Journal of Irrigation and Drainage Engineering

A reliable and continuous streamflow simulation capability is essential for systematic management of water resource systems. Thus, predicting streamflow is important for water management and flood control. This study evaluated the effectiveness of a few data-driven procedures, such as the least squares support vector machine (LS-SVM), M5P tree, and random forest (RF) algorithm for estimating streamflows of the Bernam and Tualang rivers of Malaysia. Three standard statistical measures, i.e., correlation coefficient (CE), root mean square error (RMSE), and mean absolute error (MAE), were used to evaluate the performance of the developed model. The performance of RF-based models was found to be higher than that of LS-SVM and M5P-based models with respect to predicting streamflow for both the rivers.

Submerged hydraulic jumps commonly occur downstream of irrigation structures. Submerged hydraulic jumps dissipate energy to some extent, and bed water jets can be employed as a means to increase their energy dissipation. In this study, submerged hydraulic jumps with and without bed water jets, with initial Froude numbers ranging between 2.2 and 6.06, were simulated using relative jet discharges ranging from 0% to 30% with respect to the main flow discharge. Computational fluid dynamics (CFD) modeling was applied to solve the equations for the conservation of the mass, momentum, and energy of the fluid flow. The volume of fluid (VOF) method was employed to compute the characteristics of the submerged jumps. In modeling the turbulence stresses, $k\text{-}\omega$ shear stress transport (SST) and Reynolds-averaged Navier-Stokes (RANS) equations were employed. The modeled velocity profiles agreed well with corresponding experimental measurements, proving the consistency of the computational results. Simulated results indicated that the bed water jets improved the efficiency of the submerged hydraulic jumps by up to 85.4% and reduced the submerged jump lengths by up to 59% compared to the nonjetted system.

Corrugated high density polyethylene pipes, where groundwater enters through perforations on the pipe wall, are widely used in subsurface drainage systems on agricultural lands. There has been a growing interest in using circular holes in the valleys of corrugated pipes to improve the hydraulic performance of subsurface drains. However, the effects of these circular perforations on the entrance resistance (${\alpha }_e$), delivery ratio ($Q/Q_0$), drain spacing, and water table drawdown have not been adequately investigated for corrugated pipes. This study uses a numerical model, calibrated with datasets from sand tank experiments, to simulate the effects of perforation shape, size, and configuration on ${\alpha }_e$ and $Q/Q_0$. The results show that $Q/Q_0$ in corrugated pipes with circular holes is 20% lower than that for plain wall pipes with the same perforation configuration. Perforations shaped as rectangular slots have half the ${\alpha }_e$ of circular holes with the same surface area. It is concluded that the use of rectangular slots is hydraulically more advantageous than circular holes in the valleys of corrugated pipes.

A water jet aeration method was used to address the problem of high water application rates for rotating impact sprinklers operating at low pressures at the distal end of the wetted radius that cause uneven water distribution. Based on a Jinlong Spray Irrigation Co. model PY20 impact sprinkler, a gas suction component was adopted to form an aeration impact sprinkler. The performance characteristics of the impact sprinkler with and without aeration were compared at operating pressure levels of 200 and 300 kPa. Additional tests on the water jet breakup characteristics of the two impact sprinkler types were conducted using high-speed photography techniques. The initial aeration lengths of the aeration impact sprinkler and two jet breakup lengths of both the aeration impact sprinkler and original impact sprinkler were studied. The experimental results demonstrated that the wetted radii of both impact sprinkler types were nearly the same at the same operating pressure and flow rate. The aeration method increased the water application rate at the midpoint of the wetted radius. At a lower operating pressure of 200 kPa, Christiansen’s uniformity coefficient increased to 68.5% for the aerated sprinkler and from 65.4% for the nonaerated impact sprinkler. The aeration impact sprinkler produced a larger average droplet diameter than that of the original impact sprinkler in the middle of the sprinkler profile, while the average droplet diameter toward the distal end of the profile was smaller. For the aeration impact sprinkler under operating pressure levels of 200 and 300 kPa, the aeration durations were 0.0137 and 0.007 s, and the initial aeration lengths were 7.7 and 8 mm, respectively. The jet breakup lengths were lower for the aeration impact sprinkler than for the original and increased with increasing operating pressure for both sprinkler types. The experimental results proved that the aeration impact sprinkler is not only feasible for agricultural irrigation, but it improves important performance characteristics at low operating pressures compared to a standard impact sprinkler.

