مجله علوم و مهندسی آبخیزداری ایران
پیاپی 26 (پاییز 1393)

Due to transmission losses and absence of initial flow prior to flood occurrence، it is impossible to estimate seepage losses and flow routing for an ephemeral stream with several branches and complex connections by using common routing methods، and it is necessary to develop a routing method for such streams. To this end present research prepared a computer for irregular stream cross section، in which partial differential equation for non-uniform unsteady flow (saint- Venant equation) are solved by using finite difference method and alternative technique (staggered method) after being linearized. Water flow elevation at fluvial connection is determined at any time step completely implicitly by using influence line method. Model accuracy was examined in terms of programming، its ability to simulate uniform flow، and to satisfy continuity relationship by using a loop stream consisted of 8 open channels. The results of verification showed 0. 7 and 0. 0209 percent as maximum calculation error for discharge and flow depth، respectively. With very high accuracy، therefore، present model estimates discharge and water surface profiles at each branch. Employing Lane hydrograph and characteristics of Hughes Wash River، prediction of flow behavior and transmission losses showed that compared to other experiment relationship، Muskat’s estimates seepage losses and peak flood better. Under seepage condition، a highly complex system of open channel with 24 branches and low slopes was employed، in which the flow of any branches is sensitive to small changes in flow depth. Also، in this network، the model is able to detect flow direction at any branches. For steady flow، the results showed a 1. 127% decrease in system output discharge due to seepage losses. For unsteady flow، with the present seepage، system output hydrograph volume is 6. 37% less than that of input hydrograph volume.

Karstic water resources are of the most important fresh water sources. Analyzing recession curve of Karstic rivers and springs is one of the common methods for determining Karstic aquifer characterizations. In this survey for achieving the best formula of Karstic recession curve، in three selected watersheds (Khersan، Gamasiab and Zymkan)، nine hydrometric gauges were selected and six index years in each station were chosen by using Standard Index of Annual Precipitation (SIAP). After separating recession curves، different formulae (Boussinesq (1903)، Maillet (1905)، double exponential function (Horton 1933) and Hyperbolic function (Drouge 1973))،were fitted to them. N coefficients were calibrated in Drouge and Horton equations by fitting estimated and observed discharges. Also we use RMSE and correlation coefficient. Results show that in 72. 22% of the cases hyperbolic function is the best formula and its N coefficient is between «1. 5 - 2. 1».

Riparian zones are the zone of direct interaction between terrestrial and stream systems. Different methods are used to derive condition ratings، using subsets of variables collected within each component، but according to Aras river ecological condition، the A-Syst method is designed to survey the stream condition، it provides a ''snapshot'' of the physical and environmental condition of streams. For this purpose، across the river the homogeneous stream sections are divided into A-E units. by using A-Syst method، an assessment of condition is derived for each homogeneous stream section. results indicated that the condition of unit B and D were medium، but other units were in good condition.

Sand and gravel mining from the bed and banks of river causes change in the hydraulic، hydrological and current carrying capability conditions and increases erosion of river bed and banks and degradation of existing structures is in the river. Awareness of the impact of sand and gravel mining on the amount، quality and sediment transport is inevitable. The present study was therefore formulated to evaluate the effect of sand and gravel mining from the Kojour River at Educational and Research Forest Watershed of Tarbiat Modares University in Mazandaran Province on changing suspended and bed loads quantity and the diameter changes of the bed load transport. Towards this attempt، 12 and 3 samples were taken before and after sand mining at the main outlet of the watershed، respectively. The suspended load samples were taken using bottle samplers and bed load samples were taken with a basket-type bed load sampler. Bed load granulometery was performed using standard sieves. The analysis also was carried out in GRADISTAT and Excel 2007 softwares. The results showed that after sand and gravel mining the rates of suspended load increased from 300 to 547 %، bed load was an average of 1130 %. On average، the ratio of bed to suspended load was 120% higher than that recorded for period without sand and gravel mining conditions. The D10 diameter of bed load had increased for low، moderate and intensive sand and gravel mining conditions at rate of 17، 24 and 35%، respectively. The D50 also increased 21% in low and moderate removal and base flow conditions and also had complex behavior in intensive removal and different flow discharges. The D90 had subtle changes in low removal and increased in moderate and intensive removal from 100 to 900%.

