Journal of Irrigation and Drainage Engineering

The evapotranspiration crop coefficients ($K_c$) that are used to estimate actual evapotranspiration (${\mathrm{ET}}_a$) using a two-step approach (i.e., $K_c\times \text{reference}\mathrm{ET}$) for limited irrigated and rainfed maize are extremely rare. The effects of full and limited irrigation and rainfed practices on maize ${\mathrm{ET}}_a$ and soil water dynamics were quantified. Grass- and alfalfa-based crop coefficients ($K_{\mathrm{co}}$ and $K_{\mathrm{cr}}$) were developed for full- and limited-irrigation settings as well as for rainfed conditions. Four irrigation regimes [fully irrigated treatment (FIT), 75% FIT, 60% FIT, 50% FIT] and rainfed treatments were implemented. In general, depletion in available soil water increased with the decrease in irrigation regime from FIT to rainfed treatment. Maize ${\mathrm{ET}}_a$ increased with irrigation amounts and ranged from 481 mm for the rainfed treatment to 620 mm for the FIT in 2009 and from 579 to 634 mm for the same treatments, respectively, in 2010. Reduction in seasonal ${\mathrm{ET}}_a$ relative to FIT were 22, 9, 7, and 2% for the rainfed, 50% FIT, 60% FIT, and 75% FIT, respectively, in 2009. The reductions were 9, 4, 2, and 1% in 2010 for the same treatments. On average, a two-step approach overestimated maize ${\mathrm{ET}}_a$ by approximately 26% in 2009 and 17% in 2010. The difference between the two methods ranged from 18% for the FIT to 38% for the rainfed treatment in 2009. The difference in 2010 was smaller owing to a greater amount of precipitation (563 mm in 2010 versus 426 mm in 2009), ranging from 21% for FIT to 12% for the rainfed treatment. One method was not able to effectively account for the impact of water-limiting and rainfed conditions on $K_c$ when estimating ${\mathrm{ET}}_a$, resulting in considerable error in 2009. A new set of maize $K_{\mathrm{co}}$ and $K_{\mathrm{cr}}$ values under rainfed, limited, and fully irrigated settings were developed as a function of the thermal unit and days after emergence. The midseason average $K_{\mathrm{co}}$ values were 1.26, 1.20, 1.11, 1.08, and 1.10 for the FIT, 75% FIT, 60% FIT, 50% FIT, and rainfed treatments, respectively. The midseason average $K_{\mathrm{cr}}$ values were 1.05, 1.00, 0.97, 0.95, and 0.92 for the same treatments, respectively. In general, more water limitation and crop water stress resulted in lower midseason $K_c$ values, and there was a gradual decrease in the peak $K_{\mathrm{co}}$ and $K_{\mathrm{cr}}$ values from FIT toward the rainfed treatment. The new set of $K_{\mathrm{co}}$ and $K_{\mathrm{cr}}$ equations can be beneficial for estimating maize water use for in-season irrigation management under full- and limited-irrigation settings as well as estimating evaporative losses under rainfed conditions for the locations that have similar soil, crop, climate, and management conditions of this study.

To develop a proper irrigation management program, determination of crop water requirements and crop coefficients during growth stages is essential. In addition, water requirements and crop coefficients of most medicinal crops, especially in arid and semiarid climates, have not yet been reported. Experiments were carried out from March 2010 through July 2011 to determine the water requirements and single and dual crop coefficients of coriander in a semiarid climate. Three drainable lysimeters, each with diameters of 1.20 m and soil depth of 1.40 m, were used. The Penman-Monteith and water balance equations were applied to determine plant potential and actual evapotranspiration (ET). In all lysimeters, the irrigation was carried out after 30% depletion of available soil moisture to avoid any water stress during the planting period. The moisture contents of all lysimeters were measured at different depths of 20, 40, 60, 80, 100, and 120 cm by time-domain reflectometer (TDR). The actual ET and single and base crop coefficients for the initial, developing, middle, and final stages of coriander growth were determined to be 647 mm and (0.66, 1.19, 1.36, 0.98) and (0.21, 0.72, 1.10, 0.79), respectively.

Significant water savings might be realized, regionally and nationally, if an additional fraction of cultivated land were converted to a more effective form of irrigation (e.g., from furrow flooding to center pivot or drip, where feasible). To quantify potential savings, the ArcMap-based USDA Agricultural Research Service (ARS) Soil and Water Assessment Tool (SWAT) software was used to model hydrologic budgets in the San Miguel Creek watershed, Texas; findings were applied to regionally similar agricultural land in the Edwards Aquifer Groundwater Conservation District and Texas State Regional Water Planning Area L (RWPA-L). Up to 26.1 and $99.8\mathrm{million}{\mathrm{m}}^3$ of potential agricultural water savings were identified in these two areas, respectively. The straightforward approach can be used to predict water demand and potential water savings in closed rivers basins; across borders; or in other areas in which agricultural irrigation is prevalent, water scarcity may be a concern, or competing rural/urban interests persist among various user groups.