The study evaluates the accuracy of measured and estimated crop evapotranspiration fluxes (${ET}_c$) on Citrus in a semiarid Mediterranean climate (Sicily, Italy). Specifically, ${ET}_c$ rates derived from in situ techniques [eddy covariance (EC) and sap flow heat pulse velocity (HPV)] and modelling approaches [Food and Agricultural Organization of the United States (FAO) Irrigation and Drainage Paper No. 56 (FAO-56) single and dual crop coefficient ($K_c$)] were compared under deficit irrigation scenarios. Results of the comparison showed that the single and dual $K_c$ approaches provided similar ${ET}_c$ estimates (292 and 324 mm), even if these approaches overestimated ${ET}_c$ measured by EC (${ET}_{EC}$) (17% and 30% respectively). HPV was able to show transpiration (T) reductions caused by deficit irrigation strategies when compared with T under full irrigation condition (ranging from 70% to 82%). Overall, the assessed methodologies were able to capture ${ET}_c$ trends, but the selection of the most appropriate one will depend on the specific crop and study site characteristics.

Recent advances in remote-sensing technology using multispectral images provide a powerful tool to estimate crop-water evapotranspiration (ET) at the watershed scale with large spatial and temporal precision. However, most current sensors onboard operational satellites that capture radiances from the thermal infrared (TIR) spectral region are still constrained by limited spatial resolution, which creates a potential error called the edge effect. This consists of information intrusion from surrounding areas that crosses the boundary of the region of interest due to coarse pixel resolution. To reduce this error, a buffer zone is defined as a fixed distance from the field boundary, and the information contained in this zone is excluded from the sample. This study evaluates the optimal buffer distance needed to minimize the bias associated with the aggregated edge effect in annual ET estimates when using Landsat-7 enhanced thematic mapper plus (ETM+) data. Theoretical and statistical analyses indicate that a buffer of 2-TIR pixel equivalent distance ensures that the remaining field area contain radiances free of edge effects with 98.4% confidence. However, the analysis shows that in a circular turfgrass field of 50.9 ha, this process would eliminate half of the area. The analysis using annual ET data shows that applying a buffer distance of 0.75 TIR pixel is sufficient to mitigate the cumulative edge effect while preserving field representative valuable data. Although this analysis was based on Landsat-7 ETM+ images, the results could also be applied to annual ET maps with different thermal infrared pixel sizes.

The hydraulic performance of triangular labyrinth weirs with an upstream pool was experimentally studied in both free and submerged flow conditions. The discharge coefficients based on channel width $B$ and the weir length $L$ were calculated from experimental data. It was found that the additional length provided by the pool can significantly increase the capacity of the new weir design. The tested weir models were found efficient and required less concrete in comparison with classical labyrinth weirs for a relatively low head water to weir height ratio of $h_o/P=0.17$. Empirical formulations were developed to predict the discharge coefficient and the critical depth of flow for labyrinth weirs with an upstream pool. The discharge reduction factor $\psi$ of the new weir design was found to be slightly lower than the $\psi$ value of sharp-crested weirs. Performance of the tested weir models in submerged flow condition was directly compared with the sharp-crested weirs. It was found that the submerged flow discharges of the tested weir models were significantly higher than the corresponding submerged flow discharge in sharp-crested weirs. A power law model was proposed to predict the submerged flow discharge from a given water head. The superior performance of labyrinth weirs with an upstream pool over classical labyrinth and sharp-crested weirs in both free and submerged flow conditions make them a suitable choice as a flow measuring device, depth regulator, and flood control structure.