Journal of Irrigation and Drainage Engineering

Electromagnetic instruments are increasingly being used for in situ analysis and mapping of soil salinity in irrigated soils. This study develops calibration models for salinity assessment over regional scales on the order of tens of thousands of hectares. These models relate apparent soil electrical conductivity measured with the EM-38 electromagnetic induction meter (Geonics Ltd.) to traditional laboratory-measured saturated paste electrical conductivities $\left({\mathrm{EC}}_e\right)$ . The study area is located in the Lower Arkansas River Valley, Colo. and is divided into two regions. At each of 414 randomly selected calibration sites, an EM-38 reading was taken and multiple soil samples were extracted for analysis. The sites chosen have soil ${\mathrm{EC}}_e$ values ranging from $1\text{to}18\mathrm{dS}∕\mathrm{m}$ , gravimetric water contents (WC) from 0.02 to 0.4, and textures ranging from sands to clays. The best model for predicting soil ${\mathrm{EC}}_e$ in both study regions is bivariate nonlinear and includes EM-38 vertical readings $\left({\mathrm{EM}}_V\right)$ and WC as covariates. Uncertainty in the calibration equations is addressed and tests are conducted at 48 independent sites. Results indicate that, while uncertainty is considerable in regional scale surveys, electromagnetic instruments can be calibrated for rapid reconnaissance of soil water salinity, providing reasonably accurate identification of salinization categories.

In this study, annual water application costs per unit area (ha) have been analyzed at the level of irrigation subunit in set sprinkler irrigation systems designed with pipes of different materials. In the cost, investment (pumping, pipes, sprinklers, ditches), energy, labor, maintenance, and water costs have been considered. Four systems were studied: one with buried pipes, in a permanent solid-set system, using: (a) polyvinyl chloride with buried pipes (PVCb), and three with pipes on the surface in surface solid-set systems, using (b) polyvinyl chloride pipes, (c) polyethylene pipes, and (d) aluminum pipes. The correct selection of the irrigation subunit size and shape can lead to a significant decrease in cost. The most economic irrigation subunits, among the four systems studied, were those formed by four laterals and a number of sprinklers per lateral of 10, 9, and 6 at $12\mathrm{m}\times 12\mathrm{m}$ , $12\mathrm{m}\times 18\mathrm{m}$ , and $18\mathrm{m}\times 18\mathrm{m}$ spacing, respectively. The most influential factor on the annual water application cost was spacing. Considering total annual cost, water cost was the most important, followed by investment and energy. Among the analyzed systems, the permanent system using PVCb produced the lowest annual water application cost per unit area.

The objective of this study was to determine the total irrigable area in the Santa Elena Peninsula Water Delivery System (TRASVASE) under several land use scenarios based on a simple water budget model requiring estimation of: (1) crop water requirements (CWR); (2) irrigation efficiency; and (3) dams and canals evaporation utilizing weather data. CROPWAT, a software package developed by the United Nations Food and Agriculture Organization (FAO), was used to calculate CWR and irrigation requirements. The reference evapotranspiration $\left({\mathrm{ET}}_0\right)$ was calculated using Santa Elena Peninsula historical average weather data and results used to create average monthly ${\mathrm{ET}}_0$ surface maps using ArcMap. Nine scenarios were created to calculate available agricultural water and irrigable area. The total calculated irrigable area during the dry season (June–November) was compared to estimate from the Commission for the Development of the Guayas River Basin in Ecuador (CEDEGE) and to the average estimate done by the farmers. CEDEGE estimate was $\mathrm{23,000}\mathrm{ha}$ , 48% more than the most water conservative scenario (CB) analyzed in this study, whereas farmers’ projected average was $\mathrm{16,500}\mathrm{ha}$ or 0.06% more. The advantage of this method is that it requires minimal climatic and geographic information coupled with well-established FAO models to produce tangible results. It can be of important use in locations where climatic data is limited, reducing dependency on weather stations to calculate system wide irrigation requirements.

Soil moisture, evapotranspiration, and other major water balance components were investigated for six Nebraska Sandhills locations during a 6 year period (1998–2004) using a hydrological model. Annual precipitation in the study period ranged from 330 to $580\mathrm{mm}$ . Soil moisture was measured continuously at 10, 25, 50, and $100\mathrm{cm}$ depth at each site. Model estimates of surface $(0–30\mathrm{cm})$ , subsurface $(30–91\mathrm{cm})$ , and root zone $(0–122\mathrm{cm})$ soil moisture were generally well correlated with observed soil moisture. The correlations were poorest for the surface layer, where soil moisture values fluctuated sharply, and best for the root zone as a whole. Modeled annual estimates of evapotranspiration and drainage beneath the rooting zone showed large differences between sites and between years. Despite the Sandhills’ relatively homogeneous vegetation and soils, the high spatiotemporal variability of major water balance components suggest an active interaction among various hydrological processes in response to precipitation in this semiarid region.

In the past, various methods have been used to estimate the parameters in the nonlinear three-parameter Muskingum model to allow the model to more closely approximate a nonlinear relation compared to the original two-parameter Muskingum model. In this study, the Broyden–Fletcher–Goldfarb–Shanno (BFGS) technique, which searches the solution area based on mathematical gradients, is introduced. The technique found the best parameter values compared to previous results in terms of the sum of the square deviation between the observed and routed outflows, using the smallest number of computational iterations. A sensitivity analysis showed that the initial values of certain parameters were critical when finding the optimal solution. Although this gradient-based technique makes use of initial value assumptions and involves complicated calculus, different initial values reach the same optimal or near-optimal solution within less time. Moreover, this mathematical technique does not require the algorithm parameters that are essential factors in meta-heuristics such as genetic algorithm or harmony search. The technique also considers the hydrologic parameters to be continuous rather than discrete variables for pure structures.

