sensitive points and the model was implemented for different return periods. The results showed that channels 2, 16, 17, 25 and 31 are sensitive to flooding for a return period of 25 years. In order to calibrate and validate the model, 3 rainfall events were measured on 9.02.2020, 20.02.2020 and 30.04.2020. In these events, depth, flow and velocity were measured and compared with the results of the model. Took. In the calibration and validation process, the NS criterion value was higher than 0.5 in all cases, and the evaluation results showed a good agreement between flow rate, speed and depth. Therefore, in this study, the SWMM model has sufficient ability to predict flood risk and manage the watershed and prioritize areas to solve the problem of flooding.

The study aimed to provide a pilot plan to integratedly manage the Barar-rud Watershed in Mazandaran Province based on existing problems. Accordingly, various strategies and their prioritizations were developed for the watershed. Towards that, SWOT was developed through field observation and face-to-face interviews with local stackeholders. The SWOT and quantitative strategic planning matrix were then developed to prioritize strategies. Based on the results, the condition of the study watershed was moderate and the most appropriate type of strategy was found to be conservative. The best strategy for the watershed was strengthening the sense of satisfaction of residents.