JWSS - Journal of Water and Soil Science

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Of the many hydraulic structures developed by man, the weir is perhaps the oldest. Weirs are used for the measurement of discharge and regulation of water flow. The most common types of weirs are broad-crested, sharp-crested, circular-crested and cylindrical, and ogee crest weirs. Advantage of the circular-crested and cylindrical weir compared to the other weirs include simplicity of design, stable overflow pattern, larger coefficient of discharge and the associated lower costs. In the present study, potential flow around a circular cylinder are adapted to determine the velocity distribution at the crest section and to develop a model for coefficient of discharge (C_d) for circular-crested weirs. These results were evaluated using present test data for three types of weir models, namely, cylindrical, semicylindrical and semicylindrical with different heights and also Dressler theory. The results of the study showed that the experimental velocity profile agree very well with the theoretical profiles for the range of the study. Also, the prediction of the velocity distribution over the weir crest using Dressler theory is always less than the proposed model and measured data. The predicted values of coefficient of discharge (C_d) based on the proposed model agree well with C_d determined from direct discharge measurements. For the cylindrical model, the coefficient of discharge can be predicted from the proposed model within an error of –7% and for the semicylindrical and semicylindrical with different heights within ± 5%.

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In this study, two data ranges of uniform flow (bulk parameters) and non-uniform flow (local parameters) are employed to investigate resistance to flow and the factors affecting it using velocity distribution of boundary layer theory. The results indicate that the cross-section form factor or adjustment roughness coefficient of logarithmic law can not improve the prediction of flow resistance. On the other hand, it is possible to ameliorate the prediction of resistance to flow by application of the Froude number and the Shields parameter along with the integration constant of the logarithmic velocity distribution. Also, there is no improvement in flow resistance prediction by taking into account power equations. On the other hand, the application of boundary-layer characteristics such as displacement thickness and momentum thickness in velocity profile can remove the risk of spurious correlation. Based on the measured velocity profiles for non-uniform flow in Gamasiab river, a new flow resistance equation is suggested in which the following bulk parameters are considered: flow depth, maximal velocity at the water surface, and friction slope.

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The use of slot through a pier is a new method proposed to control local scour at bridge piers. In this study, control of local scour at bridge pier is studied using 20 pier models under clear water conditions. The models consist of one circular pier without slot, three round-nosed piers without slot, and 16 piers with slot. Two slot lengths were chosen (yl=b and yl=2b, where y1 is the length of slot and b is the width (diameter) of the pier). Furthermore, they were located at two positions (near the bed and near the water surface). The results showed that for a circular pier, the slots with the lengths of b and 2b, located near the water surface, had no influence on the equilibrium scour depth. It was also found that for all piers, maximum reduction in scour depth occurred for piers with a slot length yl=2b and close to the bed. Also, the efficacy of a slot for scour protection in the case of a round-nosed pier was more than a circular pier (with a diameter equal to the width of a round-nosed pier).

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Suitable stable channel design and optimization of river geometry can reduce cost of projects. The regime theory provides the possibility of empirical and semi-empirical investigations of stable channel design in which erosion and sediment transport are in equilibrium. The objective of this research is an investigation and a comparison of the influence of uniform and non-uniform flows on the prediction of stable channel characteristics. The following empirical and semi-empirical (extremal hypothesis) equations were selected to study the effect of uniform flow: Lacey, Chital, Kondap and Garde, and Chang. Using 24 regime channels in USA, the statistical and graphical approaches were applied to compare and to evaluate the power of prediction of the selected equations. In order to investigate the effect of non-uniform flow structure on the stable channel characteristics, 21 measured velocity profiles in Gamasiab River were applied. Using the boundary-layer theory, shear velocity was computed for each profile. Accordingly, the estimated Shields parameter using the boundary-layer approach is the most effective parameter on the regime channel prediction. Simultaneous application of the non-uniform flow effect and the boundary-layer theory not only remove the risk of spurious correlation but also improve the estimation of stable channel characteristics.

