Journal of Irrigation and Drainage Engineering

A complete methodology to predict water distribution in laterals and units of subsurface drip irrigation (SDI) is proposed. Two computer programs have been developed for the hydraulic characterization of SDI; one for laterals and the other for units. Emitter discharge was considered to depend on hydraulic variability, emitter’s manufacture and wear variation, and soil pressure variation. A new procedure to solve the hydraulic calculation of SDI looped network has been established. Moreover, spatial distribution of soil variability was estimated by a geostatistical modeling software that is coupled with the computer programs. Thus the evaluation and performance of laterals and units of SDI can be addressed by changing input variables such us: length and diameters of laterals; coefficients of emitter’s discharge equation; coefficient of variation of emitter’s manufacture and wear; local losses at the emitter insertion; inlet pressure; and soil hydraulic properties and its spatial variability. Finally, the methodology has been applied to different scenarios, and some recommendations are outlined for the selection of emitter discharge and inlet pressures.

The performance of drip irrigation and subsurface drip irrigation (SDI) laterals has been compared. Two emitter models (one compensating and the other noncompensating) were assessed. Field tests were carried out with a pair of laterals working at the same inlet pressure. A procedure was developed that recorded head pressures at both lateral extremes and inlet flow during irrigation. Both models showed similar behavior and soil properties affected their discharge. On the other hand, the performance of a field SDI unit of compensating emitters was characterized by measuring pressures at different points and inlet flow. Finally, the distribution of water and soil pressure in the laterals and the unit were predicted and irrigation uniformity and soil pressure variability were also determined. Predictions agreed reasonably well with the experimental observations. Thus, the methodology proposed could be used to support the decision making for the design and management of SDI systems.

Researchers developed several mathematical models for simulating furrow irrigation using the Saint-Venant equations. Most of these irrigation models use numerical techniques to solve these equations, which in general, require extensive programming and computational skills. Moreover, several of these models consider uniform soil and use empirical equations for modeling infiltration. In this article, a physically based furrow irrigation model was presented for simulating flow in irrigated furrows under both uniform and layered soils. The model consisted of an overland flow and an infiltration module that are modeled using analytical solution of the zero-inertia and the Green and Ampt [one-dimensional and two-dimensional infiltration equations) equations, respectively. Furthermore, the infiltration was also modeled using the Kostiakov-Lewis infiltration equation. The model considered all possible furrow shapes and included graphical user interface. The developed model was evaluated using the field data and the model performance was discussed in the second part of the article.

In this study, the physically based furrow irrigation model presented in Part 1 was evaluated using the experimental data collected from a field plot consisting of three 40-m-long free-drained furrows of parabolic shape and having a top width of 0.30 m, a depth of 0.15 m, and a slope of 0.5%. The irrigation experiments were carried out with a constant inflow of $0.2–0.5l{s}^{-1}$ and $0.3–0.7l{s}^{-1}$ on bare and cropped fields, respectively. The field data pertaining to furrow cross section, advance and recession times, water depth and velocity, and runoff rate and volume were collected from the irrigation experiments. The model performance was studied for simulating advance, recession, infiltration, and runoff using two–dimensional (2D) Fok, one–dimensional (1D) Green-Ampt, and KL infiltration functions (Part 1) by estimating the root mean square error and index of agreement $\left(I_a\right)$ . For all the irrigations performed under bare and cropped furrow conditions, the model slightly overpredicted the advance time and runoff rate and slightly underpredicted the recession time and infiltration using the 2D Fok, 1D Green-Ampt, and KL infiltration functions. Furthermore, simulated results were closer to their observed counterparts for 2D Fok infiltration function than for 1D Green-Ampt and KL infiltration functions. Sensitivity analysis was carried out to study the effect of ±5 and ±10% change in 2D or 1D infiltration parameters (i.e., $K_s$ and $S_{\text{av}}$ ) and KL infiltration parameters (i.e., $A_k$ and $B_k$ ) on outputs. $K_s$ is the most sensitive parameter for predicting advance time, infiltration, and runoff followed by $S_{\text{av}}$ . In the KL infiltration parameter, $B_k$ is the most sensitive parameter for estimating advance and recession times, infiltration, and runoff. The test results of the model suggested that the model can be used as a tool for designing and managing furrow irrigation.

A methodology based on indicators was developed to study the quality of service provided in irrigation distribution networks. The indicators were divided into network descriptors and operational indicators, some calculated periodically and others in real time. The methodology has been applied to the Palos de la Frontera irrigation district (Spain) using information on flows, volumes, and pressures collected via remote metering devices linked to a central computer database. The results showed that the service provided in the district has good quality in terms of flow adequacy, distribution efficiency, and pressure and supply reliability. Problems dealing with the remote control system have been identified. Categories for the indicators have been established, studying the percentage of control points included in each and their probability of occurrence. The methodology is useful to determine the main problems in a distribution service and areas in the network which need improvement.

