مجله پژوهش آب ایران
پیاپی 7 (پاییز و زمستان 1389)

There are various mathematical water uptake models for simulating plants response to combined effects of drought and salinity stress. The reduction functions are classified as additive, multiplicative and conceptual models. As transpiration is the largest component of the agricultural water budget in arid systems, the efficacy of the simulation models depend on their ability to predict transpiration. In this study 6 different macroscopic reduction functions, namely; van Genuchten (additive and multiplicative), Dirksen et al., van Dam et al, Skaggs et al and Homaee were evaluated. The experiments were carried out on wheat crop in a factorial split plot design with 3 replicates. The treatments consist of four levels of irrigation (50, 75, 100 and 120%of crop water requirement), and three water qualities (1.4, 4.5, 9.6 dS/m). The result indicated that the crop response to drought and salinity stress was multiplicative at high salinity. Among multiplicative models, reduction function of Skaggs et al models provided better fitness to measured data than the other functions.

The growth and activity of microorganisms in arid soils have always been constrained withpersistent drought stresses. The aim of this study was to assess the role of superabsorbent Superab A200 in reducing drought stresses and its effect on N dynamics and enzyme activities of sandy and clay soils under laboratory conditions. A 2×4 factorial experiment consisting of two levels of soil moisture (30 and 70 % of the field capacity), and four levels of the superabsorbent (0, 0.1, 0.3 and 0.5 %, w/w) arranged in a completely randomized design with three replicates were carried out using two soil textures (sandy and clay). The application of the superabsorbent had a significant, positive effect on most measured properties. But the effect was largely depended upon the quantity of superabsorbent, soil texture and moisture level in the soil. Nitrogen mineralization, ammonification and nitrification rates, microbial biomass N, alkaline phosphatase and urease activities were significantly greater in the clay soils with 70% of the field capacity moisture than in the sandy soil with the same amount of moisture. This is likely due to the high level of C contents. Moisture and texture effects on most soil biological properties were significant. Results indicated that the cumulative ammonification and nitrification increased with increasing superabsorbent level where much of the increases occurred at lower levels than higher levels. The increase in nitrate and ammonium production with 0.1 % superabsorbent was greater than that with other superabsorbent levels.

Inflow forecasting plays an important role in reservoir operation and water resourcesmanagement. In this paper, Artificial Neural Network (ANN) and multiple regression modelshave been used to forecast inflow into Dez reservoir using data from upstream hydrometric stations. The paper aims to define the best pattern of spatial and temporal correlations among the stations in upstream the reservoir. using the correlation coefficient and mean square of errors (MSE), The performances of different models were compared. The results indicited that the ANN forecasts the reservoir inflow better than the multiple regression models. The best one day prior forecasting was obtained using the data of the nearest station to the reservoir (Tangpanj station). Furthermore, the best three days prior forecasting model is obtained using Kamandab, Vanaee, Doroodtireh and Daretakht stations. Hence, by increasing the distance of forecaster stations from the target station, the forecasting time would increase from one day to three days, but forecasting accuracy would decrease by 42%

Reservoirs are one of the most important infrastructures that play a vital role to supply water in specially drought events. By optimum operation of reservoirs the target objectives can be obtained in an acceptable level. But, hence the optimum operation of the large water resources systems by using the optimization models is complicated, time consuming and sometimes inaccessible, the use of other methods which yields the satisfactory near-optimum results with acceptable precession seems to be an acceptable solution for this type of problems. In this study the performance of MODSIM and WEAP simulation models have been compared to those obtained by Lingo optimization packages for a single-reservoir systems as well as in a multireservoir system in a period of low flow condition. For better evaluation of model's performances, some criteria have been developed and applied for the reservoir systems in this study. The results showed that by considering the volume reliability as the operation goal, the simulation models can be replaced by the optimization models in single-reservoir systems.However, in such systems the simulation models increases the relational deficit for about %38, whereas the temporal reliability, resiliency and vulnerability of the system yielded by simulation models is about half of those obtained by the optimization models. Moreover, the volume reliability and resiliency of the system are not the same in simulation and optimization models. The discrepancy of the volume reliability in optimization and simulation models is about 25% and the discrepancy of resiliency in the mentioned models is 40%. The discrepancy of other performance indices is more than 300%.

