Journal of Irrigation and Drainage Engineering

Surface energy balance models developed for mapping evapotranspiration at high resolution use weather station data. Previous models such as SEBAL or METRIC use wind and reference evapotranspiration from a single weather station. A third model (ReSET) uses wind run from multiple weather stations but uses a single weather station for the internal calibration. Because these models solve the energy balance equation for areas that usually have significant spatial variability, it is more appropriate to have all inputs and calculations in a raster format. This paper presents a full rasterized model, which uses all inputs and performs all calculations in a raster format (ReSET-Raster). The ReSET-Raster model provides the flexibility to use several weather stations as data sources to generate interpolated weather parameters in a raster format. It explicitly takes into account the spatial variation of weather parameters between weather stations, which can be significant. This paper presents examples showing that evapotranspiration calculated with the raster approach can vary as much as 17% compared with evapotranspiration calculated with point values.

Knowledge of reference potential evapotranspiration (${\mathrm{PET}}_{\mathrm{ref}}$) conditions is important for a number of vegetation- and hydrological-related applications. Direct estimations of ${\mathrm{PET}}_{\mathrm{ref}}$ are difficult and require sophisticated instrumentation. The Food and Agriculture Organization (FAO), therefore, proposed a method for the estimation of ${\mathrm{PET}}_{\mathrm{ref}}$ using only meteorological data. This equation has been widely accepted as the standard method for the estimation of ${\mathrm{PET}}_{\mathrm{ref}}$ because of its good fit with measured values. Nevertheless, it requires several meteorological variables (e.g., wind speed), which are rarely available. Where such data are not available, its application is hampered. To overcome this problem, a number of simpler, empirical equations requiring only a fraction of the meteorological input variables required by the FAO ${\mathrm{PET}}_{\mathrm{ref}}$ have been developed. Before using these equations, it is important to evaluate their performance and choose the equation that will have the lowest possible bias in the estimation of ${\mathrm{PET}}_{\mathrm{ref}}$. Using daily meteorological observations obtained from seven meteorological stations on the island of Crete (southern Greece), the performance of 13 empirical equations (radiation- and temperature-based) for the estimation of ${\mathrm{PET}}_{\mathrm{ref}}$ has been evaluated against the estimations of ${\mathrm{PET}}_{\mathrm{ref}}$ using the FAO equation. Performance was evaluated on a daily and a monthly basis, and five different measures of goodness of fit were used. The results showed that when the use of the FAO equation is not possible because of the unavailability of data, some empirical methods can serve as appropriate alternatives. The radiation-based equations generally performed better than those that included only temperature-related input variables. The equations proposed by Hansen and Turc were the most useful because they had an average monthly absolute error ranging from 5.7 to 17.7 mm and 5.5 to 19.2 mm, respectively.

The performance of the widely used conventional closed-form models of Brooks and Corey and van Genuchten is restricted to soils characterized by a specific shape form of the water retention curve. Hence, the van Genuchten model more accurately describes “S”-shaped retention curves characterizing finer-textured soils, whereas the Brooks-Corey model is much better adapted for “J”-shaped retention curves characterizing relatively coarse-textured soils. In this work, a new closed-form soil hydraulic model is proposed. The suggested continuous-form function accurately describes soil retention curves irrespective of their specific shape form. New algebraic expressions based on Mualem’s statistical model and another new model that is a combination of the Mualem and Burdine theories were derived for the prediction of the unsaturated hydraulic conductivity function. Comparisons of ten soils known from international bibliography were performed. It is concluded that the proposed water retention curve expression as well as the hydraulic conductivity predictions showed significant improvement over the conventional van Genuchten and Brooks-Corey closed-form models, particularly for conductivity values near the residual water content and saturation.

Compared with other rotating sprinklers, the fluidic sprinkler controlled by an outlet clearance has a simpler structure and better hydraulic performance. The offset effect, happening in the fluidic component of the sprinkler, drives the sprinkler and controls its rotational direction. Theoretical and experimental research are conducted to study the water offset jets with a small ratio of 0.675 for the 10PXH sprinkler and 0.355 for the 30PXH sprinkler in the fluidic components. Analytic solutions and other calculations deduce the reattachment lengths of the offset jets. Computational fluid dynamics (CFD) software simulates the offset flows in simplified models and real models of the fluidic components, in two dimensions and three dimensions, respectively, utilizing the volume of fluid (VOF) method to trace the shape of the interface between water and gas. Simulation results of the sidewall pressure distribution also obtain the reattachment lengths. The resulting experimental measurements of the static pressure and reattachment length are in line with the predicted results of the calculations and the simulations. These results indicate that CFD simulation can approximate the offset flow in fluidic components. On the basis of this study, some of the component sizes are confirmed.

