Journal of Irrigation and Drainage Engineering

Stream deflectors are in-stream hydraulic structures that limit the flow channel width, thereby accelerating the flow through the constricted section. Single-wing and double-wing log deflectors are the two most commonly used types of in-stream eco-friendly structures. The purpose of this paper is to investigate the scour phenomena downstream of log deflectors in straight horizontal channels. The main goal is to obtain design equations to predict the main scour parameters and describe the scour morphology. All the experiments have been carried out in a horizontal channel and in clear water conditions. Log deflectors with different heights and angles were tested. Different hydraulic conditions including densimetric Froude numbers, water head drops, and tailwater values were studied. Results show that the tailwater depth and deflector angle are important variables to determine the scour parameters. Dimensional analysis leads to design equations to estimate the maximum scour depth, maximum length of the scour, and maximum height and length of the dune. Two types of scour morphology downstream of log deflectors have been defined.

This research seeks to address questions about the reduction in soil infiltration rates due to masking or embedding when a layer of open-graded aggregate is placed on top of soil. This is pertinent to the design and modeling of many low impact development (LID) technologies that incorporate infiltration such as porous pavements, infiltration trenches, and dry wells. A large permeameter was used to first measure the infiltration rate of five different soils and a No. 67 aggregate separately, and then measure the effective infiltration rate of the soils with an aggregate layer on top and with aggregate embedded in the top of the soil. The actual effective infiltration was then compared to the theoretical effective infiltration, assuming no masking or embedding effect. It was found that the measured infiltration rate was consistently lower than predicted, indicating a reduction in infiltration due to the presence of the aggregate layer. The average reductions were 29 and 43% for masking and embedding, respectively, which are consistent with computer modeling results from a previous study, but are significantly less than the reduction factors used in other porous pavement modeling applications. As such, existing modeling approaches for LID infiltration technologies may underpredict actual performance.

To maximize irrigation efficiency, applied water has to be precisely adjusted to the crop water use. This study develops a method based on the energy balance of a single apple leaf to calculate potential transpiration ($E_p$) for the whole apple tree. The $E_p$ model was based on two main submodels predicting canopy temperature ($T_c$) and total canopy conductance ($g_T$). The $g_T$ model was derived by simplifying the energy budget to rely on only climatic data and an empirical coefficient. These submodels were evaluated using the canopy temperature data collected in a Fuji apple orchard during the 2007, 2008, and 2013 growing seasons. The applicability of the $E_p$ model was examined on (1) well-watered, young Fuji apple trees, and (2) well-irrigated, older apple trees bearing little fruit. Predicted potential transpiration rates at both scenarios were compared with those predicted by the ASCE standardized Penman–Monteith values for alfalfa (${\mathrm{ET}}_r$). Daily average weather data collected during the three growing seasons provided the inputs to the $E_p$ model and its components. With the exception of air temperature measured in the orchard, the rest of the meteorological data were obtained from a local weather station. The canopy temperatures of the fully watered trees were predicted during midseason with mean absolute errors (MAEs) of about 0.41, 0.33, and 0.23°C in 2007, 2008, and 2013, respectively. These MAEs were better than the individual IRT accuracy of $\pm 0.6°\mathrm{C}$. The coefficient of variation (CV) of the predictions averaged 2% over the experiment $\mathrm{plots}/\mathrm{years}$, being better than that of the measurements ($\mathrm{CV}=4.8\%$) with the exception of one plot in 2007 with little difference (3% versus 2%). $E_p$ was fairly correlated with ${\mathrm{ET}}_r$ on warm and dry days ($R^2=0.58$, $p<0.001$) with slope and intercept values of close to 1.0 and 0.0, respectively. The model was able to reflect the high degree of coupling between the apple trees and the humidity of the surrounding air during cold and humid periods as $E_p$ resulted in significantly lower values. The overall results of the experiments with Fuji apple trees showed that the non-water-stressed baselines and potential transpiration of Fuji apple trees can be estimated using the proposed approach.

Steady-state water tables above parallel lines of cylindrical drains in an infinitely deep soil with uniform surface rainfall were modeled using a computer package that considers the flow in both the groundwater and unsaturated soil regions. The results were compared with analytical results obtained using a hodograph solution that considers only the groundwater region and assumes that the flux through the water table is equal to the surface input. Steady-state water tables above horizontal drains at the level of an impermeable floor were also modeled and compared with previous analytical results. Agreement of modeled and theoretical results was obtained in both drainage cases when the drainage was modeled for both sand and silty clay soils using a model for soil-water relationships that does not include an air-entry value in their soil-water characteristics. Water tables were lower than the analytical values when simulations were undertaken with sand and silty clay soils with characteristics described in a model that included air-entry values. Midway between drains they were higher than those obtained analytically for a completely tension-saturated soil above the water table, but in the vicinity of the drain lines they were slightly lower. The study shows that steady-state drainage theory accurately describes water table profiles in many soils while indicating the need for less intense drainage for soils that display tension-saturated capillary fringes. It gives confidence in the assumption of one-dimensional vertical flow in the unsaturated soil above the water table in the general consideration of groundwater flows.

Pre-rain-event soil moisture (preSM) plays a crucial role when evaluating runoff formation during heavy rainfall. Using sprinkling experiments and numerical modeling, this study investigates the impact of preSM on runoff formation at the small hillslope scale ($\le 100{\mathrm{m}}^2$). Sprinkling experiments were conducted on three sites in the Austrian Alps and observed hydrological behavior was simulated by using the hillslope model HILLFLOW. For each site, runoff was modeled with different preSM scenarios, covering the whole soil moisture range between permanent wilting point and saturation. Depending on the dominant runoff processes, the results showed impacts of preSM on both the maximum runoff and the total runoff. A predominant threshold was observed near field capacity (35 and 32% by volume). In general, the results clearly showed that the consideration of preSM is a prerequisite to reproduce runoff formation and total runoff amounts accurately. Field capacity turned out to be a good indicator (threshold) for surface runoff estimates.

Arch and elliptical pipes are commonly used as roadway culverts. The pipe section is composed of three radii, which result in complex equations to compute cross-sectional geometry and hydraulic parameters, such as normal and critical depths. Basic sizing charts do not allow direct calculation of hydraulic properties of these pipe sections. Therefore, general formulas were developed to compute hydraulic properties for any given arch pipe cross section. An Excel workbook capable of calculating normal and critical depths for given flow rates was created using the developed formulas and the solver function. Worksheets to compute geometric properties and water surface profiles using the direct-step method were also developed. These user-friendly worksheets are useful for hydraulic design and analysis of arch and elliptical culverts. A case study was conducted on several standard pipe geometries to demonstrate the comparative results from the developed workbook and existing sizing charts.