Journal of Irrigation and Drainage Engineering

The Penman method using hourly and daily weather data was evaluated to estimate daily reference evapotranspiration over a well-established stand of Alta fescue under different atmospheric conditions. The performance of the Penman equation was evaluated using evapotranspiration measured by the Bowen ratio energy balance (BREB) method. Good agreement between the BREB method and Penman using hourly weather data was observed. On an hourly basis, the overall standard error of estimate (SEE) and absolute relative error (ARE) were 0.06 mm$\dot{s}$h ⁻¹ (40.8 W$\dot{s}$m ⁻² ) and 5.2%, respectively. On a daily basis, the SEE was 0.55 mm$\dot{s}$d ⁻¹ and the ARE was 6.9%. The SEE and ARE for the Penman model using daily weather data were 0.74 mm$\dot{s}$d ⁻¹ and 9.8%, respectively. These results suggest that the accuracy of the Penman equation could improve if hourly weather data were used as inputs and strongly suggest that the Penman equation with hourly weather data could be used in the Willamette Valley to predict daily evapotranspiration for irrigation purposes.

This paper is concerned with the design of a practical quadratic weir of a simple geometrical shape, having an inward trapezoidal weir of crest width 2 w and vertex angle 2θ, over which a rectangular weir is fitted at an optimum depth p = 0.95 d ( d = overall depth of the inward trapezoidal weir) above the weir crest. It is shown that the flow through this weir is proportional to the square root of head h measured from the datum or reference plane situated at 0.5 d above the crest, for all flows in the range of p ≤h≤ 2.95 p within a maximum error deviation of ±2% from the exact theoretical discharge. A numerical optimization procedure is developed to obtain the optimum parameters of the weir yielding a maximum quadratic head-discharge relationship. Experiments with two different weirs show excellent agreement with the theory by giving a constant average coefficient of discharge. The application of the weir in the proportionate method of flow measurement using a bypass in an open channel and as a sensitive flow-measuring device in irrigation canals are highlighted.

The pesticide aldicarb is extremely soluble in water, which causes it to be mobile in ground water. A field study was conducted to monitor the fate of aldicarb in a poorly drained soil in the North Carolina coastal plain. The research site consisted of three experimental plots with three water-table management treatments: conventional drainage, controlled drainage, and subirrigation. Surface and subsurface drainage rates were measured continuously and water-table elevations were monitored in each plot. A total of 651 soil and water samples were collected over a six-month period. Aldicarb degraded to nontoxic compounds with a half-life of approximately 7 days. The maximum aldicarb loss through drainage outflow and surface runoff was 0.02% and 0.05% of total applied aldicarb, respectively.

Transport of water-soluble agrichemicals has been intensively studied in the past few years for its use in the protection of ground water from contamination. An accurate description of solute transport is largely based on the knowledge of the transport process of aquifer recharge. Aquifer-recharge processes can be described by a number of models. However, field evaluations of those models are scarcely seen in the literature because most models have too detailed a description of the water-transport process, which results in the inefficient computations and impossible field measurements. In this paper, we try to develop a simple one-dimensional aquifer-recharge model that is easy to implement in a heterogeneous field condition. The model predicted pressure head for several soil depths and the water-table level on an hourly basis during and after rainfall events. The performance of the model was evaluated using field data. Most of the model results matched the field data quite well.

Current public concern for the environment has focused on the environmental effects of chemical applications to turfgrass areas. There is little research on the environmental effects of nitrogen (N) applied to turfgrasses. Our objectives were to investigate the hydrology of 50 cm of undisturbed soil columns with a Kentucky bluegrass turf and intact macropores under a heavy (four 2.54 cm applications) and a light irrigation regime (sixteen 0.64 cm applications), and to measure the fate of N, using ¹⁵ N as a tracer, when applied to an undisturbed soil column. Mean leachate values for columns under the heavy irrigation regime totaled about six times the amount collected from columns under the light irrigation regime. We found that the heavy irrigation increased N, which leached through the 50 cm of undisturbed soil columns by 30 times and decreased the volatilization of liquid urea compared with columns under the light irrigation.

