Journal of Irrigation and Drainage Engineering

Extensive field investigations allowed depiction of soil water salinity within two large representative regions of a river valley that has been irrigated for more than 120 years. The nature and severity of the salinity problem is captured by hundreds of field surveys, encompassing tens of thousands of measurements and spanning 9 years. Soil water extract salinity, averaged over all surveys and all measured locations, is $4.1\mathrm{dS}{\mathrm{m}}^{-1}$ in the Upstream Study Region and $6.2\mathrm{dS}{\mathrm{m}}^{-1}$ in the Downstream Study Region. Variability over the measurements is substantial, with a coefficient of variation of approximately 0.51 Upstream and 0.39 Downstream. Relationships to soil and groundwater conditions also were explored, providing field-based insights into major contributing factors and into the value of measuring those factors as part of a salinity reconnaissance. A broad survey, like that described herein, affords a sense of the magnitude of economic loss, in terms of crop-yield reduction, that is exacted by irrigation-induced salinity. Evaluation of the measurements in relation to an estimated average threshold for crop-yield reduction indicates that approximately 42% of the more than 122,000 locations surveyed over both regions had ${\mathrm{EC}}_e$ values exceeding the corresponding threshold. Average yield reductions due to soil water salinity are approximately 6% over surveyed locations Upstream and 17% over locations Downstream. Moreover, survey results point toward general targets for irrigation and drainage planning and form a basis for the development of more detailed solutions using computational modeling.

A river salinity model has been developed on the 21 major canal areas in the lower Arkansas River Basin in Colorado to address the impact of irrigation return flow on the river. The quantity of the return flow is predicted by constructing response functions for tailwater, canal leakage, and in-field deep percolation so that the spatial and temporal distribution of the return flow can be simulated. A groundwater table surface is generated using water table elevation data from 974 wells in the study area to establish flow paths and travel time for groundwater. The quality of the return flow is predicted by simulating the evapoconcentration process in the root zone soil in which hydro-chemical reactions occur and affect the salinity of in-field deep percolation water. The effects of shallow water table and high soil salinity on crops are simulated to account for the impacts that these two factors have on crop consumptive use. Model calibration and validation over a 192-month period from January 1986 to December 2001 show strong agreement between the observed and simulated values of river flow volume and river salinity. The simulation results show that irrigation return flows, including tailwater and groundwater return flows, significantly increase river quantity, but that groundwater return flow is also a major component of river salinity. There is significant seasonal fluctuation in river salinity and soil water salinity. The increase of soil water salinity from the soil surface to the bottom of the root zone is significant and will cause salt to be loaded to the groundwater. The simulation from 1991–2001 indicates that 20.9% of the 19,944 million ${\mathrm{m}}^3$ of irrigation water applied to Colorado’s lower Arkansas Valley becomes canal leakage, 22.5% is in-field deep percolation, and 22.9% becomes tailwater. This study assesses the effect of reducing agricultural irrigation on river salinity. Consider the scenario of three major canals stopping irrigation and transferring a portion of the curtailed water to off-basin cities with the remaining portion released to the river. The results indicate that, in order not to increase river salinity for downstream reaches, the portion of water transferred to cities should not exceed 50%.

Accurate estimates of spatially distributed evapotranspiration (ET) are essential for managing water in irrigated regions and for hydrologic modeling. METRIC (Mapping ET at high Resolutions with Internal Calibration) energy balance algorithm was applied to derive ET from six high-resolution aircraft images (0.5–2.0 m pixels). Images were acquired over the USDA Agricultural Research Service (USDA-ARS) Conservation and Production Research Laboratory (CPRL) in the semiarid Southern High Plains. The remote sensing (RS) campaign occurred during the 2007 summer cropping season. Daily ET estimations were evaluated using measured ET data from five monolithic weighing lysimeters located in the CPRL. On average, errors in estimating hourly ET were $-0.7\pm 11.6\%$; for daily ET, errors were $2.4\pm 9.3\%$. Results indicated that METRIC algorithm estimated ET values well when the surface roughness for momentum transfer considered heterogeneous surface conditions and when the grass reference ET fraction was used to extrapolate instantaneous estimates of ET. Results showed that it was possible to apply METRIC with airborne images in a semiarid environment. However, an appropriate (or combination of) surface roughness length and ET extrapolation methods have to be incorporated into the ET algorithm.

