Journal of Irrigation and Drainage Engineering

Crop evapotranspiration $\left({\mathrm{ET}}_c\right)$ and crop coefficient $\left(K_{\mathit{co}}\right)$ values of four clean-cultivated navel-orange orchards that were irrigated with microsprinklers, having different canopy features (e.g., age, height, and canopy cover) were evaluated. Half-hourly values of latent heat flux density were estimated as the residual of the energy balance equation using measured net radiation $\left(R_n\right)$ , soil heat flux density $\left(G\right)$ , and sensible heat flux density $\left(H\right)$ estimated using the surface renewal method. Hourly means of latent heat flux density (LE) were calculated and were divided by the latent heat of vaporization $\left(L\right)$ to obtain ${\mathrm{ET}}_c$ . Crop coefficients were determined by calculating the ratio $K_{\mathit{co}}={\mathrm{ET}}_c∕{\mathrm{ET}}_o$ , with reference evapotranspiration $\left({\mathrm{ET}}_o\right)$ determined using the hourly Penman–Monteith equation for short canopies. The estimated $K_{\mathit{co}}$ values ranged from 0.45 to 0.93 for canopy covers having between 3.5 and 70% ground shading. The $K_{\mathit{co}}$ values were compared with $K_c$ values from FAO 24 (reported by Doorenbos and Pruitt in 1975) and FAO 56 (reported by Allen et al. in 1998) and with $K_c$ values from research papers that estimated reference ET from pan evaporation data using the FAO 24 method. The observed $K_{\mathit{co}}$ values were slightly higher than $K_c$ values for clean-cultivated orchards with high-frequency drip irrigation in Arizona and were slightly lower than for nontilled orchards in Florida. The $K_{\mathit{co}}$ values were considerably higher than $K_c$ values from FAO 24 and FAO 56 and were higher than $K_c$ values from border-irrigated orchards near Valencia, Spain.

Photosynthetically active radiation (PAR) intercepted by orange orchards (Frost Nucellar navel) having different canopy sizes was measured to determine the relationships with crop coefficient ( $K_{\mathit{co}}$ and $K_{\mathit{cr}}$ ) values and crop evapotranspiration (ET) $\left({\mathrm{ET}}_c\right)$ . Three separate experiments were carried out near Lindsay, Calif. during the months of July and August 2004 to compute the fraction of light PAR intercepted by mature and immature orange orchards. Periodic readings of PAR data were compared with near simultaneous measurements of net radiation $R_n\left(\mathrm{mV}\right)$ , heat transfer through exposed flux plates $F_h\left(\mathrm{mV}\right)$ , and incident total solar radiation $R_s\left(\mathrm{mV}\right)$ . The PAR data were used to calculate canopy light interception and the results were compared with those computed from the $F_h$ and $R_s$ data. The other sensors were studied as possible substitutes for the more expensive PAR light bar. Light interception by the different canopies was related to crop coefficient ( $K_{\mathit{co}}$ and $K_{\mathit{cr}}$ ) values that were determined by micrometeorological measurement of ${\mathrm{ET}}_c$ and Penman–Monteith reference evapotranspiration ${\mathrm{ET}}_o$ and ${\mathrm{ET}}_r$ .

Potential solutions to high soil salinity levels and waterlogging problems are investigated on a regional scale using calibrated finite-difference flow and mass transport modeling for a portion of the Lower Arkansas River Valley in Colorado. A total of 38 alternatives incorporating varying degrees of recharge reduction, canal seepage reduction, subsurface drainage installation, and pumping volume increases are modeled over three irrigation seasons (1999–2001). Six performance indicators are used to evaluate the effectiveness of these alternatives in improving agroecological conditions, compared to existing conditions. Predicted average regional decrease in water table elevation (as great as 1.93 m over the irrigation season) is presented for selected alternatives, as well as the spatial mapping of results. Decrease in soil salinity concentration (with regional and seasonal average reduction as high as 950 mg/L) is also predicted and mapped. Estimated groundwater salinity changes, reduction in total salt loading to the river, increase in average regional crop yield, and changes in net water consumption indicate the potential for marked regional-scale enhancements to the irrigation-stream-aquifer system.

