Journal of Irrigation and Drainage Engineering

A calibrated flow rating equation is often used to determine the flow rate through a hydraulic structure as a convenient and relatively inexpensive method to avoid the difficulties of direct discharge measurements in an open channel. In South Florida, there are hundreds of gated culverts, where accurate and quick estimation of discharge in real time is critical for effective water resource management. Flow through culverts under various conditions and geometries has been studied extensively; however, studies of stage-discharge relationships through gate-controlled culverts are rare and, to the authors’ knowledge, not discussed in any open-channel hydraulics books, relevant journals, or design manuals. In this paper, two approaches to improve the stage-discharge relationships at gated culverts are presented, and case studies demonstrate their successful and cost-effective use: first, the application of computational fluid dynamics (CFD) for flow data simulation to supplement field measurements to resolve data limitations and, second, the application of dimensional analysis to improve gated-culvert rating equations. The proposed nondimensional flow rating approach is useful for data planning and consistency testing of hybrid data (field flow data and CFD results) and reduces the flow types occurring at a culvert, making the flow classification less complex while maintaining reasonable rating accuracy within 6% of field flow measurements.

Paddy fields play a critical role as storage for the retention of surface water in hydrological processes, but their water balance is complicated by irrigation and drainage management. Studies have proposed flow routing methods for paddy fields by simplifying the hydrological and hydraulic complexity associated with drainage processes. However, the performance of paddy field routing schemes has not yet been sufficiently evaluated to assist in the selection of routing methods for a water balance analysis. This study evaluated three common drainage routing schemes developed for paddy fields, including the simple water balance (SWB), linear reservoir with threshold (LRT), and broad-crested weir (BCW) models, in terms of complexity and performance. This study also compared the accuracy of irrigation water requirement and sediment load estimates simulated using the three schemes. Results showed that the BCW model produced the best statistical accuracy when predicting daily flow, but the three routing methods performed similarly over a 10-day time scale. Results suggested that the simple structure of the SWB model was not accurate enough to reproduce high and low flow on a daily scale, which produced relatively higher irrigation water requirements and sediment loads compared with those of LRT and BCW. LRT provided performance statistics similar to those of BCW using fewer calibration parameters. The comparison confirmed a trade-off relationship between model complexity and performance, highlighting the importance of model selection for hydrological analysis.

Water delivery scheduling was investigated in this study using fuzzy state, action, reward, state, action (SARSA) learning (FSL) and ant colony optimization (ACO) methods to find the advantages of a new robust model (FSL) over a conventional model (ACO) in both normal and emergency conditions. The mathematical models of these methods were developed. Three water shortages of 10%, 20%, and 30% were considered in the East Aghili canal, Iran, for the simulation process. Water depth and delivery indicators were used for evaluating the performance of the developed models. The results revealed that the FSL and ACO methods offered almost the same performance for the normal operation condition with high and acceptable indicators. However, the FSL method outperformed the ACO method in terms of performance in three considered emergency operations. It can be concluded that the FSL, as a new method, can schedule water delivery efficiently, adequately, equitably, and dependably. Furthermore, the FSL method is likely to lead to less maximum absolute error (MAE) and integral of absolute magnitude of Error (IAE) in comparison to the ACO method and is therefore recommended.

Low-head hydraulic structures, like weirs or barrages, are constructed on rivers for irrigation or power-generation purposes. As the upstream water level rises due to these structures, it is necessary to build an energy-dissipation structure such as a stilling basin downstream of the low-head hydraulic structures. The control of hydraulic jumps using abrupt bottom elevation changes at stilling basins may cause wave-type flows. In this study, wave-type flows at abrupt bottom rises and drops were investigated experimentally. For practical reasons, it is important to predict the local energy losses encountered at bottom changes for wave-type flows. Empirical equations for local energy losses and loss coefficients were obtained by evaluating the experimental results for various values of rise or drop heights, discharges, and tailwater depths. The local energy loss in wave-type flows was compared to that of a simple hydraulic jump. It is shown that for some cases local energy losses may become larger than the local energy loss in a simple hydraulic jump. Furthermore, it is difficult to predict the force on a step in the case of wave formation. In this study, a drag coefficient was obtained experimentally to compute the force acting on the step. The variation of this drag coefficient with relative step height is presented.

