مجله علوم و مهندسی آبخیزداری ایران
پیاپی 20 (بهار 1392)

Soil infiltration is one of the most important factors in successful operation of floodwater spreading projects. The suspended particle in floodwater reduces the rate of soil infiltration. The objective of this research was firstly to monitor the variation of infiltration and secondly to determine the effective factors in decreasing the infiltration rate. In this research، three representative strips of the floodwater spreading network were selected. Each strip was divided into three rectangular areas، and by drawing rectangulars diameters، each rectangular area was further broken into 4 triangulars. The soil infiltration rate was measured in two steps at the center of each triangle during 2004 – 2005. In each step، 9 measurements were undertaken in each rectangle، implying totally 27 measurements were collected from each strip. Based on the obtained results، there was no significant difference between the infiltration rate at the strips over this two-year experiment. Also، there was no significant difference between the infiltration rate in the experimental strips compared to the control strips. Comparing the soil infiltration rate of the stripes in the first and second year showed that its values in the second year are less than the first year. Also، a significant difference at a 95% confidence level was observed in the infiltration rate of the first and second strips in two years.

This study aims to compare Soil Conservation Service and Bennett Soil Moisture Accounting models in the rainfall-runoff process simulation. To do this، rainfall-runoff data obtained from the Zard River watershed، the East Khuzestan province and the HEC-HMS hydrological model were used. First، the physiographic parameters of the study area were collected and studied. Recorded rainfall data and their corresponding flood events collected from the Mashine station were utilized. Of the data collected، 3 rainfall-runoff events were considered for model calibration and 3 events were chosen to compare the models. The results showed that the SCS model is not capable to estimate losses due to evapotranspiration and surface maintenance. This leads to significant errors in estimating the peak and volume of floods with a long time-base Statistical tests including mean residual error، the remaining mass index، relative error and root mean square residual error as well as the compliance index were used to compare simulated and observed hydrographs. The statistical analyses showed that the hydrograph resulting from the soil moisture model (SMA-B) has a better ranking compared to other models. In estimating the flood peak and volume، the SMA-B model was associated with least differences between the simulated and observed values produced.

Due to diversity، high frequency and transportation as suspended materials، clay minerals can be used as sediment source indicators in drainage basins. In this study، clay minerals were used in Amrovan and Atary catchments، Semnan Province، Iran. To identify clay minerals، X-ray diffraction analyses were used. By performing four different treatments on the samples (K، KT، MG، MGG)، the respective graphs were obtained. To determine the percentage of each clay mineral، the area-under-a-curve method was used. Finally، the potential of each clay mineral in differentiation of sediment sources was determined using Kruskal-Wallis and Discrimination Function Analysis (DFA) statistical tests. The results of the Kruskal-Wallis test showed that all characteristics were below critical probable amounts، and، therefore، are suitable for differentiating sediment sources. Smectite is a clay mineral with the highest differentiation ability. It correctly classified 57. 5 % and 62 % of samples in the Amrovan and Atary Catchments، respectively. The results also showed that the combination of source indicator characteristics increases the differentiation ability of the characteristics up to 72. 5 % in the Amrovan catchment and 76 % in the Atary catchment.

Debris floods are high concentrated flow that occurs in steep mountain areas. Slit dam is one of the structures designed for controlling these kinds of floods. A two dimensional model is proposed for simu-lation of debris flow in slit dam reservoirs. In this model، the finite difference MacCormack explicit scheme is used for discretization of governing equations، and a formula is proposed for the slit dam boundary condition. Due to lake of observed data of debris floods in slit detention dam reservoirs، the numerical model is compared with an experi mental model. The model results shows that the applied scheme using the proposed initial and boundary condition is capable to simulate the t-o dimensional movable hydraulic jump in slit dam reservoirs. Finally، the com parison of numerical results and experimental data confirms that the numerical model is acceptably capable to simulate the outflow hydrograph of slit dam.

