Evaluating longitudinal dispersion of scalars in rural channels of agro-urban environments

Abstract

In agro-urban environments, the water resource conveyed by rural channels is susceptible to a gradual impoverishment due to the continuous combined sewer overflow release, constituting a pending and urgent issue for water management companies and the entire community. Reliable one-dimensional longitudinal dispersion coefficients D are required to model and study the hydrodynamics and water quality patterns at the scale of rural channel networks. Empirical formulas are usually adopted to estimate D but the accuracy in the prediction could be questionable. In order to identify which are the most suitable formulas to determine D in rural channels, field tracer measurements were carried out in three rural channels with typical geometry and configuration. The obtained D values were then compared with the most commonly used predicting formulas that the literature provides. The accuracy of the predictors was further checked by simulating different flow rates inside the tested channels by using a one-dimensional hydraulic model. Starting from the obtained results, indications and guidelines to choose the most suitable formulas to predict D in rural channels were provided. These indications should be followed when developing realistic quality models in the agro-urban environments, especially in those cases where direct measurements of the longitudinal dispersion coefficient D are not available.

Investigating First Flush Occurrence in Agro-Urban Environments in Northern Italy

“…In Basin 2, a water level sensor (Diver ® , Eijkelkamp, Giesbeek, The Netherlands) was installed in the Roggia Gamberina, immediately after the fourth spillway, to monitor waterlevel fluctuations induced by the CSOs during wet periods. A stage-discharge relationship was derived using the HEC-RAS ® model to convert water level into discharge [35]. Rainfall data were collected (with a time resolution of 1 min and aggregated at 10 min) at six rain gauges located around the study area within a radius of approximately 2 km from the position of the water level sensor (Figure 1 shows the position of only one rain gauge, as the other five fall outside the boundaries of the figure).…”

Investigation of Deoxygenation Rate Determination in Cikakembang River, West Java, Indonesia

“…River discharge was obtained through calculations using flow velocity data, yielding values of 0.86 m 3 s -1 during rainy season and 0.252 m 3 s -1 during dry season. In this model, the value of the reaeration coefficient (k a ) used the equation from Jha et al (2004), while the dispersion coefficient (Ex) used the equation from Iwasa and Aya (1991); Jain and Jha (2005); Peruzzi et al (2021). Based on previous studies, combining these two coefficients provided adequate analysis results and was suitable for Cikakembang River (Polisar, 2023).…”

High-Resolution 2D Modelling for Simulating and Improving the Management of Border Irrigation

“…The flow rate during the irrigation event was determined by measuring the flow level in the supply canals, where the flow can reasonably be considered to be in uniform condition. The roughness parameter was calibrated at the beginning of the irrigation season, using the well-known Manning-Strickler formula (Ven Te Chow, 1959) in which: 1) the flow rate was measured by a manual portable magnetic-inductive flow meter (Flow Sensor NAUTILUS C 2000, OTT, USA) by using the so-called conventional current meter methodology (Anon, 2010;Peruzzi et al, 2021), 2) the canal slope was evaluated using a portable Global Positioning System (GPS) (GRS-1, TOPCON, Japanvertical accuracy of ± 2.5 cm), 3) the cross-section area and the hydraulic radius were computed considering the shape of the cross-section (trapezoidal) and a graduated rod (precision is ± 1 mm) for the measurement of the water depth. Using this information, the estimated Strickler coefficient was equal to 75 m 1/3 s -1 .…”