مجله علوم و مهندسی آبخیزداری ایران
پیاپی 10 (بهار 1389)

Surface seal formation which is common in cultivated soils of semi arid and arid regions significantly affects infiltration and soil erosion and creates serious problems for crop production. Soil samples (18 samples) were selected from Guilan, Qhazvin and Zanjan provinces. The soil samples were analyzed for electrical conductivity, pH, organic matter, cation exchange capacity, primary and secondary particle size distribution, mean weight diameter and geometric mean diameter, fractal dimension of aggregates, and bulk density. For estimating erosion rate and runoff, soil samples packed in a 30×35 cm drainable detachment tray and subjected to simulated rainfall for 30 minutes. Runoff rate and sediment concentration were measured during the experiment. An undisturbed surface sample was collected to identify seal formation by thin section analysis using image tools software. Collected data were examined by multiple regression analysis to determine the relations between aggregate stability, seal formation, runoff and soil erosion and soil properties. There was a significant relationship between aggregate stability indices and surface sealing formation which controls runoff and erosion rate. Results indicated that runoff rate and soil erosion are related to soil texture, organic matter, sodium exchange percentage and aggregate stability.

Landslide is one of the natural hazards that occurs in mountainous regions. Landslide changes the morphology of region and results in damages on buildings, roads, agricultural land and etc, therefore making it an important consideration in hazard mitigation planning by researchers and research institutes. In this study landslide hazard map produced using bivariate statistical model in Ilam dam basin. This model was included of three methods, density area, value information and weights of evidence modelling. The results of evaluation of this bivariate statistical model using landslide index, precision of the predicted results and density ratio show that the density ratio method was more efficient for evaluation of model than the others. Therefore this method has been recognized for assessment of the model efficiently. Based on results of density ratio method, density area, weights of evidence modelling and information value were the most accurate in separability of hazardous landslides classes. The separability index of hazardous class in density area, weights of evidence modelling and information value were 2.6, 1.7 and 1.12, respectively.

Application of empirical methods in estimation of surface runoff is a must in ungauged watersheds. The runoff coefficient is one of the important input variables in empirical models. Proper calculation of runoff coefficient and study on its variation in different conditions facilitates proper estimation of runoff and flood peaks. So far, many studies have been conducted for estimation of runoff coefficient on monthly, seasonal and annual bases. However, limited researches have considered the variation of runoff coefficient during a storm event. The present study was therefore formulated to study on the intra variation of runoff coefficient and its affecting factors in Bar Neyshabour watershed comprising an area of 11388ha. Towards this attempt, 32 storm events, with duration of equal to or more than watershed concentration time of 2.9h and significant changes in hydrographs were selected from 440 events recorded during 1980 to 1989 and corresponding hydrographs and hyetographs were collected. The mean runoff coefficient and associated quarterly and deciles were also calculated. The relationships between different rainfall and excess rainfall with mean runoff coefficient and its components was then analyzed with the help of bivariate and multivariate regressions and applying ordinary and transformed data. The results of the study verified a dynamic drastic change from 0.6 to 45.7% in runoff coefficient with respective arithmetic, median, antilogarithm mean and standard deviation of 10.65, 7.96, 7.59 and 9.35%. In general, the results of the study also revealed the inter changes of runoff coefficient during storm events and feasibility of its simulation by using bivariate regression with correlation coefficient from 28 to 88% (0.003≤p≤0.68). It was also found that the 2nd and 3rd quartiles could estimate the runoff coefficient variability better than other rainfall components in the study watershed.

Autographic rain-gauge networks are designed to provide the density and distribution of stations so that characteristics of the rainfall events both in time and over the region can be determined with sufficient precision. Development and application of scientific methods for network design is probably one of the most complex issues of hydrology. In this study, annual rainfall data for rain-gauge stations of khorasan province consisting of Northern, Razavi and Southern Khorasan were collected from Khorasan Regionl Water authority and geostatistical analysis was made for finding the spatial correlation of them. Finally, some additional rain-gauge stations were suggested based on errors of kriging method. Geostatistical studies in Razavi Khorasan province show that adding 15 rain-gauges, decreases coefficient of variation (CV) values from 14% to 17% in vast central parts and decreases approximately 7% in western parts. Also, the results of mentioned analysis of whole provinces including North, South and Razavi Khorasan show that 15 added rain-gauges, decreased CV values about 8% to 9% just in central northern and eastern parts and approximately 23% in Western parts.

One of the most sensitive parameters in groundwater investigation and modeling is estimation of groundwater recharge. In this study, parallel to tracer analysis and groundwater modeling, a geoelectric method was adopted in evaluation of recharge mechanism and aquifer reservoir changes. The results of geoelectric method were compared and used in tracer analysis and groundwater modeling. In this research, Geoelectric method was used with two specific objectives in mind. First, the relation between soil electrical resistivity obtained by dipole method and soil moisture and soil minerals investigated and showed promising results. Next, the transmisivity of Hashtgerd Aquifer was estimated by boreholes of Schlumberger method. To obtain more accurate information from reservoir characteristics, the mechanism and rate of recharge between boreholes in the past years were investigated and soil moisture and soil minerals between boundaries were evaluated and verified. The groundwater fluctuations in the region was analyzed in a more accurate manner comparing to the traditional methods.

In this research rainfall data studied in the forms of erosivity equations for the reason of determining vulnerable areas affecting by rainfall erosivity in Ardabil Province, Iran. Initially the rainfall data from 71 stations into and around of Ardabil Province collected and analysed as amounts, intensities and other related parameters for erosivity. Therefore the rainfall erosivity maps in different forms supplied and classified in ArcGIS9.3 using GIS and geostatistics common capabilities. The evaluation of different rainfall erosivity methods by the amounts of 11 distributed catchments specific sediment yields showed that the I60 index (the maximum rainfall intensity in one hour) is the best for explaining the rainfall erosivity in Ardabil Province.

Development of surface water monitoring networks is a critical factor in the assessment and protection of water resources. This study focuses on evaluating the effectiveness of surface water quality monitoring network and identify monitoring stations and water quality parameters which are important in assessing annual variations of water quality in Gorgan-roud River, Golestan Province. Cluster Analysis (CA) was used to monitor station grouping and Principal component analysis (PCA) and principal factor analysis (PFA) techniques were used for Assessment of water quality monitoring stations. The analysis of water quality data from nineteen water quality monitoring stations over a 12-year time period indicated that three monitoring stations (Taghi-Abad, Shir-Abad, and Nodeh) were identified as less important in explaining the annual variance of the water quality parameters. Also results revealed that total hardness and EC are most important parameters at first component and in the second component, pH and HCO3 are appropriate for assessing variations of water quality parameters in the Gorgan-roud River.

Over centuries, ground water has been an important source of water. So, awareness about its temporal and spatial variability, in different zones, is necessary, and Geostatistics is a vital technique for this purpose. In this study, 76 wells (water year of 1382-1383) and 71 wells related to Gonabad plains were prepared and their descriptive statistic, trend and semivariogram were separately evaluated for each season. Then, prediction maps were organized. Temporal variability of water table for each season and its spatial variability for different places were calculated. South-north trend and southeast-northwest anisotropy were observed for all seasons. Every season except winter had exponential model with major and minor range of 20 and 15 km, respectively. Winter in different years had spherical model with major (23 to 28 Km) and minor (15 km) range too. The highest uncertainty belonged to some places that have the greatest distance from each other