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Soil erosion is an important economical, social and environmental problem requiring intensive watershed management for its control. In recent years, modeling has become a useful approach for assessing the impact of various erosion-reduction approaches. ِDue to limited hydrologic data in mountainous watersheds, watershed modeling is, however, subject to large uncertainties. In this study, SWAT2000 was applied to simulate runoff and sediment discharge in Beheshtabad watershed, a sub-basin of Northern Karun catchment in central Iran, with an area of 3860 km2. Model calibration and uncertainty analysis were performed with SUFI-2. Four indices were used to assess the goodness of calibration, viz., P-factor, d-factor, R2 and Nash-Sutcliffe (NS). Runoff data (1996-2004) of six hydrometery stations were used for calibration and validation of this watershed. The results of monthly calibration p-factor, d-factor, R2 and NS values for runoff at the watershed outlet were 0.61, 0.48, 0.85 and 0.75, respectively, and for the validation, these statistics were 0.53, 0.38, 0.85 and 0.57, respectively. The values for calibration of sediment concentration at the watershed outlet were 0.55, 0.41, 0.55 and 0.52, respectively, and for the validation, these statistics were 0.69, 0.29, 0.60 and 0.27, respectively. In general, SWAT simulated runoff much better than sediment. Weak simulation of runoff at some months of the year might be due to under-prediction of snowmelt in this mountainous watershed, model’s assumptions in frozen and saturated soil layers, and lack of sufficient data. Improper simulation of sediment load could be attributed to weak simulation of runoff, insufficient data and periodicity of sediment data.

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After construction of a dam across a river, sediments settle behind the dam. It is important for dam designers to estimate the rate and distribution of sediments in the reservoir. In this study, the accuracy of area-increment and area-reduction empirical methods to predict the sediment distribution of Dez, Dorudzan and Shahid Abbaspour reservoirs is evaluated. The last measurement of sediment in these reservoirs was in 2003 (Dez), 2005 (Dorudzan) and 2005 (Shahid Abbaspour). The comparison between actual sediment distribution and predicted sediment distribution by using area-increment and area-reduction methods showed the maximum error at the depth of sediment behind the dam. At higher elevations, the error decreased and reached zero when the elevation was maximum. For Dorudzan reservoir, which has the least sediment volume (31 Mm3), the area-reduction method is less accurate, as compared to the area-increment method (81% vs. 37.5%). For Dez and Shahid Abbaspour reservoirs, where their sediment volume is high (608 and 737 Mm3, respectively), the error of the two methods is relatively equal (in Dez, 29% for both methods, and in Shahid Abbaspour, 22% for area-reduction and 25% for area-increment methods). After long-time sedimentation, the shape factor decreased and reservoir type of all three reservoirs changed to 2.

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Precise calculation of inlet pressure into sprinkler laterals is an important problem for proper distribution of uniformity. The adjusted average friction correction factor, FaAVG , provides the possibility of calculating the inlet pressure to mutli-outlet pressurized irrigation pipelines when the first outlet spacing from the pipe entrance is arbitrary. To investigate the effect of allowable head-loss in the lateral pipeline on inlet pressure, a new equation was developed for calculating this factor. A progression coefficient was assumed for variable discharge of the outlets. The results showed that though the inlet pressure of the lateral depends on the head loss between the outlets, it is negligible when more than 15 outlets are used. It was also concluded that when N is less than 15 and the ratio of distance between inlet and first outlet to outlet spacing is less than 1, the conventional approaches overestimate the inlet pressure. In this research, a new equation was also developed for Christiansen friction factor in which the first outlet is located at a fraction of outlet spacing. This new factor is dependent on the head loss between the first and last outlets, in addition to the number of outlets and the power of velocity equation. The results of applying this new factor showed good correlation with other researchers’ numerical results when a large number of outlets are coalesced.

