Anthropogenic-Induced Changes in the Mechanism of Drylands Ephemeral Stream Recharge, Western Saudi Arabia

Abstract

Wadi aquifers in Saudi Arabia historically have been recharged primarily by channel loss (infiltration) during floods. Historically, seasonal groundwater levels fluctuated from land surface to about 3 m below the surface. Agricultural irrigation pumping has lowered the water table up to 35 m below the surface. The geology surrounding the fluvial system at Wadi Qidayd consists of pelitic Precambrian rocks that contribute sediments ranging in size from mud to boulders to the alluvium. Sediments within the wadi channel consist of fining upward, downstream-dipping beds, causing channel floodwaters to pass through several sediment sequences, including several mud layers, before it can reach the water table. Investigation of the wadi aquifer using field observation, geological characterization, water-level monitoring, geophysical profiles, and a hypothetical model suggests a critical water level has been reached that affects the recharge of the aquifer. The wetted front can no longer reach the water table due to the water uptake in the wetting process, downstream deflection by the clay layers, and re-emergence of water at the surface with subsequent direct and diffusive evaporative loss, and likely uptake by deep-rooted acacia trees. In many areas of the wadi system, recharge can now occur only along the channel perimeter via fractured rocks that are in direct horizontal hydraulic connection to the permeable beds above and below the water table.

Seasonality in Intermittent Streamflow Losses Beneath a Semiarid Mediterranean Wadi

“…This complexity may in part be caused by the sediment structure that impacts recharge rates as well as moisture as suggested by Jadoon et al. (2016).…”

“…During the wet season, saturated-sediment conditions only occur during flood events, while during steady lower streamflow was insufficient to induce saturated conditions. This complexity may in part be caused by the sediment structure that impacts recharge rates as well as moisture as suggested by Jadoon et al (2016).…”

“…At the experimental site, the alluvium is formed of pebbles, sandy gravel, and boulders with different sizes. The sediments in the wadi, like most wadi systems, contain a series of stacked sediment units the fine‐upwards, from boulders, to cobbles, to grain, to sand, to clay (Jadoon et al., 2016).…”

Water Resources Assessment and Management in Drylands

“…The paper by Jadoon et al [3] entitled "Anthropogenic-induced changes in the mechanism of drylands ephemeral stream recharge, western Saudi Arabia" documents how over-pumping of a shallow aquifer system in drylands can impact recharge. The authors demonstrate that a wadi system in western Saudi Arabia can no longer recharge by conventional infiltration and percolation from a channel during storm events.…”