Journal of Irrigation and Drainage Engineering

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

This study presents an explicit solution for the flow depth in open channels of trapezoidal cross-sectional area. Four depths are encountered in most classical open-channel hydraulics problems, namely normal depth, critical depth, alternate depths from the specific energy equation, and sequent depths from the specific force equation. The study proposes new equations derived from dimensional and regression analysis to estimate directly those flow depths. The novelty of this work lies in the proposed regression equations for the prediction of the alternate and sequent flow depths, which can be regarded as a new contribution to the literature of classical open-channel flow because currently only analytical solutions of very complex formulations exist for those depths. The range of used data makes the proposed regression equations applicable to laboratory flumes, irrigation channels, and large rivers as well. The equations are examined over a wide range of flow and geometric conditions, providing satisfactory predictions when compared to the exact solution obtained from the governing hydraulic equations. Maximum and average errors in the flow-depth predictions are under 6 and 2.5%, respectively, which are acceptable in most hydraulic engineering practice. The proposed equations are coupled with fixed-point iterative equations to provide more-accurate predictions of the flow depths when desired. A sensitivity analysis showed that 6% uncertainty in the estimates of hydraulic parameters such as channel longitudinal bed slope and Manning’s coefficient provides errors in the flow-depth prediction comparable to the errors encountered in the proposed regression equations. Thus, the accuracy of the proposed regression equations for the prediction of flow depths can be regarded as satisfactory considering the errors that come from other sources of uncertainty. The proposed equations are simple and would be useful in hydraulic engineering practice when quick and accurate estimates are needed for those depths. They can also be used to find the initial values for the flow depth to be utilized in the proposed fixed-point iterative equations or any other alternative numerical scheme if the exact solution is required.

The sequential irrigation scheduling problem is one where a set of irrigation jobs have to be scheduled sequentially. In this paper, an integer program is presented to solve this problem. The objective function is a dual-goal function that avoids night irrigation and minimizes earliness or tardiness, with the former objective taking priority over the latter. A scheduled start time cost function is introduced and is user defined to reflect the behavior and preferences (and aversions) of farmers. In this paper, the scheduled start time cost function is a piecewise linear function and uses techniques from operations research. It is linearized using the disjunctive method. The integer program is implemented in a general-purpose solver and applied to a 16-job problem to demonstrate that a schedule can be prepared that avoids night irrigation and minimizes earliness and tardiness. There is a trade-off between avoiding night irrigation and earliness and tardiness compared to earlier models that minimize only earliness and tardiness. However, the increase in earliness and tardiness for the example presented is modest.

In-stream grade-control hydraulic structures have been employed to reinstate riverbeds, to protect riverbanks, and to improve aquatic habitats. This paper aims to study scour phenomena and morphologies downstream of cross-vane structures installed in curved channels, and structure orientation with respect to the flow direction. Experiments have been conducted in clear-water conditions. The results showed the important effect of the channel curvature on the maximum scour depth value and position. Increasing of the bend radius leads to a decrease in the value of the maximum scour depth. The scour morphology has been classified in three types. Observations showed that the scour typology affects the maximum scour depth value. The variation of the structure orientations has been experimentally analyzed and results showed a significant effect on the maximum scour depth position.

The purpose of the present research, was evaluating the performance of HYDRUS-3D model for simulating soil moisture under field conditions for corn and durum wheat in a Mediterranean climate. Furthermore, the PILOTE model was also used for accounting root water extraction. Soil moisture at different depths was measured by a neutron probe before irrigation. Observed soil moisture values were compared with simulated data using statistical indices i.e., the root mean square error (RMSE) and the normalized root mean square error (NRMSE). The ranges of water content NRMSE were between 6.3 and 7.5%. The performance of the model based on calculated NRMSE values have been placed in the excellent category for simulation of the soil water content. Ranges of RMSE were obtained between 0.0174 and $0.0190{\mathrm{cm}}^3{\mathrm{cm}}^{-3}$, though the values are very low. The results of these two statistical indices indicated the high ability of the model in simulating soil water content.

Side orifices are used to divide and adjust flow into aeration ponds, sedimentation reservoirs, flocculation units, and other hydraulic and environmental areas. In this study, the discharge coefficients of side orifices are estimated using the adaptive neuro-fuzzy inference system (ANFIS) and a hybrid of ANFIS and a genetic algorithm (ANFIS-GA). The genetic algorithm is used to optimize the membership function of ANFIS. To predict the discharge coefficient, the ratio of the main channel width to the side orifice length ($B:L$), the ratio of the side orifice height to its length ($W:L$), the ratio of the flow depth in the main channel to the side orifice length ($Y_m:L$) and the Froude number ($\mathsf{F}$) are considered. Eleven different models are introduced for each of the ANFIS and ANFIS-GA models to calculate the discharge coefficient. The side orifice discharge is simulated using computational fluid dynamics (CFD). To model the flow field turbulence, the standard $\kappa \text{-}ϵ$ and renormalization-group (RNG) $\kappa \text{-}ϵ$ turbulence models are used. According to the CFD model results, the RNG $\kappa \text{-}ϵ$ turbulence model simulates the flow field turbulence with more accuracy. By analyzing the results of the ANFIS, ANFIS-GA and CFD models, the ANFIS-GA model is introduced as the best model in terms of $B:L$, $W:L$, $Y_m:L$, and $\mathsf{F}$.

The work presented here is an extension of previous papers that updated the calibration of round (Armco-type) meter gates (three sizes: 0.30, 0.46, and 0.61 m), developed ratings for rectangular gates (two sizes: 0.46 and 0.61 m) on round pipes, and examined errors and uncertainty related to using these devices for water discharge measurement. Previous works examined gate discharge ratings under low supply-channel flow velocity perpendicular to the gate discharge pipeline. Here, additional testing was conducted to test the hypothesis that higher velocities in the supply channel would show decreased meter gate flow compared to the low-velocity ratings, but that the published gate calibration method would still yield accurate flow-rate calculations. All testing was conducted in a test facility with the gate discharge pipe set perpendicular to the supply channel, as is common in field installations. Velocities up to $0.94\mathrm{m}/\mathrm{s}$ ($3.1\mathrm{ft}/\mathrm{s}$) were tested with the smaller gate and $0.66\mathrm{m}/\mathrm{s}$ ($2.2\mathrm{ft}/\mathrm{s}$) for all other gates. These velocities are on the upper end of velocities found in common earthen irrigation canals (and in many lined channels at the farm delivery level) in California. Interestingly, results indicate that the Froude number of the supply-channel flow did not have a statistically significant (at an $\alpha$-level of 0.01) influence on gate discharge coefficients. Discharge percent error and uncertainty were examined to compare the discharge coefficients presented in the literature to the discharge measured during the testing at different supply-channel velocities. Under recommended operating conditions, the uncertainty was within $\pm 5\%$ without adjustments for supply-channel velocity. This extended work supports earlier recommendations that meter gates can be an accurate flow measurement device for farm water delivery flow measurement if installed and operated correctly.

Labyrinth side weirs can be preferred for the weirs with same opening instead of the other conventional side weirs. However, the vortex occurring in the cycles of the labyrinth side weirs usually obstruct to overflow in the side weirs. In this study, in order to prevent vortices in the cycles, some antivortex elements were used in the cycles of two-cycle labyrinth side weir. In this respect, a series numerical simulation was performed by a computational fluid dynamics (CFD) software. The numerical findings of two-cycle labyrinth side weir with the antivortexes were compared to the one without antivortexes and some experimental observations. The results showed that use of antivortexes regulated the flow and clearly increased the efficiency of two-cycle labyrinth side weir.