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Most furrow irrigation systems have low performance due to deep percolation at the upstream end and tailwater runoff at the downstream end of the field. To eliminate this problem improving furrow irrigation performance is necessary. Since the inflow discharge has high effect on infiltration along the furrow which consequently affects the application efficiency and water distribution uniformity, it would be important to apply different furrow inflow hydrograph shapes based on the field data such as field slope, soil texture and furrow length to save water. To produce different furrow inflow hydrograph shapes, an automatic valve which was connected to a stepper motor was designed to change the inflow discharge with time according to the desired inflow hydrograph shape. The experimental field was located at Isfahan University of Technology. A constant head water delivery system to the furrows including the automatic valve was installed in the experimental field and the tests were conducted for different inflow hydrograph shapes. The comparison of the measured furrow inflow discharges with the simulated furrow inflow discharges produced by the automatic valve showed that the automatic valve can produce different furrow inflow hydrograph shapes with high accuracy.

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There chemical and organic matter content in garbage leachate that may affect soil physical and hydraulic properties. The main objective of this study was to evaluate the influences of the leachate of Isfahan Organic Fertilizer Factory (IOFF) on some soil physical and hydraulic properties in a soil chemically enriched by Zeolite. The treatments include two soil textures (clay loam and sandy loam) and three levels of zeolite (0, 5 and 10 percent). The treatments were applied on lysimeters scale. The results showed that irrigation with the leachate caused a reduction of infiltration and hydraulic conductivity in the clay loam soil. The hydraulic conductivities in clay loam soil without zeolite (B0) before and after irrigation with leachate were 1.73 and 0.36 m/day, respectively. In contrast, there were no changes in the sandy loam soil’s infiltration and hydraulic conductivity. The hydraulic conductivities in the sandy loam soil with 5 percent zeolite (A5) before and after irrigation with leachate were 3.17 m/day. Furthermore, zeolite had a decreasing effect on those processes. The results show that irrigation with leachate caused reduction of bulk density in two types of soil and all levels of zeolite.

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In recent years, use of carbon-based adsorbents has increased in pollution reduction from aqueous solutions. Biochar is a carbon-rich porous material, with low costs, and environmentally friendly, which is prepared by pyrolysis of biomass. In this study, potential of rice husk biochar to desalinate irrigation water with EC of 5, 15 and 25 dS/m was investigated. The effect of pyrolysis temperatures of 400 (RHB4), 600 (RHB6) and 800 (RHB8) on selected physicochemical characteristics and their desalination power was considered. The results showed that pyrolysis temperature has a significant effect on biochar properties. RHB6 with 301.1 mg g-1 desalination capacity was more efficient than the other biochars. This adsorbent had maximum surface area (211 m2 g-1) and total pore volume (0.114 cm3 g-1). The results of this study could open new horizons to manage the agricultural wastes and simultaneously reduce the cost of irrigation water.

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Side weir is the structure to evacuate extra water from a canal when level of water rises. This structure is mounted on the wall of canal. It is used predominantly to set flow in irrigation and drainage systems or urban wastewater harvesting systems. Implementing guide vanes is a simple way to increase side weir efficiency. In this study, the effect of using guide vanes on discharge and discharge coefficient of rectangular sharp-crested side weirs was investigated. ADV instrument was applied for recording vertical velocity over the crest of side weir. Local discharge was calculated by vertical velocity data for both conditions of presence and no presence of guide vanes. Results showed that in both cases, increasing the Froude number results in the decrease of passing discharge and discharge coefficient of the rectangular sharp-crested side weir. Data analysis also showed that by increasing the Froude number, guide vanes have more effect on increasing discharge coefficient and local discharge. The local discharge increased along the crest and the most passing local discharge occurred near the end of the side weir.  Analysis indicates that using guide vanes leads to the increase of discharge coefficient by about 32%.

