Journal of Irrigation and Drainage Engineering

Current stormwater control measure (SCM) design often does not include the dynamic process of evapotranspiration (ET) for vegetated systems. This study compared two reference ET equations with a three-year data set from rain garden weighing lysimeters. The outcome was a tool to incorporate ET into SCM design. The weighing lysimeters at Villanova University, located in southeastern Pennsylvania, were used to measure water budget parameters for three scenarios: sandy loam with UO, sand with an unconstricted outflow (UO), and sand with internal water storage (IWS). The two ET models explored were the ASCE Penman-Monteith equation (a robust model) and the Hargreaves equation (a simple model). Estimated ET values from these two equations, both with and without modifications for water availability and crop presence, were compared and calibrated (if modified) with observed data. Comparisons and calibrations were performed on a daily and storm basis to explore the applicability of the two ET models for continuous and storm approaches. The observed ET was 28%–52% of inflow over the continuous three-year period and 16–30 mm on a storm scale, making ET a significant part of the lysimeters’ water budget. Due to the experimental nature of the lysimeters, 12 of the 36 study months had additional simulated runoff, such that a smaller ET as a percentage of inflow was expected in the rain garden SCM’s water balance. The Hargreaves and ASCE Penman-Monteith equations without modification provided an adequate estimate for rain garden ET for all systems at the storm scale. Modifications to ET estimations produced by both equations through crop coefficients and a soil moisture extraction function provided a good model for storm-scale ET by reducing errors and increasing efficiencies for all weighing lysimeter types. Evapotranspiration estimates from both unmodified equations provided, at best, a marginally better estimate than the average observed rate for continuous daily rain garden ET. The application of crop coefficients and a soil moisture extraction function to both equations reduced errors in ET estimates and increased the equations’ predictive power (Nash-Sutcliffe efficiency) for all weighing lysimeter types. Both equations with modifications on a daily scale produced good ET estimates for the IWS system. For both equations, crop coefficients were found in an expected range for UO systems (0.3–1.5) but were high in the IWS system (1.6–2.0). Soil moisture extraction functions were not needed to calibrate the IWS equations on the storm scale. Both the Hargreaves equation and the ASCE Penman-Monteith equation provided an adequate model (especially with modifications) to incorporate ET into a design-storm approach to SCM design. Use of both predictive models on a daily scale has potential use in continuous simulation, as in most cases the ET estimations predicted by the equations provided a better estimate than the average of the observed daily ET rates.

Transfers of the right to use water can provide flexibility in regions where cities and farms compete for supplies. For example, the state of Colorado’s prior appropriation water law allows purchase and transfer of water among water users. During the last half century many cities have used this mechanism to buy water from agricultural water holders to satisfy their growing water demands. However, the transfer of water from rural to urban areas has left agricultural lands fallow and had negative effects on the economies and societies of rural communities. Colorado’s Water Plan addresses this problem by seeking alternative methods of transferring water so that the ownership of water rights stays in the agricultural sector but water saved on farms can be shared with urban areas. This paper reviews the alternative methods suggested in Colorado’s Water Plan, determines their capacities and shortcomings, and summarizes the efforts in the state to implement these methods. Lessons learned have important implications for improving the efficiency of water allocation in other dry regions.

Center pivots can be used to achieve variable-rate chemigation—applying spatially variable dosages of agricultural chemicals within the same field. This paper first presents equations specifying how a center pivot and the associated chemical injection pump can be operated to vary chemical dosages among sectors of a circle or among arc-shaped zones. This paper then introduces a software tool that facilitates computations for variable-rate chemigation. This paper finally documents two field tests of commercial, uncustomized variable rate chemigation systems. In the catch can test, mean absolute relative error in zone-average adjusted chemical dosage was 17%. In the flow-proportional chemical injection test, the system chemical concentration remained within 5% of the average value despite a fivefold range in water flow rates. With rising popularity of variable-rate application and increasing development of variable-rate chemigation equipment, the time is ripe for applied research and extension of variable-rate chemigation via center pivots.

