IRAN-WATER RESOURCES RESEARCH
Year:2005 | Volume:1 | Issue:2|Papers Count:16

This paper evaluates three different methods for estimation of reference crop evapotranspiration (ET0) in Bajgah area, Fars province, in Iran. Monthly values of ET0 were estimated with Penman-FAO, Penman-Monteith and Hargreaves equations using the mean monthly weather data from 1986-2002 (17 years). The Penman-Monteith and Hargreaves equations were calibrated based on Penman-FAO method which was recognized as the most appropriate equation for ET0 estimation, according to the previous studies. This study showed that the results of Penman-Monteith and Hargreaves equations are similar to but somehow they underestimate ET0 compared with Penman-FAO method. To calibrate the Penman-Monteith and Hargreaves equations, a linear regression was used. The results of calibration for Penman- Monteith equation showed the variation of the slope of the line and ET0 the calibration coefficient (CH) of the Hargreaves equation for each month annual ET0 estimated.

In this study, a model for optimal allocation of water from a single purpose reservoir to an irrigation project with pre-determined multiple cropping patterns were developed. The model is consisted of two modules: (I) the intra-seasonal allocation model (non-linear programming) which is intended to maximize the total farm income. It is used for allocation of water among different crops for a definite combination of state variables (inflow class, rainfall class, reservoir storage classes at the beginning and at the end of the season) for growth season and (II) seasonal allocation model (stochastic-dynamic programming) which is used for the convergent operating policy over seasons for optimal expected farm income over a year. The model was applied to Ardak reservoir dam (North east of Iran) in an arid region and ensuing results were discussed. This methodology is proposed for using in similar reservoirs of Iran to ensure optimal usage of our limited national water resources.

This paper describes in detail a new two-dimensional transient model for prediction of thermally stratified reservoir flow. Unlike many other reservoir models such as CE-QUAL-W2 and Mike-Reservoir, the present model does not employ the hydrostatic approximation. The full general orthogonal three-dimensional equations of motion, which are laterally averaged by Karpik and Raithby (1990) and produced a set of two-dimensional equations in the vertical plane, are used. Using an orthogonal boundary fitted mesh, the governing differential equations are rendered discretely by a finite volume technique. The resulting set of coupled difference equations for momentum, mass, and energy are solved by MAC method. The previous studies were not accurate however, for example, the calculated underflow was predicted a thicker and slower than actually observed in the flume. Johnson suggested that these anomalous features of calculated flow were due to the fact of the model represented the sloping bottom by "stair steps" rather than employing a boundary fitted coordinate system. Another possible reason for differences that suggested by Karpik is due to the hydrostatic pressure approximation.Karpik used a semi-implicit program developed by modified SIMPLE method which was not very successful in different cases due to divergence, so an explicit MAC-type model is developed. The present model is tested in general and compared by Johnson's flume data. The results show the model is well able to I predict the important features of density under-flow. But some numerical diffusions errors occur when we have changes in coordinate system, so in future studies this model with a more accurate scheme and more uniform grid would be perfect.

Conceptual models have been often used in short- or midterm hydrologic forecasting. In this paper a framework for combining two conceptual climatic and hydrologic models is used in order to generate long-lead Ensemble Streamflow Prediction (ESP) of streamflow to Zayandeh-rud reservoir. In the proposed approach, two models based on a Fuzzy Inference System (FIS) for seasonal rainfall forecasts and Artificial Neural Networks (ANNs) for mapping hydroclimatic variables to streamflow data are used. Illusions such as clustering of rainfall and streamflow data, a proper calibration procedure as well as using a stopped training approach in ANN calibration, improve the accuracy of the forecasts. The results of the proposed approach are assessed by various criteria. Further, the results are compared with an ANN-based streamflow forecast, which uses the observed hydroclimatic data in monthly streamflow forecasting. The results show that using the proposed approach has the advantage of generating proper long-lead point and ensemble forecasts, which could be potentially used to reflect the uncertainty of future available water resources.

Due to the importance of sediment hydraulics in river engineering and its effects on hydrauhcs structures, the reliable estimation of the suspended sediment load plays very important role in real and reliable study. Because of some shortages such as technical and economical problems, the data from many sediment gauging stations in national rivers can not be relied on. Rational data is therefore necessary for some reaches. In this study, geostatistics and concepts of spatial variables were used in order to find a model for estimation of Talkherood suspended sediment load. For this purpose, a pre-developed software named "Gslib" was useii and then estimation of the suspended load of Talkherood River was carried out by both Kriging and Cokriging methods.In Cokriging method, in addition to suspended load, water discharge is also used as a secondary variable. This variable has a statistical relation with suspended load.Talkherood River is the most important river in the northern-west of Iran. In this study, the data of 5 hydrographic stations were used for suspended load estimation of Talkherood using both Kriging and Cokriging methods.For verification of the presented model, cross validation method was used. The result showed that proposed model could be adequately used for estimation of Talkherood suspended load. Two important points raised from the obtained results are as follows: Gaussian Variogram model for spatial estimation of Talkherood suspended sediment load has the best fitting on the experimental Variograms and the result of Cokriging method, in which the discharge is used as a secondary and parameter and compared to the Kriging method.

