Journal of Irrigation and Drainage Engineering

ASCE and FAO-56 standardized reference evapotranspiration $\left({\mathrm{ET}}_0\right)$ equations were compared using data from 31 meteorological stations in Andalusia, Southern Spain. Comparisons were made between daily ${\mathrm{ET}}_0$ obtained by summing hourly standardized ASCE–Penman–Monteith estimations and calculated from the addition of hourly FAO56–Penman–Monteith estimations, daily ${\mathrm{ET}}_0$ estimated on a daily basis, and calculated by the Hargreaves equation. On an hourly basis, the FAO-56 version estimated lower than the ASCE version as 6% in some locations, with a difference of 4% on the average, mainly due to the higher surface resistance $\left(70\mathrm{s}{\mathrm{m}}^{-1}\right)$ used in the FAO-56 version during daytime periods, as opposed to the $50\mathrm{s}{\mathrm{m}}^{-1}$ $r_s$ value used by the ASCE version. Differences between both estimates were higher when evaporative demand increases. The level of agreement improved when the two computational time steps were compared, because differences were lower (2% on the average) and did not depend on the wind speed or ${\mathrm{ET}}_0$ values. The Hargreaves equation showed a higher spatial variability. At coastal areas, the equation generally underpredicted ASCE Penman–Monteith ${\mathrm{ET}}_0$ and provided good estimations for inland locations. Accuracy of the equation was affected by annual averages of evaporative demand and wind speed.

Remote sensing-derived spectral data have been used in the past to partition net radiation, soil heat, and sensible heat fluxes for estimating latent heat flux as a residual of surface energy balance, and thus regional evapotranspiration. Attempts to provide a simplified procedure for estimating sensible heat flux at a regional scale have not been successful because of the relatively strong dependence of the heat transfer coefficient on the land–atmosphere boundary condition. This paper presents a remote sensing-based procedure to estimate the sensible heat flux incorporating the local meteorological conditions, and in turn to determine the regional evapotranspiration. The model utilizes satellite-derived surface albedo, surface temperature, and leaf area index along with a very few agrometeorological data as inputs. The proposed procedure has been tested on a part of the Western Yamuna Canal system, India, and is found to be computationally simple as well as stable. For a well-watered wheat crop, the average evapotranspiration by the proposed model is estimated to be $2.05\mathrm{mm}\bullet {\mathrm{d}}^{-1}$ on January 30, 1996, whereas it is estimated to be $1.89\mathrm{mm}\bullet {\mathrm{d}}^{-1}$ using the Penman-Monteith equation, indicating a difference of less than 10%. The model is subjected to sensitivity analysis for uncertainties in the observed wind velocity and the computed leaf area index (by $\pm 20\%$ ) to estimate sensible heat flux. Results reveal that the percentage change in mean sensible heat flux for the image is less than 5% in all cases, thus indicating the acceptability of the model against the uncertainties. Further, the model has been applied to three sets of Landsat-TM data covering the Sone Low Level Canal system, India, to demonstrate its usefulness in evaluating water delivery performance.

In many river basins, upstream development and interannual variations in rainfall can cause both episodic and chronic shortages in water supplies downstream. Continued rapid development of surface and groundwater throughout the Krishna Basin in southern India resulted in historically low inflows to the main canals of the Nagarjuna Sagar irrigation project $\left(\mathrm{8,955}{\mathrm{km}}^2\right)$ during a recent drought (2002–2004). This paper presents an integrated approach to assess how cropping patterns and the spatial equity of canal flow changed with water supply shocks in the left canal command area $\left(\mathrm{3,592}{\mathrm{km}}^2\right)$ of Nagarjuna Sagar. We combined $3\text{years}$ (2000–2003) of canal release data with census statistics and high temporal resolution $(8–10\text{days})$ moderate resolution imaging spectrometer (MODIS) $500\text{-}\mathrm{m}$ resolution satellite imagery. The impact of water scarcity on land use pattern, delineated by MODIS images with moderate spatial resolution, was comparable with the census statistics, while the MODIS data also identified areas with changes and delays in the rice crop area, which is critical in assessing the impact of canal operations. A 60% reduction in water availability during the drought resulted in 40% land being fallowed in the left-bank canal command area. The results suggest that head reach areas receiving high supply rates during a normal year experienced the highest risks of fluctuations in water supply and cropped area during a water short year compared to downstream areas, which had chronically low water supply, and better adaptive responses by farmers. Contrary to expectations, the spatial distribution of canal flows among the three major zones of the command area was more equitable during low-flow years due to decreased flow at the head reach of the canal and relatively smaller decreases in tail-end areas. The findings suggested that equitable allocations could be achieved by improving the water distribution efficiency of the canal network during normal years and by crop diversification and introduction of alternative water sources during water shortage years. The study identified areas susceptible to decreases in water supplies by using modern techniques, which can help in decision-making processes for equitable water allocation and distribution and in developing strategies to mitigate the effects of water supply shocks on cropping patterns and rural livelihoods.

