Journal of Irrigation and Drainage Engineering

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

Forum papers are thought-provoking opinion pieces or essays founded in fact, sometimes containing speculation, on a civil engineering topic of general interest and relevance to the readership of the journal. The views expressed in this Forum article do not necessarily reflect the views of ASCE or the Editorial Board of the journal.

A study was conducted to identify methods of achieving uniform flow distribution in compact irrigation splitter boxes over a wide range of flows but specifically operating at high flow rates. The hydraulic issues resulting from high flow rates in the boxes and their potential implications are discussed to provide a basis for the study. Two splitter boxes, one square and one rectangular in layout, were constructed for testing. Numerous improvement designs were developed, built, and installed in the boxes to inspect and measure their performance. Vertical perforated plates with varying hole diameter, perforated area porosity, and plate thickness succeeded in distributing the flow uniformly across the length of the weir. Data presented show the effectiveness of the various designs in improving the distribution and splitting the flow entering into the box. Vertical removable perforated plates are recommended to be installed in splitter boxes where uniform distribution is not currently achieved. Details for the designs that improved flow performance are discussed and the successful application of the designs into prototype splitter boxes is demonstrated.

Effects of highway traffic noise have recently emerged. Greenery has become an essential aspect in urban planning nowadays as an interesting way to improve the quality of life in urban environments. Applying road traffic noise-reducing-device envelope greening and at the same time tackling noise issues can therefore be considered as a highly sustainable goal. This work has the objective to develop a design for a modular vegetative unit as a noise-abatement wall envelope greening in a semiarid climate and determine fertigation management during plant canopy growth composed of the designed modules. The modular vegetative units are designed to provide appropriate noise mitigation in semiarid areas. These canopies could improve the aesthetic appearance of noise-abatement walls and require only moderate fertigation to complement scarce precipitation during the summer months in order to manage the green infrastructure to achieve lower noise levels.

Current models used to design agricultural drains assume that perforated pipes (field drains) are ideal drains, and some models do not include the water entrance resistance factor at pipe perforations. Drainage models used to design agricultural drains assume that perforated pipes (field drains) are ideal drains with no water entrance loss taking place at the drain perforations. However, this may not be a valid assumption for many drainage situations in which radial water flow into the drain is significant in relation to vertical and horizontal water flow. The convergence of streamlines toward the drilling of a real drain causes an additional input resistance (called entrance resistance) to flow and a pressure drop, as compared with an imaginary perfect flow drain. This work evaluates a PVC drains’ structural mechanical conditions, as related to the drainage extraction area and the water entrance resistance factor, to maximize its water discharge performance. The effects of pipe perforation density, pipe diameter, substrate hydraulic characteristics, and the incorporation of an enveloping screen were studied in an experimental setup to define water extraction efficiency, water entrance resistance factor (${\alpha }_e$), and pipe effective radius ($r_{ef}$). This work proves that the water entrance resistance should be taken into account in drainage design because the optimal distance between parallel drains is significantly smaller if pipes are enclosed in a protective screen, compared with pipes without screen, for any drainage extraction area in different substrates. The effects of perforation density and envelope screens are determined by water extraction efficiency for small hydraulic head conditions.

This paper evaluates watershed-scale hydrologic performance of low-impact development (LID) features at two catchments in the Houston, Texas, region. White Oak Bayou is a traditional urban watershed that is frequently plagued with flooding. In contrast, The Woodlands is a master-planned suburban community designed to preserve its natural hydrology by implementing large-scale conservation features. The objectives of this study are threefold: (1) to propose a method to simulate small-scale infiltration-based LID features over a large area by using a distributed hydrologic model; (2) to quantify the cumulative hydrologic responses of watershedwide LID implementation; and (3) to compare the flood reduction potential between two distinct LID strategies (conservation LID and retrofit LID). Conservation (master-planned) LID integrates large-scale features (e.g., riparian buffers and swales) early in a watershed’s development, whereas retrofit LID implements site-scale features (e.g., green roofs and rain gardens) after the watershed has been fully developed. The results of this study demonstrate varying degrees of flood reduction (i.e., peak discharge and runoff volume) at the watershed outlets with respect to different LID features and rainfall events. The results also showed that although retrofitted watersheds could not quite match the hydrologic performances of master-planned watersheds, they could still enjoy the benefit of flood reduction during smaller storms.

The objective of this study was to evaluate the FAO-56 Penman-Monteith (FAO-PM) reference evapotranspiration (ETo) equation and two Valiantzas equations for estimating daily reference evapotranspiration under limited data and four other ETo equations across Tanzania and the southwestern Kenya. The results showed the applicability of the FAO-PM equation under missing solar radiation (Rs), relative humidity (RH), and wind speed (u2) data with regression slopes varying from 0.68 to 0.89, from 0.79 to 1.00, and from 0.79 to 0.96, respectively, and root mean squared error (RMSE) lower than 0.63, 0.53, and $0.44\mathrm{mm}/\mathrm{day}$ under the respective conditions. Under lacking relative humidity data, the simplified method provided very good ETo estimates. There were large discrepancies in ETo estimates with the FAO-PM equation when two or three weather variables were missing. The Valiantzas 2 equation with full data provided the most accurate ETo estimates under the eastern Africa conditions with coefficient of determination ${\mathit{R}}^{\mathit{2}}>0.97$, regression slope ranging from 0.96 to 1.05, $\mathrm{RMSE}<0.23\mathrm{mm}/\mathrm{day}$, MBE ranging from $-0.03$ to $0.17\mathrm{mm}/\mathrm{day}$, and very low relative error ($\mathrm{RE}<5.5\%$). The Irmak, Abtew, Hansen, and Hargreaves equations produced moderately accurate ETo estimates with RMSE as high as 0.91, 0.74, 0.74, and $0.66\mathrm{mm}/\mathrm{day}$ for the respective equations, and relative error as high as 16.3%.