IRANIAN JOURNAL OF WATERSHED MANAGEMENT SCIENCE AND ENGINEERING
Year:2009 | Volume:3 | Issue:6|Papers Count:11

In this study, the Independent Unifonn1y Distributed Random Numbers (IUDRN) method as a hydrologic synthetic data generation technique has been modified to simulate the stream flow in annual time scale.A hybrid approach based on hydrological conditions-random number combination has been developed and proposed. The three hydrologic conditions as wet, nonna1 and dry conditions have been defined in one third of each of random number that varies from 0 to 1. The annual mean values of 52 years discharge of Arieh River situated in North of Neyshaboor in Khorassan province of Iran has been applied for validation of proposed approach. The comparison between the results of two methods (IUDRN and proposed method) shows that the error estimation has been reduced from 25% to 17%. This result indicates that new approach (MIUDRN) can be applied to simulate the stream flow data with a high efficiency.

Estimation of runoff hydro graph from ungauged catchments has been an important subject of research for planning, development and operation of different water resources projects. In this study, Nash's linear reservoir model was applied to predict direct runoff hydrograph characteristics in Jafar-Abad watershed (l09 km2) located in Golestan province. Using hourly hydro-meteorological data, the Nash model parameters (n and k) calculated by Moment method for 33 storm events. Then the mean value of n and k, were used for simulation of second subset of storm events as model validation. The efficiency of Nash model was evaluated by statistical comparison with the observed hydrographs. The results indicated that the model predicts direct runoff hydro graphs with good accuracy, 70% according to the Nash-Sutcliffe criterion. Also mean relative error of peak discharge, relative error of time to peak, model bias for water balance and RMSE are 10%, 10%, 25% and 3.94, respectively. The good agreement between observed and simulated hydro graphs shows that n and k were calculated reasonably by Moment method. Results show that the Moment method in estimation of n and k parameters gives good results. So that regionalization of Nash's model parameters (n and k), in ungauged catchments is suggested for development and application of this hydrological model.

The study of changes of sediment beds is of the issues which has attracted River engineers. Attention to investigate the rate' of scour and sedimentation is significant in bend of rivers rather than straight rivers. The change of bed topography, scour and sedimentation pattern have caught the attention of hydraulic engineering profession. This paper examines the topography changes using experimental data in 90 degree bend and bend with T shape spur dike in outer bank. For this purpose interpolate methods such as IDW, KRIGING and SPLINE Tension used to convert point measurement to continuous surfaces. Accuracy assessment accomplished by validation method. The result showed that KRIGING methods have best accuracy to create surfaces for studying bed topography in Bend Rivers.

The outer banks in river bends are subject to sever bank erosion due to secondary flows. Therefore, it is essential to have some measurements for protection. The protection must be based on maximum scour hole. Any measurements to reduce the scour hole would be beneficial for protection. In this paper the effect of horizontal footing on reduction of scour hole has been investigated. To reach such goals, an experiment with a 90 degree flume was carried out and series of horizontal footing were installed at outer bank in four different elevations of 0, 20, 40 and 60 percent of maximum scour depth.By comparison of the bed topography with and without footing; a maximum scour reduction of more than 44.5% was obtained with footing installed at elevation of 40% of the maximum scour depth. The results of this study reveal that the point of maximum scour hole has been displaced from the outer bank to the center of the flume.

Operation optimization of the reservoirs has been mostly carried out based on general objectives, including water demand supplies, power generation, flood management, and environmental constraints. In most of the previously developed models, sediment removal from reservoirs has not been included. Flushing is one of the most important and common ways of retrieving the lost volume of reservoirs due to sedimentation. Despite its adverse effects on the environment of downstream rivers, this method has received lots of attention by engineers and researchers in the past. One of the main drawbacks of the previous studies in the field of reservoir operation optimization has been lack of modeling tools for considering the relation between sediment removal and other objectives of reservoir operation. In this paper, a new approach has been developed for monthly reservoir operation optimization. For this purpose, a model has been formulated to minimize the total deficit in supplying demands and to maximize the total volume of sediment removed from the reservoir. The objective function for sediment outflow has been developed using the flushing method. The optimization model has been formulated using Varying chromosome Length Genetic Algorithm (VLGA). The efficiency of the model has been tested in the case study of Sefidrud Reservoir in North of Iran. The results of the optimization model for a 5-year period have been compared with the historical records of the operation of the reservoir. The results of the case study have been summarized in the form of practical operating rules for flushing and operation management.

Soil erosion and its associated impacts, is one of the most important of today's environmental problems because, agricultural land is seriously degraded. Erosion is the removal of solids in the natural environment. Water is the most important erosion agent and erodes most commonly as running water in streams and rivers. Also when flow speed in rivers is halted, the river deposits its sediments and may cause some problems. In rivers with flood plain, the erosion happens when the flow contact strongly to bank of river. To prevent these, spur dikes have been widely used to protect eroding stream banks and causing sedimentation to change the flow direction away from river banks to the river center. However, much is yet to be researched about the influence and effects of spur dikes during large amount of flow (floods). For these reasons some experimental tests are designed to predict the behavior and influence of length and shape of spur dikes. In this paper the result of scour at spur dikes ending, which are installed in floodplain in a series as single side of flood plain with the length of 10 and 20 centimeters of spur dikes. The scour and sedimentation pattern and also maximum scouring at the end of spur dikes are measured and the experimental results are analyzed and discussed.

The present study has analyzed the effects of different grazing intensities on soil chemical properties including nitrogen, phosphorus, potassium and organic matter content in different conditions of reference area, key and critical areas located in Savojbolagh, Iran during 2004-2005. Data produced based on randomized complete block design plot. In this case, study area, time and depth of sampling were appropriated for main plots and sub-plots, respectively. Statistical analysis was done using SPSS version 12. If significant differences were found between treatments then Duncan test was used for comparison of means.According to the results, there were significant differences between NPK rates during two years. The rate of organic matter, nitrogen and phosphorus was increased in second year and the amount of potassium was decreased. Animal grazing significantly affected soil chemical characteristics in all areas (reference, key and critical). There were significant differences between content of nitrogen, phosphorus, and potassium in two years, during the grazing season and between the two depths.

Rainfall temporal pattern has a marked influence on design of dams, urban water harvesting, culverts, drainage design, flood potential and soil erosion. In this research we used data of 146 autographic rainfall stations of Iran to implement the rainfall temporal pattern. Rainfall depth were calculated for each time interval from rainfall charts and were categorized to four quarters. The ranking method was used to arrive at rainfall temporal patterns corresponding to time intervals of 1, 3, 9 and 12 hours. After normalizing the rainfall mass curves, every quarter of rainfall was ranked, number 1 for the highest. The final pattern was derived by averaging the quarter ranks and percentage of rainfalls corresponding to each duration. Adopting Ward method, 5, 9, 9, and 8 homogeneous regions were detected for short (<3 hr), medium (3-6 hr), and long (6-12, and>12 hr) rainfall time period, respectively. Design rainfall temporal pattern was . derived for every homogenous zone. There is a danger for mis-used temporal pattern by type patterns.