The ASCE Standardized Reference Evapotranspiration (ET) Equation expects wind speed measured at a height of 2 m over and downwind of a smooth measurement surface, such as actively growing clipped grass. Many agricultural weather stations used for evapotranspiration estimation may not meet such siting conditions. A physically based approach to translate wind speeds measured at various heights and weather measurement surface conditions to equivalent wind speed at 2-m height over actively growing clipped grass is tested in agricultural settings. The translation algorithm assumes neutral or near-neutral boundary layer stability conditions. Mean daily wind speeds measured at 2- and 3-m heights above ground surface over and downwind of variable-height alfalfa during the 2008, 2009, and 2010 growing seasons in several southeast Colorado locations were translated to equivalent mean daily wind speed at 2-m height over clipped grass and compared. Translated alfalfa weather station mean daily wind speeds were also compared with mean daily wind speeds measured at 2-m height over 0.12-m grass for parts of the 2009 and 2010 seasons at two pairs of sites. The translation algorithm produced translated mean daily wind speeds in good agreement with wind speeds measured under the standard weather station condition. The effects on computed daily tall crop reference evapotranspiration are illustrated.

The rational method for peak discharge ($Q_p$) estimation was introduced in the 1880s. The runoff coefficient ($C$) is a key parameter for the rational method that has an implicit meaning of rate proportionality, and the $C$ has been declared a function of the annual return period by various researchers. Rate-based runoff coefficients as a function of the return period, $C(T)$, were determined for 36 undeveloped watersheds in Texas using peak discharge frequency from previously published regional regression equations and rainfall intensity frequency for return periods $T$ of 2, 5, 10, 25, 50, and 100 years. The $C(T)$ values and return period adjustments $C(T)/C(T=10\mathrm{year})$ determined in this study are most applicable to undeveloped watersheds. The return period adjustments determined for the Texas watersheds in this study and those extracted from prior studies of non-Texas data exceed values from well-known literature such as design manuals and textbooks. Most importantly, the return period adjustments exceed values currently recognized in Texas Department of Transportation design guidance when $T>10\mathrm{years}$.

The uniform distribution of water delivered through microirrigation emitters on a lateral line is an important objective that greatly affects a system’s efficiency. Among the various uniformity parameters, distribution uniformity (DU) is one of the most frequently used indexes in industry. In this study, an easy-to-use analytical method for directly calculating the DU of tapered microirrigation laterals laid on horizontal or uphill slopes is developed. The proposed equations are derived assuming that the system’s hydraulic characteristics and the ground slope are the only factors affecting the DU. A comparison test with a numerical stepwise solution indicates that the proposed analytical method is reasonably accurate and can be used to evaluate the system uniformity. The results also show that the accuracy of the method increases as the total number of outlets increases or the value of the emitter exponent approaches unity.

Multicropping is the practice of growing two or more crops in the same space during a single growing season. Planning rules are mathematical equations that use previous experiences of a water resource system to balance the system’s water supply and demand, and calculate multicrop areas in various periods. In this paper, linear and nonlinear planning rules are developed for optimal multicrop irrigation areas associated with reservoir operation policies in a reservoir-irrigation system. Reservoir operations are related to water allocations to each irrigated area by considering inflow and storage volume of the reservoir as the water supply in a monthly operation period. Evolutionary algorithms (EAs) can determine optimal multicropping patterns planning rules by considering various mathematical patterns. In this paper, three EAs, namely, (1) genetic algorithm (GA), (2) particle swarm optimization (PSO), and (3) shuffled frog leaping algorithm (SFLA) are employed and compared to maximize the total net benefit of the water resource system by supplying irrigation water for a proposed multicropping pattern over the planning horizon. Results show that the SFLA achieves the best solution, with the maximum value of the objective function in both linear and nonlinear planning rules compared to the GA and PSO. Moreover, the best yield of nonlinear rules is 45.52% better (higher) than that obtained by linear rules.

The effect of clogging on the long-term infiltration capacity and porosity of two 18- and 24-year-old porous asphalts was examined by using replicate double-ring infiltrometer tests and analyzing asphalt core samples. Tests were carried out to see if high pressure washing and vacuum cleaning could restore the hydraulic performance. The infiltration capacity of the porous asphalts decreased substantially, primarily due to surficial clogging ($0.50\pm 0.26$ in Luleå, Sweden, and $0.22\pm 0.12$ in Haparanda, Sweden, compared to initially $>290\mathrm{mm}{\min }^{-1}$). In Luleå, washing and vacuum cleaning could partially restore the infiltration capacity ($3.48\pm 3.00\mathrm{mm}{\min }^{-1}$), but in Haparanda, no effect was measured. The porosity was constantly between 16 and 18%. The difference of the long-term behavior and effect of cleaning in Luleå and Haparanda is primarily attributable to different street maintenance, age, and winter maintenance (application of fine gravel and/or sand). Although the infiltration capacity in Luleå was far below initial values, the asphalt still has the capacity to infiltrate an intense design rainfall (100 year average return interval, 15 min duration), underlining that porous asphalt can be a resilient feature also under nonfavorable conditions.

The piano key weir is a cost-effective solution for rehabilitation as well as for new dam projects with a high level of constraints (e.g., limited space, high specific flood discharge, small reservoir level variation). Although the higher efficiency of the piano key weir compared with standard linear weirs has already been demonstrated, its optimal geometry is still poorly defined. To improve the design of the complex geometry of this structure, the use of parapet walls has been tested. They consist of vertical extensions placed over the weir crest. Following a former study of the influence of the weir height on its discharge capacity, this paper presents the results of an experimental campaign dedicated to investigating the effect of parapet walls to increase weir height while reducing bottom slopes and keeping the weir height constant. These results indicate the relative influences of the alveoli bottom slopes and of the weir height on the piano key weir release capacity. Comparisons with former experimental results are also provided.