The first and most important step in any floodwater-spreading project is the identification of the most appropriate areas for water infiltration into the aquifers. For this purpose، conjunctive use of Geographical Information System (GIS) and Multi-Criteria Decision Making (MCDM) may lead to more accurate results. In this study، the study area is Garbaygan Watershed located in the Fars province، Iran. Then، parameters affecting the site selection of floodwater spreading projects were defined and appropriately classified. To enhance the accuracy of the study output، Gray Clustering Analysis (GCA) and Analytical Hierarchy Process (AHP) approaches were considered. In the GCA، the data have grey membership functions and in contrast to fuzzy systems، they have defined limits. Grey membership functions aim to enhance the quality and weight of data by valuation of information layers. The GCA and AHP approaches were applied using this data set and the final maps of the watershed based on each model were prepared in different suitability classes. The results of both models showed that quaternary formations including Qscg، Qgsc، Qb، Mm-1، Qc2 and PLQb have the suitable condition for floodwater spreading. Also، upper parts of alluvial fans، pedimonts and sparse rangelands have acceptable conditions for such projects based on geomorphologic and land use characteristics. Meanwhile، the results showed the GCA outperformed in site selection compared to the AHP approach.

Water as a renewable resource, always has been a key element of development. Nowadays, population growth and water demand rise for different sectors including agriculture, industry, drinking and health, groundwater resources have faced severe pressure. This issue along with severe and prolonged droughts particularly in arid and hyper arid areas, has created serious challenges in the field of water quantity and quality. The Yazd-Ardakan plain as the study area in this research is one of the tense populated areas in the Yazd province at central Iran. The existence of large cities in this plain and significant water storages in its aquifers have doubled its importance as a case study. In this study, the intensity and duration of meteorological drought and hydrological drought were evaluated using the Standardized Precipitation Index (SPI) and the Groundwater Resources Index (GRI), respectively. These indices were estimated at monthly and annual time scales. Then, the relationship between these indices was investigated. The results showed that, over the last 50 years, meteorological drought conditions has been approximately 1.3 times more than climatic wet years in the study area. The repetition of meteorological drought in the last decade compared to its past four decades has increased 4 times. The results also revealed that variation in ground water level has been in a downward trend in the last four decades, so that the average annual decline in water table has been around 0.5 meters per year. The relationship between monthly SPI and GRI indices indicated that by increasing the time scale, the regression coefficient will increase. The results also showed that, at the annual scale, there is a 1- to 2-year delay between the occurrence of meteorological and hydrological droughts.

This study aims to investigate the effect of separating snowy and rainy seasons on the accuracy of suspended sediment estimations in Gorganrood River at the Gazaghly gauging site، Iran. In this site، there are about 2000 concentration samples taken during six years. In a comparative research، 20 sets of 52 weekly samples each year (including 22 samples during snowy-rainy seasons and 22 samples during rainy seasons) classified in four treatments and five replications were taken. Then، 20 sets of extra random samples in four different sizes (0، 25، 50 and 75) were extracted from high flow periods and were added to the respected treatments. With regards to the sampling strategies، 60 sample sets (including 20 for rainy seasons، 20 for snowy-rainy seasons and 20 mixed) were produced. Suspended sediment loads for each sample set were estimated using five different sediment rating curves including one curve (conventional)، parametric، non parametric، and FAO correction factors (PCF، NPCF، RCF) and logged mean load within discharge classes (LMLWDC) based on daily discharge data. Therefore، 100 (20×5) estimates for each treatment –rainy season، snowy-rainy season، mixed data، and sum of two seasons loads– (400 estimates altogether) were obtained. To evaluate different load estimation scenarios، three indices including percent error، coefficient of variation and normalized root of mean square deviation were calculated. The results showed that the LMLWDC and PCF rating methods produce better estimations with the lowest percent error، and more precise and accurate than other rating curves. The results also revealed that separation of rainy and snowy periods has no positive effect on the estimations. In addition، the results showed that the accuracy and precision of estimations in the rainy season were lower than the snowy-rainy one.