In this study, a new procedure for calibrating on-demand irrigation network models was developed. This procedure used a new objective function called maximum data with a reasonable error (MDRE) for calibrating the network. It was compared with the two more commonly used objective functions in calibration procedures that are the simple least squares (SLS) and the maximum likelihood estimator for the heteroscedastic error case (HMLE). In order to carry out the calibration, a quasi-Newton optimization method was used having as variable the Hazen-Williams head losses coefficient (C). This procedure was applied to an on-demand irrigation network located in Tarazona de La Mancha (Albacete, Spain) where flow and pressure at hydrant level was measured. The calibration procedure using the MDRE objective function was applied considering all the pressure control points simultaneously and the obtained results were compared with the results of considering the pressure control points independently. Therefore, the effect of the location of the pressure control point was studied. Results showed that, when the proposed objective function was used, the root mean squared error (RMSE) comparing the measured and simulated data after calibration was lower than when the SLS or HMLE objective functions were used. The location of the pressure control points throughout the irrigation network could affect the results; therefore, it was more accurate to use all the control points simultaneously than independently in the calibration process.

The SIMGRO hydrologic simulation model was extended to include irrigation practice. It could then be used to evaluate the effect of hydrologic changes in an irrigated area in the province of Mendoza, Argentina where, given an average annual rainfall of approximately $200\mathrm{mm}$ , irrigation is crucial for agriculture. A storage dam was recently constructed in the Mendoza River to control the fluctuating river flow and to guarantee that the demand for water is met throughout the year. The dam will impact on parts of the irrigation system where groundwater levels are already high and salinization occurs. To evaluate these changes and possible mitigation measures, two performance indicators that consider groundwater and surface water were used: Relative evapotranspiration and the depleted fraction. Scenario runs revealed that the irrigation water losses from the canals affect the groundwater levels in the downstream part of the irrigated area; an increase in salinity was also revealed.

Improving the performance of the major irrigation projects is one of the economically viable options in meeting the growing water demands and sustaining the productivity of irrigated agriculture under present financial, environmental, and physical constraints. Hydraulic simulation models offer unlimited opportunities for improving the performance of the irrigation systems by studying the flow behavior in a large and complex canal network under a variety of design and management scenarios. This paper presents a hydraulic simulation model developed for steady and unsteady flow simulation in irrigation canal network. The model uses the implicit four-point Preissmann scheme for discretization of the Saint-Venant equations and solves the resulting equations using the sparse matrix solution technique. The model is applicable for simulating flow in a series of linearly connected reaches, and branched as well as looped canal networks. The different boundary conditions that can be modeled are discharge hydrograph at the source node(s) and stage hydrograph, rating curve, uniform flow, and discharge hydrograph at the terminus node(s). The model is capable of handling different hydraulic structures such as weirs, sluice gate, drops/falls, pipe outlet, and imposed discharge. It also allows computation of gate opening for a given full supply level and discharge at the cross-regulator and offtaking points, respectively. For entering and editing canal network description and boundary conditions, including different hydraulic parameters and displaying the results, a user friendly graphical user interface has been provided. Accuracy and numerical stability of the model tested using the mass conservation test and test with ramp discharge as inflow hydrograph, indicated that the model performs satisfactorily. Comparison of simulated and observed discharges at the tail regulator of the Right Bank Main Canal of Kangsabati Irrigation Project showed that the model performs satisfactorily for most of the irrigation events. Further, comparison of the model simulated stage and discharge with that of the HEC-RAS model showed that the results of both the models are almost identical. The different simulation results, thus, suggest that the developed model can be successfully used as a tool for hydraulic simulation of canal network.

This work assesses the state of maintenance of the concrete-lined trapezoidal canals of the Menemen irrigation system at the end of the Lower Gediz Basin according to the values of roughness $\left(n\right)$ and active canal capacity (ACC). The study was carried out on two main canals, five secondary canals, and 12 tertiary canals at 45 measurement points. Average values of $n$ and ACC were found to be 0.023 and 69%, respectively, for the main canals, 0.018 and 93%, respectively, for the secondary canals, and 0.023 and 81%, respectively, for the tertiary canals. The fact that values of $n$ for the selected canals were higher than projected values and higher than the limit values, which would indicate adequate maintenance, and that the related ACC values were low, indicates that maintenance is insufficient in these canals. In order for maintenance work to be carried out more effectively, it may be suggested that new techniques should be applied for canal linings, which are economical and longer lasting, that farmers who benefit from the system should be given a more active role in maintenance work, and most importantly, that the associations responsible for maintenance should be supported financially in these activities.

Rain sensors (RSs) appear to be a useful tool for water conservation at a relatively low cost. However, little evidence related to RS performance and/or reliability exists. The objectives of this experiment were to: (1) evaluate two RS types with respect to the following: Accuracy of their set point, number of irrigation cycles bypassed, and duration in bypass mode; (2) quantify the amount of water that RSs could save; and (3) estimate their payback period. Mini-click (MC) and wireless rain-click (WL) rain sensor models were monitored. For the WL treatment, the dry-out ventilation windows were set half open, and for the MC treatments, rainfall set points of 3, 13, and $25\mathrm{mm}$ were established. On average, all treatments responded close to their set points with the WL, $3\mathrm{mm}$ MC, $13\mathrm{mm}$ MC, and $25\mathrm{mm}$ MC treatments averaging 1.4, 3.4, 10.0, and $24.5\mathrm{mm}$ , respectively. However, some replicates showed variable behavior. The number of times that these sensors shut off irrigation (81, 43, 30, and 8 times, respectively) was inversely proportional to the magnitude of their set point, with potential water savings following a similar trend. Where water costs exceed $0.53 per cubic meter ($2.00 per thousand gallons), the payback period is less than a year for WL and MCs set at $13\mathrm{mm}$ or less.