There are numerous criteria which should be assessed in order to locate potential underground dam sites، and that’s what makes the location process difficult. Therefore، in this study، in order to create a link between these criteria and thus to make an accurate decision and to save time and money، we use a method which combines GIS (Geographic Information System) and RS (Remote Sensing) with SDSS (Spatial Decision Support System). This method was implemented in three steps. In the first step، unsuitable areas for underground dam construction were omitted through applying GIS and RS with regard to exclusionary criteria، and ultimately 9 sites were identified suitable for the construction. In the second step، the best gorge of each selected area in the first step was chosen by using a terrain map and was considered as dam axis. In the third step، we used the criteria derived from expert opinion to compare and evaluate the axes against the criteria through AHP method (Analytical Hierarchy Process) and to rank the axes by each axis’s final fit index. Eventually through field visits and complementary experiments such as geophysical studies، mapping، permeability tests and etc. the model accuracy was studied in three first priorities including the axes number 2، 4 and 1. These studies showed that the results of the model presented in this study، are consistent with the results of complementary studies، and the accuracy of the model was confirmed.

Land degradation due to soil erosion makes out of reach a large part of available water in addition of soil losses. There are several ways to study soil erosion. A new method is flow accumulation which emphases on stream power. The stream power can mathematically be derived from hydraulic shear stress and flow velocity. The study catchment is located in the western part of the Zanjan River valley، an area below the dam watershed of Sefidrood. An operator which given the drainage direction matrix and a weight matrix، determines a resulting matrix such that each element represents the sum of the weights of all elements in the matrix which drain to that element. Flow accumulation procedure for creating the cumulative streampower was done by using Digital Elevation Model (DEM)، the SWFM program، the drainage network، C-factor map، slope map and GIS. The results of applying the streampower approach with the SWFM in this study showed low erosion on relatively large areas، even in bare units، except where flow concentrated in drainage networks and the main river.

Each year to control costs and prevent the destruction of heavily structure of scour in the downstream water is spent. This phenomenon can be extended endanger the stability of the structure، while the accumulation of eroded material by changing the digital output on the performance of coastal structures will be affected. Change the scour depth and length، height and the height of a pile of sand a pile of sand to the bottom section was fitted with a logarithmic relationship. According to the results over time، profiles of scour increased while increasing the size of the reduction profiles were discussed. In other words، most of the time scour the initial testing occurred، and then it is reduced significantly. Also studied the changes of the parameter profiles were then scour، scour profiles that are independent of time.

In climatic studies، although the total amount of precipitation is an important factor for determining weather conditions and، finally، ecology، its seasonal distribution and، in other words، compliance with environmental needs، especially in agriculture، is significant، too. In this research، first، the aim was to recognize precipitation regimes at the province scale for each location in Kurdistan province; then the precipitation regimes were compared and، the basis type and classification of each were found on the map. Therefore، 83 synoptic، climatology and rain gauge stations data were used in this study for a period of 30 years (1978-2007). The statistical problem of stations was completed using the regression model relative to 30 years in the most homogenous station. To perform of this classification، first، monthly precipitation of each station was divided by the total precipitation for the same year in order to obtain relative precipitation in each month for the stations. After that، cluster analysis was used along with Ward technique and the classification of the precipitation regimes of the province was prepared. Based on this method، there were two different regimes of precipitation، namely winter and winter – spring precipitations، which were separately illustrated; the winter precipitation in west and the winter-spring precipitation in the center of Kurdistan province were dominate. The winter regimes contained 44% of annual total precipitation، which related to the winter season. After that، autumn and spring precipitations had 28% and، 27% annual total precipitation، respectively. In the winter-spring regime، more amount of precipitation occurs approximately equally or with a little difference of about 2% in winter and autumn، so that the winter and spring seasonal precipitation came up to about 36% and، 34% of annual total precipitation، respectively. After that، autumn season had 28% of annual total precipitation of this area.

Side-weirs are one of the major parts of floodwater spreading systems. Their essential role is spreading floodwater and increasing floodwater infiltration into the ground. In this paper، the hydraulic behavior of side-weir in floodwater spreading systems and the existing formulas for the prediction of side-weir discharge coefficient are discussed. In the first part of this study، the basic concepts of floodwater spreading systems are presented. Then the dynamic equation of side-weir is investigated. One of the main concerns about floodwater spreading system is that if the presented equations by the other researchers are applicable to the side-weir in floodwater spreading system or not. To answer this question a laboratory flood water spreading channel is made at the Soil Conservation and Watershed Management Research Institude and the discharge coefficients of the side-weir are measured. Afterwards، by using dimensionless analysis، the effective parameters on the discharge coefficient of the side-weir have been indicated. Finally the experimental values of discharge coefficents have been compared with other researchers’ equations. It was shown that those equations that are only a function of the upstream Froude number are impropor for use in the floodwater spreading systems. The results also indicated that side-weir discharge coefficient is influenced by four main parameters which are upstream Froude number، dimensionless weir length، the ratio of flow depth to the main channel width and the ratio of flow depth to the side-weir height.