فصلنامه مهندسی منابع آب
پیاپی 45 (تابستان 1399)

Flow in river usually has a 3 dimensional character. While 3 dimensional flow simulations is time consuming process, enhanced 2D numerical modeling with depth and width averaged are introduced. In this article using field data, numerical simulation of unsteady flow field and non-uniform and non-equilibrium sediment transport in one reach of Karon River with length of 5.2 km for duration more than 6 years is performed using CCHE2D numerical model. Numerical outputs clearly demonstrate that CCHE2D numerical model can predict flow field in the study area. also the flow field analysis clearly demonstrate that high shear stress and high velocity has different zonal location and sediment transport analysis shows that van Raijn (1984) formula for adaptation length for bed load and Wee (1999) formula for adaptation factor for suspended load can better predict the bed change in the study area with good accuracy. Moreover the software accuracy for bed change varies between 11.045% to 68.07% in the study area.

Nowadays, Producing and using chemical compounds in different industrials has caused environmental pollution. One of these compounds that can bring a widespread pollution in natural resources is Methyl Tert-Butyl Ether (MTBE). This organic compound that is produced in petrochemical industries is used as a substitute to produce lead free gasoline in all over the world. Human exposure to MTBE may cause dizziness, coughing, fever, headaches, vomiting, muscular aches, sleepiness and skin and eye irritation. Concerning the destructive consequences of MTBE on the environment, and human health, clearing polluted resources are vital. The main objective of this study is dedicated to treat MTBE-contaminated waters through adsorption process in the presence of granular activated carbon (GAC). In this study, the effect of pH as well as exposure time on the removal of MTBE from aqueous solution have been examined and finally the efficacies of the process is assessed in terms of organic compounds removal and GAC reusability. According to the results, the adsorption capacity of used activated carbon depends considerably on the PH and reaction time. In this study, after 45 minutes of reaction time at PH of 8 the maximum COD removal efficiency of 62% was achieved. In this research both the Langmuir and Freundlich isotherm model best represented the MTBE adsorption behavior of GAC, having R2 of 92.2% and 84.6%, respectively. Moreover, maximum capacity of adsorption, in optimized condition, was estimated to be 67 mg of COD per each gr of GAC.

The purpose of this study was to investigate the effect of the use of slot in the pier of a rectangular bridge to control scour. For this purpose, four shape of pier, trapezoidal, invers trapezoidal, triangular and invers triangular, with the same cross-sectional area, were placed in three levels on bed, 1.5 cm and 3 cm above the bed, in four Froude number 0.3 and 0.27, 0.24 and 0.19 were tested. The experiments of present study, were carried out in a laboratory flume in Tehran's Soil Conservation and Watershed Management Institute. The results show that increasing the level of the slot from the bed, increased the scour depth upwards of the piers. Also topography changes along the canal and the dimensions of the cavity also increase. So that in all Froude numbers, the slots placed on the bed, reduced the depth of scouring about, 15.5-51.81 percent for invers triangular, 21.16-62.18 percent for invers trapezoidal, 26.67-65.28 percent for triangular and 38.83-73.58 percent for trapezoidal slots has best performance compared to the two other levels.

The heterogeneous temporal and spatial distribution of fresh water and rapid population growth in recent decades have led to problems in supplying required water resources for various uses. Therefore, new mathematical models have been developed to study the complex hydrological processes. In this study, SWAT model in Samalqan catchment with area of 1148 km2 was used to simulate the flow. In the modeling process, the basin was divided into 21 sub-basins and 402 hydrological units. Modeling of watersheds has uncertainties due to limited access to enough hydrological data. For this purpose, model calibration and validation were performed using SUFI2 algorithm for 1995 to 2012 and 2012 to 2014, respectively. Based on the sensitivity analysis results, the parameters RCHRG_DP (value of penetration into the deep aquifer), GWQMN (amount of water in the shallow aquifer to produce the base stream), ALPHA_BF (groundwater reaction coefficient), SOL_AWC (soil available water capacity) and CN (SCS curve number) had the most effect. The results showed that the values of Nash-Sutcliffe index and R2 coefficient were 0.65 to 0.80 for calibration period and 0.40 to 0.65 for validation period. Out of the total inflow into the basin, 87% is spent on evapotranspiration, 3.2% for surface runoff, 3% for infiltration and the rest is related to changes and moisture storage in soil. Since no estimation of water balance components in this basin has been done so far, this research can provide useful information about the water balance of the basin and help to plan water resources more accurately.

