Journal of Irrigation and Drainage Engineering

The method of Gardner was used to estimate the evaporation rate from bare soils under high water table conditions, at Ichkeul marshes, of northern Tunisia. For this purpose, water content, soil-water suction, and water table depth were measured at three sites. Other common approaches that provide estimates of water table evaporation such as the Averianov and Coudrain-Ribstein et al. empirical formulas and the approach used by the U.S. Geological Survey's groundwater flow model MODFLOW were also evaluated. Next, a 2D groundwater simulation model, using the Gardner equations for computing evaporation rate, was developed to quantify the aquifer budget and groundwater losses via evaporation at the total area of the marshes. The model was calibrated in a steady-state condition. The results indicated significant groundwater losses by water table evaporation. The sensitivity of the groundwater model to the Averianov and MODFLOW approaches was analyzed. The best results (piezometric head and the area distribution of the evaporation discharge) were obtained with the Averianov formula.

Water application characteristics of a very low pressure spray sprinkler (40 kPa), a low pressure spray sprinkler (100 kPa), a medium pressure impact sprinkler (170 kPa), and a high pressure impact sprinkler (345 kPa) were evaluated under field conditions. Average field application rates varied from 42 to 156 mm/h and maximum 5-min application rates varied from 54 to 226 mm/h. Both were inversely related to sprinkler nozzle pressure in a manner that can be described by a logarithmic relationship. Maximum 5-min and 10-min application rates were, respectively, about 20 and 10% higher than average rates for the irrigation events. The 100, 170, and 345 kPa sprinklers produced application uniformity coefficients of 95% for single events and up to 99% for sequential events. About 70% of applied irrigation water reached the soil surface within a 200-mm diameter area at the base of corn plants. Maximum water application rates at the base of corn plants were amplified from three to four times when compared with above-canopy rates.

This paper presents a methodology to select a sprinkler lateral from different design alternatives for a duration shorter than its full life cycle. The selection is made by determining the time period up to which an alternative would be more economical than others. The developed methodology uses the break-even analysis involving total annual cost with escalating cost factors. The analysis is carried out by using a numerical method to solve a function of difference between total annual cost of two design alternatives. The application of the developed methodology is illustrated by solving an example.

Regulated rivers are used in many countries to sustain summer low flows and supply water for different users (drinking water, industries, irrigation, hydropower, salubrity). An upstream dam is used as storage, and the river is used as a channel to convey water-to-water users. Such systems are characterized by long and variable time delays between upstream and downstream points. This paper deals with the automatic control of such systems, where the action variable is the upstream discharge released by the dam, and the controlled variable is the downstream discharge of the river. As there are multiple outputs given by intermediate measurement points distributed along the river, the system is a cascade of single input, single output systems and is considered as a single input, multiple output one. A generic robust design synthesis is developed for internal model-based controllers. Simulations carried out on a nonlinear model of the Gimone River in the southwest of France show the improvement compared to present semimanual regulation.

This paper presents an analytical solution for the quantity of seepage from a rectangular canal underlain by a drainage layer at shallow depth. The solution has been obtained using inverse hodograph and conformal mapping. Using the solution for the rectangular canal and the existing analytical solutions for triangular and trapezoidal canals, simplified algebraic equations for computation of seepage loss from these canals, when the drainage layer lies at finite depth, have been presented, which replace the cumbersome evaluation of complex integrals. Using these seepage loss equations and a general uniform flow equation, simplified equations for the design variables of minimum seepage loss sections have been obtained for each of the three canal shapes by applying a nonlinear optimization technique. The optimal design equations along with the tabulated section shape coefficients provide a convenient method for design of the minimum seepage loss section. A step-by-step design procedure for rectangular and trapezoidal canal sections has been presented.