A wide range of estimated soil erosion in Iran is reported in different references. In addition, there is no acceptable priority of erosion rate and sediment yield among the main basins of Iran. In this research Suspended Sediment Yield (SSY) and soil erosion are estimated about 350 and 1000 million ton per year respectively for the country. Average specific SSY are also calculated 214 t/km2/yr using 209 hydrometric stations records. The maximum average specific SSY are observed in Hamoon-e-Jazmoorian, Minab and Baloochestan-e-Jonobi, and Maroon and Zohreh second order basins with more than 700 t.km-2.Three significant regression equations are developed between SSY with area, mean annual discharge and specific discharge. This study shows that specific SSY is proportionally related to area, which means relatively higher erosion rates in piedmonts and hilly land to high mountains. Primary study of watersheds with more than 1000 t/km2/yr specific SSY shows that the susceptible geological formations, landslides and vegetation cover play important roles on specific SSY.

Observations show that the global surface air temperature has risen by 0.6 during th 20th century. Global warming causes extreme events and bad weather in the near term. The loss of seasonal distinctions, larger fluctuation in intra-day temperature and large fluctuations in precipitations, and increasing of frequency and magnitude of the extreme events may be due to global warming. World Meteorological Organization (WMO), Intergovernmental Panel of Climate Change (IPCC) and the other responsible groups began to develop guidelines related to detection of climate change by applying statistical methods.The purpose of this paper is to present a few simple and complex statistical models staking into account the effects of climatic change. In addition, the result of a few related projects which evaluated climate variability by statistical methods in the country has been presented. It has been shown, there are a number of changes including trend, jump, unusual fluctuation, changes in distribution of elements and also changes in extreme indices including heat waves, diurnal temperature range, growing length season, ext.

Estimation of spatial distribution of rainfall in different time scales is one of the basic steps in water resources studies. Problems in selection of proper methods for spatial variation of rainfall can produce error in input parameters of rainfall runoff models in design or prediction stages. Also, reducing uncertainty in rainfall distribution is important in water budget studies. There are different methods for estimation of spatial distribution of rainfall based on raingage point data. Geostatistical methods are among such techniques. Geostatistical methods are favored in engineering studies since these methods consider spatial structure and location of data points. In this study, a number of methods were evaluated to estimate spatial distribution of monthly and annual rainfall in southwest of Iran. These methods consist of Thin Plate Smoothing Spines (TPSS), Weighted Moving Average (WMA) and Kriging. Cross validation technique was used for comparison of the methods. Results showed, although the TPSS method with power of 2 was marginally the most accurate method (with minimum MAE) in estimating annual rainfall but co-kriging method showed better consistency with topography of the study area. Analysis of variogram and error variance also demonstrated that generating missing data decreases accuracy of the interpolation.

Understanding the trend of changes and also prediction of Karoon water quality now and in the future through the development programs for urban, agriculture, and industry sectors enable the policy-maker to predict the future problems and plan accordingly. So, the study of Karoon river training program has been undertaken to investigate the water quality condition. For distinguishing the problems which are emerging from poor operation of reservoirs in the past as could be seen from the prior investigation, a simulation model is needed. Also considering the importance of new data of the water quality, one year of data is collected and new status have been proposed. Qua12E simulation program has been calibrated and used. The results show the poor water quality of the river at present and in the future if the waste waters are not treated property.

The present study has been conducted to evaluate the efficiency of Clark Instantaneous Unit Hydrograph Model in regenerating flood unit hydrograph in Bazoft watershed in Chaharmahal and Bakhtiari Province. The comparative evaluation is conducted between the 2h-Unit hydographs simulated using Clark model and the one obtained from averaging the observed ones. This comparison is made with the help of statistical criteria viz. relative error, root mean square of error, coefficient of efficiency and bias. It verified high level of compatibility between two unit hydrographs using the dark model and the hydrograph obtained by averaging the observed data.

The Esfahak plain is located in the south of Tabas and the west foot Hill of Shotori Mountain. The present study is an attempt to provide the necessary water resource for the Tabas coal mine. The thickness of the sediment deposits in this plain are reaching up to 450 m.In this study, based on the field observations, geophysic, and chemical analysis of water, the shape and placement of the bed rock are determined. The iso-piezometric and iso-salinity maps, have also been prepared and the hydrogeologic studies of the aquifer has been performed. The results show that in the position of bore hole No. 38, water is injected to the aquifer sediments through the bed rock. Moreover, the dynamic, static, and economic resources of the aquifer have been estimated.