Journal of Irrigation and Drainage Engineering

A method was developed based on the radiative properties and energy budget of a single apple leaf to calculate the actual transpiration ($T$) of apple trees. The model uses canopy temperature ($T_c$), air temperature ($T_a$) measured in the orchard, and other meteorological data from a local weather station as inputs. The model was applied to two scenarios, as follows: (1) well-watered, young Fuji apple trees in the 2007 and 2008 growing seasons; and (2) older apple trees, bearing little fruit in the 2013 growing season. Simulated transpiration rates at both scenarios were compared with Penman-Monteith (PM) model predictions corrected by regionally adjusted crop coefficients, i.e., values of $E{T}_c$. In 2007 and 2008, a linear regression analysis of the relationship between daily mean transpiration ($T_{\mathrm{avg}}$) and $E{T}_c$ revealed that they better agreed on warm and dry days (correlation coefficient $R^2=0.57$, $\mathrm{slope}=1.16$, and $\mathrm{intercept}=0.4$) than during cold and humid periods ($R^2=0.48$, $\mathrm{slope}=0.69$, and $\mathrm{intercept}=2.3$). Combining the results of the 2007 and 2008 seasons, $T_{\mathrm{avg}}$ and $E{T}_c$ presented a fairly good agreement, with the relationships $R^2$, slope, and intercept of 0.77, 1.0, and 1.08, respectively. In 2013, the actual water use calculated by a soil water budget approach ($E{T}_{WB}$) was considerably less than $E{T}_c$ while there was no significant difference between the total simulated transpiration ($\mathrm{\Sigma }{T}_{\mathrm{avg}}$) and $E{T}_{WB}$. In 2013, a linear regression analysis of the relationship between midday $T$ ($T_{\mathrm{mid}}$), $T_{\mathrm{avg}}$, and midday stem water potential (${\mathrm{\Psi }}_{\mathrm{stem}}$) showed they were highly correlated ($T_{\mathrm{mid}}$, $R^2=0.85$; $T_{\mathrm{avg}}$, $R^2=0.87$). The experiments presented varied results on the linear relationship between air vapor pressure deficit ($D_a$) and $T_{\mathrm{avg}}$ from year to year. On the other hand, canopy and air temperature difference ($\mathrm{\Delta }{T}_m$) was linearly related to $T_{\mathrm{avg}}$ in all of the seasons. According to the model for the actual transpiration (i.e., the T-model), the apple trees had an intense transpiration in the morning and then there was a decline around solar noon. The transpiration increased again late in the afternoon. Real-time estimations of water use using the T-model can provide a basis for a fully automated system of irrigating apple orchards.

Understanding variable evapotranspiration (ET) throughout a field can help maximize yield on a per-acre basis, as well as assist with proper irrigation scheduling. The results from this study indicate that irrigation system distribution uniformity (DU) has a significant effect on the uniformity of ET during water-stressed periods. The study site involved intensely managed forage (alfalfa and winter grain hay) irrigated by center pivots being supplied with reclaimed water near Palmdale, California. During spring and early summer 2007 the center pivots were operating under deficit irrigation. In 2010, after the installation of reservoirs, water was applied to meet full evapotranspiration (${\mathrm{ET}}_c$) demands. Using remote sensing of actual evapotranspiration, the variability in ${\mathrm{ET}}_c$ for the same pivots with the same crop was quantified. During the non-water-stressed period, ET uniformity was significantly better than during the water-stressed period (2007). The difference in uniformity was found to be attributable to irrigation system distribution uniformity. For the 540 ha used in this study, irrigation system DU was found to explain 55% of the ET nonuniformity during deficit irrigation. A method to predict the nonuniformity in ET as a result of irrigation system DU and water-stress level is presented.

This study deals with the development of an analytical solution for predicting seepage into an array of ditch drains dug in a three-layered soil underlain by an impervious barrier and receiving water from a ponded field of infinite extent. The solution is of a general nature and can account for partial penetration, finite width and spacing of drains, finite depth of the impervious stratum, anisotropy of individual layers, and a uniform ponding distribution at the surface of the soil. The validity of the developed solution for the single-layered situation is checked by first reducing the proposed multilayered solution to that of a single-layered one by treating the conductivity of the layers as the same and then comparing for a few flow situations the hydraulic heads as predicted by the reduced model with corresponding values obtained from the analytical and experimental works of others. A numerical check on the developed analytical model for a multilayered soil is also carried out. The study shows that flow to a multilayered ponded ditch drainage system is sensitive to the magnitude of the hydraulic conductivity as well as on the anisotropy of the constituent layers. Further, the study also corroborates the work of others that the presence of a plow sole layer in a paddy field greatly restricts the movement of seepage water through such a soil and that for such a situation considerable time may be required by a water particle to move from the surface of the field to a recipient subsurface drain in the soil.