An analytical solution and finite-element numerical solution of a linearized and nonlinear Boussinesq equation, respectively, were obtained to describe water table variation in a semi-infinite sloping/horizontal aquifer caused by the sudden rise or fall of the water level in the adjoining stream. Transient water table profiles in recharging and discharging aquifers having 0, 5, and 10% slopes and receiving zero or constant replenishment from the land surface were computed for t = 1 and 5 days by employing analytical and finite-element numerical solutions. The effect of linearization of the nonlinear governing equation, recharge, and slope of the impermeable barrier on water table variation in a semi-infinite flow region was illustrated with the help of a numerical example. Results suggest that linearization of the nonlinear equation has only a marginal impact on the predicted water table heights (with or without considering constant replenishment). The relative errors between the analytical and finite-element numerical solution varied in the range of −0.39 to 1.59%. An increase in slope of the impermeable barrier causes an increase in the water table height at all the horizontal locations, except at the boundaries for the recharging case and a decrease for the discharging case.

This paper describes the formulation of a model for optimized crop and water planning decisions in an irrigation system in Thailand. It facilitates consultation in which representatives of stakeholders, officials, farmers, and researchers can contribute to the decision making. Linear programming and the analytical hierarchy process are the principal modeling tools to optimize the collective system objectives: productivity, equity, and security. The results of the model are compared with observed events of one dry season. The optimized policy generated by the model suggested a diversified cropping pattern, which would decrease the water requirement by 16.4% and enhance net benefit per cubic meter of water used by 39.9%. The erratic water availability from the reservoir and the operational procedures inside the system are reviewed, analyzing historical data in terms of reliability, resiliency, and vulnerability. These include lack of proper assessment of available water, effective farmer organization, and prompt data processing and communication. Furthermore, for the effective implementation of an optimized irrigation policy, a water release pattern of the storage reservoir has been suggested.

A hinged rod, when immersed in flowing water, deflects against its weight due to the hydrodynamic force of water. A relationship was derived to calculate the average flow velocity in small channels from the deflection of the rod, length and thickness of the rod, density of the rod's material, flow depth, and an experimentally determined rod's velocity coefficient. The rod's velocity coefficient was found to be invariant with flow velocity (V) and Reynolds number (R) for the range investigated in this study (V ⩽ 60 cm/s and 25,000 ⩽ R ⩽ 60,000). The calculated velocity compared very well with the measured velocity, with an average error of only 0.7%. Analysis suggested that a rectangular rod made of seasoned wood (density ⩾ 0.7) with length = 100 cm, width = 2 to 4 cm, and thickness = 3 to 5 cm will provide a simple but acceptable technique for determination of average flow velocity in small prismatic channels having a flow velocity ⩽1 m/s and flow depth ⩽45 cm with less than 5% error.

Sudan grass is a moderately salt-tolerant annual that is capable of substantial osmotic adjustment under high soil salinity conditions, but little is documented about its actual water use and yield under saline conditions. We estimate water use and evaluate the effects of “reduced-runoff” irrigation on soil salinity associated with Sudan grass hay production during a three-year field study (1996–98) in the Imperial Valley, California. The reduced-runoff irrigation method relies on the application of a simplified volume-balance surface irrigation model, and can result in negligible surface runoff; however, its use may have adverse impacts on soil salinity. Despite an anticipated salinity-induced yield reduction of about 15% associated with an average soil salinity of 6 dS/m (0–0.6 m depth), use of the reduced-runoff method resulted in satisfactory crop yields, practically no tailwater runoff, and a slight decrease from the initial average profile soil salinity. The average applied water depth and estimated consumptive use (ET_c) during the project were 1,019 and 935 mm, respectively, resulting in an average hay yield of 14.4 Mg/ha versus the 1996–98 county average of 12.6 Mg/ha. The project average ET_c/ET₀ and yield/ET_c ratios of 0.73 and 15.5 kg/ha⋅mm, respectively, were approximately 15% less than those estimated from water-use-efficiency studies, probably as a result of salinity-induced hay yield reduction.