مجله مهندسی و مدیریت آبخیز
سال چهارم شماره 2 (تابستان 1391)

There are two parametric and nonparametric approaches for frequency analysis of hydrological data. Current methods of frequency analysis are based on the parametric methods. Moments، maximum likelihood and probability weighted moments are from various parametric methods for frequency analysis. In this research، maximum likelihood and L-moment methods are used for precipitation frequency analysis. L-moment is a new method for frequency analysis and one of the specific kinds of probability weighted moments. The results of frequency analysis with L-moment are compared with maximum likelihood method and kernel functions of nonparametric methods of normal، log-normal، rectangular and triangular kernel function. In this research، monthly and annual precipitations are fitted to thirteen distribution functions such as Logistic، Generalized Extreme Value and etc. with estimation of L-moment and maximum likelihood methods. The results showed that L-moment parametric method is best fitted to monthly and annual data due to mean relative deviation and mean square relative deviation goodness of fit tests compared to maximum likelihood parametric method. The L-moment parametric method is also best fitted to Boushehr، Jask and Mashhad annual data due to mean relative deviation and mean square relative deviation goodness of fit tests compared to kernel nonparametric methods with rectangular، triangular and normal functions. Therefore، L-moment method is a suitable method for frequency analysis of other hydrological parameters such as flood and drought for planning of water resource management and hydrological analysis.

Most of Iranian rangelands are located in arid and semi arid areas، therefore، drought resistance is an important issue in this regions'' plants. Drought resistance variation of forage yield for 11 genotypes of Elymus hispidus was examined in complete block design with three replications under normal and dryland farming system، in Islam Abad Gharb، Kermanshah، Iran، during 2004-2006. Significant variation (p<0. 01) for forage yield were observed between with and without tension environments and between genotypes. Drought resistance indices of genotypes were measured for dry matter forage yield (Yp) of irrigated and dryland (Ys) conditions، like sensitivity to stress index، Tolerance (Tol)، Mean Productivity (MP)، Drought Tolerant Index (DTI)، Harmonic Mean (HM) and Geometrical Mean of Productivity (GMP). Variance analysis of drought resistance indices showed that genotypes had significant variation at 1% level for DTI، MP and Yp and at 5% level for HM and GMP. Significant variation for SSI، Tol and Ys were not observed among genotypes. The indices of MP، GMP، HM and DTI showed the significant positive correlation with Ys and Yp، therefore selection for drought resistance were performed based on this indices. Also، the results of mean product comparision of Ys، Yp and drought resistance indices by Duncan method at 5% level showed that genotypes 890-5 and 890-6 has higher drought resistance value and can be introduced as a suitable genetic material for rangeland reclamation or breeding programs for drylands in Kermanshah province. This results were confirmed by claster and principle component analysis.

This study investigated the status of sediment transport and deposition in Khar-rud River، Qazvin province، Iran. The aim was to determine the possibility of construction of sand and gravel mining workshops in the margin of Khar-rud Flood-plain. Here with calculating sediment transport rate and specifying the distribution of sediment deposits in various parts of the river، an applied program for sand harvesting from the river bed، is developed. In this project، after preparing the basic information، such as information about river geometrical shape، roughness coefficients of different sections، information related to size gradation of suspended sediments and bed material، river hydrology data and boundary conditions of downstream hydraulic system، using HEC-RAS model، sediment loads and its distribution along the river was simulated. Simulation was done based on classified data from daily flow discharges during a 37-year period. After calibrating the HEC-RAS model and selecting Yang sediment transport equation as the closest relationship to the sedimentary data measured by regional Hydrometric stations، the average volume of sediment yield from the river was estimated 1. 75 million tons per year. Finally، considering the changes in the river bed elevation for each cross-section، the amount of sediment passing during simulated 37-year was calculated. Using the results of the model and sedimentation changes along the study reaches، the volume of sediment transport in each river cross section، the river width and its private region and considering the maximum permissible depth of bed-material removal equal to 1 m، the most suitable mining length and period in the different reaches of river was determined، discussed and showed in ARC-GIS environment. Based on simulation results، the average depth of sand which can be taken safely from the river-bed was estimated to be 40cm and the most suitable period of time for sand mining along the river was recommended from January to May. It was determined that HEC_RAS hydraulic model، covers about %63 of initial engineering judgments for the amount and location of sand mining.

Rangeland ecosystems in semi-arid regions are vulnerable systems to climatic changes specially precipitation. In such conditions droughts are predictable. In this study the relationship between rangeland production and spatial and temporal changes of precipitation was investigated. Therefore، rangeland production through 10 years data set (1377-1387) in steppic bioclimatic of Esfahan province (Alavije، Muteh، Kalahrood and Gardaneshadian) using Standard Precipitation Index (SPI)، the relationship between SPI series of 3، 5 and 8 month time scales، and rangeland production of 10 years. Thus Anova and correlation matrix between production and SPI factors were formed. Results indicated that the most severe drought has occurred in 1387 simultaneously، with the least production. A harmony between change trend of production and SPI in the sites showed that in most cases maximum and minimum production have occurred simultaneously with maximum and minimum of SPI series. Also، the production correlated with SPI series of three، five and eight months'' time scales with correlation coefficients more than 63 percent which were significant in 1% and 5% level. Due to efficacy of production from spring precipitation and soil depth less than 30 cm in the sites، it is proposed to use SPI series of three months scale to evaluate drought in similar rangelands.

In most projects of watershed management، studies are necessary for monitoring، evaluation and comparing the parameters with the indices in projects. In water spreading projects there is such a necessity for measure، process and evaluate obtained information from performance results. According to the important role of aquifer management in rangeland improvement، as a new method، the purpose of this study is investigation and evaluation of flood spreading effects on vegetation cover changes and status and trend of rangeland during 2000 to 2004 years. In this study، two areas of flood spreading and testimonial control points were selected. Flood spreading network consisted of five strips and 12 fixed plots (2×2 m) were chosen in each strip with random-regular method. A testimonial area was selected to evaluate the results with eight plots similar to flood spreading areas. Results demonstrated that the status of rangeland condition in testimonial area was very weak and in flood spreading area was very weak to weak and was changing from to moderate condition. The trend of rangeland in testimonial area was negative while in flood spreading area was positive. Also، results showed that the forage production were 144. 3 and 113. 6 kg per hectare in the first year and 224. 5 and 202. 3 kg per hectare in the last year، in flood spreading and testimonial areas respectively.

According to abundant damages and the extension of mass sliding in the country، its zonation mapping and investigating effective factors on its occurrence is necessary for preventing and control. Therefore، a research has been conducted in the Ilam dam watershed to create geologic، physiographic، Land use، vegetation cover، soil erosion، climatologic، pedologic and geomorphologic maps، using earth data layers، topographic maps، Geographic Information Systems (GIS) and field surveys. The methodology of this research has been accomplished base on distinction of geomorphologic units while using aerial photos and crossing basis maps. Then، the effective factors on mass movement occurrence were investigated using logistic regression equations. So that، the factors such as slope، geological formation، pedologic، climatic، etc. were considered as independent variables and the frequency of mass movement occurrence was considered as dependent variable. Results demonstrated that factors such as slope، geological formation، the kind and the amount of soil minerals، and land use are the most effective factors on frequency of land sliding in the watershed.