Journal of Irrigation and Drainage Engineering

This paper presents a procedure based on a lateral, where the flow rate of all the emitters and the pressure every $10\mathrm{m}$ were measured. Our goal was to obtain a general formula for directly calculating the local losses of on-line emitters as a function of the number of emitters, the average emitter discharge, and the ratio between the protrusion area and the pipe cross-sectional area. A total friction factor, including the local losses and the Blasius friction factor, was obtained as well. Both approximations accurately predict the local and total losses for the experimental data obtained in an irrigation loop system placed in the Rural Engineering Laboratory. Finally, an estimation of these local losses using a computational fluid dynamics model was carried out by the writers. Our numerical approach accurately predicts the local losses and allows the use of this technique to obtain a better estimation of the local turbulence originated by the emitter’s connection.

The use of subsurface drip irrigation (SDI) is increasing for many reasons, including its many agronomic advantages and the ability for safe application of wastewater to crops. In contrast to surface drip irrigation, soil hydraulic properties may affect SDI performance, particularly for new SDI systems designed to operate under low pressure (e.g., $2\mathrm{m}$ of head). This work introduces a new approach for solving problems of predicting discharge in SDI laterals. We accomplish this by coupling models of head loss in laterals and soil impacts on dripper discharge. The coupled model enables an evaluation of the performance of SDI laterals while changing inputs, such as the lateral diameter, length and slope, dripper nominal discharge and exponent, inlet pressure head, soil hydraulic properties, and soil spatial variability. This model is used to determine the coefficient of variation of discharge for two numerical comparisons.

Adequate hydraulic analysis of a multiple outlets pipelines is very important for the design and evaluation of irrigation systems. In this paper, an analytical direct design procedure for a single multiple outlets pipelines is presented. The proposed equations, taking into consideration the influence of local energy loss, are suitable for designing laterals and manifolds in both trickle and sprinkler irrigation systems, and can be applied for various types of outlet, different flow regimes, and uniform line slope ranges. In this analytical procedure, for any desired uniformity level and given design slope range with remaining known parameters, the pipe diameter and the pipe length can then be directly designed. For any desired uniformity level, the procedure also provides an opportunity to evaluate the influence of local energy loss, as well as the influence of different uniform line slopes on the pipe geometric characteristics (pipe size and length), and on the corresponding hydraulic variables (operating inlet pressure head, downstream end pressure head, and total energy loss). Comparison test with a revised step-by-step numerical method for various slope combinations indicated that the presented methodology produces sufficiently accurate results for various design cases in both trickle and sprinkler lateral design. The methodology is simple, easy to apply, and useful for hydraulic analysis and direct design of a multiple outlets pipelines in irrigation subunits.

A model is introduced that utilizes geographic information systems (GIS) to predict relative reductions in crop yield due to salinity and waterlogging at a field-scale by incorporating spatially and temporally variable crop, climatic, and irrigation data to simulate crop yields. This model utilizes soil and water data commonly collected in field-scale studies. The model’s algorithms are integrated into a GIS (ARCVIEW 3.2) as an extension. The result is a model that does not require extraordinary data collection but will provide practical insight into the spatial effects of salinity and waterlogging on crop yields.

