Journal of Irrigation and Drainage Engineering

Flow field characterization in high-aerated flows often involves flow imaging techniques through transparent sidewalls, and the results may be subject to sidewall effects and thus differ from the central flow behaviors. This paper contributes an experimental investigation of the sidewall effects on the air-water flow distributions in quasi-two-dimensional hydraulic jumps in a rectangular flume. The tested hydraulic jumps are characterized by preaerated approach flows and large inflow Froude numbers from 10.6 to 15.1. The air-water flow properties are measured intrusively along the centerline, sidewall, and transverse cross sections to provide a three-dimensional view of the aerated flow structure. Substantial redistribution of the bubbly flow is observed due to the presence of lateral aeration boundary layers in the high-speed jet-shear region, compared to the less affected free-surface roller. The magnitude difference between the central and lateral air-water flow properties is more distinct in terms of bubble count rate and less evident for void fraction and interfacial velocity, while the affected area is broader for void fraction distributions. The results suggest a concentration of high-speed jet flow in the central bottom flow column, where the jet layer is thicker, the recirculation roller is smaller, and the proportion of small-size bubbles is higher. The width of the central flow region free of the sidewall effects is approximately 60% to 80% of the flume width in the present facility, narrower on the bottom, and broader at the free surface. The findings demonstrate that the transverse variation of air-water flow and the difference between the central and lateral flow fields should not be ignored for the high-speed flow regions of hydraulic jump. A correct assessment of the sidewall effects is essential for interpreting imaging-based measurement of highly-aerated flow.

Abstract

Understanding the hydrochemical composition of water resources in the Ngorongoro Conservation Area (NCA, Dodoma, Tanzania) related to climate variability is essential for sustainable development. Thus, the current study used the HYDRUS-1D model to assess the groundwater quality change due to the leaching of hydrochemicals from surface water under the climate variability of the NCA. This study observed that the area’s surface water had varying hydrochemical contaminants, whereas the groundwater is currently most suitable for drinking and domestic purposes. However, it is predicted that two anions (${\mathrm{Cl}}^{-1}$ and $\mathrm{PO}{4}^{-3}$) and two cations (${\mathrm{Na}}^{+}$ and ${\mathrm{K}}^{+}$) are expected to exceed the permissible limits from 2036 to 2050, considering the anticipated climatic conditions. Changes in groundwater quality for cations and anions are significantly correlated to evapotranspiration and temperature, with Pearson’s coefficient of determinations $r$ between 0.35 and 0.66. The findings of this study are necessary to benchmark better water resources management planning.

Abstract

Understanding the hydrochemical composition of water resources in the Ngorongoro Conservation Area (NCA, Dodoma, Tanzania) related to climate variability is essential for sustainable development. Thus, the current study used the HYDRUS-1D model to assess the groundwater quality change due to the leaching of hydrochemicals from surface water under the climate variability of the NCA. The hydrochemical assessment results for the composition of major cations and anions to the subsurface indicate the significant influence of future changes in the climate of the study area. The results indicate, two cations (${\mathrm{Na}}^{+}$ and ${\mathrm{K}}^{+}$) and two anions (${\mathrm{Cl}}^{-1}$ and ${\mathrm{PO}}_4^{-}$) would exceed the World Health Organization (WHO) and Tanzania Bureau of Standards (TBS) permissible limits between 2036 and 2050. Statistically, changes in groundwater quality for both cations and anions are significantly correlated with evapotranspiration and temperature. Therefore, apart from other factors such as volcanic activities and accelerated human interventions that could affect water quality, climate change can be considered the main driver for hydrochemical movements to the groundwater. Hence, a detailed climate change study should be conducted to precisely inform the impacts of future changes in climate parameters on water quality deterioration. The findings from such studies can be used for sustainable management of the water resources in this area.

In river engineering, scouring around hydraulic structures constructed on erodible beds is highly attractive because of its impact on the stability of these structures. Accordingly, various researchers have always been looking for approaches to control or reduce the harmful consequences of this phenomenon in terms of both economic and environmental points of view. In this study, the application of geonets is introduced as a new approach to reduce local scour downstream of a sluice gate with a rigid apron. For this purpose, a geonet was installed in a specified depth under an erodible bed downstream of a sluice gate to prevent the development of scour hole. The experiments were performed on two different Froude numbers, three grain size distributions of noncohesive sediments, three types of geonets, and three different geonet installation depths. First, a number of tests were performed without a geonet (control experiment); then the other tests were conducted to investigate the effect of geonets on scour hole dimensions. The results showed that if the geonet installation depth is lower than the maximum equilibrium scour depth in the control experiment, the maximum equilibrium scour depth and the scour hole volume decreased and the scour hole length increased. In the following, to estimate the maximum equilibrium scour depth in the presence of a geonet, a relationship was developed for practical applications. In addition, using sensitivity analysis on the developed relationships, the effect of various parameters on the changes in maximum equilibrium scour depth in the presence of a geonet was evaluated.