Despite the conceptual simplicity of Monte Carlo-simulation methods in assessing uncertainty in hydrogeological systems, their use is limited by expensive computational requirements in terms of the large number of realizations that must be processed. Cluster analysis was applied in this paper to reduce the number of realizations to be processed by flow simulators while efficiently approximating flow-response statistics. Different clustering techniques were used to partition the ensemble of realizations into a few clusters that were significantly different from each other and had maximum intracluster similarity. The clustering step was achieved by using different similarity metrics. Then a subsample of the realizations was collected to represent the uncertainty in the whole ensemble. Two methods for collecting the subsample were investigated: the stratified sampling and centroid-based sampling. The performance of different clustering and sampling techniques was tested by evaluating the mismatch between the statistics of the ensemble response (the reference response) and the subsample response, which are estimated from the clusters. Results show that 25% of the realizations in the ensemble may be sufficient to estimate the uncertainty in the flow responses when a suitable clustering method and suitable similarity measures are used.

This study presents a linear and a mixed-integer linear (MIL) model for optimizing an irrigation water allocation and a multicrop planning problem. The main objective was to maximize net benefit for all cultivated crops within irrigated areas in a reservoir-irrigation system in Iran. The linear model was optimized with linear programming (LP) method and continuous particle swarm optimization (CPSO) algorithm to make a detailed comparison between the LP method and CPSO algorithm results. The optimal solution obtained by the CPSO algorithm and LP method in the linear model were comparable. However, the optimal allocated areas for both crops and orchards in the linear model obtained by the LP method and CPSO algorithm were not directly applicable in real crop planning situations. Consequently, the MIL model was developed for which a discrete particle swarm optimization (DPSO) algorithm was used to obtain an applicable and allowable solution for the problem. Contrary to LP and CPSO, the DPSO algorithm was competent to deal with the MIL model. The results showed that the discrete nature of cropping area variables in the MIL model had a significant effect on assigned areas and reservoir operation policies. It was found that the inapplicable assigned area by the LP method and CPSO algorithm for some crops was eliminated from optimum selected cropping areas by the DPSO algorithm. The statistical assessment showed that the CPSO and DPSO algorithms were both able to limit the variations of annual net benefit within the acceptable range of no more than 2%. The number of function evaluations for obtaining optimal annual net benefit and the standard deviation of the results in 50 independent runs in the MIL model was 167,000 and 0.81, respectively by the DPSO algorithm as compared with 200,000 and 1.09 by the CPSO algorithm in the linear model. Thus, the DPSO algorithm could direct the objective function value in a faster way and with more accuracy than CPSO algorithm.

The objective of this study is to assess stable irrigation water capacity and erosion on the basis of water and sediment balance analysis of land use change. The reservoir water balance analysis is calculated by the daily irrigation reservoir operation model (DIROM) for simulating daily inflow and release rates for irrigation reservoirs. The reservoir capacity change for assessing the sediment flux is predicted using the universal soil loss equation (USLE), sediment delivery ratio (SDR), and trap efficiency. To analyze soil erosion changes according to land use changes, Landsat-5 images were selected. Spatial distribution of deposited sediment is estimated by the U.S. Bureau of Reclamation (USBR) method and the hydrodynamic, sediment and contaminant transport model (HSCTM-2D), which is a finite-element model for simulating surface water flow and sediment transport. The model performance was verified by comparing simulated and observed data. The simulated results, which were validated using an internal mass balance method because of the scarce observed data, showed that the soil erosion of the Lake Asan watershed has increased at a rate of 2% per year from 1986 to 2000, and the storage capacity after 50 years will decrease by 65% without proper sediment conservation implementation. It is necessary to maintain stable irrigation water capacity by appropriate management of reservoir rehabilitation. The annual dredge amount was determined by various dredge scenarios according to the sediment removal volumes using frequency analysis. This approach will be useful for managers to identify the location and amount in which sediment dredging would be best for stable irrigation water supply maintenance.

The correct estimation of conveyance water losses from an irrigation system is vital for the proper management for the system. Seepage is the most dominant process by which water is lost in the canal. Thus, for the effective operational planning and management of an irrigation system, a dependable forecasting of the seepage is very important. Seepage rates are obtainable either by direct measurement or by estimation. This study investigated the usefulness of the equations of Moritz and Davis-Wilson in estimating the seepage losses of concrete-lined canals. Seepage losses of the concrete-lined trapezoid canals of the Menemen irrigation system at the end of the Gediz basin were measured by the inflow-outflow method and the results were compared with the estimates of seepage losses given by the use of these two equations. Average seepage losses were measured as $107.6\mathrm{l}{\mathrm{s}}^{-1}{\mathrm{km}}^{-1}$ for the main canal, $32.1\mathrm{l}{\mathrm{s}}^{-1}100{\mathrm{m}}^{-1}$ for the secondary canals, and $11.7\mathrm{l}{\mathrm{s}}^{-1}100{\mathrm{m}}^{-1}$ for the tertiary canals. Standard deviation and variation coefficients were found to be $79\mathrm{l}{\mathrm{s}}^{-1}{\mathrm{km}}^{-1}$ and 73%, respectively, for the main canal, $29\mathrm{l}{\mathrm{s}}^{-1}100{\mathrm{m}}^{-1}$ and 89%, respectively, for the secondary canals, and $17\mathrm{l}{\mathrm{s}}^{-1}100{\mathrm{m}}^{-1}$ and 158%, respectively, for the tertiary canals. Actual seepage losses from the main canal, the secondary canals, and the tertiary canals were all much higher than the standards and showed a wide margin of variability. As in the study area, seepage losses in other irrigation systems in Turkey are much higher than the standards, and since the seepage losses estimated by the Moritz and Davis-Wilson equations are much lower than the measured values, the use of these empirical equations in the estimation of seepage losses is not possible. These equations, if used, should be calibrated for existing canal conditions.