Data from over 1,600 storms at 91 stations in Texas are analyzed to evaluate an instantaneous unit hydrograph (IUH) model for rainfall-runoff models. The model is fit to observed data using two different merit functions: a sum of squared errors function, and an absolute error at the peak discharge time $\left({\mathrm{Q}}_{\mathrm{p}}\mathrm{MAX}\right)$ function. The model is compared to two other models using several criteria. Analysis suggests that the Natural Resources Conservation Service Dimensionless Unit Hydrograph, Commons’ Texas hydrograph, and the Rayleigh IUH perform similarly. As the NRCS and Commons’ models are tabulations, the Rayleigh model is an adequate substitute when a continuous model is necessary. The adjustable shape parameter in the Rayleigh model does not make any dramatic improvement in overall performance for these data, thus fixed shape hydrographs are adequate for these watersheds.

Side weirs are flow-regulating devices commonly encountered in hydraulic engineering. In the past, the discharge coefficient for flow past a side weir was investigated experimentally by many researchers. In this study, a modified discharge coefficient $C_d$ for side weirs in rectangular channels and circular channels is defined. The multivariable nonlinear partial least square (PLS) method is used to determine the empirical equations relating $C_d$ with the dimensionless weir parameters ${\mathsf{F}}_1$ , $S∕Y_1$ , and $L∕D$ . Compared to the previous studies, the procedures to calculate the discharge of the side weirs is simplified. The discharge predicted using the empirical equations based on the nonlinear PLS method is in good agreement with the measured discharge. The nonlinear PLS method can also be applied to many other hydraulic flow configurations characterized by a large number of variables.

In this study, errors in determining bed shear stress caused by errors in theoretical bed surface data or roughness size selection using one-point velocity, two-point velocity, or a group of velocity measurements within the log-velocity region are systematically and quantitatively analyzed. The smaller the roughness element, the smaller the error in the bed shear stress estimate. For a fixed roughness size and absolute error in selecting the theoretical bed data, the closer to the bed the velocity measurement is taken, the larger the error in the friction velocity estimate. The velocity profile near the bed is very sensitive to the selection of the theoretical bed surface data. The velocity profile near the bed will deviate significantly from the true log profile if the theoretical bed surface data is over- or underestimated by $5\mathrm{mm}$ or more. This study shows conclusively that using the upper measurement data points, instead of the near-bed measurement, in the regression analysis yields better roughness size and bed shear stress estimates.

In open channels, the relationship between the specific energy and the flow depth exhibits a minimum, and the corresponding flow conditions are called critical flow conditions. Herein they are reanalyzed on the basis of the depth-averaged Bernoulli equation. At critical flow, there is only one possible flow depth, and a new analytical expression of that characteristic depth is developed for ideal-fluid flow situations with nonhydrostatic pressure distribution and nonuniform velocity distribution. The results are applied to relevant critical flow conditions: e.g., at the crest of a spillway. The finding may be applied to predict more accurately the discharge on weir and spillway crests.

Water resources engineering assessment requires simple but effective evaporation estimation procedures, especially from readily measurable meteorological factors. Unfortunately, such approaches are rather scarce in the literature. In this paper, an adaptive neural-based fuzzy inference system (ANFIS) was applied to daily meteorology data from the Lake Eğirdir region in the southwestern part of Turkey. Daily evaporation, solar radiation, air and water temperatures, and relative humidity measurements were used to develop the ANFIS method, which helps to assess possible contributions that each input variable has on the evaporation estimates. Such an assessment is not possible by any conventional procedure including the Penman method. However, the Penman method daily evaporation estimations were used as output data for the verification of the ANFIS approach. Classical evaporation estimation models treat the data individually. However, ANFIS models process past data collectively and then adaptively provide estimates as new sets of data become available. In the ANFIS architecture as developed in this paper, there are four measured input variables and one output variable to estimate evaporation. The estimation results from the ANFIS model had a high coefficient of determination of 0.98 when compared with the Penman method results and a low average performance error of 4.6% among other alternatives. The average performance error is less than the practically acceptable limit of 10%.

A procedure for calculating the flow depletion from a finite length of a stream induced by a pumping well in an adjacent aquifer is developed. Four management cases of finite length of the stream including a basic case are considered. A “basic flow depletion factor” is defined, in terms of which the flow depletion factors for all cases are expressed. The basic flow depletion factor is twice the Hantush $M$ function. A computationally simple and accurate practical approximation of the basic flow depletion factor is presented that encompasses the full practical range of the solutions. Using this approximation, an optimization method is proposed for the estimation of the aquifer hydraulic diffusivity and effective distance from the pumping well to the line of recharge from the measured temporal variation of stream flow depletion between two sections. During optimization, repeated computation of stream flow depletion is required; use of the proposed approximation simplifies the computation.

The flow at critical condition of an open channel is unstable. At critical condition, a small change in specific energy will cause abrupt fluctuation in water depth of the channel. This is because the specific energy curve is almost vertical at critical state. Therefore, if the design depth of the channel is near or equal to critical depth of the channel, the shape of the channel must be altered to avoid a large fluctuation in water depth. In the present study, a nonlinear optimization model is presented for designing an optimal channel section incorporating the critical flow condition of the channel. The optimization model derives the optimal channel section at a desirable difference from the critical condition of the channel so that a small change in the specific energy of the channel will not cause an abrupt change in flow depth. The objective of the optimization model is to minimize the total construction costs of the channel. Manning’s equation is used to specify the uniform flow condition in the channel. The developed optimization model is solved by sequential quadratic programming using MATLAB. Applicability of the model is demonstrated for a trapezoidal channel section with composite roughness. However, it also can be extended to other shapes of channel.