A steady-state theory is developed for the seepage of ponded water into equally spaced drainage ditches in a homogeneous and anisotropic soil overlying an impervious barrier. Solutions are obtained for two general cases of the problem: (1) zero depth of ponded water; and (2) finite depth of ponded water. Equations of the hydraulic head, the stream function, the surface inflow velocity distribution, and the seepage rate per unit length of a ditch are derived for both cases of the problem. A verification of the proposed solution for case 1 is made by comparing a few results obtained from it with corresponding results obtained from the analytical and experimental works of Fukuda (1957).

This paper describes the use of buried-pipe systems and flexible surface hoses in Hebei Province, China and their contribution to improved water use and increased management flexibility. Buried-pipe and hose systems facilitate the mixing and delivery of saline shallow ground water with fresh surface water or deep ground water. The average area served by a buried-pipe system is 4–5 ha. A substantial increase in irrigation command areas has resulted from the adaptation of existing buried-pipe systems to incorporate the use of surface hoses to distribute irrigation supplies from the outlet. New developments use a flexible hose directly connected to a tubewell pump or to larger buried-pipe systems, in many cases facilitating the conjunctive use of water from several sources. The distinctive features of system design, construction, and operation are described, along with capital cost estimates and an outline of benefits, which include flexibility to grow small areas of high-value crops.

Many bridges are destroyed or fail completely during severe floods. If the cause of the damage is not a structural deficiency, it may be excessive local scour around bridge piers and/or abutments. Although the mechanics of the local scour around these obstacles has been studied extensively, the studies investigating the hydrologic design aspects are limited in the literature. Insufficient hydrologic and hydraulic evaluations may result in uncertainties in bridge design. The optimum return period for a flood hydrograph may be determined through a hydro-economic analysis for bridge design. Lack of relevant hydrologic data, such as precipitation and runoff may lead to difficulties in obtaining the design parameters. Realistic judgment of the hydrologist on the local hydrologic behavior of the project area is then required. In this paper, a case study performed for the hydrologic design of a bridge located in a small basin subject to frequent floods is presented. Scour computations of the bridge have been performed for various combinations of runoff to check the foundation stability.

This paper discusses the design and experimental verification of a geometrically simple logarithmic weir. The weir consists of an inward trapezoidal weir of slope 1 horizontal to n vertical, or 1 in n , over two sectors of a circle of radius R and depth d , separated by a distance 2 t . The weir parameters are optimized using a numerical optimization algorithm. The discharge through this weir is proportional to the logarithm of head measured above a fixed reference plane for all heads in the range 0.23 R ≤ h ≤ 3.65 R within a maximum deviation of ±2% from the theoretical discharge. Experiments with two weirs show excellent agreement with the theory by giving a constant average coefficient of discharge of 0.62. The application of this weir to the field of irrigation, environmental, and chemical engineering is highlighted.

The Penman-Monteith, Makkink, Priestley-Taylor, Turc, Hargreaves-Samani, and Thornthwaite methods were used to estimate reference evapotranspiration (REF-ET) at three sites in eastern North Carolina. The Penman-Monteith method with grass as the reference crop was selected as the standard of comparison for evaluating the other five methods. Good correlation was found between the REF-ET values estimated by each of the five radiation- and temperature-based methods and the Penman-Monteith method, although there were some differences. Based on the statistical analyses, the methods that performed the best in estimating daily and seasonal Penman-Monteith REF-ET at each location were recommended. Reliability of the radiation methods was also evaluated when data from another site were used. Penman-Monteith estimates were used to develop correction factors for their potential use in the temperature-based Thornthwaite and Hargreaves methods at each location and in the study areas in general.

