Engineered log jams (ELJs) are used widely in practice as a river restoration measure. One desired feature of an ELJ is its porous nature, which plays an important role in hydrodynamics and sediment response. Currently there are very limited studies of porous hydraulic structures such as ELJs, and ELJs often are treated as solid obstructions for the purpose of flow and scour predictions. In this study, laboratory experiments were conducted to examine flow and bathymetric response near porous versus nonporous ELJ structures emplaced in an experimental flume. Time-averaged velocity, turbulent fluctuations, and the initial and final bathymetry were measured for four cases of porous and nonporous structures. Alterations in the flow field near the porous structure resulted in reduced maximum scour depths and lower total transport of bed material. It was found that existing predictive equations for scour geometry fail to match experimental data for the porous structures due to the lack of consideration of porosity’s role in altering the flow conditions. Conceptual models of the flow zones and the stages of erosion were presented and discussed. A simple predictive model for scour depth around ELJs was developed.

Results from laboratory experiments on conservative density current confluence are reported. Hydraulic characteristics and morphodynamic consequences of the confluence of two continuous release density currents in a horizontal, 45° asymmetrical junction are examined and compared to those of terrestrial subaerial river junctions. It was observed that density current confluence is markedly different than those in river junctions primarily due to the ease of the dense fluid to convect into the ambient fluid in the junction zone. Upward convection in the junction resulted in low horizontal velocity and shear stresses on the bed of the junction zone, followed by replunging to the layer of neutral buoyancy downstream of the junction where acceleration occurs. In the downstream reach was a distinctive erosional pattern similar to central scouring seen in river junctions but starting at the downstream junction point rather than at the upstream junction point. It was found that terrestrial river models match well with the density current case in terms of maximum velocity downstream of the junction, backwater effect, scour face protrusion into the downstream reach, and maximum scour orientation. Poor matching was found in terms of separation zone dimensions and shape, streamline deviation angle on the junction line, and maximum scour depth.

Alternative irrigation between saline water and groundwater can alleviate shortages of available agricultural water while effectively slowing the adverse effects of saline water on the soil-crop system when compared with continuous irrigation with saline water and blending irrigation between saline water and groundwater. In 2018, we tested the effect on soil CO₂ and N₂O emissions by two types of irrigation regimes (alternating groundwater and saline water (GW-SW), and alternating groundwater, followed by two cycles of saline water (GW-SW-SW)) between groundwater and three levels of salinity of irrigation water (mineralization of 2 g/L, 3.5 g/L, and 5 g/L), analyzed the correlation between gas emissions and soil properties, calculated comprehensive global warming potential (GWP), and investigated the maize yield. The results show that, with the same alternate irrigation regime, cumulative CO₂ emissions decreased with increasing irrigation water salinity, and cumulative N₂O emissions increased. Cumulative CO₂ emissions were higher in the GW-SW regime for the same irrigation water salinity, and cumulative N₂O emissions were higher in the GW-SW-SW regime. The GW-SW-SW regime had less comprehensive GWP and maize yield as compared to the GW-SW regime. The 2 g/L salinity in both regimes showed larger comprehensive GWP and maize yield. The 3.5 g/L salinity under the GW-SW regime will be the best choice while considering that the smaller comprehensive GWP and the larger maize yield are appropriate for agricultural implication. Fertilizer type and irrigation amount can be taken into consideration in future research direction.

Typical engineering design of rock weirs rely on simplified one-dimensional equations dependent on empirical coefficients. However, most simplified methods fail to accurately predict the hydraulics through rock weirs because they do not consider flow through interstitial spaces between rocks and the way interstitial flow alters the head-discharge relationship. To improve the design methodology and better capture the complex hydraulics past rock weirs, a three-dimensional high-resolution computational fluid dynamics model was utilized to study the problem. The simulation results demonstrate that the flow phenomena and head-discharge relationship are significantly different between broad-crested weirs and rock weirs. The interstitial spaces between rocks not only drain a portion of total discharge, but also accelerate the weir overflow. Based on the results, a flow decomposition approach is proposed to quantify the discharge through a rock weir. The decomposition includes contributing flows from (1) weir flow over the individual rocks, and (2) interstitial flow between rocks. Discharge coefficients for both contributing flows were found to be approximately linearly proportional to the porosity. The applicability of the proposed decomposition was demonstrated with an independent case. Despite the success, future improvement is needed with more rock weir variations.

For a channel with a constant discharge, the characteristics of the surge wave entering a junction are obtained from the classical Stoker solution, and then the effect of the junction is analysed by applying the momentum and mass conservation equations. Experimental cases involving different combinations of the tributary lake height and the main channel discharge were tested, and measurements show good agreement with the theoretical solution. The experiments showed that the initial lake height and initial velocity in the main channel influence the surge wave characteristics. The ratio between the Reynolds number in the lake and in the main channel can be used to predict time to peak and peak flow rate. Furthermore, power-law relations for surge wave height and velocity downstream of the junction were developed from the analytical solution.