Journal of Irrigation and Drainage Engineering

Disjunctive kriging (DK) is a nonlinear geostatistical model that provides unbiased estimates of the conditional probability (CP) that the true value of the property of interest does not exceed a defined threshold. It has important implications in aiding management decisions by providing growers with a quantitative input that can be used for evaluating the variability of the crop productivity at different zones in fields. The objectives of this study are (1) to identify the yield potential percentage (YP%) for several crops at different zones in fields under multiple soil salinity thresholds; (2) to evaluate the YP% of whole fields for several crops under multiple soil salinity thresholds; and (3) to provide guidelines to help growers decide which crops to grow. To achieve these objectives, the DK technique was applied to data from a project conducted in the southeastern part of the Arkansas River Basin in Colorado to generate CP maps. Two data sets of soil salinity (316 and 136 points) that were collected in two fields in 2004 and 2005 were used to generate the CP maps and to evaluate different scenarios of the expected YP% of several crops at multiple soil salinity thresholds. These data sets represented a wide range of soil salinity conditions to evaluate a wide variety of crops (i.e., a larger set of crops than those grown in the study area) in accordance with their soil salinity tolerance, The following crops were evaluated: the field crops, barley, sorghum, and corn; the fruit crops, pomegranate, apples, and strawberries; the vegetable crops, beets, tomatoes, and lettuce; and the forage crops, barley (i.e., hay), crested wheat grass, and alfalfa. This selection was set so that the three crops of each type represented high, moderate, and low soil salinity tolerances. Scenarios were created for each of the aforementioned crops and the DK technique was applied to each scenario to generate CP maps and to evaluate the expected YP%. The results of this study show that the CP maps generated by using the DK technique give an accurate characterization and quantification of the different zones of the fields. CP maps can be used to assess the expected YP% of whole fields for several crops under multiple soil salinity thresholds. On knowing the YP% of different areas, a management decision action can be undertaken to manage the productivity of a field in low productivity areas by selecting another crop or adjusting inputs such as fertilizer, seeding rates, and herbicides.

Water scarcity, which is typical of arid and semiarid regions such as Castilla-La Mancha (Spain), makes necessary the efficient use of water and energy resources. For this aim, there are several decision support system tools, including the benchmarking technique. The aim of this work is to compare two of the most extended irrigation systems (sprinkler and drip irrigation systems) in Castilla-La Mancha (Spain) by using performance indicators related to management of irrigated areas. The benchmarking technique was applied during three irrigation seasons (2006–2008) in six water users associations (WUAs) in Castilla-La Mancha Region (Spain). The indicators utilized in the benchmarking techniques were classified into two groups: descriptive and performance indicators. The information required to calculate the indicators was obtained from managers and farmers of each WUA, complemented with data obtained by using specialized equipment. To determine the grouping and differences between WUAs with different irrigation systems, a cluster analysis was applied. The results obtained showed a notable difference between WUAs with drip irrigation systems and WUAs with sprinkler irrigation systems. Regarding crop water management, in drip irrigation systems, the amount of irrigation water applied in most of the plots is slightly higher than crop water requirements, which were computed considering a regulated deficit irrigation management. This can be explained by the fact that farmers of areas with drip irrigation systems did not apply deficit irrigation management.

The Soil Conservation Service Curve Number (SCS-CN) method is a widely used empirical rainfall-runoff equation. Although the physical basis of the method has been debated, several researchers have suggested that it can be used to predict the watershed fraction that is saturated and generating runoff by saturation excess from variable source areas (VSAs). In this paper, we compare saturated runoff-contributing areas predicted with the VSA interpretation of the SCS-CN method with field-measured VSAs in a 0.5 ha hillslope in central New York State. We installed a trench below a VSA and simultaneously recorded water flux from different soil layers at the trench face and water table dynamics upslope of the trench. This setup allowed us to monitor runoff initiation and saturation-excess overland flow in response to rainfall and different water table depths in the hillslope during 16 storm events. We found that the SCS-CN method accurately predicted the observed VSA and showed best agreement if the VSA was defined as the area where the water table was within 10 cm of the soil surface. These results not only demonstrate that the VSA interpretation of the SCS-CN method accurately predicts VSA extents in small watersheds but also that the transient water table does not necessarily need to intersect the land surface to cause a storm runoff response.