Nonuniform pressure of microirrigation systems negatively impacts crop productivity, water utilization, and nonpoint source pollution. However, achieving network pressure uniformity can be prohibitively expensive. This paper presents an economic optimization method that seeks to balance competing costs and benefits. A custom computer software script is developed to implement the method and an irrigation case study is presented. Regression analysis showed that the relationship between economic efficiency and Christiansen uniformity (CU) is a cubic function with an optimum uniformity (i.e., in reference to CU) at 0.78 for cotton and 0.86 for olive trees. The results also indicate that water cost is the most important factor influencing total cost and economic efficiency, and next is capital cost. Also, irrigation systems with a relatively small subunit size (0.1–0.42 ha for cotton and 0.72–2.16 ha for olive) commonly lead to a high economic efficiency. Finally, to guarantee adequate uniformity, the most efficient microirrigation system design will necessarily use the smallest possible size of the manifold.

In this paper, fluctuation in reservoir water quality is simulated and evaluated upon the sudden entry of a biological load. By using Version 3.2 of the two-dimensional quality simulation software CE-QUAL-W2, Iran’s Karaj Reservoir is simulated, and a biological pollutant with coliform index is considered as the level of the pollutant. By considering factors involved in dispersion, advection, and decay of coliform, nine factors (nine sets of scenarios) are defined, and their influences on the pollution behavior are investigated. To investigate further, pollutant behavior is evaluated in various scenarios: water release, level of water withdrawals, input pollutant load volume, coliform decay rate, stored water volume in the reservoir, entry location of pollutant load, effect of water temperature on coliform decay, inflow to reservoir, and coliform sedimentation rate. Results show that some factors affect the pollutant behavior significantly, such as stored water volume in the reservoir and entry location of the pollutant load, so that the main changes in released pollution concentration appear with a decrease and increase of 25% in reservoir storage volume. Also, the closer the pollutant load entry location to the reservoir outlet, the higher the released pollution concentration. Maximum pollution released from the reservoir in the condition of entry of pollutant load in the lower third of the reservoir relative to the entry of pollutant load in the upper third is 15 times more.

This paper addresses a possible decrease in flood damages by using structural methods and determines proper locations (layout) to construct protective levees and height of levees (design of levees) in high-risk areas. Because of discontinuity of the objective function and a large number of decision variables, the optimization uses the genetic algorithm (GA). The simulation of the region is carried out with the Hydrologic Engineering Center’s River Analysis System (HEC-RAS) model. The GA is employed to maximize the benefit of flood control and also to minimize the cost of protective levees’ construction. Thus, the fitness function of the algorithm maximizes the net benefit of the project. After a sensitivity analysis, mutation and crossover probability are assumed to be 0.03 and 0.7, respectively. Thus, 1,000 generations and 98 chromosomes for each run are considered. The optimization model is run 5 times for floods with return periods of 50 and 100 years. Furthermore, the algorithm is used to evaluate flood damages in the Sarm and Khoor Abad River, located in the Qom province of Iran. Project net benefits resulting from the optimization model for rivers using 100-year flood exceed those for a 50-year flood. Results indicate that construction of protective levees reduces the rate of damages up to 99% in comparison with a nonconstruction of levees scenario. By taking into account the construction cost of levees, net benefits decrease by 0.97% and 1.1% for floods with 50-year and 100-year return periods, respectively.

This study attempted to quantify the effects of rice straw mulches on runoff and nonpoint source (NPS) pollution under a future climate change scenario. For this, regression equations between the observed rainfall and runoff curve number (CN) were developed to estimate NPS pollution from radish fields. Rainfall data from the special report on emissions scenarios (SRES) A1B were applied to the regression equations in order to predict future runoff and NPS pollution by surface covers. The results show that future rainfall was estimated to increase by 0.8% in the 2020s, 14.4% in the 2050s, and 15.1% in the 2080s. Under the projected rainfall conditions, the loose straw and the straw mat mulches were estimated to reduce runoff by 65.7 to 66.8% and 95.8 to 96.9%, respectively, while the selected pollutants were reduced by 44.1 to 98.8% and 58.9 to 94.9%, respectively. Both types of straw mulch were effective in controlling both runoff and NPS pollution, and thus offer a very promising means to cope with the effect of climate change such as flood, drought, and water quality conservation. Similar studies should be conducted on a wide range of crops, soils, and rainfall conditions to better estimate the effectiveness of mulches more broadly and to assist in the development of national NPS pollution management strategies with respect to expected changes in climate.

The governing equation for converging kinematic wave (KW) flow was derived and compared with laboratory measurement and field tests. The key factors for converging KW flows are found to be excess rainfall depth, surface slope in the radial flow direction, and converging geometry in terms of fan angle and radius. Although the complete analytical solutions for KW flow rate and depth on a converging surface are not yet found in this study, the peak flow under equilibrium condition has been derived for the prediction of design flow. The numerical solution provides a deterministic approach to predict the KW water surface profile on a converging surface. This new method will definitely improve the current practice for determing the boundaries of a floodplain on a converging alluvial fan and the radial flow patterns towards a culvert entrance.