پژوهشنامه مدیریت حوزه آبخیز
پیاپی 5 (بهار و تابستان 1391)

The present research aimed to compare different methods of statistical analysis and to select the best method for achievement to the model among components of synthetic unit hydrograph by using of the physical characteristics of catchments, in northern catchments of Iran, with the area of 177000 km2 in Giulan, Mazandaran and Golestan Provinces. For execution of the research, 9 physical characteristics of catchment and 8 characteristics of unit hydrograph components for 44 storms in the north parts of Iran have been chosen. Regression test by using bivariate approach and various forms such as linear, logarithmic, inverse, quadratic, cubic, exponential, power and combined forms has been used after execution of factorial analysis. The obtained models were evaluated by relative errors, RMSE and efficiency coefficient. Results showed that the bivariate models have more accuracy in estimation of the amounts especially in the case of temporal variables (base time, time to peak, time to depletion). Regression of several variables has high accuracy in estimation of discharge and recursion regression of several variables has the highest accuracy.

Drought is a natural and recurring phenomenon which causes water scarcity in various sectors. In comparison with other natural hazards and disasters, drought is more important considering intensity and frequency as well as spatial extent and total damage. In the current research, the Standardized Precipitation Index (SPI) and Standardized Discharge Index (SDI) were used to analyze the temporal characteristics of droughts. To this end, monthly precipitation time series of 23 raingauge stations and 7 hydrometry stations across the Atrak River basin were used and SPI and SDI for six time intervals (3, 6, 9, 12, 24 and 48 months) were calculated and analyzed. For assessment of drought impact on surface water resources, first the correlation between rain and discharge time series of different lag times were calculated within the study area. Then, the Pearson correlation method was applied to calculate the correlation between SDI and SPI series for different time intervals at each individual subwatershed and whole watershed of the Atrak River. The results showed that the correlation between meteorological and hydrological droughts was significant at 99 percent confidence level. The maximum correlation was found for SPI and SDI of 3 months time intervals. This indicates that droughts cause decrease in surface flows and this impact is remarkably observed in the discharge values of the same month or one month later. The highest Pearson correlation was found for the Shirabad station and the Darband subwatershed.

Complication of initiation process, expansion of gully erosion and unfamiliarity of the function of soil physicochemical characteristics, effective in this type of erosion, is one of the most important challenges to achieve functional approaches in order to prevent it. According to the importance of loss areas in Golestan Province which is embarrassed a wide area and has an important role in production of sediment in Gorganrood river, exact configuration of types of erosion in loss is seemed essential for offering a proper function to control the erosion and sediment, especially gully erosion. So in this research, in order to identify initiation mechanism and gully erosion in loss areas, we are going to recognize airy photos with the scale of 1:20000 and the soil physicochemical characteristics in Temer Ghareh Ghozi region. Through direct revision, 10 gullies were identified, topography and merfometry, after recognizing the gully situation on activity units map in GIS environment. Then the sample from the soil of each gully, in the scale of 25, 50 and 75% of the length of the gully were done, in order to specify the soil physicochemical characteristics. At the end, by using SPSS software, the relationship between the soil physicochemical agents and development and expansion of gully erosion were offered through regression model. The outcome of analysis and corrosion of the data demonstrate the effective role of the soil physicochemical characteristics, specially the scale of silt, dissolvable and the soil saturation degree in initiation and expansion of gully erosion in loss areas.

In spite of The uncontrolled exploitation of groundwater that has caused a sharp drop in water level, Agricultural, industrial and urban activities enter contaminant to various aquifers. Due to Dehgolan plain importance in water supply of industrial, drinking and agriculture, for the vulnerability assessment DRASTIC model was used. The DRASTIC model uses seven environmental parameters (Depth to water, net Recharge, Aquifer media, Soil media, Topography, Impact of vadose zone and hydraulic Conductivity) to characterize the hydrogeological setting and evaluate aquifer vulnerability. These factors were produced as 7 layers in Arc GIS 9.3 software and by Weighting, Rating and combination, final map of Groundwater vulnerability to pollution was provided 5 zones as: without risk of pollution, very low, low, low to moderate and moderate to high and finally DRASTIC Index ranging from 41 to 159 for all the case studies were estimated. Nitrate concentration and EC were used to validate the final map of vulnerability. Overlying these elements, concentration to the DRASTIC final map, illustrated that all point with high concentration stand in the high pollution zones and this result showed the acceptable accuracy of DRASTIC model. From point of area view, 7.79% of plain lies in without risk of pollution class, 40.92% of plain in very low class, 41.61% of plain in low class, 9.66% of plain in low to moderate class and only 0.02% of plain drops in moderate to high class.

Among the variety of methods used for estimating runoff in the watershed, the SCS method has universal applicability, so the main aim of this study is the calibration of SCS method and the creation of flood hydrograph. The HEC-HMS hydrologic (rainfall-runoff) model has been used for Idanak watershed flood estimation. Using the residual sum of squared minimization function”, calibration process was completed and the results were evaluated at the end. The results indicate that models with no use of calibration would not be trustful. Relying on model parameters (CN, Ia) estimation using experimental relationships causes poor match between observed and simulated runoff and proves the necessity of calibration. In the models calibration and validation the difference of peak flows between hydrograph and simulated hydrograph is always less than 10 percent and coefficient of determination between the two is 0.82. the calibration model results show the efficiency of the model in estimation of runoff and flood peak flow. The validation results associated with the volume of runoff is not acceptable, because the difference between observed and simulated runoff volume is more than 31 percent.

Complex in hydrological and hydraulic processes are one of the distinguishing features of urban areas. Therefore, accurate determination of the input variables of urban models and their impact on model output is time consuming and difficult. Sensitivity analysis shows which parameters impact more severely the results and ranked model parameters according to their effect on model output which can be calculated using this method. In this study the sensitivity of affective variables that influence urban flood peak, was studied by using the SWMM model in Imam Ali town in Mashhad city. The initial value of the eight-parameter including percentage of impervious area (%Imperv), slope, width, N-Manning for impervious area, N-Manning for pervious area, depth of depression storage on impervious area, depth of depression storage on pervious area and percent of impervious area with no depression storage reduction (%Zero-Imperv) and increases in the range of acceptable change and flood peak discharge was selected as the dependent variable. Result showed that with 30% increase in the amount of impervious areas, peak discharge increases 3.38 percent and this parameter was recognized as the most effective parameter and percent of impervious area with no depression storage has the minimum impact on peak discharge. It is recommended to increasing in the amount of impervious areas that causes from land use change, urbanization, no doctrinaire infrastructures causes increases in peak discharge and flood risk hazard in urban area.

Identifying areas with different potential to landslide occurrence is one of the primitive actions in natural resources management. In view of importance of recognizing appropriate method to estimate landslide, in this research, the efficiency of two methods of landslide hazard zonation including methods of Mora and Varson and Multivariate regression were compared. In this research, first, layer of landslide was created in Arc GIS using aerial photographs with scales of 1:20000 and 1:50000, field monitoring and GPS. To zone landslide hazard in research area using methods of Mora and Varson and Multivariate regression, efficient layers for each method were created. After creating and weighting each layer, research area zonation to be done. Assessment of results of different models using quality sum index (Qs) and correlation coefficient shows that Multivariate regression is the best model in zonation of research area from the view point of the landslide hazard. According to the Multivariate regression, research area was separated to six classes of landslide hazard. Therefore we can manage the basins and fighting with landslide hazard by less cost and time By selecting the best method.