Four rectangular sluice gates were calibrated for submerged-flow conditions using nearly 16,000 field-measured data points on Canal B of the B-XII irrigation scheme in Lebrija, Spain. Water depth and gate opening values were measured using acoustic sensors at each of the gate structures, and the data were recorded on electronic data loggers. Several gate calibration equations were tested and it was found that the rectangular sluice gates can be used for accurate flow measurement. The Energy-Momentum (E-M) equations proved to be sound. The calibration of the contraction coefficient, to be used in the energy equation, allowed good estimations of the discharge for three of the four gates studied. The gate for which the E-M method did not perform satisfactorily was located at the head of the canal with a unique nonsymmetric approach flow condition. Alternatively, we investigated the performance of the conventional discharge equation. The variation of the discharge coefficient, $C_d$ , with the head differential, $\Delta h$ , and the vertical gate opening, $w$ , suggests that $C_d$ be expressed as a function of these two variables. For the sluice gates considered in this study, the best empirical fit was obtained by expressing $C_d$ as a parabolic function of $w$ , although an exponential expression tested previously by other writers also produced satisfactory results. The greatest uncertainty in the variables considered in this study was in the calculated coefficient of discharge, and based on the uncertainty analysis, it is possible to quantify the uncertainty in the estimated discharge through a calibrated sluice gate. The discharge uncertainty in each of the four gates in this study decreases with increasing gate opening, and it decreases slightly with increasing head differentials.

One basic principle of fluid mechanics used to resolve practical problems in hydraulic engineering is the Bernoulli theorem along a streamline, deduced from the work-energy form of the Euler equation along a streamline. Some confusion exists about the applicability of the Bernoulli theorem and its generalization to open-channel hydraulics. In the present work, a detailed analysis of the Bernoulli theorem and its extension to flow in open channels are developed. The generalized depth-averaged Bernoulli theorem is proposed and it has been proved that the depth-averaged specific energy reaches a minimum in converging accelerating free surface flow over weirs and flumes. Further, in general, a channel control with minimum specific energy in curvilinear flow is not isolated from water waves, as customary state in open-channel hydraulics.

A graphical procedure is presented for sizing single-outlet detention basins to control stormwater runoff from small catchments in the semiarid southwestern United States. The approach relies on the modified rational method to provide the catchment runoff hydrograph, a linearized relation between basin water depth and storage volume, and a rainfall-intensity-duration equation for which coefficients can be found easily for any location covered by NOAA Atlas 14, Volume 1 (Arizona, Southeast California, Nevada, New Mexico, and Utah). Numerical solutions of a dimensionless form of the differential detention storage continuity equation are carried out, and solution values are related to a dimensionless discharge coefficient that provides a comprehensive characterization of catchment hydrology, outlet structure type and size, and regional precipitation. Graphs that supply dimensionless values of the maximum peak outflow rate from a basin, the maximum storage volume, and the critical storm duration (that is, the storm duration that produces the peak outflow and maximum storage volume) are prepared from the numerical solutions. The method avoids repetitive calculations and provides accurate solutions rapidly in an uncomplicated way for small catchments of about 12 ha or less with times of concentration less than about 30 min.

Understanding water flow and its relative quantities through different pathways is vital for watershed management. Like many problems in hydrology, numbers of methods have been proposed for streamflow partitioning. Five methods were identified as being the most relevant and least input intensive. This study tested performance of these methods against separately measured surface and subsurface flow data from the coastal plain physiographic region of the southeastern United States. Separately measured surface and subsurface flow were collected for 12 years (1970–1981) in a field scale watershed by the Southeast Watershed Research Laboratory of the USDA-Agricultural Research Service. Results of comparative analysis indicated that Method IV performed the best. Results also indicated that accuracy of this method is highly dependent upon the proper estimation of the “fraction coefficient” that is based on many physical and hydrologic characteristics of the watershed. This study concluded that deterministic/empirical methods such as Boughton’s Method IV, require proper parameter value for increased accuracy.

Analytical but approximate invertible equations for time base of gamma unit hydrographs or unit kernel hydrograph (UKH), which are applicable to all catchments, are derived in terms of the parameters of the unit hydrograph. The time base has been linked to the time to peak and lag time for the gamma UKH. The gamma UKH is redefined taking the time base and time to peak as parameters, as these parameters are physically more conceivable than the conventional parameters. The widely used National Resource Conservation Service empirical equations for the time base are found not applicable to all catchments. The proposed equations can also be used for determining the conventional parameters from the known values of the time base and time to peak or lag time. Using the proposed equations for time to peak and time base, the gamma UKH is fitted to few published storm events considering the time base as a parameter.