Journal of Irrigation and Drainage Engineering

The widely used Penman-Monteith equation to estimate crop evapotranspiration (ET) has limited utility in many areas of the world because of its requirement for full meteorological data. Legal and engineering water agencies commonly use the original Blaney-Criddle method in their efforts to manage competing water demands in mountain basins, both for its longtime familiarity and minimal data requirements. The original Blaney-Criddle equation predicts crop ET based solely on readily available mean monthly air temperature, $t$, and percentage of daylight hours. However, in semiarid, high-elevation environments, Blaney-Criddle underestimates crop ET. Subsequent modifications have not fully corrected this underestimation. Low nighttime temperatures at high elevations incorrectly weight the estimate, resulting in significant variation between computed crop ET and lysimeter measurements. Our objective was to evaluate three modifications of the Blaney-Criddle temperature expression against the original equation with mean $t$, and another temperature method, Hargreaves, using lysimeter measurements from nine irrigated grass meadow sites in the upper Gunnison River basin of Colorado (1999–2003). Two of the modified temperature expressions resulted in improved correlation of Blaney-Criddle estimated crop ET with lysimeter ET. Similar improvements were observed when estimating with Hargreaves, which incorporates an additional term, $T_{\mathrm{diff}}$, the difference between maximum and minimum daily temperature. Correlations of solar radiation ($R_s$, the primary energy input to ET) with alternative temperature expressions and $T_{\mathrm{diff}}$ were improved over correlations of $R_s$ with mean $t$, supporting the improved prediction performance of alternative temperature expressions. These modifications to the original Blaney-Criddle can be applied successfully throughout Colorado mountain basins and may be globally applicable to high-elevation areas.

Dimensions of the most hydraulically efficient trapezoidal and triangular drainage channels (that is, those with the smallest possible cross-section areas) whose banks are lined with loose rock riprap are found along with the stable stone diameter by solving a constrained nonlinear minimization problem. The problem statement is made dimensionless and less complicated by normalizing solution variables and combining parameters into two dimensionless quantities that describe the composite roughness of a channel and the stability of the rock lining. Normalized values of section bottom width, water depth, and rock diameter, along with the channel side-slope ratio, are found numerically. Results of the analysis are presented graphically and, when practical, in the form of empirical expressions. The solutions, which are comprehensive, give cross-section dimensions and the rock size needed to maintain a stable bank lining, greatly simplify design of hydraulically efficient riprap-lined open channels.

The scour mechanism downstream of a block ramp in clear water conditions is quite a complex phenomenon that depends on several parameters. Majors role are played by ramp configuration, hydraulic conditions (downstream tailwater level and discharge), material granulometry, and stilling basin geometry. Previous studies analyzed both the scour phenomenon and the effects of all the parameters involved except the last one (i.e., the case in which the ramp has the same width as the downstream stilling basin) and the case of symmetrically expanding stilling basins. This last basin configuration represents an optimal equilibrium between the necessity to dissipate energy and to create a natural pool for the biological species, thus it has a prominent ecological value. The present paper aims to assess the effect of both the width and length of the downstream stilling basin on scour features and flow pattern in clear water conditions. Different scour morphology types are distinguished and classified according to hydraulic and geometric conditions. Simple novel relationships are proposed to evaluate the scour depth and length and the maximum water level in the stilling basin. The results are valid for unsubmerged block ramps.

Water infiltration into soil plays a vital role in the performance of surface irrigation. Real-time information on infiltration characteristics is necessary to use surface irrigation models to manage irrigation systems. The present field study deals with the evaluation of the Kostiakov infiltration parameters using water front advance information at three different locations (50, 75, and 100% of the field length) along the alfalfa irrigated borders. Two irrigations were conducted on four border checks. The parameters of the Kostiakov infiltration model were determined using the one-point and two-point methods for these locations. The infiltration parameters for each border were used in a surface irrigation model to evaluate their impact on irrigation performance measures. The mean irrigation performance measures, such as inflow volume, application efficiency, tailwater ratio, deep percolation ratio, and low quarter distribution uniformity, were significantly different for one-point and two-point methods. However, the mean performance measures were not significantly different for infiltration functions evaluated at three different locations using the two-point method. Furthermore, performance of individual irrigation events was in close agreement for all three locations. Thus, infiltration parameters can be estimated using the water front advance information up to 75% of the field length (to reduce the impact of soil spatial variability) and can be used to predict irrigation performance measures reasonably well. A cutoff strategy that ensures the advancement of the wetting front to the downstream end of the field was devised on the basis of the infiltration parameters evaluated at 75% of the field length. This cutoff strategy resulted in savings of applied water (18%) and reduction in both tailwater and deep percolation losses, which gave higher application efficiency. The methodology presented in this article has the potential for use in real-time management of border irrigation systems.

