مجله علوم و مهندسی آبخیزداری ایران
پیاپی 11 (تابستان 1389)

To Adequately design density and distribution of rain- gauges in rainfall networks of each region, is an effective step toward success of water projects, regional programming and proper use of information. In this research, the locations of new rain- gauges in rainfall network of Gav-khuni basin have been determined using transinformation entropy concept based on annual rainfall data of stations (1356-1385).Sequential and genetic algorithms have been used in order to seleet the proper rain- gauges sites. Two objectives of maximizing the minimum transinformation entropy and maximizing the mean of transinformation entropy have been defined for each algorithm. Then the performances of different models have been compared. The results imply on the better performance and relative supremacy of genetic algorithm, with maximizing the minimum entropy (maximum supremacy is +1.31, +1.34 and +0.12% in zone 1, 2 and3, respectively) and maximizing the mean entropy (maximum supremacy is +0.35, +0.21 and +0.02% in zone 1, 2 and 3 respectively) objectives to sequential algorithm.

Flow in streams of arid and semi-arid regions is not perennial and usually floods occur after seasonal precipitations. Therefore, the bed material is dry and underneath soil is in unsaturated condition prior to occurrence of floods. As a result, volume of flood hydrographs decreases due to infiltration as they travel downstream. This reduction in hydrograph volume is usually termed as transmission losses. Because of the existence of ephemeral rivers in most parts of Iran, study on transmission losses in these areas is necessary. In this paper, regression equations are developed for estimating transmission losses in ephemeral rivers of Ghara-Ghoom catchment in Khorasan Razavi province. To achieve this, gauging station's data and physical characteristics of Kashafrud, Kardeh and Zoshk rivers were collected and analyzed. Transmission losses in the first kilometer was considered as dependent variable in regression analysis and its dependency was tested against upstream flow volume, flow duration, antecedent moisture content, hydraulic conductivity, slope and width of the river as independent variables. Upstream flow volume was found to be the most important variable in explaining transmission losses. Three regression equations (linear and nonlinear) were developed for relating transmission losses to the most significant involved variables for Ghara- Ghoom catchment. Estimates of transmission losses can be made for any unit length (km) by calculating the flow volume at the beginning of the unit length as flow volume minus the transmission loss in the previous unit length. Such equations can be used by water resources managers and hydraulic structure designers.

Considering the current trend of ever decreasing water resources and their associated qualitative and quantitative variations, managers are now facing the challenge of offering adaptable planning and allocation decision methods for integrated watershed management. This study focuses on the understanding of the trade-offs among the various outcomes of allocation decisions for Boostan Dam reservoir on the Gorgan-Rud River in Golestan Province of Iran. Control of water level in the reservoir such that enough water is available during dry months to satisfy different needs of the downstreamas well as the capability of dam to mitigate floods considered as the objectives of the study. The recorded flow data suggested that there are four months with high likelihood of flooding events. Sixteen mutually exclusive scenarios were developed to accommodate different and competing water demands of water users in the area. The monthly riverflow discharge for one Iranian water-year started from October 2007 were forecasted by a Seasonal Auto Regressive Integrating Moving Average (SARIMA) model. The water allocation analysis was conducted on the basis of the forecasted monthly flow data. To quantify the effects of implementing the scenarios, five indices were selected and quantified. The indices included water storage capacity during flood-prone months, stored water volume at the end of the wateryear,the likelihood of overflowing, outflow discharge simulated by a flood routing technique and the risk of dam collapse because of floods. The multi-criteria decision making technique was used to trade-off the outcomes and therefore to identify the best allocation scenario. To weight the indices, the process of expert knowledge elicitation was completed using AHP (Analytical Hierarchy Process) technique. The TOPSIS (Technique Ordered Preference by Similarity to the Ideal Solution) model was used to identify the best scenario among the 16 allocation scenarios. The results show that the scenarios can be categorised in nine different groups among them scenario 7 has been identified as the best allocation scenario followed by scenario1. Scenario7 is characterised by emphasis on flood control objective for the floodpronemonths (May and August) as well as water supply to meet the water demands of the downstream. The integrating approach implemented in this study is capable of assisting the decision makers and dam operators to understand and investigate the possible allocation scenarios, and to recognise the likely outcomes and the trade-offs among them. Thus, the approach supports the decision makers to achieve their objectives capturing different criteria associated with the allocation problems.

