Title
Shallow rainwater lenses in deltaic areas with saline seepage
Author
de Louw, P.G.B.
Eeman, S.
Siemon, B.
Voortman, B.R.
Gunnink, J.
van Baaren, E.S.
Oude Essink, G.H.P.
Publication year
2011
Abstract
In deltaic areas with saline seepage, fresh water availability is often limited to shallow rainwater lenses lying on top of saline groundwater. Here we describe the characteristics and spatial variability of such lenses in areas with saline seepage and the mechanisms that control their occurrence and size. Our findings are based on different types of field measurements and detailed numerical groundwater models applied in the south-western delta of The Netherlands. By combining the applied techniques we could extrapolate in situ measurements at point scale (groundwater sampling, TEC (temperature and electrical soil conductivity)-probe measurements, electrical cone penetration tests (ECPT)) to a field scale (continuous vertical electrical soundings (CVES), electromagnetic survey with EM31), and even to a regional scale using helicopter-borne electromagnetic measurements (HEM). The measurements show a gradual S-shaped mixing zone between infiltrating fresh rainwater and upward flowing saline groundwater. The mixing zone is best characterized by the depth of the centre of the mixing zone Dmix, where the salinity is half that of seepage water, and the bottom of the mixing zone Bmix, with a salinity equal to that of the seepage water (Cl-conc. 10 to 16 g l -1). Dmix manifests at very shallow depth in the confining top layer, on average at 1.7 m below ground level (b.g.l.), while B mix lies about 2.5 m b.g.l. Head-driven forced convection is the main mechanism of rainwater lens formation in the saline seepage areas rather than free convection due to density differences. Our model results show that the sequence of alternating vertical flow directions in the confining layer caused by head gradients determines the position of the mixing zone (Dmix and Bmix and that these flow directions are controlled by seepage flux, recharge and drainage depth. © Author(s) 2011.
Subject
Earth & Environment
GM - Geomodelling
EELS - Earth, Environmental and Life Sciences
Geosciences
delta
drainage
electromagnetic field
field method
flux measurement
groundwater
in situ measurement
infiltration
numerical model
rainwater
salinity
sampling
seepage
spatial variation
temperature effect
water availability
water depth
Netherlands
To reference this document use:
http://resolver.tudelft.nl/uuid:f7abb165-2c64-4a80-8f76-4635253a3012
TNO identifier
436034
ISSN
1812-2108
Source
Hydrology and Earth System Sciences Discussions, 8 (4), 7657-7707
Document type
article