Journal of Water Resources Engineering
Year:2013 | Volume:6 | Issue:16|Papers Count:8

In this study, rice husk (RH) and activated carbon (AC) adsorbents was used for removing of cadmium ion from aqueous solution at pH=6. Equilibrium time was shortened with a decrease in initial concentration of Cd from 50 mg/l to 1 mg/l for both adsorbent. This time was 60 and 45 minutes for rice RH and AC, respectively. Furthermore, not only the equilibrium time decreased with increasing initial concentration from 50 mg/l to 500 mg/l, but it became identical for both absorbents. Adsorption efficiency increased with a decrease in initial concentration of solution for both adsorbents. Maximum adsorption efficiency was found for RH and AC at initial concentration of 1 mg/l. Obtained adsorption efficiency at this concentration were approximately 98.0 and 99.7 percent for RH and AC, respectively. Fitting the results to the Lagergren (1898) and Ho et al. (1996) models was also attempted; the latter model better described the outcome. Moreover, the Freundlich isotherm better described the data than the Langmuir isotherm.

Proper design and management of irrigation systems requires knowledge of soil infiltration rate, which is in turn influenced by water salinity and sodicity. The objectives of this study were to investigate the spatial variability of irrigation water electrical conductivity (EC) and sodium adsorption ratio (SAR) and to map these parameters using geostatistical methods. The main objective was to predict the spatial distribution pattern of soil infiltration rate over the study area based on water salinity and sodicity. Water samples were collected from 76 observations wells in the Kerman Plain in 2008. The geostatistical methods used were ordinary and log-normal kriging. The performance of interpolation methods was evaluated through cross-validation with comparison criteria of root mean square error (RMSE) and mean absolute error (MAE). Geostatistical analysis showed that both EC and SAR had strong spatial correlations, and these fitted a spherical model. The cross-validation results are indicated that the two methods provided similar accuracy for estimating salinity and sodicity. Furthermore, it was evident from the kriged maps generated through both methods for EC and SAR that the estimation error maps produced were only slightly different. Therefore, whenever the aim is to produce only a map of spatial distribution of soil properties, ordinary kriging, which is mathematically simpler than other methods, is preferred. Soil infiltration rate distribution pattern was also predicted based on the kriged maps of EC and SAR, and, some approved standards. The results indicated that most of that area, including northern and western regions had good infiltration rates. The rest, which cover mostly the northeastern and southeastern of the study area, had moderate infiltration rates.

A side weir is a hydraulic structure with free flow, which is installed at one side and parallel to an open channel. It allows the water to overflow when the surface of the water in the channel rises above the weir crest. This structure affects the depth and the flow rate in the channel. Awareness regarding the effect of this structure on the depth of water and flow rates can affect decision making for the proper hydraulic design of the channel and its side weir. In this research, 36 semi elliptical side weirs were tested in 298 settings, varying in an experimental main channel geometrical characteristics, and subcritical conditions. The range of discharge was varied from 10 to 70 lit/s. The water surface profiles over semi elliptical and rectangular side weirs were investigated and interpreted through velocity profiles. Additionally, the effects of increasing the discharge in the main channel, and varying the height, length and curvature of weir on the water surface profile were examined for this type of weir were studied. Moreover, the result of experimental water surface profiles were compared with the water surface profiles calculated by the Runge-Kutta method over rectangular and semi elliptical side weirs. The results indicated that the accuracy of this method was increased by raising the height and length of the weir, and the reducing the discharge.

Water quality is a matter of utmost importance as it determines its suitability for particular purposes. As rivers are the lifelines everywhere, especially in an environments having information regarding the quality of their water is extremely useful for the water users. As a river’s water quality varies with the seasons of the year and the geological formations through which it flows, establishing a trend as to where and when to expect certain changes in the quality of a river’s flow gains importance. It is fortune that the newly developed technologies facilitate achieving these objectives. Therefore, we used the GIS and the Rockware software and the data collected during the 2000-2004 period at 2 hydrometry stations on the Maroon River to better classify the water quality spatially and temporally. The Chemical analyses consisted of pH, EC, TDS, CL, SO4, Ca, Mg, and NaCo3. It was revealed that the water quality deteriorated from the rainy season towards the dry season. Furthermore, as the river advanced from the mountainous area towards the low-laying plains the quality diminished, too. Most of the water samples were low in Cl and So4 conceal rations according to the Schoeller’s diagram; therefore suitable for drinking. According to the Wilcox’s classification, the water at the Aydnak station was in the C3S1 class and at the Dehnavi station was in the C2S1 class, both suitable for irrigation purpose.