Emitters inserted in drip irrigation laterals cause local head loss, generally estimated as a product of a coefficient and the velocity head. This local head loss coefficient and the emitter discharge curve hydraulic parameters may exhibit considerable variability attributable to the manufacturing process. This paper provides a framework for assessing whether the variability in the hydraulic parameters could lead to significant differences in the performance of rolls of drip irrigation laterals from the same manufacturing batch. A system approach with inlet pressure as input, pressure distribution along the drip lateral and inlet discharge as outputs (or responses), and a drip lateral hydraulic model as the transfer function is explored. Within a Bayesian statistical framework of parameter uncertainty based on the Metropolis algorithm, the hydraulic parameters of pressure-compensating drip lateral rolls from the same manufacturing batch were inferred (calibrated). Overlapping of the space (region) of the hydraulic parameters of different drip laterals give an indication of compatibility (similarity) of the drip laterals. Results indicated that half of the drip lateral rolls tested were strongly compatible, a third were weakly compatible, and the remainder were not compatible with any other. This finding has significant ramifications in the design of drip irrigation lateral networks. Therefore, it is essential to closely examine the hydraulic properties of drip laterals for the design of drip irrigation networks to avoid poor performance of the system.

Owing to the difficulties in measuring daily reference potential evapotranspiration, its estimation by means of the ASCE Penman-Monteith approach and various other empirical equations that are less demanding in terms of input data is favoured for various applications in vegetation science and climatology. This study presents the development of a Visual Basic software that can be used for the estimation of the daily ${\mathrm{PET}}_{\mathrm{ref}}$ by means of the standardized ASCE Penman-Monteith equation for both short (clipped grass) and tall (full-cover alfalfa) crops and thirteen additional empirical equations. Statistical measures of goodness of fit are also calculated to make it easier for users to compare and detect the empirical equations that have the minimum bias of estimation against the ASCE Penman-Monteith equation.

Control of irrigation canals usually consists of control of water levels upstream from regulators or check structures. Regulators provide the necessary head to offtakes. Generally, influence factor is used to express the extension of the backwater curve effect within the controlled reach. This factor shows how a change in water depth exercised by a regulator can influence the water surface profile along an irrigation canal. No direct equation is available in the technical literature up until now for calculating this factor on the basis of the steady gradually varied flow theorem. In current research, using the steady gradually varied flow equation for a prismatic canal, an elegant algebraic equation for this factor is derived. Control of water levels upstream from regulators is an important application of this equation in irrigation networks.

Unpredictable rainstorms can pose greater risks of soil erosion on newly formed unprotected railway batters. A bioengineering approach consisting of revegetation can be an effective tool for soil-erosion control. Perennial species, such as buffel grass, are preferred for durability of vegetation cover in the arid and semiarid tropics. However, it takes a longer time to establish buffel than annual species such as Japanese millet (JM). A replicated plot-scale field trial consisting of different proportions of grass-seed mixtures of buffel and JM was conducted on railway-batters slope in the semiarid tropics of central Queensland, Australia. A supplementary automated drip irrigation system was set up to aid seed germination and early establishment of the grass cover. JM alone or JM-dominated seed mixtures significantly reduced soil erosion during the earlier stages. For example, during the second sampling interval (SI), which occurred 63 days after seeding, JM alone reduced soil erosion by 50% (20.2 versus $10.21\mathrm{t}/\mathrm{ha}$) in comparison to the sole buffel. This trend began to shift as the growth of buffel commenced at the latter stages. By the end of the 11 months, erosion from all seeded plots was not significantly different among the plots with more than 90% soil-loss reduction in comparison to the bare scenario, resulting in more than 60% grass cover. Results suggested that a monoculture of JM or JM-dominated seed mixture with buffel grass could be an effective bioengineering approach for revegetation of railway batters for protection against soil erosion. Quick establishment owing to faster seed germination, seedling establishments, and growth-producing sizable canopy cover developed by JM in the early stage of batter could reduce soil erosion in comparison to a sole crop of slow-growing perennial species buffel. The established vegetation self-regenerated and responded dynamically and naturally to changing conditions of the railway batter within a year, after which JM started to die back.