Journal of Irrigation and Drainage Engineering

This study identifies five normalized depth-duration functions (NDDFs) that can be used to represent the rainfall characteristics in various regions of the United States. An analysis of the NDDFs at 9,240 hydrometeorological stations showed that most local rainfall distributions are within one standard error of the five canonical NDDFs identified in this study. The geographic regions corresponding to each of the five NDDFs are identified. Comparison of the normalized temporal rainfall distributions with the conventional Types I, IA, II, and III rainfall distributions shows fairly close agreement; however, the corresponding geographic areas were not in agreement, indicating that continued use of the type curves in engineering practice should be discouraged.

Traditional irrigation systems of northern New Mexico are limited by river flow, and thus water scarcity due to drought and population growth menaces their permanence. This study was conducted to examine the relationship between river flow and ditch flow in an agricultural valley of this region to better manage these ancient systems. Daily flow records for the March–November 2010–2015 periods were analyzed. Positive moderate-to-strong associations were identified with Pearson correlation coefficients. Statistical evidence at a 5% significance level was found in the overall relationships using a model-based approach accounting for serial autocorrelation and heteroscedasticity. The overall change in flow from the main ditches to every unit increase in river flow ranged from 0.0561 to 0.1397. Covariance analysis indicates that ditch flow at a given point in time is best understood as a function of current river flow and recent-past river-ditch flow. Observations indicated dynamic irrigation management in this valley subject to water availability. The findings can be used to develop water management strategies to best use the limited water resources feeding these systems.

A series of four cascading basins were installed at Hambleton Creek Farm in Chestertown, Maryland, to treat agricultural stormwater from a 45.4-ha watershed. The basin system was monitored from July 2013 to April 2015 for concentrations and mass loads of suspended sediments, phosphorous, and nitrogen species. Over the duration of the study, 26 storm events were successfully sampled and tested. During this time, the basin system provided statistically significant reductions of sediments, total phosphorus, and total nitrogen mass loads. The total volume reduction exhibited by the system was 56%; total mass reductions based on an input and output approach for suspended solids, total phosphorus, and total nitrogen were 65%, 59%, and 64%, respectively. Volume reduction appears to be the main mechanism of removal for suspended sediments, phosphorus, and nitrogen. Evidence of sedimentation and nutrient processing between storm events was found.

Designing urban water infrastructure systems for environmental sustainability requires consideration of hydrologic performance design criteria and results from life cycle assessment (LCA). The objective of this paper is to present a study of merging hydrologic and LCA criteria into the evaluation of the environmental sustainability of rainwater harvesting (RWH) to control combined sewer overflows (CSOs). A case study of the City of Toledo, Ohio combined sewer system serves as the platform to investigate the two approaches and to compare RWH with centralized gray infrastructure strategies for controlling CSOs. Results show that the four RWH scenarios studied (two RWH-only: one to supply toilet flushing demand and the other to serve as extended detention; and two hybrids based on combining the two previous with gray infrastructure) delivered higher combined sewage volumes to wastewater treatment facilities compared to a gray infrastructure–only scenario. This resulted in elevated life cycle global warming potential (GWP) impacts (1.10 kg ${\mathrm{CO}}_2\mathrm{e}$ per $1{\mathrm{m}}^3$ of reduced CSOs) on average for the four RWH scenarios. The gray infrastructure–only scenario reduced GWP impacts because it included sewer separation leading to lowered amounts of combined sewage volume treated ($-1.89{\mathrm{kg}\mathrm{CO}}_2\mathrm{e}$ per $1{\mathrm{m}}^3$ of reduced CSOs). But, due to the untreated stormwater discharges to receiving waters, the gray infrastructure–only scenario led to a higher ecotoxicity water (ETW) impact [$-12.11$ comparative toxic unit for ecotoxicity (CTU eco) per $1{\mathrm{m}}^3$ of reduced CSOs] compared to the RWH scenarios ($-19.62$ CTU eco per $1{\mathrm{m}}^3$ of reduced CSOs on average). In conclusion, the new watershed-scale LCA framework led to more information on the CSO control strategies compared to hydrologic-only analysis, but it created a more complicated decision. Information from Toledo water stakeholders must be taken into account before nominating a scenario as the one that globally outperforms the others according the multi-hydrologic-LCA criteria.

The quantification of evapotranspiration (ET) is highly important in water resources planning. The most reliable method for determining ET is to measure it in the field using lysimeters. However, the use of lysimeters for measurement of crop ET (${\mathrm{ET}}_c$) is both expensive and time consuming, thus necessitating a cheaper yet reliable alternative method. One such method is to determine ET using the Penman-Monteith equation, which requires daily meteorological data as inputs. Three vapor pressure models (Models 1–3) are mentioned in Irrigation and Drainage Paper-56 of the Food and Agriculture Organization (FAO-56) for the estimation of actual vapor pressure ($e_a$) that is used in the estimation of reference ET (${\mathrm{ET}}_0$) by the FAO Penman-Monteith equation. Model 1, which uses daily maximum and minimum temperature and relative humidity (RH) data, is the preferred method to estimate $e_a$; other models are used in data-constrained situations. Another vapor pressure model (Model 5) is proposed in this study. The performance of the vapor pressure models along with two other models (Models 4 and 6) existing in the literature is compared with that of Model 1 in estimating daily $e_a$ and ${\mathrm{ET}}_0$ values. The $e_a$ values were underestimated by Model 2, whereas Models 3, 4, and 5 overestimated $e_a$. Results show that Models 4 and 5 (proposed model) performed better than FAO-56 Models 2 and 3 for estimating daily $e_a$ values for Roorkee station, India. However, Model 4, which uses only daily mean temperature and RH data, has lower accuracy in ${\mathrm{ET}}_0$ estimation when compared to Model 5. This is because Model 4 underestimated the daily saturation vapor pressure values. This suggests that daily mean temperature is not enough for the accurate estimation of daily ${\mathrm{ET}}_0$ values. The overall performance of Model 5, which uses the Lawrence dewpoint temperature-RH relationship, was more consistent and closest to Model 1 when compared to the other vapor pressure models for the study region in data-constrained situations. Furthermore, the effect of wind speed ranges on the performance of the vapor pressure models in ${\mathrm{ET}}_0$ estimation is also assessed. The effect of vapor pressure models in ${\mathrm{ET}}_0$ estimation is not considerable for light winds but becomes substantial for higher wind speeds.

New theoretical stage-discharge relationships of different sharp-crested weirs were developed in this study using the new Malcherek’s outflow theory. Although Torricelli’s outflow theory is basically used to estimate the stage-discharge formula for overflow structures, it is indicated in this work that the stage-discharge curve obtained by Malcherek’s outflow theory improves the theoretical estimation significantly. The new theoretical stage-discharge formula requires estimating the momentum correction factor ($\beta$) using velocity profiles instead of using an unknown discharge coefficient. Accordingly, for the rectangular weir, it was indicated that the available velocity profiles over the weir crest could be used to estimate the momentum correction factor and associated stage-discharge curve accurately. Moreover, the optimum $\beta$-values for rectangular, triangular, and circular overflow structures were suggested to be calculated using indirect prediction of the momentum correction factors by introducing the stage-discharge data points available in the literature. The performances of different stage-discharge approaches were evaluated and practical advice was suggested. It was found that the proposed stage-discharge curves were in an excellent agreement with the observed values.