Raised-bed plasticulture is used globally to produce fresh market vegetables, fruits, and other crops. A novel compact bed geometry, designed to improve the system efficiency of plasticulture, was evaluated for its ability to reduce water and other inputs and facilitate the adoption of precision irrigation using savings from reduced input costs. Using measurements and modeling (HYDRUS), precision soil moisture–based irrigation management (SM) and grower-based irrigation management (GR) were evaluated for conventional and compact beds. Similar to previous studies, SM reduced applied irrigation by 20% and deep percolation losses by 30% compared to GR for conventional beds. However, the significant investment needed to buy and maintain modern soil moisture measurement systems is likely to limit the adoption of SM. Compact bed geometries, taller and narrower than conventional beds, can sustain yields while reducing inputs of water, pesticide, fertilizer, fuel, and plastic. Cost savings of $\mathrm{\$}154–\mathrm{\$}789/\mathrm{ha}$ associated with the reduced inputs for compact beds can cover the cost of a soil-moisture sensor network with an automated irrigation system for a typical 65-ha fresh produce farm. Model simulations showed that compact beds with SM reduced irrigation volume by 8%–36% and deep percolation losses by 18%–54% compared to the traditional practice of conventional beds with GR. Compact beds with SM also reduced runoff volume by increasing evaporation by 15%–35%, available soil water storage by 12%–13%, and field infiltration of rainfall by 9%–18%. A basin-wide adoption of compact beds with precision irrigation can help reduce excessive downstream flows and nutrient loads in warmer and ecologically sensitive production regions such as the Everglades and the Chesapeake Bay.

This paper aims to solve an optimal irrigation water resources allocation problem applied to Alqueva River Basin irrigation system in Portugal. A multiobjective model was developed for this purpose in which the economic, social and environmental benefits are considered. This work makes use of a what-if analysis tool intended to help decision makers and stakeholders evaluate proposed sets of weights and intends to identify real and applicable water resources allocation plans for an irrigation system. The possible interaction with these actors in order to get more adequate results is an added value compared with the studied models. The results obtained based on an augmented weighted Chebyshev’s approach represent a commitment between the results achieved in each single-objective model, having two main solutions vectors: Solution 1 for a large variability of sets of weights, with higher representation; and Solution 2 for a specific set of weights. For a few sets of weights, there are several solutions with low representation. The 5 crops under analysis were distributed to the 18 counties and to three water sources according to the weight coefficients assigned to each objective function. The outcomes of the study are valuable for supporting the adjustment of the existing irrigation patterns and to identify a desired irrigation plan. If the decision maker considers that the crop area should be different, a constraint is introduced, gathering a different crop allocation.

For the hydraulic design of a stepped channel, it is crucial to estimate the limit of flow regimes. Step flow in the quasi-uniform region of a stepped channel is analyzed theoretically in this paper. The present work adopts a flow-regime criterion and some assumptions from a method from the literature, a specific energy equation is established, and a weak assumption from the literature is modified to determine the flow conditions in and out of the control volume (CV). A pragmatic method is therefore provided to predict the onset of skimming flow in the quasi-uniform region, and its accuracy is examined through comparison with data from two experimental tests and previous studies.

Accurate volumetric water delivery is key to fairly distributing water in pressurized systems. Discharge control valves facilitate water monitoring and management in pressurized networks. In this study, the application of a mechanical choked orifice plate (MCOP), also called a discharge control valve, is illustrated in pump discharge control. A MCOP includes a float-spring blockage system inserted into an ordinary orifice that maintains a quasiconstant flow by being insensitive to both upstream and downstream pressure fluctuations. The design principle of a MCOP is revisited in this study. A general discharge-differential pressure formula was developed for a cylindrical orifice configuration, based on which an initial design method was proposed to estimate the float shape line for the design discharges of 5 and $10\mathrm{l}/\mathrm{s}$. Then, MCOP performance was improved by adjusting the spring precompression. Experiments were performed to investigate the hydraulic behavior of a MCOP in a variable speed pumping system. The results indicate that the MCOP can adjust the operating point of the pumping system to keep an almost constant flow rate. Furthermore, the application of MCOP for regulating a single pump with constant rotational speed was studied. It is found that a MCOP is a useful tool to regulate the pump operating point at the highest efficiency even if the total head loss changes in the system.