Evaporation takes place in from water surfaces such as lakes and also from soil surface. In this study, several methods were applied to estimate evaporation of water surfaces including Mayer, Marciano, Shahtin, Hefner, Ivanof, Tichomirof, USBR and neutral network. The estimated values were compared with measured pan evaporation values. Sensitivity of these methods to input parameters of wind speed, temperature and relative humidity were evaluated using variation rates of ±10%, ±20% and ±30%. Analyzing results by statistical indices such as R2, MBE, RMSE and 1:1 line showed that estimated water surface evaporation using Ivanof method offers the best correlation with pan evaporation values followed by, Ivanof, Meyer and Tichomirof methods. In situations with probability of systematic and human faults in measuring input parameters, Ivanof, Marciano and USBR methods are more acceptable rather than other methods, because of lower sensitivity to input parameters. Obtained results showed a high efficiency of Multilayer perceptrons model for estimating water surfaces evaporation. The values of R2, RMSE and MBE in the best models) neutral network (are equal to 0.95, 0.72 and 0.22, respectively. Accurate estimation of evaporation from surface water provides a vital tool to better manage essential decisions for decreasing harmful effects of drought crisis and protect water resources.

Natural rivers are rarely straight and usually tend to take a winding course, called as meandering. Due to mutual interaction between flow and bed in river meanders, understanding the flow characteristics is an interesting issue in river engineering field. The main problem with describing the characteristics of flows in river bends is the existence of strong secondary flows and its impact on the distribution of longitudinal and transverse velocity. The issues of flow in river bends has been investigated by several researchers, and a variety of different equations for identifying the parameters of flow have been proposed. However, the proposed equations do not provide a good solution; this is especially the case in sharp bends in which strong secondary flows influence velocity patterns. In this research, firstly, taking the properties of longitudinal velocities in sharp bends into consideration, a new model for computing the velocity was proposed which includes two power and sinous sections. Then, the new model is compared with some longitudinal velocity models on bend. The results achieved from the study on 1930 bend showed that the new model not only has the properties of a longitudinal velocity in sharp bends but also enjoys less error than the other models. Also, comparing the new model with 3 series of data from 3 bends with different curvature radius to width, showed that the new model is able to have good predictions in different bends.

Because of difficulties in the field monitoring of overhanging riverbanks, it is not possible tomonitor its deformations before failure, and therefore it is sometimes admittedly difficult todiscriminate between shear versus toppling failures in the field. In This paper evaluated the extent to which uncertainties in the parameterisation of controlling factors feed through to influence the reliability of the resulting overhanging stability estimate. Thus, the impacts of variations in each individual parameter on the factor of safety are investigated, while keeping all other parameter values constant. In estimating the magnitude of the uncertainty typically associated with each of the parameters, discriminating between (i) measurement errors and (ii) uncertainties associated with the inherent natural variability of each parameter is helpful. The results showed that the care should be taken when estimating the values of cantilever block height, block width, tension crack depth, block material cohesion, and the block material unit weight as the safety factor is more sensitive to the variation of these factors. Since parameter uncertainties are derived primarily from the inherent variability of the parameters, rather than measurement errors, much more careful attention should be paid to field sampling techniques.

In the present paper, subsurface water profiles through coarse materials are investigated using a laboratory model. The laboratory model of a typical rock drain having 6.4m length, 0.8m width and 1m deep was prepared and then was filled using both crushed and rounded materials. For different flow rates and three slopes (horizontal, 4% and 20.3 %) of the flume, experiments were conducted and consequently water surface profiles,The upstream and exit depths of the flow were recorded. Finally the results of experimental observations were analyzed and compared with the theoretical formulas. Results showed that water surface profiles through coarse porous medium for horizontal and 4% slopes, followed by gradually varied flow theory and drawdown profiles were taken place while this theory was not valid for 20.3% slope and a uniform flow were established. Assumed critical depth to occur at the outlet of the rock drain was not approved and caused more than 200% error in gradually varied flow calculations.