Weirs are structures that allow uppermost layers of liquids to flow by gravity downstream. They are, therefore, inherently gravity skimmers, and have successfully been used as skimmers in numerous applications, including oil-spill cleanup and various stormwater and wastewater treatment operations. This study examines the hydraulic skimming properties of sharp-crested weirs. The skimming properties of basic rectangular, triangular, and trapezoidal weirs are first characterized with a nondimensional skimming function. The triangular V-notch weir is shown to be a superior skimmer when compared to the other basic weirs. The V-notch weir has a maximum skimming rate $q_m^{\prime }=1.44$, occurring at an elevation $y_m^{\prime }=\frac{2}{3}$. Considerable enhancements of skimming properties are, however, achieved with higher order polynomial weirs. Polynomial weirs of order $n>1$ have maximum skimming rates $q_m^{\prime }>1.44$, occurring at desirable elevations $y_m^{\prime }>\frac{2}{3}$. The results of this work can be applied to design high performing sharp-crested skimmer weir outlets.

The apparent shear stress acting on the vertical interface between floodplain(s) and main channel has been shown to be very influential for the estimation of the zonal and overall discharge in compound channels. Experimental results of 21 test runs from different researchers and six datasets for natural river systems are considered in the present analysis wherein apparent shear stress has been empirically incorporated in the calculation of discharge. The range of datasets included different asymmetric channels, which have large variations in width ratios ($B/b$), aspect ratio ($b/h$), and bed slope ($S_o$), where $B$ is the total width of channel at bankfull, $b$ is the main channel width, and $h$ is the bankfull main channel height. In total, 201 data points considered cover small-scale channels to natural river systems, which lays a foundation for validation for seven apparent shear models given in the literature. The momentum exchange models used here are motivated by scaling arguments and allow a simple analytical solution for the zonal discharge in each section. However, it was found that the apparent shear models perform differently based on different depth ratios. None of the models performed well in channels with low depth ratio. Performance of the different models for apparent shear that are based on width ratio and slope were found to give diverse results, which is discussed in detail. Compared with the traditional divided channel method (DCM), this apparent shear-based method can better predict both overall and zonal discharge with a percentage error of only 8.9% for overall discharge.

This work experimentally investigated a modified venturi flume formed by placing portable cylinders vertically upright in trapezoidal channels, referred to herein as the cylindrical central baffle flume (CCBF). This mobile device causes flow constriction that creates a critical flow condition. Experiments were conducted in a specially fabricated experimental trapezoidal channel, having the facility to change the side slopes. The side slope of the channel was varied between 0.50 H:1 V and 2 H:1 V at an interval of 0.25 H. Experimental investigation of a mobile flume for such a wide range of side slopes has never been reported. Different variables describing the flow through this flume were selected, and a number of forms of equations relating stage with discharge were developed using Buckingham’s $\mathrm{\Pi }$ theorem and self-similarity hypothesis. The various forms of the stage–discharge equation were calibrated using the measurements made during the laboratory experiments. The stage–discharge equations were evaluated for fit by statistical measures, root mean square error (RMSE), relative mean error (RME), predicted residual error sum of squares (PRESS), and predicted ${\mathrm{R}}^2$. Based on the values of the statistical measures, two forms of stage–discharge equation were selected. The two selected forms were further compared for their performance, first by using additional experimental observations recorded for the same contraction ratio and then by using experimental observations collected for the changed flume dimensions. The performance of the selected forms of equation was also assessed by comparing them with a model available in the literature for a similar flume in a trapezoidal channel having a $1:1$ side slope. Based on the results of the comparison and distribution of errors, one of the two forms of stage–discharge equation that had a maximum relative error between predicted and measured discharge of less than 10% was proposed for flow measurement in such flumes under free flow conditions. The proposed mathematical model proves useful for its versatility, as it was developed and validated for a range of side slopes and contraction ratios, and is valid for a submergence ratio up to 62%. The proposed flume facilitates flow measurement at any desired location including small laterals or turnouts in agricultural settings or water treatment plants conveying water with trapezoidal channels. The flume is mobile, inexpensive, easy to install, and does not require high maintenance.

Accounting for variation in infiltration over space and time is essential in planning for land management. One such example is the consideration of sites for mitigation wetlands, where knowledge of the water cycle is essential to a determination of whether a site will have sufficient water to support wetland functioning. A methodology and an implementing script (GAINS) were developed using the Green–Ampt equation to calculate instantaneous and cumulative infiltration, moisture content, and excess water on the land surface. Results are available in tabular form, as well in GIS maps displaying the individual parameters at a site at any given point in time. GAINS, written in Python, was demonstrated for a site within Pershing State Park in Missouri, a location that traditionally has supported wetlands. Results showed that the Green–Ampt equation was correctly modeled. The successful demonstration is an important step toward providing a single tool to support decision-making regarding potential wetland mitigation sites.