One of the significant hydrological processes affecting the sustainability of river engineering is sedimentation. Sedimentation has a major impact on reservoir and dam operations. This study conducted an experiment using a rainfall simulator with varying intensity of rainfall ($1–3\mathrm{L}/\min$) with slopes from 0° to 5°, leading to the generation of runoff and sediment loads (SLs). Precipitation and runoff data from the rainfall simulator were used to develop a sediment load model via hybrid machine learning approaches. Predictive abilities of a robust phase space reconstruction integrated with support vector machine and firefly algorithm (PSR-SVM-FFA) were investigated for estimating sediment load. The accuracy of the PSR-SVM-FFA was assessed versus that of integrated support vector machine and firefly algorithm (SVM-FFA) and conventional support vector machine (SVM) models. In phase space reconstruction (PSR), the delay time constant and embedding dimension were determined to select optimal parameters in the SVM-FFA model. Four performance measures, namely RMS error (RMSE), mean absolute percentage error (MAPE), Willmott index (WI), and bias, were employed to evaluate the performance of the proposed models. The results revealed that prominent values of WI were 0.942, 0.955, and 0.966 for the SVM, SVM-FFA, and PSR-SVM-FFA methods, respectively, for a slope of 4°. PSR-SVM-FFA had better performance than SVM-FFA and conventional SVM for each slope. Based on analysis of the obtained results, it is evident that PSR-SVM-FFA can estimate SL more accurately.

Foodborne outbreaks have been associated with the use of irrigation water contaminated with human and animal wastes. The use of subsurface drip irrigation may reduce the contamination of leafy green produce. The goal of this study was to quantitatively assess the impact of a subsurface irrigation system on the contamination of romaine lettuce contaminated with a fecal bacterium and a virus. Plants were transplanted and grown in bottom watering pots. They were irrigated with contaminated water containing Escherichia coli and MS2 bacterial virus. The HYDRUS 2D/3D program was used to model the water movement in the soil to ensure that the soil surface did not become wet and consequently contaminated. Neither E. coli nor MS2 were detected on the surface or internally on/in romaine lettuce. The results demonstrated that subsurface irrigation may successfully reduce the risk of contamination by bacterial and viral pathogens so long as the contaminated irrigation water does not reach the soil surface and thereby come in direct contact with the aboveground portions of the plant.

Laboratory experiments were conducted on a radial gate to evaluate the energy equation for free-flow calibration. The experiments were used to develop new equations for the radial gate contraction coefficient for free flow. These were compared to equations for the contraction coefficient of radial and vertical sluice gates developed from prior studies and potential flow theory. The new radial gate free-flow contraction coefficient was related to both the gate lip angle and the gate opening relative to the energy head on the gate. The pressure distribution and velocity distribution coefficients were also evaluated. The energy loss through the gate was expressed as a function of the velocity head in the vena contracta, with a gate energy loss coefficient that varies with the relative gate opening. With the revised energy equations, the free-flow discharge predictions were computed for three data sets: (1) experiments presented here conducted at the USWCL laboratory in 2004–2005, (2) experiments performed by Jan Tel in 2000 and earlier using the same USWCL facility operated over a narrower range of conditions, and (3) experiments performed in the early 1980s by Clark Buyalski in the Bureau of Reclamation’s hydraulics laboratory. The coefficients were developed based on the later USWCL data only. The average discharge computation error for the combined data sets was 0.37%, and the standard deviation was 1.03%. Submerged flow predictions are the subject of future work.

The effects of geometrical parameters (crest height, number of cycles, and plan weir configuration), are investigated experimentally on labyrinth weirs, over a range of headwater ratios of 0.1 to 0.6. Trapezoidal and triangular weirs have a constant angle $\alpha =15°$, whereas rectangular weirs have the same footprint size $B$ as the trapezoidal configuration. Data uncertainties are quantified at a relatively small overall average of 1.88%. For taller labyrinth weirs, current experimental models achieve lower discharge coefficients when all other geometrical parameters are kept the same. Increasing the number of cycles also leads to a reduction in flow rate and discharge coefficient. These hydraulic performance reductions were most significant for trapezoidal followed by rectangular and triangular configurations. For the same geometrical conditions, a rectangular configuration had a higher flow rate for each head, followed by trapezoidal and then triangular. Nappe behaviors were significantly different between the configurations, whereas modifying the geometrical ratios had less significant effects on the flow characteristics of each configuration.