This paper describes the derivation of the total direct and relative reduction factors for both discrete and continuous outflow along mixed service sections of close end multiple outlets pipes. Discrete outflow factors depend on the numbers of outlets along the section and the entire pipeline, while for continuous distribution there is no such dependence. Solutions for close end pipes are also derived. The total relative factors are related to those previously calculated total factors for close end pipes. The concept of “effectiveness” is presented here for close and open end pipes by taking into account the friction loss occurred downstream of the first outlet, resulting in both head and flow variation between that upstream outlet and the remaining outlets along the line. The dependence upon the extremity spacing is also considered. There are also proposed formulations for mixed factors for intermediate sections between two locations along a close end pipe.

Experimental investigations of an irrigation gun water jet revealed that the flow is a mixture due to the degassing of the air dissolved in the supply water. The expansion of resulting air bubbles allowed velocity measurements in the region of the free jet close to the nozzle by a nonintrusive method (particle image velocimetry). Additional measurements were also implemented with an intrusive double-tip optical fiber probe. In this study a comparison was undertaken on the dynamic parameters of the outflow from a gun with fins and a second unfinned. Results underline the effects of fins and degassing on the jet internal properties and their consequences on the irrigation process.

The 340,000 ha Lake Dakota Plain area in north-central South Dakota has the topographical and soil characteristics required for the use of combination subsurface drainage and irrigation systems. Corn yield data from a research site and a county-wide reporting service were used to determine that DRAINMOD, a water balance and corn yield estimation computer model, could be employed to assess the feasibility of using a combination system for the area. Three soils ranging in texture from a sandy loam to a silt loam and 19 years of climatic data were used in the feasibility analysis. Drain line spacings were determined for average yield goals of 90, 95, and 100% of estimated maximum corn yields for each soil. There are possibilities for the economical use of combination subsurface irrigation and drainage systems in the Lake Dakota Plain area.

The performance and potential of perforated pipes for stormwater quantity and quality control is evaluated. The studied design consists of a grass swale underlain by a section of perforated pipe enclosed in an infiltration trench. The grass swale-perforated pipe system results in a pleasant curbless design, which may replace open ditch systems, in low density residential areas. Current design practices and construction methods were assessed by a survey completed by 53 towns and municipalities in Ontario, Western Canada and the United States. The survey of municipal experience showed that while 50% of the municipalities have experience with perforated pipes used as storm sewers, only few municipalities used a combined system of grass swales and perforated pipes for the purpose of urban runoff infiltration. Seventy six percent of the respondents however are willing to use the system as an alternative to other stormwater management methods. Through a series of laboratory tests, it was found that exfiltration rate out of pipe perforation is not directly proportional to the orifice area. The analysis of the results indicated that the orifice discharge coefficient varied with orifice size and the head above the orifice. Field tests were conducted to measure the infiltration rates of typical grass swales and existing pipe trenches. The infiltration rates obtained were found to be consistent with literature values. Finally, according to a 3 month field monitoring program, the total seasonal discharge for a properly designed perforated pipe system was found to be 13 times smaller than for a conventional stormwater system, which shows the favorable effect of the perforated pipe system on the hydrologic budget and pollutant loading.

When velocity estimates of channel flows are not available, the slope-area method is widely used to make discharge estimates. The accuracy of such estimates depends on many factors but is generally believed to be low. In this study, fuzzy set analyses were used to compute the distribution of slope-area discharge estimates, with the distribution very similar to that assessed using statistical methods used in hydrology. The effects of errors in channel roughness, channel width, channel side-slopes, and flow depth on the accuracy of discharges were assessed. The large errors possible in channel roughness are a primary source of error in discharge estimates. Channel incision and vegetal growth are shown to significantly influence the accuracy of slope-area discharge estimates and the length of time before a slope-area rating curve should be recalculated. Records as short as 10 years can be seriously biased due to a failure to account for the effects of incision or vegetal growth.

To reduce the size of the dissipation basin, the stepped chute has been accepted to be the most powerful hydraulic structure to dissipate large flow energy downstream from steep hills. This paper presents the flow characteristics and factors for energy dissipation in various types of stepped chutes: horizontal steps, inclined steps, and steps with end sills. Delineated and descript flow regimes are observed. The relationships between relative energy loss and relative critical flow depth on three stepped chutes are presented and discussed. The steps with end sills seem to be the most efficient configuration in terms of relative energy dissipation. The effect of number of steps is evident since the relative energy loss increases with the number of steps. In addition, new correlations showing the relation between relative energy loss and relative critical flow depth are proposed for practical applications.

A computationally simple kernel method is proposed for obtaining drawdowns due to unsteady pumping of large diameter wells. The kernels can be worked out even on a hand-held calculator. The new method can also be used to obtain residual drawdowns. The new method yields results as good as those obtained using earlier methods.