An adverse relationship between irrigated agriculture and wetlands in arid regions could be mitigated by using recovered shallow ground water for irrigation. Salt and water balances for the Carson Division of the Newlands Project in Northwest Nevada were created to identify the suitability and the potential annual recovery of ground water from the shallow aquifer for crop irrigation. Project salt balances and salt concentration ratios suggest that the shallow aquifer acts as a salt source for total dissolved solids (TDS), Na, Ca, and SO ₄ , but is suitable for irrigation. Annually, 7.38 × 10 ⁻² km ³ (60,000 acre-ft) of shallow ground water could be available for irrigation. Exchanging the intercepted ground water (TDS = 1,235 mg/L), which presently flows to the wetlands, with an equal quantity of uncontaminated reservoir water (TDS = 150–300 mg/L) would benefit the wetlands.

A conceptual agronomic model EPIC was extended to consider the effects of salinity in alfalfa production under optimal and water stress irrigation conditions. The extended model was calibrated and validated with observed lysimeter data. The model parameters that affected alfalfa yield and soil salinity the most were wilting point, field capacity, hydraulic conductivity, nitrate concentration, biomass energy ratio, seeding rate, average soil salinity EC _e at which crop yield is reduced by 50% ( EC₅₀ ), and initial soil gypsum concentration. The calibrated and validated model was then applied to an alfalfa deficit irrigation study. The four irrigation treatments included optimum check, minimum stress, short stress, and long stress, each of which produced differential alfalfa yields. The purpose of summer deficit irrigation was to ascertain how much agricultural water at what cost could be made available for urban water uses during water shortfalls. The results of model simulation were found to be satisfactory under all irrigation treatments though the model slightly overestimated the yields and underestimated the soil EC _e at the end of short and long stress treatments. An economic component is included to determine the appropriate compensation for farmers undergoing a range of deficit irrigations.

Sloping borders with free outflow were studied to determine the effect of inflow hydrograph shape on maximum application efficiency. A zero-inertia model describing the movement of water along the border run with infiltration was used to predict the maximum application efficiency for five inflow hydrograph shapes. The irrigation parameters considered were four infiltration families, three slopes, three roughness coefficients, two field lengths, and three volumes. The maximum application efficiencies averaged over all combinations of the irrigation parameters for the five hydrographs were as follows: constant, 68%; cutback, 77%; cablegation, 59%; modified cutback, 80%; and modified cablegation, 78%. Efficiencies for each hydrograph shape ranged from zero to 92%, with the low values occurring for high infiltration rates and roughness, small slopes, long fields, and low volumes of application. The infiltration family and its cross products with the other irrigation parameters were the most important variables affecting the maximum application efficiency for the five inflow hydrograph shapes.

The computation of the well function is required in the analysis of pump test data for leaky or confined aquifers. Approximate expressions have recently been proposed to compute the well function over the whole range of the argument values. These proposed expressions are more computationally intensive and less accurate than some standard exponential integral approximations. Analysis of a synthetic data set using slope-matching technique shows that use of these recent expressions results in severe overprediction of the storage coefficient, especially for aquifers with low storage coefficient or high transmissivity.

The feasibility of off-line storm-water infiltration specifically for the reduction of peak rates of storm-water discharge are analytically evaluated. Hydrograph routings are applied to a range of possible conditions and to a trial site to compare the requirements and hydrologic effects of off-line infiltration, on-line infiltration, and detention. Off-line infiltration required much less basin capacity than either of the other methods for a given degree of peak-flow control. These results encourage the use of this approach for peak-flow control where on-line infiltration is not feasible for this purpose. However, off-line infiltration has little effect on flow duration and only a moderate effect on flow volume; it would have little effect on water quality. On-line infiltration is a more complete solution to these problems where it is feasible.

The minimum area, or the maximum velocity cross section, is generally adopted for lined irrigation canals. Such a section is economically most efficient because it involves the least amount of earthwork and the least lining surface. For various practical sections there exist equations between the design variables. Because the design variables themselves are unknown, such relationships cannot be applied directly. In the present investigation, explicit equations for the design variables of various irrigation canal sections have been obtained. It is hoped that these equations will be useful to the engineer engaged in the design of lined canals.