Geologic and hydrologic settings for development of freshwater lenses in arid lands

Abstract

Satellite observations were used to test the validity of previously identified favourable conditions for the formation of freshwater lenses, identify additional potential occurrences, and model modern potential recharge in the Raudhatain Watershed (3696) in northern Kuwait. Favourable conditions include infrequent yet intensive precipitation events, drainage depressions to collect the limited runoff, and presence of conditions (e.g. high infiltration capacity) that promote groundwater recharge and preservation (e.g. underlying saline aquifer) of infiltrating groundwater as freshwater lenses floating over saline aquifer water due to differences in density. Specifically, the following field and satellite‐based observations were noted for the Raudhatain Watershed: (1) Over ~30 precipitation events were identified from the Tropical Rainfall Measuring Mission precipitation data (1998–2009); (2) slope is gentle (2 m/km), and the surface is largely (80%) covered by alluvial deposits with high infiltration capacities (up to 9 m/day); (3) no flows and long‐term ponding were reported at the watershed outlet or detected from Landsat thematic mapper images; (4) infiltration is high based on increases in soil moisture content (from an advanced microwave scanning radiometer) and vegetation index following large precipitation events; and (5) freshwater lenses that overlie highly saline [total dissolved solids (TDS): >35 000] unconfined aquifers underlying the watershed are absent in the southern regions, where infiltrating fresh water mixes with the less saline groundwater (TDS: <10 000). Twenty potential locations (size: 1 to 75 km2) for freshwater lens development were identified in northern Kuwait, and continuous rainfall–runoff models (Soil Water and Assessment Tool) were applied to provide a first‐order estimation of the average annual recharge in the watershed (127 × 106 m3) and freshwater lenses (8.17 × 106 m3). Results demonstrate the settings for enhanced opportunities for groundwater recharge, outline the amounts of and preservation conditions for the groundwater feeding the freshwater lenses, and highlight potential applications and locations of freshwater lenses in similar settings elsewhere in the Arabian Peninsula and beyond. Copyright © 2013 John Wiley & Sons, Ltd.

Transient Evolution of Inland Freshwater Lenses: Comparison of Numerical and Physical Experiments

“…Similar systems have been identified within the deserts of the Middle East, Asia, Australia, South America, and Africa but have declined in use. A return to these systems with a focus on the interplay between meteoric recharge and the underlying saline groundwater offers development opportunities through modern and traditional methods to meet the growing demand for water resources in arid environments [18,57].…”

“…However, Bedouin communities likely once utilized these resources along with other ancient irrigation techniques (i.e., runoff harvesting), but abandoned these systems due to changes in the governing authority, modern agricultural practices, and inadequate drainage [17]. Recent studies have identified more than 100 potential locations throughout the Arabian Peninsula with conditions favorable (e.g., climatic, geomorphic, hydrogeologic) for the development and sustainability of IFLs [18]. Investigations into the formation and transient evolution of IFLs offer freshwater resources sustainability and development opportunities throughout the Arabian Peninsula and elsewhere with similar environmental settings.…”

Estimating groundwater recharge for a freshwater lens in an arid region: Formative and stability assessment

“…Potential recharge, which is estimated from surface‐water and unsaturated‐zone studies, is water that has infiltrated but may not actually reach the water table because of unsaturated‐zone processes, such as bank storage and evapotranspiration, or the inability of the saturated zone to accept recharge due to factors such as low transmissivity or a shallow water table (Rushton, ). Compared with actual recharge, potential recharge estimates based on the surface zone were higher and had a wider range of values, ranging from 4.9 to 33.9 mm/year for the entire Rawdatain watershed (8.2–46.8 million m 3 /year) (Al‐Dousari et al, ; Al‐Senafy et al, ; Din et al, ; Milewski et al, ). Their studies used SWAT model simulations and modern precipitation records to estimate the potential recharge, with the exception of Din et al (), who used physical techniques.…”

“…The existence of that pre‐development data, as well as the quality and quantity of that data, makes Rawdatain an ideal and potentially unique candidate to use for evaluating the formative and potentially changing dynamics of lenses in arid regions. A number of studies have been dedicated to the hydrogeological aspects of the depressions in the Rawdatain basin and the general hydrogeology of the area (Al‐Dousari, Milewski, Din, & Ahmed, ; Al‐Senafy et al, ; Bergstrom & Aten, ; Din, Al Dousari, & Al Ghadban, ; Ebrahim, Siwek, & Al‐Ruwaih, ; Grealish, Omar, & Quinn, ; Kwarteng, Viswanathan, Al‐Senafy, & Rashid, ; Milewski, Sultan, Al‐Dousari, & Yan, ; Parsons Corporation, ; Robinson & Al Ruwaih, ; Viswanathan, Al‐Senafy, Mukhopadhyay, Kodittuwakku, & Al‐Fahad, ). These studies are discussed in detail in Sections 2.2 and 2.3.…”

“…The annual average rate of recharge must be quantified more accurately to assist with water management strategies in the region. Milewski et al () discussed the challenges of estimating the recharge of the freshwater lenses in the deserts due to the unique hydrological processes such as, infrequent‐intensive rainfall events, losses through the wadis, infiltration capacity, and salinity of the hosting aquifers. Inclusion of dispersion to allow for mixing of recharge water with ambient groundwater yields a better representation of the recharge mechanism, with the former remaining an open question in the literature (Garabedian, LeBlanc, Gelhar, & Celia, ; Gelhar, Welty, & Rehfeldt, ; LeBlanc et al, ; Schulze‐Makuch, ).…”