Journal of Irrigation and Drainage Engineering

A laboratory experiment was carried out to study the relationships of emitter discharge rate (EDR) and distribution of water and salt for two typical coastal saline soils. The objective was to find a simple method to determine a suitable EDR for reclamation of coastal saline soil using drip irrigation. The experiment included five EDR treatments in a coastal saline sandy-loam soil (SAS): 0.23, 0.55, 0.8, 1.5, and $2.9\mathrm{L}·{\mathrm{h}}^{-1}$; another five EDR treatments were conducted in a coastal saline silt soil (SIS): 0.23, 0.55, 1.0, 1.5, and $2.0\mathrm{L}·{\mathrm{h}}^{-1}$. The water distribution and the low-salinity zone (with electrical conductivity of the saturated soil extract $\le 1$, $\le 2$, and $\le 4\mathrm{dS}·{\mathrm{m}}^{-1}$) were clearly affected by EDR. The relationships of EDR and wetted front, wetted zone volume, and low-salinity zone were difficult to obtain because of the requirements of determining and calculating the vertical wetted front and the volume of wetted, saturated, and low-salinity zones in the field. For this reason, these relationships could not be used to directly calculate EDR. Steady-state ponding area radius and EDR were linearly related, and constant ponding area was related to EDR but not to time. A method was proposed to rapidly determine EDR from this linear relationship. Based on this method, a specific radius of the steady-state ponding area, proposed at 3–4 cm, was substituted into the linear relationship to calculate suitable EDRs of 1.3–1.9 and $0.16–0.40\mathrm{L}·{\mathrm{h}}^{-1}$ for SAS and SIS soils, respectively. Two field experiments were used to test the practicability of the method; there was no runoff or erosion in the irrigation period, and plant survival rates were not affected by salt. The method proposed can rapidly determine EDR (within 300 min) with a small amount of water (12 L), which saves labor (one or two persons), and it can be implemented in multiple locations without destroying soil and plants.

Microirrigation has become quite a common practice in agricultural production in various parts of the world. To achieve the optimum (hydraulic and economic) system performance, designers are often faced with the problem of designing a maximum lateral length which results in a desired coefficient of uniformity (CU) or an allowable pressure head variation (${\delta }_H$). Previous theoretical design approaches are usually based on a constant Darcy–Weisbach (DW) friction factor along the lateral and this assumption can lead to substantial errors. In the research reported in this paper, a new analytical design approach does not require the constant DW assumption for zero-slope laterals while it still takes into account the emitter exponent and the effect of minor friction losses caused by emitters. Assuming a constant friction factor along the lateral might result in errors up to 14% in the calculation of the maximum lateral length. Conversely, the maximum relative error caused by the application of the proposed method compared to the stepwise solution generally does not exceed 1.1%. The suggested technique for determination of maximum lateral length is simple to use and does not require iteration, as is usually the case for previous analytical methods. The method is applicable to various types of emitters for lateral lengths less than 300 m. It also provides an additional check on other analytical and numerical methods that are available elsewhere.

Climate change in recent years has been affecting agriculture and especially crop production worldwide. This study analyzes the effect of two different climate change scenarios on crop production of an experimental site in southern Québec, Canada. The DSSAT model, which was calibrated for years 2008 and 2009, was used to simulate corn growth with 30 years of synthetic data for climate scenarios baseline (1961–1990), A2 (2040–2069), and B1 (2040–2069). In comparison with the baseline scenario, the A2 and B1 scenarios projected a decrease in grain and biomass, an increase in crop ET and evaporation, and an early crop emergence and maturity dates. Reduction in grain yield of up to 40% for A2 and 24% for B1 scenarios was observed, which could be attributed to water-deficit conditions resulting from decreased rainfall and increase in temperature during the growing season. Because drought indices were found to be significantly correlated with grain yield and crop water stress, it could be used to define the variability of grain yield and water stress at the field scale. This study indicates that climate change might have a negative effect in terms of corn crop production under the given study area.

