نشریه پژوهش های آبخیزداری
پیاپی 121 (زمستان 1397)

Drought is one of the most destructive environmental phenomena that causes extreme damages to the natural resources and human lives. As the Province of Kurdistan supplies many agricultural products in the country, the occurrence of drought is very important and that is the main reason behind the execution of this study. The data of twenty-three hydrometric and seven synoptic stations were used in a 29-year common statistical period (1985-2013). To calculate the meteorological drought, the SPI and PNI indices, and for the hydrological drought, the SDI index were used at the annual time scale. Results of the Mann-Kendall and Thilson tests indicated the existence of a trend for the meteorological drought at Sanandaj, Marivan, Ghorveh, Zarrineh and Saqez Stations. Also, the running of this test on the SDI index indicated a downward trend in all of the hydrometric stations, except for the Sentin Khorokhoreh, Ghashlagh, Qeblv and Meyar stations. Results also showed that the root mean square error for SPI, PNI, and SDI were 0.41, 0.49 and 0.47, and the coefficient of determination (R2) were 0.65, 0.51 and 0.59, respectively. Therefore, the SPI index is the best function among these three.

Soil erosion and nutrient loss threaten the soil and water resources worldwide. Application of soil conditioners, particularly organic amendments, is an effective way to mitigate this problem. This study was undertaken to assess the effect of application of two organic amendments, biochar and ship manure, under two rainfall intensities of 51 and 65 mm/h by using a rainfall simulator on intact soil. No significant difference was observed in the treatments at 51 mm/h, while with an increase in the intensity to 65 mm/h, the biochar amendment made a decrease of about 64% in the suspended load and runoff coefficient; sheep manure reduced the runoff coefficient and suspended load by about 76% and 74%, respectively at the 99% significance level.

Flood plalins are usually affected by the quantity and quality of the suspended load of the floodwater that inundates those areas. This is made possible by pumping the turbid water for irrigating the cropland adjacent to the river. This study was performed to assess the effects of addition of the suspended load carried by the Hirmand River on some physico-chemical properties of the farm fields irrigated by the pumped turbid water. It was observed that there was no statistically significant difference in the sand percentage, pH and Ca and Mg concentration between the irrigated and the control area. However, K, C, N, organic matter content and water saturation percentage showed a highly significant difference (p<0.01) between the two treatments. Moreover, SAR, ESP, and P concentration and silt and clay content of the irrigated area showed higher quantities at the (P<0.05) significance difference. Soil texture changed from loamy sand in the control area to loamy in the irrigated cropland. The turbid water irrigation of the sandy flood plain of the Hirmand River has improved most of the physico-chemical characteristics of the cropped area. Therefore, this irrigation method may be termed a desertification control technology.

Precipitation is one of the main components of the hydrological cycle, and its data are required for the analysis of meteorological and hydrological models. Due to lack of rainfall data in spatial and temporal scales, this study was performed to evaluate the accuracy of the precipitation estimation by the TRMM Satellite and its modified form in the Shapour Basin in the Fars Province. The daily and hourly rainfall data of the Shapour Basin stations, 28 precipitation events (on an hourly basis), and the daily basic precipitation events (2011–2016) for 5 stations in Boushigan, Kazeroon, Chitti, Arjan, and Posghalat Plains located in the Kazeroon study area were used. The correlation coefficient, the root mean squared error, the probability of detection, the false alarm ratio, and the critical success index were calculated for both rainfall estimations. The results showed that the modified TRMM and TRMM models were not accurate enough on the hourly and daily bases, yet the correlation between the observational data on the hourly basis and the modified TRMM was higher than that of the TRMM. By modifying TRMM rainfall data, the TRMM correlation coefficient improved from 0.52 to 0.75, indicating a relative correlation between the TRMM rainfall data and the ground station data. The correlation coefficient of the estimated precipitation values obtained from the TRMM and TRMM satellites were corrected on a monthly basis, with the ground data at all the studied stations having a high correlation coefficient (greater than 0.85). Correction of the TRMM precipitation data, improved the coefficient of explanation.

Gully erosion is types of water erosion that its occurrence and development lead to the loss of fertile agricultural soil, depletion of soil and groundwater. The objectives of this study were to investigate gully erosion and determine the sensitive areas in terms of gully erosion on the Sorkh Abad Watershed. Information layers such as slope, land use, distance from faults, aspect, distance from the stream network, distance from roads, lithology, rainfall and altitude above the mean sea level were prepared, classified and weighted using the Arc GIS software. Analytic network process (ANP) was used in the data analysis and modeling. The DEMATEL method was used to design the network structure among the criteria. The receiver operating characteristics (ROC) and the area under curve (AUC) were used for validation of the gully erosion map. The results indicated that four criteria: distance from roads, lithology, land use and precipitation were the most important factors leading to cause gully erosion. The results of validation of the gully erosion zonation map showed that the AUC with 0.684 had an appropriate function to determine susceptibility of the localities to gully erosion in the studied watershed.

Morphological changes in rivers lead to serious damages, including changes in the width of the waterways, changes in the drainage plan, erosion and sedimentation of the bed and banks, structural failure and loss of valuable land. A two-dimensional numerical model called CCHE2D was used to simulate the effect of the flow pattern on the river bed changes in the reach of the natural floodplain of the Kor River between the Abbas Abad Bridge and the Dorudzan Bridge, the Province of Fars. The topographical maps of the study area, the geometry of the model, and the computational grid with different dimensions were prepared. Based on the measured flow parameters, a two-dimensional hydrodynamic model of the mean depth, performance and results such as the changes in depth, flow velocity, secondary flow and shear stress were extracted. Finally, two data sets of the RMSE and MAPE were compared using the numerical model simulation versus the collected data. The results showed that this model had a good accuracy in predicting the flow parameter values, ​​and the simulated data were similar to those obtained from field measurements. The results of changes in the flow pattern as an effective indicator in predicting the hydraulic behavior and hydrodynamics showed that by correcting the path and removing the bends in the clay meadows of the Kor River by straightening the meanders, the heavy erosion of meander most agricultural land will be prevented. It must be emphasized that straightening the waterway entails its lining with erosion-resisting materials. It can be seen that using the computational fluid dynamics for modeling the stream bed variations brings researchers closer to a more general predictions for governing the processes in riverine plains. Also, the CCHE2D model has a good ability to predict changes in meandering rivers.

One of the most important problems in the world nowadays is the soil erosion, which reduces soil fertility, increases sediment concentration in rivers and dam’s reservoirs. For this purpose, the present study was conducted to investigate soil surface resistance changes using a polyvinyl acetate polymer with rates of 5, 10, 15, 20 and 25 ml and application concentrations of 5, 10, 15, 20, 25 percent in laboratory conditions and plot scale. The polymer application with a concentration of 25 percent and a rate of 25 ml in the level of 0.79 m2 had the most soil surface resistance with a rate of 3.3 kg cm-2. According to the obtained results and the economic cost (each litre of polyvinyl acetate of 100000 Rials) can state that the level of 15 percent can be selected as an optimum level for increasing soil surface resistance. With regard to the results it can be concluded that the used polymer in addition to the increasing soil surface resistance can have an effect on the soil conservation and control of water erosion.