Journal of Irrigation and Drainage Engineering

In this study, remote sensing technology and crop production functions were used to compare the theoretical crop coefficient ($K_c$) and the theoretically optimal or potential crop evapotranspiration (ET) with actual ET for 751 alfalfa fields in the Lower Rio Grande Valley, New Mexico. Results of the remote sensing showed that, although potential alfalfa water use for the year 2008 was 1,451 mm, actual water use at the field level ranged from 386 to 1,241 mm with an average ET of 901 mm for the growing season. Average ET was also calculated using the average yield and published crop production functions. The average ET estimated from average yield using two different crop production functions was between 975–979 mm. Reasons for field-level ET and crop coefficient variability include current irrigation methods and technology, lack of knowledge of irrigation scheduling, limited water supply, interference of harvesting schedule with the irrigation, cultural practices, and economic factors. The results of the study have implications on water rights adjudication and economic return from alfalfa production. The results also reflect the potential for improvement in agricultural productivity and economic return by changing irrigation techniques and agronomic practices.

The Hargreaves equation (HE) is the most reliable and diffused temperature-based method for the estimate of the reference crop evapotranspiration ${\mathrm{ET}}_o$ in areas with limited meteorological data. Several studies proposed its further enhancement by adopting correction equations for recalibrating its parameters, specifically the empirical Hargreaves coefficient, $C=0.0023$. In this paper, a local recalibration for southern Italy is shown, taking as a reference the Food and Agriculture Organization of the United Nations (FAO) Penman-Monteith (PM) equation applied over 137 (34 coastal and 103 inland) meteorological stations, allowing the estimation of 357,920 daily ${\mathrm{ET}}_o$ values in the period 1994–2011. Through a regression analysis, the adjusted Hargreaves coefficients (AHC), minimizing the errors for each individual station between the HE and the FAO Penman-Monteith equation, and providing better performances than the original HE applied at the monthly scale, were correlated to the available daily meteorological data; reliable regionalization equations of the AHCs were found determined by either the average daily temperature range $\overline{\mathrm{\Delta }T}$ or the ratio between the average daily temperature $\overline{T}$ and $\overline{\mathrm{\Delta }T}$, with similar coefficients to analogous relationships proposed in the literature. Specifically, the $\overline{\mathrm{\Delta }T}$ dependent model proved to be very reliable over the whole study area for all climate types, from the shore up to 1,928 m. The improvement in the performances of the regional model with respect to the original HE was on average 22%, and it also proved able to simulate the yearly cumulative ${\mathrm{ET}}_o$ evolution in several meteorological stations. The strength of the model was positively tested through a jackknife resampling procedure and a sensitivity analysis, taking into account possible trends for the average daily temperature range.

A method is presented for the hydraulic design and analysis of labyrinth weirs based upon the experimental results of physical modeling. Discharge coefficient data for labyrinth weirs with quarter-round and half-round crest shapes are presented for sidewall angles ranging from 6 to 35°. Cycle efficiency is also introduced as a design aid, which compares the hydraulic performance of different cycle geometries. Geometric parameters that affect flow performance are discussed. The predictive accuracy of the design method is evaluated through comparisons to previously published labyrinth weir head-discharge data. The companion paper examines nappe behaviors that affect flow performance and presents hydraulic design considerations specific to nappe characteristics.

Nappe behavior should be considered in the design of labyrinth weirs to ensure hydraulic optimization and to account for potential vibrations, pressure fluctuations, noise, and flow surging. Information regarding nappe aeration conditions (clinging, aerated, partially aerated, and drowned), nappe instability, and nappe vibrations for trapezoidal labyrinth weirs on a horizontal apron with quarter- and half-round crests ($6°\le \text{sidewall}\text{angle}\le 35°$) is presented. Corresponding headwater ratio ranges and hydraulic behaviors associated with nappe aeration conditions are documented and discussed to aid in labyrinth weirs design, including design options directly related to nappe behavior (e.g., crest shape, crest roughness, vents, nappe breakers, notches, and staged cycles). The effects of artificial nappe aeration (a vented nappe) on nappe behavior and discharge capacity are also discussed, including recommended placements of nappe breakers.

Calibration of gates under free-flow and submerged-flow regimes is a classical hydraulic problem. In this paper, dimensional analysis was applied to investigate both free- and submerged-flow conditions through a radial gate. The original Ferro’s method for submerged flow regime was modified by introducing the maximum allowable tailwater depth permitting free flow. Based on the Buckingham theorem and applying the incomplete self similarity (ISS) concept, different forms of the dimensional equations were proposed. According to the current available experimental data, the most accurate dimensionless formula was proposed. The proposed dimensional equation not only is more accurate than the original Ferro’s method but can also be applied for free- to submerged-flow conditions continuously and through the transition zone. Finally, a new discharge reduction function (DRF), which is applicable for other water measuring structures and gates working under submerged flow condition, was identified.

