مجله مهندسی و مدیریت آبخیز
سال ششم شماره 1 (بهار 1393)

Recognition of effective processes of erosion, especially, threshold is one of the most important strategies in water and soil resources management. Gully erosion is one of the most important sources of sediment yield in watersheds that is defined as different thresholds like area-slope or topography. In this paper, the area- slope threshold was investigated in Zahirabad Watershed in Markazi province, Iran. First, based on field surveys and digital elevation model, morphometric characteristics of 14 gullies were measured, accompanied by soil sampling and vegetation cover measurements. Second, homogeneous groups of gullies were defined by factor and cluster analysis and power relations of area-slope was prepared. Results demonstrated that there was no considerable correlation between area and slope of gully watersheds. So, coefficient of determination of creation point and head-cut of gullies were 0.111 and 0.181, respectively. According to the results, the dominant process in creation and head cut development of gullies in Zahirabad was related to flow concentration and rill erosion of high slopes. Considering the prevail of loamy texture of soils land use changes and deterioration of vegetation cover, it is suggested to investigate the optimization of land use schemas, and land cover improvement on sloppy lands with the objective of gully control.

Drought is the most hazardous natural phenomenon. Although not preventable, its negative effects can be reduced through taking some measures. One of the systems severely affected by drought while less considered is the groundwater. In this study, drought status and its impact on groundwater resources was investigated in Alashtar Plain using Standardized Precipitation Index (SPI) at monthly, quarterly, and annual scales and the Groundwater Resource Index (GRI) during the statistical period of 1991-2010. After data collection, statistical errors were corrected by subtraction and ratios method. Then, to determine the status, SPI and GRI were calculated with DIP software on an annual, seasonal, and three, six, nine, 12, 18, 24, and 48-month time scales for Alashtar Plain. Then, according to SPI and GRI value, the moisture status were determined for each period. Results indicated that the trend of plain meteorological and groundwater drought is negative. Correlation between SPI at different time scales with and without the time delay and with average groundwater level and GRI was analyzed. Statistical analysis showed that SPI was significant at the level of 0.01, in the 24-month time scale without any time delay with mean groundwater level and GRI and had the highest correlation coefficient, suggesting the impact of drought on Alashtar plain groundwater. Regression relation between the mean level of the water table and SPI_24 showed that 64.4% of the variance at the mean level of water table was affected by SPI_24 and 35.6% was affected by other factors. Drought magnitude (DM) analysis showed that meteorological and groundwater droughts are consistent with winter and autumn, respectively. Undoubtedly, optimized utilization management, especially in spring and summer, may have a critical impact on preventing damages to the groundwater resources of the region.

In this research, a spatial prediction model (a quantitative method) and the fuzzy sets theory (a semi-quantitative method) have been used for landslide hazard and risk assessment, respectively. A procedure, compring two analytical stages, has been proposed to show the location of future slope instability. In the first step, 75% of the pixels with landslide have been entered to the model as the estimation set, in which new landslides have occurred with a moderate to high intensity or at least have displaced once or more in the last 50 years. At the second stage, the accuracy of prediction map has been examined by ROC curve (Receiver Operating Characteristic curve) based on 25% of the landslide pixels that have not been entered in the model. Landslide risk evaluation was considered by combination of the hazard potential and resource damage potential and using the fuzzy algebraic product operator in the region. The hazard potential and resource damage potential obtained typically from the hazard zonation map and the land cover/land use map. The area under the ROC curve is 0.795 for hazard zonation map, equivalent to an accuracy of 79.5%. In the base of multi-method approach results, 13.8% of the region is located in a high and very high risk level zone, and 78.1% of the area is placed in low and very low risk categories. Proposed method was used for landslide risk assessment in Hashtchin region and the results could be used to established land use planes, developmental activities, displacement and extension of settlement area, and patterns of building regulations.

Nowadays, wise scheduling of water resources is an important task for sustainable development. In this scope, accurate knowledge about daily evaporation from surface water is important for optimum agricultural products. Shortage or lack of evaporation sites, quality of the data and gaps in pan observations force the researchers to use prediction models. In this work, three different time series were applied for estimating daily pan evaporation in Hamedan province (Ekbatan dam, Kooshk-Abad and Agh-Kahriz). Evaluations of time series data indicated that pan evaporation of all stations, contains no seasonal trend. Based on the results, the ARIMA showed the highest performance in estimating the daily pan evaporation for the selected sites. With respect to the obtained errors, the best time-series structure were ARIMA(1,1,1) for Agh-Kahriz and ARIMA(2,0,1) for Ekbatan dam and Kooshk-Abad, respectively. The calculated R2 and RMSE for selected sites were 0.93 and 2.44 mm/day for Agh-Kahriz, 0.93 and 1.23 mm/day for Ekbatan dam and 0.92 and 1.03 mm/day for Kooshk-Abad. For the selected model, the Mean Percentage Errors (MPE) varied between 5.85 to 6.92 percent, which denotes models overestimation versus the measurements. The standard deviations of the best performance model are: 0.15, 0.14 and 0.13 mm for Agh-Kahriz, Ekbatan dam and Kooshk-Abad, respectively.

