Drawdown of urban drain trenches triggering 2-D transient seepage in soil massifs subject to managed aquifer discharge: sandbox experiments, analytical and HYDRUS2D modeling

• Published in: Urban water journal Vol. 19; no. 3; pp. 299 - 313
• Main Authors: Al-Yaqoubi, Shahad, Al-Maktoumi, Ali, Obnosov, Yurii, Kacimov, Anvar
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis 16.03.2022; Taylor & Francis Ltd
• Subjects: Aquifer management; Aquifers; boundary-value problem and the keldysh-sedov formula; Capillarity; complex potential-conformal mappings; Control stability; Discharge; Drawdown; Equilibrium flow; Erosion control; Exact solutions; Flow rates; Flow velocity; Gradients; Groundwater table; Hydraulic gradient; HYDRUS2D simulations; Isobars; isobars-isohumes-isotachs-streamlines; Massifs; Mathematical analysis; Mathematical models; Pore pressure; Pore water pressure; sandbox drawdown experiments; Seepage; Slope stability; Soil; Soils; Stability analysis; Streamlines; Trenches; Unsteady flow; Urban areas; Urban drainage by trenches; Water levels; Water table
• ISSN: 1573-062X; 1744-9006
• DOI: 10.1080/1573062X.2021.1999989

Managed Aquifer Discharge (MAD) through trenches lowers the water table of 'shallow perched aquifers' in urban areas (Muscat-Oman). Drawdown of the water table in periodic trenches or a single trench is experimentally studied in a sandbox, and modelled numerically (by HYDRUS2D) and analytically. Evaluation of transient flow fields of pore pressure and hydraulic gradients is necessary for assessing the stability of trench slopes to seepage-induced erosion. A controlled emptying of trench's water level is examined. An analytical solution is obtained for an unconfined seepage at an early stage of drainage. Numerical simulations are conducted for early and late stages of seepage towards a partially filled trench in soils with capillarity. For a steady-state Darcian flow limit, comparisons of HYDRUS results with the Charny analytical formula for capillarity-free soils are done. The flow rates, isobars, isotachs and streamlines are determined, with assessment of zones of high hydraulic gradients susceptible to seepage erosion.