Weirs and gates have numerous applications in open channels as flow measurement and water-level control structures; therefore, their combination provides a structure, which offers the advantage of both structures in the passage of floating objects over the crest of the weir and the discharge of the suspended sediment under the gate. In the present study, a laboratory investigation was implemented to the variations of discharge coefficient of cylindrical weir-gate according to dimensionless parameters H/D (the ratio of upstream depth to the structure’s diameter) and H/a (the ratio of upstream depth to the gate opening) using a 10m long flume whose width and height were 0.6 and 0.7m, flume (10×0.6×0.7 meters of length, width and height, respectively). Furthermore, the variations in the trend of weir and gate discharge coefficient were determined by measuring the separate velocity profile under and above the structure and compared them to those of the discharge coefficient of the combined model of cylindrical weir-gate. The results show that the discharge coefficient of the combined cylindrical model decreases initially and then rises due to an increase in the dimensionless parameters, H/a and H/D. The trend of discharge coefficient in the combined model is decreasing for gate and shows an ascending trend at first, then becoming eventually constant for the weir. Moreover, the structure’s diameter and the gate opening affect the discharge coefficients of weir, gate, and the combined weir-gate model. The cylindrical weir-gate discharge coefficient ranges between 0.75-1.05 under the experimental conditions. An equation with a significant correlation for the weir-gate discharge coefficients estimation was obtained.

Unsaturated hydraulic conductivity is one of the basic properties of soil that governs the water movement in the field. As application of any of the various available methods in the field deemed impracticable due to its difficulty of implication and high costs, we resorted to a laboratory method and modeling to develop a method, which may be easily used in determining this important parameter. Saturated hydraulic conductivity was determined by the falling head method. Hydrometry method was used for grain size distribution; pH, EC, and contents of mineral carbonate and gypsum were also determined using the approved methods. Unsaturated hydraulic conductivity (Ku) was estimated using the discharge equation in a unit area, the Darcy’s law, neural network, and the RETC, SPSS, Curve Expert, and Excel software. It was observed that the Power subroutine of the SPSS, with the maximum coefficient of determination and the highest correlation coefficient, and the minimum RMSE presents the best model.

Freshwater scarcity in the Borazjan Plain is approaching a crisis state. Helleh and Dalaki, as two of the most important surface water resources, are claimed to be the main source of salt pollution of the local Borazjan aquifer. To validate this claim, and to develop strategies to mitigate this disturbing process, water samples were obtained from 22 representative production wells scattered on the plain, and from the Helleh River. Results of the chemical analyses of these samples were correlated with their positions relative to the geological formations and other potential sources of contamination. Results indicated that both the Dalaki and Helleh Rivers were instrumental in the water quality deterioration. Furthermore, dissolution of halite and gypsum from the geological formations that abound in the area contribute NaCl and CaSO4 as the main contaminants of the aquifer; the discarded brine from the oil wells and the irrigation return flow contribute to water pollution as well. The distinct linear trend between Na and Cl concentrations in the ionic ratio diagram indicated the mixing of fresh and saline water, and an occurrence of surface water intrusion, especially in the central and northwest of the plain. However, recharge from limestone formations in the eastern part of the plain improves the water quality in that area. Over-pumping tends to increase the thickness of the fresh-saline water mixing zone, thus increasing the salinity of production wells'' salinity. Prudent management of groundwater is a practical policy in sustaining the use of this limited precious resource in the Borazjan Plain.

Gravity or density current is produced due to a density contrast among two different fluids or among two layers of a single fluid. In this research work, the saline gravity current near bed with slope reduction was simulated numerically, using FLUENT software. The experimental results were used in order to calibrate the numerical model. The obtained results showed that density current was simulated accurately, using turbulent model (RNG type) and optimized grid. This result was found especially for the vertical profiles of local velocity and volumetric concentration (for both sub and supercritical sections), the density height, the maximum value of mean velocity and the corresponding height of this velocity. The numerical results showed that both standard and RNG turbulent model was accurate for calculation of saline gravity current height. In this paper, using turbulent model (RNG type), better similarity collapses of velocity profiles were obtained in comparison with concentration profiles. Moreover, due to ambient water height limitation, a circulation flow was found in numerical results. Finally, the numerical model indicated that for given initial conditions, as initial bed slope increases, the location of the density jump is moved farther downstream, and also the amount of ambient water entrained along the supercritical regions increases with the increase of the initial bed slope.