Abstract
A component of designing a managed aquifer recharge system in a dune aquifer is the control of diffusive evaporative loss of water which is governed by the physical properties of the sediments and the position of the water table. A critical water table position is the “extinction depth”, below which no further loss of water occurs via diffusion. Field experiments were conducted to measure the extinction depth of sediments taken from a typical dune field in the region. The soil grain size characteristics, laboratory porosity, and saturated hydraulic conductivity were measured. The sand is classified as well-sorted, very fine sand with a mean grain diameter of 0.15 mm. Soil moisture gradients and diffusion loss rates were measured using sensors in a non-weighing lysimeter that was placed below land surface. The sand was saturated carefully with water from the bottom to the top and was exposed to the natural climate for a period of about two months. The moisture gradient showed a gradual decline during measurement until extinction depth was reached at about 100 cm below surface after 56 days. Diurnal temperature changes were observed in the upper 75 cm of the column and were negligible at greater depth.
Highlights
Western Saudi Arabia is a hyper-arid area that receives only about 50 mm of rainfall each year in the coastal area and slightly greater accumulations in the interior higher altitude areas [1].When rainfall does occur, it is an intense event that causes flash floods through ephemeral channels, known as wadis [2,3]
No precipitation occurred during the period of the field experiment
Several samples of the sand were subjected to porosity, hydraulic conductivity and grain size distribution laboratory analyses
Summary
It is an intense event that causes flash floods through ephemeral channels, known as wadis [2,3]. Recent research on future climatic changes in this region suggests that a greater degree of variability will occur with longer drought periods and more intense rainfall events with corresponding floods [7,8]. Collection of Sand Samples from Dune Fields. A field experiment was carried out to measure the diffusive extinction depth of dune sand and to monitor the soil moisture and temperature dynamics during summer for 59 days The sand used in the experiment was excavated from a desert dune in the southwestern region of Saudi Arabia (22 ̋ 081 7.5011 N, 39 ̋ 161 17.3511 E). No rainfall events occurred during the period of the field experiment
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