JWSS - Journal of Water and Soil Science

In this research, by using FLOW3D, the performance of non-linear (arced) piano key (PKW-NL) in plan and linear piano key weir (PKW-L), with equal length of weir, was compared. Results showed that nonlinearity of the weir caused 20% increase in the discharge coefficient. Investigating the velocity contours for these two weir models also showed that maximum velocity within the PKW-NL weir structure is about 30% lower than the PKW-L weir. Also, the performance of non-linear piano key weir was evaluated under inward (PKW-IC) and outward (PKW-OC) curvatures to the channel. Results showed that in the case of PKW-IC weir, the discharge coefficient was increased by 8% as compared to the PKW-OC weir. Investigating the pressure contours for these two weir models also shows that the average pressure within the PKW-IC weir structure is about 5% higher than the PKW-OC weir. This increase in pressure leads to a decrease in the speed and better distribution of flow over the weir keys.

Today, the rising surface temperature of the planet and its effects on the water cycle have attracted the attention of many researchers. The aim of this study was to investigate the effect of climate change on the Tajan (the upstream of Shahid Rajaei dam) catchment area. In order to study the output of CanESM2 model, the SDSM method was used to estimate the magnitude of the data. Flow discharge changes in Shahid Rajaei Dam were simulated using the weather data of Kiasar synoptic station and the temperature and precipitation changes were simulated using the climate scenarios of RCP2.6 and RCP8.5 for the 2016-2066 period. Also, the effect of different scenarios on the outflow of the Soleiman Tangeh hydrometric station was evaluated by SWAT hydrologic model. The results showed that the annual precipitation would be decreased by 58% and the air temperature would be increased by 14% under RCP2.6 scenario. Also, in the RCP8.5 scenario, precipitation would be decreased by 59.5% and the temperature would be increased by 21%. Peak discharge for RCP2.6 and RCP8.5 scenarios would be increased by 4% and 5.7%, respectively, and the average annual discharge might be decreased by 16% and 16.5% in the future period (2016-2066). Therefore, it can be planned by the investigation of conditions for cropping patterns in the downstream to consider the environmental impacts for future periods.

The flow fields over a trapezoidal labyrinth weir (two-cycle) and a piano key weir were simulated using Flow3D, studying the impact of each model on the flow field in the weirs and the coefficient of discharge in comparison with the available experimental data. Moreover, the models were investigated experimentally in a 12.5 m long, 0.3 m wide, and 0.4 m high rectangular flume under clear-water conditions. The results showed good agreement between the data from the numerical and experimental models. The piano key weirs had a higher coefficient of discharged compared with labyrinth weirs. The coefficient of discharge was observed to increase by 26 percent as the height of the PKW was increased by 50 percent (from 5 to 7.5 cm). This increase was 24 percent for labyrinth weirs.

Few studies have been done regarding the role of the raindrop in the hydrodinamic mechanism of soil erosion. In this study, rainfall simulation experiments were conducted to evaluate the role of raindrop in runoff discharge, sediment concentration and hydraulic properties of flow under four slope gradients (5, 10, 15 and 20%) in a clay soil using a 90 mm.h^-1 rainfall intensity to reach the steady state flow. Soil sample was packed into the erosion flume with 0.3m× 0.4m × 4 m in dimensions and tested under two soil surface conditions:  one with raindrop impact and one without raindrop impact. The results showed that runoff discharge, sediment concentration, flow depth, shear stress, stream power, Reynolds number and runoff velocity under without raindrop impact condition were significantly lower than those in the condition  with the raindrop impact with a factor of 0.62 to 3.54, 0.08 to 11.83, 0.91 to 0.96, 0.26 to 3.25, 0.52 to 4.45, and 0.36 to 3.27, 0.23 to 0.79 times, respectively; on the other hand, the Darcy Wysbach, Chezy and Manning coefficients were increased significantly under without raindrop impact (P<0.01). Flow velocity was the key hydraulic parameter strongly affecting the hydraulic properties. These findings indicated the importance of raindrop impact in the detachment rate of soil particles through the change of the hydraulic characteristics. This study also revealed the key role of raindrop impact on the runoff hydraulic characteristics, as well as particle detachments rate in rills. Information about the role of raindrop impact is a substantial step in modeling the rill erosion. Therefore, elimination of raindrops impact, especially in the steep slopes, with the conservation of natural vegetation cover can sufficiently prevent runoff production as well as the particle detachment rate.

