Journal of Irrigation and Drainage Engineering

Cognitive mapping based on interviews with Colorado's water‐management officials indicates that institutional factors inhibit the Soil Conservation Service (SCS) from beneficially applying the so‐called Interactive Accounting Model (IAM) in the Arkansas River Basin. Modeling confuses the drainage problem and the design of remedial strategies by focusing attention solely on technical factors instead of the basin's central issues of economic viability and environmental regulation. The IAM is incapable of conceptualizing the relevant flow processes without support from a detailed model, which, however, the SCS has no plans for using. Finally, modeling cannot guide data collection or provide additional information for decision making because it is precisely the lack of interest by the SCS in pinpointing the sources of salinity in the basin that secures farmer support for on‐farm management projects. Institutional and modeling remedies are proposed to realize the potential benefits of modeling in the river basin.

The problem of a lateral pipe with equally spaced emitters and uniform slope is investigated. Individual emitters are considered in discharge and pressure estimations along the lateral. The friction head loss between successive emitters is estimated by the Darcy‐Weisbach formula, taking into account the variation of the Reynolds number, the different zones on Moody diagram, and the friction coefficient formula corresponding to each zone. In addition, the change of the velocity head is accounted for at different emitters. As the net pressure head at each emitter is evaluated, the corresponding emitter discharge is estimated accordingly. A computer program is presented for analyzing and designing trickle‐irrigation laterals. The results of two numerical examples solved using the presented technique are in close agreement with those of other rational analysis. Laminar flow prevails in a considerable length at the downstream end of the lateral, whereas an upstream length may be subject to fully turbulent flow. The estimation of the lower‐quarter distribution uniformity shows that considering individual emitters rather than longitudinal slot is of practical importance. Design criteria for trickle‐irrigation laterals are provided.

Clay soils frequently develop large cracks after irrigation. Infiltration equations therefore need to be modified to take cracking soil properties into account when modeling and optimizing furrow irrigation. In this article, we propose an infiltration equation for cracked soils, based on two parameters. Other parameters of the global model are assumed to be known (furrow length, shape, slope, and estimated roughness). One parameter is linked to the type of soil and is calibrated separately for the entire irrigation process. The second parameter takes soils' cracks into account and is calibrated in real time during the advance phase (before the water front overruns the middle of the plot). This global furrow irrigation model for cracked soils is derived from a conceptual approach and can be used either to predict in real time, water‐use efficiency during irrigation (infiltrated volume, runoff water losses, uniformity) or to optimize irrigation parameters (head flow, irrigation duration). The model was tested and validated on three irrigation applications on 60 furrows in a corn field in Tarascon in southeastern France. This conceptual model can be easily adapted to the statistical approach, which is based on the variability of water advance between the furrows.

The reliability of furrow‐infiltration parameters computed from advance measurements was analyzed. Lumped parameters were obtained using the least‐squares approach. The objective function was formulated using advance time and velocity observations as a function of distance. Predicted values were calculated with a finite difference hydrodynamic model with wetted perimeter‐dependent infiltration. The Extended Kostiakov equation was used to describe infiltration‐rate variation with time. Reliability was examined by comparing recorded total intake and runoff with values predicted with the single average parameters. Results showed that reliability of coefficients depends on the relationship between infiltration variability, furrow length, and inflow rate. In particular, relatively short irrigation times hampered the identification of the steady infiltration rate. Spatial trends in infiltration rates affected the reliability of parameters as well. The magnitude and nature of the resulting prediction errors was found to be dependent on the direction of the trend relative to the flow direction. In general, velocities appeared to provide better estimates of average infiltration characteristics than advance times but weighted least squares may be required to compute the parameters from field data.

The U.S. Department of Agriculture's Water Erosion Prediction Project (WEPP) is a new technology based on fundamentals of hydrology, soil physics, plant science, hydraulics, and erosion mechanics. WEPP hydrology includes simulation of excess rainfall using the Green‐Ampt infiltration equation, surface runoff routing, evapotranspiration, percolation, and subsurface drainage to tiles (or ditch). Soil water flowing to an artificial drain (tiles or ditch) reduces the antecedent water content of soil and results in increasing soil‐infiltration capacity and reduction of storm runoff. Hydrometeorological, vegetation, topographical, and soil data from a poorly drained watershed subjected to subsurface drainage system were used to evaluate the WEPP hydrology components. Model‐simulated and measured storm‐runoff hydrographs were compared for the pre‐ and postsubsurface drainage installation. The results indicate that, in general, the model does an acceptable job of predicting storm and peak runoff rate for pre‐ and postsubsurface drainage installation.

