Method of Relating Grain Size Distribution to Hydraulic Conductivity in Dune Sands to Assist in Assessing Managed Aquifer Recharge Projects: Wadi Khulays Dune Field, Western Saudi Arabia

Abstract

Planning for use of a dune field aquifer for managed aquifer recharge (MAR) requires that hydraulic properties need to be estimated over a large geographic area. Saturated hydraulic conductivity of dune sands is commonly estimated from grain size distribution data by employing some type of empirical equation. Over 50 samples from the Wadi Khulays dune field in Western Saudi Arabia were collected and the grain size distribution, porosity, and hydraulic conductivity were measured. An evaluation of 20 existing empirical equations showed a generally high degree of error in the predicted compared to the measured hydraulic conductivity values of these samples. Statistical analyses comparing estimated versus measured hydraulic conductivity demonstrated that there is a significant relationship between hydraulic conductivity and mud percentage (and skewness). The modified Beyer equation, which showed a generally low prediction error, was modified by adding a second term fitting parameter related to the mud concentration based on 25 of the 50 samples analyzed. An inverse optimization process was conducted to quantify the fitting parameter and a new empirical equation was developed. This equation was tested against the remaining 25 samples analyzed and produced an estimated saturated hydraulic conductivity with the lowest error of any empirical equation. This methodology OPEN ACCESSWater 2015, 7 6412 can be used for large dune field hydraulic conductivity estimation and reduce planning costs for MAR systems.

Water Resources Assessment and Management in Drylands

“…A critical design aspect for MAR project development in a dune sand aquifer is the prevention of diffusive evaporative loss of water from storage during system operation. Mughal et al [8] determined that the diffusive evaporative extinction depth is about 1 m in dune sands within the size range evaluated by Lopez et al [7]. Therefore, if a MAR system were to be developed, a 1 m cover of sand above the water table position would be sufficient to prevent water loss.…”

“…In two companion papers, Lopez et al [7] in their paper "Method of relating grain size distribution to hydraulic conductivity in dune sands to assist in assessing managed aquifer recharge projects: Wadi Khulays dune field, western Saudi Arabia" and Mughal et al [8] in their paper "Experimental measurement of diffusive extinction depth and soil moisture gradients in a dune sand aquifer in western Saudi Arabia: Assessment of evaporation loss for design on an MAR system" deal with two important issues in assessing the feasibility and design of Managed Aquifer Recharge (MAR) systems in a hyper-arid region. The location of MAR projects in stabilized dune fields requires screening of large landscape areas to assess potentially feasible sites.…”

“…The location of MAR projects in stabilized dune fields requires screening of large landscape areas to assess potentially feasible sites. Lopez et al [7] developed a mathematical method using grain size distribution data to estimate hydraulic conductivity. Their research documents the changes of hydraulic conductivity and effective porosity with grain size distribution across dunes and allows the development of saturated water storage to be made without the collection of large amounts of data.…”

Experimental Measurement of Diffusive Extinction Depth and Soil Moisture Gradients in a Dune Sand Aquifer in Western Saudi Arabia: Assessment of Evaporation Loss for Design of an MAR System

“…The porosity was determined by dividing the water volume by the sediment volume. This analysis was conducted on three samples collected from the excavated sand and 50 samples on which grain size distribution and hydraulic conductivity were measured from the same dune field by Lopez et al [15]. Additional porosity measurement were made during moisture calibration.…”

“…The aquifer must have adequate storage capacity (porosity or specific yield) to receive the stormwater, satisfactory hydraulic conductivity to allow infiltration of the water and recovery through wells or underdrains, a degree of stability to maintain the subsurface reservoir, a low hydraulic gradient to keep the water in storage, and a known extinction depth to allow a design that minimizes evaporative loss. A method of determining dune aquifer hydraulic properties and a rapid screening process in this region is presented in this special issue by Lopez et al [15]. The primary purpose of our research is to experimentally measure the evaporative extinction depth of dune sands in this region of Saudi Arabia.…”