Water supply at a desired rate at any time to meet the water requirements regardless of river discharge must be considered in the general design of intakes provided that the needs do not exceed the river flow. Due to the lack of necessary information in this field and the importance of sediment transport to the lateral intakes at river bends, this study aimed at understanding the mechanism of this phenomenon. To this end, the combined effect of convergence and divergence in lateral intakes on the sediment transport was investigated. According to the results, the diversion discharge to the intake was increased by converging the laboratory flume. By narrowing and converging the end of the flume, the diversion discharge was increased further, so that as the flume was converged to the size (b/B) of 0.75 and 0.5, the diversion discharge to the intake was increased by 13.6% and 75%, respectively. This could be connected to narrowing, flow obstruction and backflow to the intake. In contrast, different results were found by diverging the flume. In other words, the inflow to the intake was decreased by diverging the flume. As the flume end was diverged, the diversion discharge was decreased further. By diverging the flume to the size (b/B) of 0.75 and 0.5, the diversion discharge to the intake was decreased by 21.9 and 31.8%, respectively. The average diversion discharge to the intake at 30, 60 and 90º was 13.2, 15.2 and 11.5%, respectively. By converting the flume to the size (b/B) of 0.75 and 0.5, the diversion sediment to the intake was increased by 18.5 and 71.4%. In contrast, by diverging the flume to the size (b/B) of 0.75 and 0.5, the diversion sediment to the intake was decreased by 35.4 and 49.9%, respectively.

Due to the increasing number of small crops, the system of irrigation without a pump can be an economical way. Therefore, in this research, the effects of the type of droplet and the height of water supply system utilization on the characteristics of water distribution (discharge, dispersion uniformity coefficient (CU) and coefficients of variation of discharge) were investigated. In this research, the pressure functions of 1, 2, 3 and 4 meters and three irrigation repeats were investigated; also, the discharge characteristics of jet pots of 2 and 8 nozzles, easy dripper and netafim were addressed. The results indicated that at 1 m pressure, drippers of pots of 2 and 8 nozzles with the uniformity coefficients of distribution were equal to 89.39 and 99.30%, and the discharge rate was 3.60 and 3.62 liters per hour at a pressure of 2 m. An easy-drain drip with a discharge rate of 3.85 L / h and a uniform distribution of 99.44%, at a height of 3 and 4 m, the droplets of the netafim with an outlet discharge were 3.87 and 3.97 liters per hour and the uniformity coefficients of 99.32 and 99.47 percent had the best broadcast conditions. According to these significant differences (P <0.05), it can be concluded that at pressures less than 2 m of jar droplets and at more than 3 m, netafim and Easy Dipper types could  have better leakage due to pressure regulators. In general, each of the four types of emitters produced a uniform dispersion and the optimum discharge at different pressures.

In this study, the discharge coefficient of sharp-crested weirs located on circular channels was modeled using the ANFIS and ANFIS-Firefly (ANFIS-FA) algorithm. Also, the Monte Carlo simulations (MCs) were used to enhance the compatibilities of the soft computing models. However, the k-fold cross validation method (k=5) was used to validate the numerical models. According to the input parameters, four models of ANFIS and ANFIS-FA were introduced. Analyzing the numerical results showed that the superior model simulated the discharge coefficient as a function of the Froude number (Fr) and the ratio of flow depth over weir crest to the weir crest height) h/P(. The values of the mean absolute relative error (MARE), root mean square error (RMSE) and correlation coefficient (R) for the superior model were calculated 0.001, 0.002 and 0.999, respectively. However, the maximum error value for this study was less than 2%. 

The scour around the bridge piers is one of the main causes of bridge failure and the extraction of aggregates may aggravate this phenomenon. The present study comprehensively investigated the scour around the groups of bridge piers in the presence of aggregate extraction pits, using different discharges. The bridge piers roughened by gravel had been compared with the simple bridge piers; so, the results showed that the roughening caused the reduction of the scour depth. Scour depth change rate led to an increase in the equilibrium time. The results also showed that the reduction of the scour depth at the downstream groups of piers was more than that in the upstream. For the lowest discharge, the aggregate extraction pits had a considerable effect on the scour depth difference for the groups of piers in the downstream and upstream. On the other hand, the effects were decreased when the rate of discharge was increased. The experimental results obtained by the rough surface models showed that as the discharge was increased, the local scour was increased too; at the same time, the bed profile was posed at the low level. Generally, the scour depth of the groups of piers in the downstream of the extraction pit was more than that in the upstream. The results of the current research, therefore, demonstrated that the surface of the bridge pier roughened by gravel reduced the scour depth.