In this research work, besides analyzing the scour hole at the downstream of the siphon spillway physical model, some equations have been presented to predict scour hole developing. A physical model of siphon spillway along with three flip buckets of angle 30°, 45° and 60° for three types of sedimentary materials of mean size 1.8, 3.5 and 1.4 (mm) were used to study scour hole formation process. Geometric characteristics of the scour hole were collected for four flow discharges of 39.2, 42.12, 42.12, 49.76 (lit/s) and five tail-water depths of 15, 20, 25, 30 and 35 (cm) using a mesh grid size of 10 (cm) ×10 (cm). Three dimensionless parameters were extracted for analyzing experimental results using dimensional analysis. Of all scour hole dimensions, scour depth (ds), scour length (Ls) and distance of downstream hill up to bucket lip (L6) were adjusted for numerical modeling. Results showed that increasing flow rate causes growth and developing of scour hole geometric properties simultaneously. Increasing the particle size showed an inverse relationship with three dimensions of the scour hole. Also, the reduction of the bucket's angle led to a reduction in ds, Ls and L6. The maximum correlation coefficient obtained between ds, Ls and L6 with particle size, flip bucket angle and discharge/tailwater, respectively. Finally, predictors were presented to describe above-mentioned dimensions of scour hole dimensions.

One of the drawbacks of anaerobic digestion technique is the slow rate-limiting hydrolysis of organics. Different pretreatment techniques such as ultrasonic, chemical and thermal were applied to increase secondary sludge disintegration, in order to enhance sludge anaerobic digester performance. Hydrodynamic cavitation (HC) technique has fewer disadvantages compared to other pretreatment methods. Additionally, HC is simple and energy efficient. In this study, the effect of cavitation on sludge properties including soluble chemical oxygen demand (sCOD), turbidity, electrical conductivity, disintegration degree and other parameters downstream of orifice plate was investigated. The geometry of orifice plate had been optimized previously for specific cavitation number (0.2) which is desirable for cell disruption. SCOD rose from 857 mg/L to 5376 mg/L within 60 min pretreatment. By using cavitation pretreatment, degradation of cells occurred in several minutes instead of days. So it can be expected that anaerobic digestion performance will improve due to the release of intracellular substances and availability of enzymes for biological degradation. Experiments performed in this study indicated that cavitation causes the significant increase in sCOD and disintegration degree as a result of breaking up microorganisms’ cell walls and releasing organic substances into soluble phase. The turbidity of soluble phase also rose dramatically from 300 NTU to 5675 NTU within 60 min due to the collapse of cavitation bubbles and other effects of cavitation phenomena. Eventually, a linear relationship was derived for sCOD and turbidity of the soluble phase of pretreated sludge which can be applied to calculate one from another alternatively.

Density current is caused by a slight density difference with the environmental fluid. These currents are of two-phase current type. These currents are non-linear in nature, which are complex and sensitive to initial conditions. Fractal geometry is used as a powerful tool to investigate geophysical phenomena including density current and many complex natural phenomena. This study aimed to conduct a comprehensive study on the fractal and multi-fractal properties of density current and established a significant relation between the Richardson number evolution and the entrainment of ratio density current through fractal analysis. For this purpose, three experimental models in 28 different states were performed by changing the bed slope, density and inlet discharge. The developed codes in MATLAB were used to calculate the multi-fractal generalized dimension indices D(q), singularity spectrum f(α), singularity angle α, the scaling exponent T(q) and fractal dimension Df. The results and various investigations indicated that the fractal dimension decreased a little with the increase of flume bed slope. Further, the fractal dimension increases with increasing the concentration and current discharge. As the Richardson number increases, the scaling exponent has a linear pattern. Furthermore, the fractal dimension changes are monotonic than q in these experiments, and the singularity angles are larger with less range. A significant relationship with 92% coefficient was made between Richardson number and entrainment ratio by fractal analysis.

The discovery of groundwater resources as one of the ways of drinking water in the world is imperative and inevitable given the increasing need of the world for water.The objective this study is investigation of Karstic Water Resources Potential in the Leili-Keyno anticlines on the northeast of Khuzestan province. For this purpose, effective parameters of Karstic Water Resources Potential such as rainfall, lineament density, distance from lineament, slope, drainage density, lithology, land use and temperature are identified and evaluated. Using the expert group opinion and to help the Analytical Hierarchy Process (AHP) The weight of effective layers in the potential of karst water resources was calculated: precipitation (0.331), linear density (0.261), distance from linearity (0.151), slope (0.098), water drainage density (0.064) , Lithology (0.047), vegetation (0.029) and temperature (0.024) and finally, Karstic Water Resources Potential map extracted with integration of related layers by overlapping in ArcGIS software and using the Raster Calculator module. Based on this method, the area is classified into five categories, viz. very high, high, moderate, poor and very poor. The northwest foreland (Garu formation) has the least potential. Springs and dolins are located in the areas with high potential in central part of the anticlins.