Total phosphorus (TP) in storm-water runoff is a common regulatory target for maintaining the quality of receiving surface water. Previous storm-water treatment studies show that it is difficult to consistently achieve TP removal higher than 40%, whereas regulatory goals of 50–65% removal are becoming common. To meet these goals, storm-water filtration technologies utilizing an expanding array of filtration media are being deployed, especially in areas with protected water bodies such as Puget Sound and Chesapeake Bay. One challenge is that if the media has no adsorption capacity, particulate phosphorus can redissolve into solution and form liberal orthophosphate (Ortho-P), resulting in lower overall TP removal. Therefore, effective Ortho-P adsorption capacity in filtration media is crucial to meet more stringent TP removal goals. Additional media characteristics that should be considered include gradation, permeability, surface area, morphology, cost, and toxicity. In response to these requirements, an engineered media (EM) was developed and evaluated by Ortho-P adsorption isotherms and breakthrough in typical storm-water runoff conditions. Three other media, perlite, zeolite, and granular activated carbon (GAC), widely used in storm-water treatment, were also investigated under the same experimental conditions. With adsorption isotherms, EM showed the highest adsorption capacity of $7.82\mathrm{mg}/\mathrm{g}$ , nearly seven times that of GAC ( $1.16\mathrm{mg}/\mathrm{g}$ ). In adsorption breakthrough testing, overall removal efficiency decreases as the number of treated empty bed volumes (EBVs) increases. To reach 50% overall removal, EM provided 838 EBVs, whereas GAC could only treat 12 EBVs. In addition, for the lifetime of media, EM outlasted GAC with 2,297 EBVs, compared to 1,000 EBVs, respectively. Results indicate that EM is an adsorptive filtration media for treating storm-water phosphorus.

A field study was conducted to assess biases of suspended sediment concentration (SSC) analyses (ASTM Standard D3977-97) performed on discrete samples obtained by automatic sampler in comparison with actual sediment concentrations from large volume sampling. Research results indicate that the biases attributed to the monitoring of sediment event mean concentration (EMC) and median particle size in parking lot runoff by automated samplers (nonisokinetic) were minimal. Large volume samples ($\sim 15,000\mathrm{L}$) of the first-flush event runoff were taken from a storm-water sewer system for eighteen storm events over two years. The intent was to obtain a complete portion of a storm to accurately determine EMCs and particle size distributions (PSDs). Concurrently, flow-weighted discrete samples were obtained by automatic samplers for the same portion of the events. Thus, characteristics of sediments from a whole-storm sample were compared with those of subsamples obtained by an automatic sampler using nonisokinetic sampling. SSCs and PSDs were compared for the two respective field sampling methods. The two methods showed a strong correlation for median sediment EMCs ($R^2=0.98$, $n=18$). Biases to particle size distributions were found to be both for the large particles ($>75–150\mu \mathrm{m}$) and smaller fines ($<25\mu \mathrm{m}$). Specific sediment size fractions captured by the large volume sampling and automatic sampler were not significantly different ($\alpha =0.05$) for $D_{50}$, which = 58 and $46\mu \mathrm{m}$, respectively.

Overland flow travel time given by the formula developed by the Natural Resources Conservation Service (NRCS) on the basis of kinematic wave theory can underpredict for short, steep, flow planes having low flow resistance and high degrees of imperviousness. Underestimation is caused by inaccurate representation of average rainfall intensity for durations shorter than approximately 15 min. Although the formula was developed based on only NRCS 24-h Type 2 and Type 3 rainfall distributions, it is used without restriction in regions that experience NRCS Type 1 and Type 1A storms. An alternate overland flow travel time formula based on rainfall intensity-duration relations developed previously by the writer to represent accurately high-intensity portions of each NRCS storm type is presented.

Kinematic-wave models of surface irrigation assume a fixed relationship between depth and discharge (typically, normal depth). When surface-irrigation inflow is cut off, the calculated upstream flow depth goes to zero, because the discharge is zero. For short time steps, use of the kinematic-wave model can create an incorrect water-surface profile. Issues include difficulty in solving the continuity equation in the first upstream cell and a calculated adverse water-surface profile. The kinematic-wave model produces a recession time at the upstream boundary that is too small, that can lead to incorrect calculation of recession times when water continues to recede from the surface. This problem becomes more severe for smaller values of bottom slope. In this paper, we present a zero-inertia approximation to the water-surface profile at cutoff, which can be extended to the start of recession, after which calculations continue with the kinematic-wave model.