Journal of Irrigation and Drainage Engineering

The effects of partial infiltration and furrow geometry information on furrow irrigation design and economic return to water were quantified on a single furrow (reference furrow) and field-wide (10-furrow set) basis using a kinematic-wave furrow irrigation model in conjunction with an economic optimization model. A furrow sampled at 10 locations was assumed to represent the actual field condition. Subsamples were randomly drawn from the 10 samples and return to water was maximized. These suboptimal designs were applied to the actual furrows and monetary loss due to lack of information was simulated. The monetary loss was less for furrow irrigation designs having high inflow rates ($0.38/furrow, $17/ha) than for the low inflow rates ($2.27/furrow, $100/ha). Average loss decreased from $31/ha ($0.71/furrow) to $0/ha in the case of the reference furrow, and from $1.0/furrow ($44/ha) to $0.3/furrow ($13/ha) in the case of the 10-furrow set for the samples sizes of 1 and 10, respectively.

A number of nonlinear optimization-based multiple-objective management models for sustainable utilization of coastal aquifers are formulated and solved. The management objectives represent plausible scenarios for planned withdrawal and salinity control in coastal aquifers. The first multiple-objective management model is developed for spatial and temporal control of aquifer salinity through planned pumping (withdrawal) from locations closest to the ocean boundary. The second multiple-objective management model is useful for maximizing sustainable water withdrawal from the aquifer for beneficial uses, while limiting the maximum salinity in the aquifer. The third multiple-objective management model is developed for maximizing sustainable water withdrawal from the aquifer for beneficial uses and minimizing the total pumping at locations adjacent to the ocean boundary to control the salinity in the aquifer. The nonlinear finite-difference form of the steady-state density-dependent miscible flow and salt transport model for seawater intrusion in coastal aquifers is embedded within the constraints of the management model. The constraint method of generating noninferior solutions is used to solve the multiple-objective management problems. The management models are solved for a hypothetical unconfined coastal aquifer system. The projected augmented Lagrangian method of nonlinear programming is used to solve the resulting large-scale optimization problem. The solution results demonstrate the feasibility of the developed optimization models and also the conflicting nature of the various objectives of coastal aquifer management.

Investigated were physical processes governing vadose zone water flow and solute transport in a heavy-textured crack-prone soil of the semiarid Canadian Prairies. Soil moisture, soil temperature, and relevant meteorological observations were recorded over a period of about two years. Environmental chloride and tritium concentrations in the soil water were determined. Analysis of the data indicates that during snow melt, water and solutes are flushed down rapidly via cracks and fissures in the root zone. The soil at these depths is still frozen during snow melt. In late spring after the entire soil profile thaws, water and solutes move downward by a diffusion dominant advective-diffusive flow mechanism. The chloride and tritium profiles obtained within the vadose zone support this argument. This conceptual model of the flow and transport processes is supported by calculations of advective and diffusive soil water flux from chloride profiles. Simulation of the tritium profile using a simple analytical model also gives very good agreement with measured data.

This article is an attempt to develop an analytical framework to address sensitivity of irrigation offtakes. The perturbation of water depth and the deviation of the setting are considered for analysis. Sensitivity of delivery takes into account the impacts of the perturbations on the delivery (to the command area of the offtake). Sensitivity of conveyance assesses the effects on the conveyance discharge of the parent canal. Analytical formulations of six sensitivity indicators are provided. The concept of head loss equivalent is introduced to explicitly take into account the hydraulic behavior in the dependent canal downstream of the offtakes. Hydraulic perturbations are considered either as upstream deviations in the parent canal or downstream perturbations in the dependent canal.

Analytical relationships between the control of canal water depth, the sensitivity of irrigation delivery structures, and the resulting internal performance are established at the system level. One system sensitivity indicator is derived for both adequacy and efficiency, and two for equity (coefficient of variation and Theil information index). The level of precision which reflects the effectiveness in controlling water depth is defined as a permissible variation of water depth at the cross-regulator (±ΔH_R) about the target. The degree of influence exercised by the cross-regulator on offtakes is accounted for through an influence factor between zero and one. The behavior of three different irrigation systems in Sri Lanka and Pakistan is studied with both analytical system indicators and numerical hydraulic simulations. It shows good agreement for a range of precision between 0.02 and 0.2 m. These global system indicators can be used to define the precision level required to achieve a given performance, to estimate actual performance from recorded precision at regulators, and to diminish the system sensitivity, improving the performance for a given precision. Practical operating policies can be inferred from sensitivity information of irrigation systems without the necessity of a complex irrigation operation model.

Estimates of annual streamflow volumes are needed in many different types of hydrologic studies. Usually a streamgauge is unavailable at the location of interest, hence regional methods that relate streamflow to readily measured geomorphic and climate characteristics provide a practical solution. Hydrologic, geomorphic, and climatic characteristics of 1,553 undeveloped watersheds across the United States are used to develop regional regression equations that relate the first two moments of annual streamflow to readily measured basin and climate characteristics. These relations are summarized for each of 18 major U.S. water resource regions. The relationships are remarkably precise, with adjusted R² values ranging from 90.2–99.8% and an average value of 96.2% across the continent. The usefulness of these relationships is evaluated by deriving their information content in terms of equivalent record length. These results indicate that regional models of annual streamflow, including runoff maps, are less accurate than suggested by traditional goodness-of-fit statistics. We also provide estimates of precipitation and temperature elasticity of streamflow, by region.

A mathematical model is developed that describes water uptake from soil by the roots of transpiring plants. Starting from a one-dimensional Richards equation with a root water extraction term, a partial differential equation predicting the moisture content in the soil profile is formulated. There are many expressions in literature that predict water extraction by plant roots, each one of them having its own merits and demerits. This study proposes a simple model with a linear root water extraction term that varies with time. The model also incorporates a sinusoidal root growth function that takes into account the root growth with time. The flow equation is subjected to a boundary condition that signifies the potential evaporation or the applied water (head) during the irrigation application time at the top boundary. The simulated model without the extraction function is validated by comparing the model results with experimental studies predicting soil moisture content for both a homogeneous and a layered medium. A linear root water extraction term is later adopted in the model, and a hypothetical case is simulated to compute the water uptake by plant roots. The comparison in all test cases was found to be reasonably good.