Environmental and economic sustainability of agricultural systems has to face the general decreasing trend of water resources through the adoption of strategies aimed at improving water-use efficiency. In the study, during three consecutive summer seasons, the effects of deficit irrigation (DI) treatments applied on mature orange trees [Citrus sinensis (L.) Osbeck] cv. “Tarocco Meli” were analyzed. Two different DI strategies supplying 70 and 50% of crop evapotranspiration (${\mathrm{ET}}_c$) were compared with irrigation at the full rate of ${\mathrm{ET}}_c$; the comparisons were carried out in terms of plant physiological response, crop production, quality, and nutritional status. The orange trees became less sensitive to moderate water restrictions (DI = 70% ${\mathrm{ET}}_c$) permitting approximately 80 mm of water saving (i.e., corresponding to a threshold for water stress integral of 60 MPa) per season without any significant impact on their water status and on agronomic performances. Severe water restrictions ($\mathrm{DI}=50\%{\mathrm{ET}}_c$) reduced fruit weight and crop production every year, with water-use efficiency values similar to those of the moderate DI (70% ${\mathrm{ET}}_c$). The study does not evidence crop mineral nutrition imbalances and yield decrease caused by mild water reductions. A moderate water restriction can be applied in commercial orange orchards because it saved water and improved fruit quality by increasing total soluble solids and titratable acidity while the fruit maturity was delayed.

The potential impact of climate change on the existing drainage infrastructure has been an essential aspect of many hydrological studies. Climate change that will increase the intensity of precipitation will also increase the magnitude of the design discharge and thus would probably result in adverse effects on the existing drainage facilities. This paper aims to evaluate the potential impact of rainfall intensity variation due to climate change on the existing drainage infrastructure by investigating whether (1) the stormwater drainage infrastructure designed for preclimate conditions is able to sustain future higher discharges, and (2) new design guidelines are necessary to be established to include the potential rainfall intensity variation due to climate change. A case study was conducted using 34 years of rainfall data (1980–2013) obtained from the National Climatic Data Center (NCDC). These data and the weather scenario data projected by the four run global circulation model (GCMs) under the three emissions scenarios coupled with stochastic weather generator model which generates daily weather time series statistically were used to update the current intensity-duration-frequency curve to reflect the rainfall intensity variation due to climate change. Furthermore, runoff simulation using a storm and sanitary software program was performed to analyze whether the increase in the intensity of rainfall due to climate change would have an adverse impact on the current drainage system to convey excess runoff. The results showed that most elements of the current drainage infrastructure in the boundary of the study area were inadequate to convey excess runoff. However, climate change magnifies the problems that already exist in an aging drainage infrastructure. Furthermore, considering the rehabilitation or replacement rates of these aging infrastructures are relatively slow, emphasis must not lie only on the future climate change, but also on identifying the weak spots in the system coupled with, the economic and environmental factors before any changes in design criteria can be recommended due to climate change.

Normal and critical epths are important parameters in the design, operation, and maintenance of open channels. Semielliptical, prefabricated channels are widely used as tertiary canals in irrigation networks. In semielliptical channels, the governing equations are highly nonlinear in the normal and critical flow depths; thus, the solution of the implicit equations involves numerical methods. The main challenge with semielliptical sections is the calculation of the wetted perimeter. The wetted perimeter of semielliptical sections can be expressed in terms of incomplete elliptic integrals of the second kind. The elliptic integrals can be computed simply using commercial mathematical software, but most engineers who use a simple tool such as Microsoft Excel need a simple yet accurate expression for computing the wetted perimeter. Because elliptic integrals cannot be directly computed using Excel, a simple and accurate expression with maximum error less than 0.07% (near exact solution) is proposed for computing the wetted perimeter. In this study, explicit solutions for semielliptical channels have also been obtained using the nondimensional forms of the governing equations. The maximum errors of critical and normal flow depths are less than 0.1%. Proposed explicit equations have high accuracy, easy calculation, and wide application range.