The modified Kovács (MK) model is a versatile and practical tool to estimate the water retention curve (WRC) of soils from their basic properties. However, the MK model has not yet been introduced in many codes or analytical solutions; most applications rather use the Brooks and Corey (BC) and/or van Genuchten (vG) formulations to express the WRC. The authors propose in this paper a direct conversion of the MK model parameters to the BC and vG equations parameters for sandy and silty materials. The proposed equations were developed using data from 15 types of sandy soils and 14 low-plasticity silts and validated using 16 other soils. The results presented in this paper indicate how the BC and vG equations parameters can be successfully predicted from the MK model parameters. The conversion procedure provides a practical means to estimate the WRC from the basic geotechnical properties of soils and to express this curve using three different mathematical formulations: MK, vG, and BC. These expressions allow obtaining a rapid estimation of the BC and vG model parameters that are frequently used in analytical solutions and commercial numerical codes to simulate unsaturated soil water flow.

Although polyacrylamide (PAM) use for reducing soil erosion and increasing water retention is common in agriculture, research suggests PAM application may also be effective in reducing seepage in unlined irrigation canals. A polymer application test was conducted on a 457-m-long section of the Bordeaux lateral canal near Wheatland, Wyoming. Flow rating curves were developed by combining discharge and water level data, and the curves were used to convert real-time water level data into real-time discharge data. Falling head permeameters (FHP) provided a spatial method of quantifying seepage. Real-time stage discharge data showed a mean pretreatment flow loss over the entire test reach of $25.5–26.6\mathrm{L}/\mathrm{s}$, whereas the mean posttreatment loss was $30.9–31.2\mathrm{L}/\mathrm{s}$ ($\alpha =0.05$), which corresponds to a 21% increase in seepage. The FHP tests also showed an increase in seepage as a result of PAM treatment. On the basis of the results of this study, it appears that PAM and suspended sediment concentrations were too low during the test to cause significant seepage reduction.

Irrigation districts in the American West and throughout the world have extensive canal networks that could be utilized to generate a significant amount of hydropower. As the world attempts to become less dependent on carbon-based energy resources, small-scale hydropower (SSH) is an attractive potential resource for new energy development. The Middle Rio Grande Conservancy District (MRGCD) in central New Mexico has an extensive canal network, and hydropower is being considered as a viable form of renewable energy. Currently, the MRGCD has identified and categorized nine potential hydropower sites within its system with the goal of maximizing its contribution to the region’s energy needs. This paper addresses key issues related to hydropower in irrigation districts and examines the feasibility of incorporating hydropower generation in the MRGCD canal system. With full year-round implementation of SSH generation at the nine locations investigated, the MRGCD could have a generating capacity of 2.2 MW and produce over $10\mathrm{million}\mathrm{kW}·\mathrm{h}$ during the year. This represents an income from power generation for the MRGCD of $1.032 million at the current power prices. More importantly, implementation of SSH would result in 1,340 homes being powered by clean, renewable energy while concurrently delivering water to irrigators. It is the hope of the authors that the case study presented will aid irrigation districts investigating the incorporation of hydropower in their canal networks.

Hydraulic performance of emitters with labyrinth channels is a primary factor that designers need to consider, and rapid prediction of hydraulic performance is very helpful for an emitter’s structural design. In this study, a new variable named pressure loss coefficient (PLC) was proposed as the evaluation index of an emitter’s hydraulic performance. By using the dimensionless analysis and orthogonal design method, the PLCs of emitters with the same shape but different geometries were calculated. The results obtained from analysis of range and variance show that the influence sequence on PLC ranks as follows: $\alpha >S/H>H/D>D/W$. A mathematical model was therefore developed between PLCs and the key parameters according to the multivariable regression method, which can be used to rapidly predict the hydraulic performance for emitters with different geometries.

An analytical method was developed to design evenly sloping, pressurized, nontapered, multiple-outlet pipes. Assuming spatiotemporal continuity of emitter flow rates, the approach was derived from the solution of analytical nonlinear differential equations. A straightforward relationship was established between the inlet discharge, the lateral slope, the diameter, and the pressure head at the upstream and downstream ends. Five pressure head grade line profiles were derived: uniformly uphill, level ground, steeply downhill, moderately downhill, and slightly downhill. For moderately downhill laterals, the theoretical analysis revealed that the pressure head at the outermost rim was independent of the inlet discharge. For the other profiles, the pressure head at the downstream edge was parameterized as a function of the inlet discharge. The iterative computation of the inlet discharge is a prerequisite for the inference of the other design parameters. This approach was successfully compared with the stepwise method that is deemed to be the most accurate.

Novel generalized analytical solutions, in closed form, of hydraulic-energy and hydraulic-force equations governing the flow in rectangular open channels are derived considering the nonhydrostatic pressure and nonuniform velocity. The derived solutions are convenient, computationally simple, and enable direct and explicit calculation of the alternate and sequent depths in the case of nonhydrostatic pressure and nonuniform velocity over the flow depth. The generalized solutions yield only three particular solutions, of which two are of practical significance. The solutions of practical significance correspond to the alternate and sequent depths in the case of hydraulic-energy and hydraulic-force equations, respectively. The particular solutions/equations of practical significance are identifiable for subcritical and supercritical flow. The new analytical solutions would be of interest to academicians, field engineers, and practitioners in directly solving problems of transitions in channel sections and determining hydraulic jump elements and the length of stilling basins.