A graphical procedure for calculating peak discharge from small catchments is developed on the basis of the standard Natural Resources Conservation Service (NRCS) rainfall-runoff hydrologic methods, in which rainfall excess obtained using the curve-number approach applied to 24-h design storms is transformed to runoff by means of triangular unit hydrographs. The solution is made dimensionless by grouping parameters, and, as a result, can be condensed into uncomplicated graphical relations that provide numerically precise peak flow rates. Mathematical expressions are also given that provide accurate approximations to the peak-discharge graphical relations. An additional result of the analysis is a comprehensive means of estimating rational-formula runoff coefficients for any location in the United States.

In this paper, the outflow process of a sharp-crested and broad weir is studied using the dimensional analysis and the incomplete self-similarity theory. The new stage discharge is theoretically deduced and its testing is carried out using measurements both available in literature and obtained by laboratory runs carried out in this investigation.

Estimation of water table and recharge is a key component in the control of groundwater level in arid and semiarid regions such as northwestern China. This study compared groundwater recharge in land subject to flood-irrigation and water-saving irrigation within the Manasi Basin, China, with the aim of analyzing the influence of irrigation method on the response characteristics of groundwater. A simulation of the two irrigation methods was conducted over four years, using a coupled MIKESHE/MIKE 11 model, from which the average water balance was calculated. Moran’s I was used to explain the spatial variability of recharge response associated with each irrigation method. ArcGIS 9.0 geostatistical and spatial analysis applications were used to interpolate/extrapolate and create grids for specific yield, bedrock elevation, and raw groundwater data. The results of the simulations are generally consistent with observed data, indicating that the method is capable of recognizing detailed characteristics of the groundwater response. The groundwater recharge intensity was found to become weaker in water-saving irrigation than in floodirrigation, but groundwater discharge is greater for water-saving irrigation than for flood-irrigation, making the reduction in depth more obvious. Furthermore, the reduction in depth of the groundwater level increases with site elevation. The results indicate that the proposed methodology are applicable to the management of groundwater resources in arid regions. The study quantified the processes affecting groundwater levels and provided an insight into their implications for the management and control of groundwater level.

With urbanization, the permeable soil surface area through which recharge by infiltration can occur is reducing. This is resulting in much less ground-water recharge and greatly increased surface run-off. Infiltration devices, which redirect run-off waters from the surface to the sub-surface environments, are commonly adopted to mitigate the negative hydrologic effects associated with urbanization. An infiltration trench alone or in combination with other storm water management practice is a key element in present day sustainable urban drainage systems. A solution for the infiltration rate from an infiltration trench and, consequently, the time required to empty the trench is presented. The solution is in the form of integrals of complicated functions and requires numerical computation. The solution is useful in quantifying infiltration rate and/or artificial recharge of ground-water through infiltration trenches and the drain time of the trench, which is a key parameter in operation of storm water management practice. The solution has been applied to a case study area in Lyon, France. MATLAB programming has been used in the solution.

Water-table heights attributable to steady uniform surface accretion rates in drained lands overlying a horizontal impermeable bed are given analytically by Engelund’s solution for toe-drains and by the approximate Dupuit-Forchheimer analysis for ditch drains. Both give the same water tables, although for different types of drain, when the spacing of the ditches in the latter is taken to be that in which the water table is drawn down to the level of the toe-drain in Engelund’s derivation. This fortuitous match also occurs in anisotropic soils when the horizontal hydraulic conductivity component is used in the formulae with the drain spacing dependent on the anisotropy factor. For soils with an infinite anisotropy factor, the Dupuit-Forchheimer analysis is exact so that the match is no longer fortuitous.