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Due to the time and space changes of hydrological events in the arid and semi-arid regions, recharge measurement in these areas is very difficult. Hence, groundwater recharge is a complicated phenomenon for which there is not a fixed method to determine. The aim of this research was to develop a method for estimation of groundwater recharge based on a hybrid method. In this study, a hybrid method for calculating recharge was presented by combining empirical methods with a mathematical model, MODFLOW, and AHP analysis. The results showed that the most important parameters affecting groundwater recharge are soil properties, unsaturated thickness, land cover, land slope, irrigation and precipitation, from which the soil properties and precipitation are most important. The results showed that the overall impact of small changes in precipitation and temperature significantly affect the groundwater recharge, and heavy soils are much more sensitive to these changes than light soils. By changing 10% precipitation, the recharge rate is changed between 16% and 77% and by changing 1ºC temperature, the recharge rate is changed between 6% and 42%. Also, results showed that precipitation and evapotranspiration changes in four months including December, January, February and March had significant effects on annual recharge rate. Using the results of this research, the vulnerable areas of the plain, appropriate places and time for artificial recharge could be identified. Overall, the results of this study can be useful in various aspects of groundwater management.

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In addition to kinematic description of biological reaction, flow pattern plays an important role in designing constructed wetlands. This study investigates the effects of flow distribution on constructed sub-surface horizontal flow wetland with a length of 26 m, width of 4 m and 1% bed slope in order to understand internal hydraulic functioning patterns. Inlet configuration is selected as a variable parameter. Three different cases of inlet and outlet configurations were 1) midpoint, 2) corner, and 3) uniform. Outlet has been fixed in all configurations. Uranine tracer was used to determine the influences of flow distribution by drawing hydraulic retention time curve in different cases. Results showed that mean residence times for each configuration were equal to 4.53, 3.24 and 4.65 days, respectively.  Retention time distribution curve provided conditions, not only for showing dispersion patterns throughout system but also for interpreting hydraulic parameters like hydraulic efficiency and effective volume. According to the retention time curve, effective volume was 87.5% in configurations 1 and 3, and 62.1% in configuration 2 following numerous short-circuiting ratios. Finally, the best configuration of inlet-outlet layout to improve the performance of effluent treatment and use the geometry effectively was found to be the uniform-midpoint based on physical experiments followed by midpoint–midpoint as the second best.

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In this paper, the efficiency of four hybrid horizontal-vertical subsurface constructed wetlands which have been built for the tertiary treatment of Isfahan North Wastewater Treatment Facility and removal of organic matters was evaluated. In these constructed wetlands three plants including Phragmites australis, Typha latifolia and Arundo donax were planted and one unit left unplanted. The results of 12 months of sampling showed that the type of vegetation has no significant influence on the organic matter removal in the subsurface constructed wetlands, although the removal efficiencies in the planted constructed wetlands were more than unplanted control one. The COD and BOD₅ removal efficiency in the constructed wetlands changes between 77% to 83% and 84% to 86%, respectively, during the operation period. The results of this research also showed that the organic matter removal was dependent on the influent organics nature and biodegradability. The first order model constants were calibrated in different wetlands for designing main projects. The organic concentration in the wetland effluents met the Iranian regulation limits for different reuse applications that shows the constructed wetland is a suitable technology for wastewater treatment in Iran.

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Flood currents are considered threatening factors by creating local scour along bridge piers. One method for decreasing local scour is to strengthen the bed against imposed tensions. Among methods which can directly be appropriate in decreasing and controlling local scour of bridge piers is to employ geotextile around bridge piers. In the present study, the effect of geotextile layer in decreasing local scour of cylindrical single-pier was investigated with the purpose of proposing the best effective method of covering bridge pier. So, layers with circular and oval shapes were put around the pier, in proportion with pier diameter, and the performance of each was compared with the unprotected pier. Test results showed that with installing the oval geotextile layer, final scour depth around the pier reached to 1.25D. Also, comparing geotextile and collar with 2D diameter, the delay of scour process around geotextile was 40 times higher than the collar, but the collar decreased the ultimate scour depth further than geotextile.
 
 

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