Soil erosion is caused, at least in part, by the effect of kinetic energy on the soil during rainfall. Therefore, a better knowledge of rain parameters is useful. To assess the influence of rain on the amount of soil loss, an experimental site was set up in the Chianti hills (central Italy). Tipping-bucket rain gauges and the Joss-Waldvogel disdrometers were used. A colocated system of gauges provided soil loss and runoff measurements for rainfall events that occurred between September 2006 and June 2007. The reliability of a widely used rainfall erosion index was also assessed and the effect of kinetic energy, computed by the measured drop size distribution, evaluated. The results highlighted the potential of the physical approach in computing the kinetic energy developed by the rain drops to the soil, especially for higher rainrates and when the hydrological balance is positive or slightly negative. The kinetic energy estimate from the rain rate well reproduces the measured values only below $10\mathrm{J}·{\mathrm{m}}^{-2}$, whereas an underestimation is present for higher rainrates, because of the contribution of large drops.

Since the early 1990s, a water quality capture volume (WQCV) has been recommended for stormwater quality enhancement designs. However, lacking further guidance on how to shape the basin for this recommended volume, the current practice is to assume that the WQCV would lead to a satisfactory sediment trap efficiency provided that the drain time can be as long as 40 hours. In this study, the sediment trap efficiency method is modified to take basin dimension, drain time, and micropool into consideration. A water quality control basin (WQCB) should be designed with a preselected drain time and water surface area and then evaluated by its sediment trap efficiency. For a typical urban residential development with sediment particles consisting of clay, silt, and sand, a drain time for WQCB can be between 12 and 40 hours with its sediment trap efficiency varied from 60 to 80%. A drain time longer than 12 hours may result in a diminishing return on sediment trap efficiency. The performance of WQCB can be improved with a micropool. The case study indicates that a micropool can only increase the sediment trap efficiency from 80 to 89% when its storage volume increases from zero to WQCV. It implies that the major function of micropool is to control resuspended solids and buoyant debris.

The suitability of the widely used existing solution for calculating groundwater mound due to artificial recharge from rectangular areas is examined for its applicability to unconfined aquifers, and this solution has been found applicable only to confined aquifers. The solution applicable for confined aquifers is derived and shown equivalent to the existing solutions. A computationally simple function is proposed for accurately approximating the integral appearing in this or existing solutions. A procedure involving analytical approximation is outlined for using this solution for unconfined aquifers. A method to calculate groundwater mound height in unconfined aquifers due to arbitrarily varying temporal recharge (percolation) is also proposed. It is hoped that the proposed methods would be of help to field engineers and practitioners.

A simple and low-cost flow-measurement method for the field calibration of weirs is described. With this method, accurate estimations of the flow rate over a weir can be made on the basis of volumetric flow measurements of a fraction of the total flow, using common equipment. Two variants of the method, suitable for the calibration of rectangular or auxiliary profiled weirs, are described. The method, under specific conditions, can be also used for the field calibration of other flow-measurement or irrigation structures.

Advanced mathematical models of surface irrigation use the equations of motion applied to a series of cells comprising the surface stream and an infiltration profile. In the simulation, a mass balance must be preserved among the inflow, surface stream, infiltrated profile, and runoff volumes. The shapes of the profiles are not known a priori, yet the curvature of the element boundaries influences the calculation of the volume contained therein, especially near the front of the irrigation stream. This paper presents a focus on the shape of the subsurface volume elements comprising the infiltration profile. Previous calculations of shape factors documenting departures from assumed first-order approximations (trapezoidal shapes) have been on the basis of empirical equations selected to describe infiltration as a function of wetting time. Modern simulations are not always on the basis of empirical formulas but increasingly rely on solutions of physically based approaches, such as the Green-Ampt or Richard's equation. These solutions provide only tabulated values of infiltration and infiltration rates along the profile. The proposed generic approach calculates shape factors for each cell of the profile on the basis of the calculated change in infiltration rates on the two sides of the cell.