Bailout test, HYDRUS‐2D, and analytical modeling for estimating permeability of ephemeral stream bed.

Accurate estimation of effective saturated hydraulic conductivity (Ksat) of a vadose zone with an underlying shallow perched aquifer is challenging. Standard pumping tests and double‐ring infiltrometers are unsuitable for this purpose. Therefore, a bailout test (BOT) was conducted in nine soil pits to evaluate the hydraulic properties of the vadose zone and the subjacent shallow‐perched aquifer in a porous bed of a wadi in Oman. The analytical (Kirkham's type) and numerical (HYDRUS‐2D) models were also used. Upon instantaneous emptying, the water level rises in a pit, owing to seepage from the ambient shallow aquifer. The draw up was monitored and compared with modeling, which assumes a homogeneous or layered van Genuchten's soil. The soils of the excavated pits were characterized as sandy‐textured, gleyed, and containing calcareous and clay‐enriched layers. A good match between HYDRUS‐analytical results for layered soils and an idealized homogeneous one illustrates that BOT is a robust and quick technique for the estimating Ksat = 2–3 cm/h in the coarse‐textured wadi bed vadose zone overlaying a transient water table. BOT is better than classical auger hole tests because they test a larger soil volume through induced seepage. BOT is also more suitable for drainage trenches and other excavations, allowing for easier observation, soil sampling from the banks, and rapid dewatering. Core Ideas: Bailout test gives an upscaled value of Ksat, as compared with one obtained by classical auger hole tests.The saturated hydraulic conductivity (Ksat) of ephemeral stream beds with a shallow aquifer was estimated using three methods: the bailout test, the Kirkham analytical model, and simulations performed with the HYDRUS‐2D model.The agreement among models shows the bailout test efficiently estimates Ksat (2–3 cm/h) in coarse‐textured wadi bed.The bailout test is ideal for drainage trenches, facilitating observation, soil sampling, and rapid dewatering. Plain Language Summary: Accurately measuring how water moves through soil (saturated hydraulic conductivity or Ksat) in areas with a shallow water table is difficult. Traditional methods like pumping tests and infiltrometers do not work well in this context. This study introduces an alternative method, the bailout test (BOT), to assess the water flow in a wadi bed in Oman. The soil in the study area was mainly sandy with some clay and calcareous layers. The BOT method provided reliable estimates of water flow (Ksat) of around 2–3 cm/h. The BOT offers a quick, reliable, and practical way to estimate how water moves through soil in regions with shallow water tables. It works better than traditional methods in areas with coarse‐textured soils, such as wadi beds, and can be useful for drainage projects and excavations. [ABSTRACT FROM AUTHOR]