The sensitivity of the standardized ASCE grass-reference Penman-Monteith evapotranspiration (ASCE-PM $E{T}_o$ ) equation to climate variables in different regions has not yet been studied. Sensitivity analyses for the standardized daily form of the ASCE-PM equation were conducted on wind speed at $2\mathrm{m}$ height $\left(U_2\right)$ , maximum and minimum air temperatures ( $T_{\max }$ and $T_{\min }$ ), vapor pressure deficit (VPD), and solar radiation $\left(R_s\right)$ in the following regions of the United States: semiarid (Scottsbluff, Nebraska, and Bushland, Texas), a Mediterranean-type climate (Santa Barbara, California), coastal humid (Fort Pierce, Florida), inland humid and semihumid (Rockport, Missouri, and Clay Center, Nebraska), and an island (Twitchell Island, California). The sensitivity coefficients were derived for each variable on a daily basis. In general, $E{T}_o$ was most sensitive to VPD at all locations, while sensitivity of $E{T}_o$ to the same variable showed significant variation from one location to another and at the same location within the year. After VPD, $E{T}_o$ was most sensitive to $U_2$ in semiarid regions (Scottsbluff, Clay Center, and Bushland) during the summer months. The $R_s$ was the dominant driving force of $E{T}_o$ at humid locations (Fort Pierce and Rockport) during the summer months. At Santa Barbara, the sensitivity of $E{T}_o$ to $U_2$ was minimal during the summer months. At Bushland, Scottsbluff, and Twitchell Island, $E{T}_o$ was more sensitive to $T_{\max }$ than $R_s$ in summer months, whereas it was equally sensitive to $T_{\max }$ and $R_s$ at Clay Center. The $E{T}_o$ was not sensitive to $T_{\min }$ at any of the locations. The change in $E{T}_o$ was linearly related to change in climate variables (with $r^2⩾0.96$ in most cases), with the exception of $T_{\min }$ , at all sites. Increase in $E{T}_o$ with respect to increase in climate variable changed considerably by month. On an annual average, a $1°\mathrm{C}$ increase in $T_{\max }$ resulted in 0.11, 0.06, 0.16, 0.07, 0.11, 0.08, and $0.10\mathrm{mm}$ increases in $E{T}_o$ at Scottsbluff, Santa Barbara, Bushland, Fort Pierce, Twitchell Island, Rockport, and Clay Center. A $1\mathrm{m}\bullet {\mathrm{s}}^{-1}$ increase in $U_2$ resulted in 0.42, 0.18, 0.37, 0.28, 0.31, 0.20, and $0.26\mathrm{mm}$ increases in $E{T}_o$ at the same locations. A unit increase in $T_{\max }$ resulted in the largest increase in $E{T}_o$ at Bushland, and a unit increase in $R_s$ caused the largest increases in $E{T}_o$ at Fort Pierce. A $1\mathrm{MJ}{\mathrm{m}}^{-2}\bullet {\mathrm{d}}^{-1}$ increase in $R_s$ resulted in 0.05, 0.08, 0.06, 0.11, 0.05, 0.06, and $0.06\mathrm{mm}$ increases in $E{T}_o$ at the same locations. A $0.4\mathrm{kPa}$ increase in VPD resulted in 1.13, 0.54, 1.29, 0.57, 1.04, 1.10, and $1.22\mathrm{mm}$ increases in $E{T}_o$ at the same locations. The $U_2$ had the most effect on $E{T}_o$ at Scottsbluff and Bushland, the two locations where dry and strong winds are common during the growing season. The sensitivity coefficient for $R_s$ was higher during the summer months and lower during the winter months, and the opposite was observed for VPD (except for Twitchell Island). The decrease of the sensitivity coefficients for $R_s$ corresponding to an increase in the sensitivity coefficient for VPD is due to a decrease in the energy term in favor of the increase in significance of the aerodynamic term of the standardized ASCE-PM equation in summer versus winter months. Because the ASCE-PM and the Food and Agriculture Organization paper number 56 Penman-Monteith (FAO56-PM) equations are identical when applied on a daily time step, the results of the sensitivity analyses and sensitivity coefficients of this study should be directly applicable to the FAO56-PM equation.

The technology of irrigated agriculture has often been controversial. The development agencies would praise its productivity, as only 18% of the world’s cultivated land is irrigated but produces roughly 33% of the world’s human food supply. Environmental and ecological concerns cite the degradation of natural landscapes, elimination of floodplains and wetlands, and profound impacts on wildlife habitats. Dr. Mark Fiege (University of Washington Press, Seattle, 1999) in his book entitled Irrigated Eden: The Making of an Agricultural Landscape in the American West proposes a possible reconciling view—that irrigation should be viewed as a manmade ecological system, in which land and water are modified to increase agricultural production. The reported research has used this ecological approach to study the Middle Rio Grande irrigated landscape, for the purpose of identifying options for water and ecosystem conservation. This article presents research findings related to opportunities in the agricultural sector to reduce water diversions from the river, primarily by changing the practice of continuous canal water delivery to rotational water delivery. Following the research recommendations since 2002, irrigation water users in the Middle Rio Grande Valley have reduced their diversions by more than 30%, which means more water is now available in the river for better ecology in general and for better fish and wildlife habitat in particular.

The effect of specific initial and boundary conditions is generally not considered when applying the Kostiakov infiltration functions. A methodology is developed to account for changes in water levels and initial soil moisture. First, Richards’ equation is solved numerically to generate a database of one-dimensional infiltration values, with varying initial (water content or pressure head) and boundary (ponding depth) conditions for three contrasting soils. These are then used to calibrate corresponding coefficients for modified Kostiakov models and, by considering linear regressions, to obtain simple correction factors. Results show that the correction factors are not universally valid, and only the correction to the Kostiakov $k$ parameter shows statistically consistent applicability. However, examples demonstrate potentially significant improvement in the accuracy of irrigation models by correcting the Kostiakov equation to account for initial and boundary conditions.