Nowadays, the prediction of river discharge is one of the important issues in hydrology and water resources; the results of daily river discharge pattern could be used in the management of water resources and hydraulic structures and flood prediction. In this research, Gene Expression Programming (GEP), parametric Linear Regression (LR), parametric Nonlinear Regression (NLR) and non-parametric K- Nearest Neighbor (K-NN) were used to predict the average daily discharge of Karun River in Mollasani hydrometric station for the statistical period of 1967-2017. Different combinations of the recorded data were used as the input pattern to predict the mean daily river discharge. The obtained esults  indicated that GEP, with R²= 0.827, RMSE= 59.45 and MAE= 26.64, had a  better performance, as compared to LR, NLR and K-NN methods, at the  validation stage for daily Karun River discharge prediction with 5-day lag, at the Mollasani station. Also, the performance of the models in the maximum discharge prediction showed that all models underestimated the flow discharge in most cases. 

The combination of a labyrinth weir with an orifice is a proper solution for floating material to pass over the weir and transfer sediment through the orifice. Additionally, creating a slot in the overflow wing leads to higher discharge. This study examined four discharges (5, 10, 15, and 20 liters per second) with channel width and height of 30 and 40 cm in trapezoidal-orifice, square-orifice, and triangular-orifice labyrinth weirs in the laboratory and using Flow3D with RNG k-epsilon (k-ε) turbulence model, the results were compared with one another. Comparing the discharge flow over weirs and measuring the discharge coefficient among the mentioned models showed that the triangular-orifice labyrinth weir had the highest discharge rate. Moreover, the increased Ht/P ratio (Ht represents total hydraulic head; P denotes weir height) for all models resulted in the increased discharge coefficient. Due to the efficiency of this type of weirs, the highest discharge coefficient was obtained at low Ht/P ratios. At lower ratios, since there was free flow, the coefficient of weir discharge increased, and as the ratio increased, the weir was partially submerged. Furthermore, for the weir design, the best Ht/P ratio was between 0.13 to 0.41, and the maximum discharge coefficient (Cd = 1.2) was within this range.

One of the crucial problems that exist in the irrigation networks is the fluctuation of the water surface flow in the main channel and changes in the flow rate of the intake structure. One of the effective methods to decrease these fluctuations is increasing the weir crest length at the given width of the channel with the use of the labyrinth weirs can be achieved for this purpose. The labyrinth weir is the same linear weir that is seen as broken in the plan view. In this study, a labyrinth weir with a length of 3.72 m, three different heights of 15, 17, and 20 cm, three different shapes of dentate (rectangular, triangular, and trapezoidal), and a linear weir were used in a recirculating flume with 15 m length and 1 m width. The result showed that for a given length and height of weir, with the increasing of the upstream water head to the weir height ratio (), the discharge coefficient decreases. The results showed that by increasing weir height, the discharge coefficient decreases for a given length of the weir. Linear weir and labyrinth weir without dentate create more water depth at the upstream by 3.3 and 1.2 fold compared with dentate labyrinth weir.

A compound sharp-crested weir is often used to measure a wide range of flows with appropriate accuracy in open channels. In this study, experiments were performed to investigate the hydraulic flow through a compound weir of circular-rectangular with changes in hydraulic and geometric parameters in free and submerged flow conditions. The characteristics of the weirs include rectangular spans width of 39 cm, a circular radius of 5, 7.5, and 12.5 cm, and heights of 10 and 15 cm. The results showed that by increasing the radius and height of the Weir, upstream water depth increases around 28.4%. At a constant h/p, the discharge coefficient increases with the increasing radius of the circular arc. Also, in the submerged conditions, the discharge coefficient is less (around 40%) than in the free flow condition, which is due to the resistance of the depth of the created stream against the passage of the flow.