In recent years, Radar based DEMs due to ease of access and being free of charge are extensively used in hydrological modeling and deriving the geomorphological properties of watersheds. One of the most important questions on application of rainfall runoff models is the effect of DEMs from different sources on simulation results. On this basis, this research focused on evaluation of the effects of DEMs derived from topographical maps at the scale of 1: 25000 and the SRTM DEM, on the performance of the KW-GIUH as a geomorphologic rainfall runoff model. The results showed that the SRTM DEM gives sub-watershed's slope, the average slope of channels and the number of channels more than that was derived from topographic based DEM, while the overland flow length and average length of channels from the latter source are greater. The outcomes of the research showed that the Q-peak, hydrograph base time and the slope of hydrograph rising limb from Radar based DEM regarding different thresholds for artificial channel network derivation have a difference of about 1-12% with that was obtained from the model when using the topographic based DEM.

In this study, a simulation has been performed using the Soil and Water Assessment Tool (SWAT) model with the data of the Ghare-sou watershed. The main objective of the study was testing the performance of SWAT and its feasibility to simulate the water balance in this watershed. Required data such as soil properties, land use and topographic maps were collected from the Natural Resource Office of Kermanshah province, and the weather data, including daily rainfall, temperature, relative humidity and discharge were collected from Meteorology Agency and regional water company of the province. Before calibration, a sensitivity analysis has been performed for all parameters, using OAT (One parameter At a Time) method to evaluate and demonstrate the influences of the model parameters on four major components of water budget including surface runoff, lateral flow, groundwater and evapotranspiration. Calibration and validation of the model were performed using the SUFI2 algorithm. River discharge data from 1982 to 2000 were used for the calibration and those of 2001 to 2005 for the validation. Different criteria were used to evaluate the performance of the simulation. During calibration, the simulated flow matched the observed values with a Nash-Sutcliffe coefficient of 0.56 and a coefficient of determination (R2) of 0.6. These values were 0.6 and 0.65 during the validation. The calibrated SWAT model is suggested to be used in simulation of the monthly flow of the Ghare-Sou watershed, in order to assess the impacts of different management practices and environment changes on the flow.

Quantitative analysis of runoff and estimates of stream flow in gauged basins and its transferring to ungauged sites has special importance for water resources planning, watershed and agricultural lands management, as the layout and optimal design of diversion structures and flow control need runoff information with different probability levels. In this research, runoff information of hydrometric stations which located in river catchments of Isfahan, Markazi, Qom, Tehran, Hamadan and Qazvin provinces was collected and investigated. In this regard, such stations which included data with the appropriate quality and quantity were selected in a common period of time. In this case study, results of cluster analysis concluded three homogeneous regions of watershed based on independent variables. According to mean annual runoff probability analysis; the best statistical distribution was fitted and runoff values were determined with return periods of 2 to 100 year. Also, regional runoff models based on hydrological and morphometric parameters were extracted with different return periods for each homogeneous region. In each homogeneous region, evaluation of regression models obtained was carried out using a number of hydrometric stations control. In this case study, area, average slope, main river slope, length and gravilus coefficient of watershed were detected as the most influential parameters in estimation of runoff. Root Mean Square Error (RMSE) for models represented minimum values of 1.2, 5, 7.6 with two years return period and maximum values of 14.4, 32.8 and 18 with 100 years return period in the first, second and third homogeneous groups, respectively.

One of the sediment controlling methods in the hydraulics structures is application of the vortex settling basin. Such basins represent the higher speed in sediment separation in comparison with other usual settling structures. One of the problems of such settling structure is the settlement of a portion of the sediments on the basin floor as a result of disruption on the structure operation caused by remaining loads. Therefore, the curvature submerged vane was introduced by this research in order to solve the problem. Several curvature vanes patterns was applied in an experimental model of the vortex settling basin to investigate the efficiency and sediment removal from the basin floor. Experiments were carried out in a basin with diameter of 96 cm and a height of 206 cm. In this model, curvature submerge vanes were used for modification and their different arrangement in 60 degree diameter section for increasing in vortexes power. Experiments were continued by 45 and 37 Ls-1 water discharge, flushing orifice diameters of 36, 46 and 59 mm and six different arrangement of vane (R2, R3, R4, R23, R34, R234). Results showed that application of submerged vane on the vortex basin floor with suitable arrangement resulted in sediment removal from basin floor and in replacement of sediments toward the orifice. Present research showed that the best efficiency was obtained from R3, R4 and R34 arrangements which were located in the farther distance from orifice. Furthermore, results showed that variation in water discharge and orifice diameter is an effective factor in the efficiency of curvature submerged vane. In the most optimum case of curvature submerged vane arrangement, 25.56 percent of the sediment was removed from the floor of vortex settling basin.