Dare- Gap River in the north of Booshehr province of Iran, in the reach of study, has a meandering pattern. Most of the arcs are left wise in the reach of study that caused to increase water level during flood events through the city. To solve this problem, it was supposed, if the arcs are omitted by making three cutoffs in designed path, river slope, flow velocity and also river erosion potential will increase. Then the average of annual erosion, aggradation and also the maximum depth of erosion and aggradation for designed flood were studied for two paths; existing path and artificial path, by using MIKE 11 model. Results showed that the maximum erosion for annual flows occured in two reaches with bridges in them. The amount of erosion in Kamarbandi Bridge was more than Main Bridge. And also deeper erosion was observed in the designed path than existing path. In the Dare- Gap River in the kamarbadni Bridge, results of the maximum depth of erosion and aggradation in the case of designed flood (100- years Flood) showedthat the maximum erosion in the designed path and for former path, was 0.65 and 0.78 meters, respectively.

The present study aimed to analyze the comprehensive relationships between suspended sediment yield, and rainfall and runoff characteristics on storm basis in Khamsan Representative Watershed with an area of 4193 ha in Kurdistan Province, Iran. In due course, 9 storm events occurred during study period were analyzed 4 of which generated runoff and consequently yielded sediment. Different bivariate regression models were then applied for estimating sediment yield. The results of the analysis verified better performance of linear regression developed based on maximum rainfall intensity with respective determination and efficiency coefficients, and estimation error of 0.843, 0.84 and 39%.

The estimation of flood hydrograph characteristics in natural rivers is of hydrologists interests. In this paper, the ability of neural networks for estimation of flood hydrograph to Shirindareh reservoir dam in Khorasan province is evaluated. Therefore, all flood hydrograph events of hydrometery station in upstream were collected and normalized. It is notable that the flood hydrometery was estimated 2, 3, 4 and 5 hours earlier using the flood discharges at 2, 3, 4 and 5 previous hours as model inputs respectively. In each pattern, four signals were selected for considering the effect of number of inputs for estimation of flood hydrograph. The results show that by increasing the estimation lag time, the accuracy of results decrease and in given lag time, by increasing the number of input, the accuracy of results increase. The results show that the amount of efficiency coefficients, which is the representation of goodness of flood hydrograph modeling,is increased from 0.79 for signal one to 0.91 for signal four.

In this research, all of existing hydrometric stations are investigated in the part of large central watershed of Iran and the main physiographical characteristics of these stations are extracted. Then, independent parameters and homogeneous watersheds were recognized by using factor analysis and clustering analysis, respectively, and were tested by using discriminate analysis. Regional analysis is evaluated by using flood index. The results showed that there are three homogeneous areas in central watershed and thebest discharge index is one that have two- year return period. Furthere more, other parameters as well a area cant improve the accuracy of results.

Establishing permanent plant cover with economical efficiency and rural participatory is a way to control water erosion of piedmonts. For this purpose, making rain water harvesting micro- catchments systems along with increasing surface runoff coefficient is necessary especially during low daily rainfalls. This research project established in Garacharyan station of Zanjan with regard to requirement of country and province of Zanjan. Because Zanjan synoptic station is considered to be the index of semiarid climatecouditions, so the daily rain frequency is prepared for every month, 45 years statistied duration and for values larger than 0, 1, 5 and 10 mm. The surface treatments of rain water harvesting plots were impediment, semi impediment and natural with 4 blocks that established on a slope and measured the depth of daily rainfall and caused runoff. The results show that daily rain frequency with depth equal to 1, 5 and 10mm or larger, have average frequency of occurence of one time in one, three and 10 years, respectively, in warm months of July August and September. The variance analysis, mean comparing and regression analysis between depth of daily rainfall and runoff showed that the treatments have significant differences at 1% level. So the threshold of daily rainfall for runoff occurrence due to treatments of impediment, semi impediment and natural are 1, 4 and 7 mm and average runoff coefficients are 43.9, 12.15 and 3.04 percent, respectively.