A procedure for developing rainfall intensity‐duration equations for short durations (less than 1 hr) for any location in the United States is described. The procedure uses readily available isopluvial maps developed by the National Weather Service for four regions of the United States: (1) The 37 eastern and central states; (2) the 11 conterminous western states; (3) Alaska; and (4) Hawaii. Rainfall depths for five durations less than or equal to 1 hr obtained for each of the regions were used to determine optimal values of parameters for four empirical forms of rainfall intensity‐duration equations. An intensive pattern search over the potential range of parameters was used to obtain the optimal values. For the central and eastern states, optimal equation parameters depend on the ratios of 5‐ and 15‐min rainfall depths to the 60‐min rainfall depth at a site. These relations are displayed graphically. For each of the three other regions of the United States, a single set of parameters provides the best equation fit to the available rainfall data. The procedure will be useful in designing minor drainage structures using the well‐known rational formula, which requires an estimate of rainfall intensity for a duration equal to the time of concentration of a catchment.

The study of irrigation water demand has generally been focused at the field level, and the question can be raised as to whether field‐level estimates can be applied successfully to predict the water usage of a region. In this case study, crop and water‐use data for a 30‐year time period were analyzed for a 200,000 ha desert region in southern California, the Imperial Irrigation District, which relies exclusively on Colorado River water. Attempts to correlate water usage with crop acreage and climatic variables were made using the Blaney‐Criddle evapotranspiration method, but showed limited success. It is unknown whether the use of more sophisticated estimation techniques, which would require a larger data set than was available for the present study, would yield better results.

The mobility of trace elements in soil reflects the chemical reactivity of the elements in the soil matrix. The result is that trace‐element mobility is both specie and site dependent. An overview of selected geochemical factors that influence the concentration of trace elements in the soil solution is presented. Factors affecting both cationic and anionic trace‐element mobility are given in the context of multiphase equilibria. Chemical processes such as ion exchange, adsorption, solid‐phase formation, and redox are considered and related to control of trace‐element concentration in solution and hence their mobility in soil. The limitations inherent in the use of a thermodynamic database for determining partition functions used in solute transport modeling are emphasized. The importance of microbially mediated biomethylation of trace elements such as Pb, Hg, Cd, and Se is discussed.

Landsat satellite Thematic Mapper (TM) data were explored as an alternative for monitoring regional soil moisture conditions. The theoretical method of using single daily temperature data sets to estimate root zone soil moisture was tested with ground‐based observations. Results indicated that the percentage gravimetric soil moisture content in the 0–24‐cm depth was inversely related to the soil surface temperature. A demonstration of Landsat‐TM based soil moisture estimation was performed for Lee County in southwestern Florida. The thermal‐infrared (IR) data from TM band 6 were overlain onto four principal land‐use categories (agricultural/irrigated, urban/clearings, forest/wetlands, water) using a geographic information system (GIS). The thermal‐IR data were used to assess four qualitative soil moisture conditions (water/very wet, wet, moist, and dry) within each land‐use category. Integration of Landsat thermal‐IR data with land‐use through GIS under certain conditions may be a useful technique for assessing regional soil moisture conditions, and further research to refine and quantify this technique is recommended.

Small‐scale irrigation plays a crucial role in agricultural production in Niger, West Africa. Despite the prevalence of traditional irrigation microsystems (average size of about 0.1 ha), not much is known about water‐management practices. This paper examines, over a range of lifting heads, the water‐lifting and water‐use characteristics of 84 manual lift microsystems and intensively investigates two manual systems and two motorized lift systems. An adaptation of the Thornthwaite‐Mather procedure to predict recharge is used to model the soil moisture budget. Because of the size of microsystems, irrigation efficiency tends to be high. While pumps offer a significant labor‐saving advantage over manual lifting devices, many pumps are not well matched to lifting head. This paper concludes that both manual and motorized lift technologies should continue to be employed in Niger, but that pumps must be better matched to lifting heads and to the particular labor constraints for field water distribution.

Sound irrigation management models require the information of root‐depth development with time in order to determine the active zone of soil reservoir. Development indicates rate of change. Sigmoidal as well as exponential root‐depth‐development models as a function of time, soil, crop, and management practices are developed. The models require as input data the maximum rooting depth to be achieved under a particular set of soil, crop, and management practices as well as the days until the root depth attains a maximum value. A comparison was made between experimental observations of a wheat crop and the estimates derived from several previously developed root‐growth models and the models developed in this study. The results clearly indicate that both of the developed models had a high degree of accuracy, which was comparable with or better than other reported empirical root‐growth models.