Hydraulic jump in stilling basins is used for the dissipation of excess kinetic energy downstream of hydraulic structures such as drops, spillways, chutes and gates. In the present research, the hydraulic jump characteristics were experimentally studied over six triangular corrugated beds in a flume of rectangular cross section at the Hydraulics Laboratory of the Department of Water Engineering, University of Shahrekord, Iran. The flume has the dimensions of 0.4 m wide, 0.4 m deep and 12 m long. A total number of 42 tests were carried out for a range of initial Froude numbers from 6.1 to 13.1. In all of the tests, the main characteristics of hydraulic jump including conjugate depth ratio, length of jump and length of the roller were measured. The dimensionless hydraulic parameters were determined as a function of the Froude number. The results showed that the tailwater depth and the length of the jump on triangular corrugated beds are smaller than those of the corresponding jump on a smooth bed. Comparison of these parameters with the same parameters in smooth bed hydraulic jump showed that the conjugate depth and the hydraulic jump length decreased by 25% and 54.7% respectively. The analysis and comparison of the shear stress coefficient showed that shear stress on corrugated bed is about 8.5 times that of smooth bed. The conclusions drawn from the research showed that there is a good agreement between the persent study results and earlier works. Consequently the triangular corrugated beds could be used to dissipate the excessive energy of the hydraulic jump in stilling basins.

Successful water management to cope with drought requires an understanding of the governing processes and causes. In this study, the frequency of drought class transitions in the first half of 20th century were compared with those of the second half based on the time series of standardized drought index (SPI) for four old weather stations of Iran including Tehran, Mashhad, Esfahan, and Bushehr.. A time window of 12 months was used to compute the SPI. Three-dimensional log-linear models were used to analyse the SPI drought class transition.Fitting log-linear models to the contingency tables of transition frequency from a given drought class to each class were evaluated by means of likelihood ratio of chi-square (G2). Odds ratio and respected confidence interval were estimated for both half of 20th century in the stations interesed. The results showed that log-linear models have an acceptable fit to the observed frequencies of transition at all stations at 5% level. In addition, with an exception for Tehran station, the transition frequencies of moderate and severe drought classes has in increased in the rest of the stations during the second half of 20th century compared to first half. The unconditional probability of moderate and severe droughts in some of stations have been increased up to 3 times during the second half of 20th century compared to the first half.

The purpose of this study was to assess the quantity and quality of groundwater in Zarand plain by analyzing groundwater table drop and thus to provide a strategy or management options to remedy the situation. Firstly, all relevant data including meteorological, hydrological, hydrogeological, geological and geographical data were collected and evaluated. Then, water table decline rate, excess discharge, as well as chemical changes of aquifers were determined and their impacts on assessed. Then the status of aquifers in the coming 10 years was determined assuming the past and present trends will be continuing in the future. The results of the this research indicated that over-pumping had led to several undesirable consequences and if the situation continues in the future, it will have both environmental impacts and economic constraints as well as social unrest will ensue. Finally, recommendations were suggested to overcome the problems.

There is a need for proper water demand management since water scarcity is a fact in Iran due to the arid nature of the region. Seepage losses constitute the large amount of losses in agriculture. In some cases, the rising of underground water levels in adjacent lands to irrigation canal cause drainage and salinity problems for surface layers of soil.Therefore, it is important to find ways to limit losses through seepage. In Iran, empirical equations are mostly used to determine seepage in unlined channels in the most of the irrigation networks. In this study, the seepage losses in three earthen canals in Gazvin plain were determined by Ponding Test method and also the empirical equations were used to estimate the rate of seepage losses in these canals. Empirical equations such as Ingham, Davis and Wilson, Moritz, Molesworth – Yennidumia and Misra were evaluated with Ponding Test. The seepage rates obtained by the ponding test on canals No. 1 to 3 were determined to be 163.6, 567.7 and 379.5, respectively. Among empirical equations, Misra and Moritz methods found to have acceptable precision for channel seepage determination at the study area. Hence, these two formulas are recommended to be used.