A mixed landscape irrigation study was conducted on 27 residential sites in Las Vegas to quantify water savings associated with satellite irrigation controllers. Seventeen sites were equipped with evapotranspiration-based (ET) satellite irrigation controllers and ten sites were designated as control sites and retrofitted with nonET-based irrigation controllers. Results showed that 13 of 16 ET-based controller sites saved water compared to four of ten of the nonET-based control sites. When all control sites were grouped together, a statistical difference occurred between the control and ET-based groups (ET-based controller= $+20\%$ savings) $(p<0.05)$ . Results from this study indicated that water savings were not because of deficit irrigations at the expense of the landscape plant material. Eighty-one percent of the variation in the total outdoor water use could be described by the total turfgrass area at each site. Such results would suggest that turfgrass limitations have merit, if the grass being restricted is tall fescue growing in an arid environment.

Soil temperature during springtime is an important factor for crop establishment and growth in poorly drained soils of northwest Minnesota. In this region, shallow water tables causing spring planting delays and excess water conditions during the growing season, may have contributed to significant unplanted cropland and yield reductions in recent years. Temperature is a regulating factor for many biological and chemical processes in the soil. One of the most commonly cited benefits of subsurface drainage on poorly drained soils is faster soil warm-up in the spring. Previous studies of this phenomenon do not provide definitive conclusions concerning the influence of soil drainage on soil temperature. The results of three site years of field observations of soil temperatures from drainage research plots at two locations in northwest Minnesota are presented herein. Replicated soil temperature and water table depths were measured continuously at five depths for two drain spacings and an undrained treatment. Subsurface drainage was found to significantly increase soil temperatures in both a coarser textured Vallers loam soil and a finer textured Hegne silty clay loam soil. Up to $4°\mathrm{C}$ temperature increases occurred primarily between May and July with the greatest increases at $30–60\mathrm{cm}$ depths. Treatments with narrow drainage spacing showed a greater spring temperature increase than treatments with wider drainage spacings.

The behavior of free surface flow at a rectangular free overfall is studied experimentally to obtain a relation between the brink depth and the flow rate. A series of experiments were conducted in a tilting flume with wide range of flow rates covering subcritical, critical, supercritical regimes, and two different roughnesses in order to develop a relationship between the discharge and the brink depth. An equation is proposed to determine the flow rate using the brink depth for a channel of known roughness and bed slope.

Reliable information on irrigation methods is important for determining agricultural water demand trends. Therefore, a study was conducted during 2002 to collect information on irrigation methods that were used by growers to irrigate their crops in 2001. The results were compared to earlier surveys to assess trends in cropping and irrigation methods. A one-page questionnaire was developed to collect information on irrigated land by crop and irrigation methods. The questionnaire was mailed to 10,000 growers in California that were randomly selected from a list of 58,000 growers by the California Department of Food and Agriculture, excluding rice, dry-land, and livestock producers. From 1972 to 2002, the area planted has increased from 15 to 31% for orchards and from 6 to 16% for vineyards. The area planted to vegetables has remained relatively static, while that planted to field crops has declined from 67 to 42% of the irrigated area. The land irrigated by low-volume (drip and microsprinkler) irrigation has increased by about 33%, while the amount of land irrigated by surface methods has decreased by about 31%. Sprinkler usage has decreased in orchards and vineyards, but it has increased in vegetable crops.

A channel or axisymmetric dimple filled with a coarse porous material and aimed at a temporary storage of infiltrated water as a perched water table aquifer is studied. The bottom shape is varied based on the criterion of maximal water storage after a certain period of drainage and evaporation. Leakage into the vadose zone through a thin liner occurs with a specific discharge proportional to the pressure drop across the liner. Evaporation through a horizontal shrinking water table is spatially uniform. An ordinary differential equation, which follows from the mass balance condition, is solved either explicitly or numerically. The class of triangular, polynomial, and conical sections is studied. The shape of maximal water retention is calculated for a given initial stored water volume or water table width, evaporation intensity, liner thickness and conductivity, vadose zone pressure beneath the liner, and selected time interval between two sequential infiltration events.

A method is proposed for identifying the head loss from the early drawdowns at the pumped well and an observation well. The new method is computationally simple and the calculations can be performed even on a hand-held calculator. The previously proposed methods for identifying the head loss requires a long duration pumping test, while the new method requires only a short duration pumping test. The use of the proposed method would save time and money and would be of help to field and practicing engineers. A nondimensional coefficient of head loss is also proposed, which permits a meaningful comparison of the efficiency conditions of different wells.