Springs that appear at multiple sites on sloping lands and create problems of excess soil moisture and reduced crop yield require the implementation of a network of intercepting drains. The water removed by the intercepting drains also needs to be conducted to a collecting shaft or main drain, whereby it can be safely utilized or discharged back to a lower-lying position in the landscape. In this paper, we present a design method for establishing the position of the first row of interceptor drains and the number of successive rows of intercepting drains, as well as the distances between them. The first row of intercepting drains must be placed upstream of the upper limit of the wet area, through those points at which water-bearing material is found at $40–50\mathrm{cm}$ underground. The number of rows of necessary intercepting drains is determined from the ratio between the thickness of water-bearing material and the thickness of the $\text{filter}+\text{drain}$ . For multiple springs that are concentrated on the surface of sloping lands, we propose the solution of a collecting chamber with a side drain and bottom filter.

Three bioretention field sites in North Carolina were examined for pollutant removal abilities and hydrologic performance. The cells varied by fill media type or drainage configuration. The field studies confirmed high annual total nitrogen mass removal rates at two conventionally drained bioretention cells (40% reduction each). Nitrate-nitrogen mass removal rates varied between 75 and 13%, and calculated annual mass removal of zinc, copper, and lead from one Greensboro cell were 98, 99, and 81%, respectively. All high mass removal rates were due to a substantial decrease in outflow volume. The ratio of volume of water leaving the bioretention cell versus that which entered the cell varied from 0.07 (summer) to 0.54 (winter). There was a significant $(p<0.05)$ change in the ratio of outflow volume to inflow volume when comparing warm seasons to winter. Cells using a fill soil media with a lower phosphorus index (P-index), Chapel Hill cell C1 and Greensboro cell G1, had much higher phosphorus removal than Greensboro cell G2, which used a high P-index fill media. Fill media selection is critical for total phosphorus removal, as fill media with a low P-index and relatively high CEC appear to remove phosphorus much more readily.

There is a worldwide movement for coastal municipalities in developed countries to replace whole series of storm drains with far fewer storm-water outfalls that discharge well offshore. Such an extended-length pipe, passing into the surf zone along an exposed coastline, is far from easy to plan, support with data, design, install, and operate. This paper is intended to school drainage engineers in these matters.

An optimal shape design problem for an empty drainage ditch is solved and it is shown that a semicircle intercepting saturated seepage from two constant potential rays is a contour of constant Darcian velocity and of maximal excavated volume at a given flow rate and ditch width. The corresponding family of isobars belongs to the class of conchoids of Nicomedes. The optimal flow is generated by a hydrodynamic dipole placed in a gravitational field.

Steady, essentially two-dimensional, tension-saturated seepage from a flat-bottomed soil channel in an arid environment is studied analytically. Physically, the action of capillary spreading, evaporative drive to the atmosphere both from the near-channel banks and capillary fringe boundary, Darcian resistance of the matrix and gravity are juxtaposed and result in trifurcation of infiltrated water into deep percolation and semi-infinite evaporation “wings” with two hinge points on the soil surface and two dividing streamlines. Mathematically, free boundary problem is solved by conformal mappings and the Polubarinova-Kochina boundary-value problem method. The dependence of deep percolation losses and evaporative return flow on the channel width, conductivity, static capillary rise height, and intensity of evaporation is found.

A continuous time function with two parameters for a curvilinear dimensionless unit hydrograph (CDUH) is derived from the unit hydrograph in the form of a gamma probability density function. This equation is then applied to the Natural Resources Conservation Service [formerly, Soil Conservation Service (SCS)] curvilinear dimensionless unit hydrograph [NRCS (SCS) CDUH]. The values of the parameters are slightly different for the rising and recessing limbs of the unit hydrograph. The NRCS unit hydrograph that expresses the time distribution of runoff of unit depth is shown to be a two-parameter gamma probability density function. Its mass curve is, therefore, an incomplete gamma function. This technical note explains mathematically that what was originally called the mass curve of the ratio of runoff volume to the total volume of the NRCS CDUH is shown to be, in fact, the mass curve of the unit hydrograph. The equations of continuous time functions derived in this study can be used in place of the NRCS CDUH tabulation and the NRCS linear triangular unit hydrograph. An example is shown to illustrate the application.