HR: 15:10h
AN: B43B-01 INVITED     [Abstracts]
TI: Role of Aquifer Heterogeneity in Salinity Persistence in Tsunami Affected Coastal Aquifers - Need for Better Characterization
AU: * Illangasekare, T H
EM: tillanga@mines.edu
AF: National Science Foundation, Hydrologic Sciences Program- Division of Earth Sciences, 4201 Wilson Blvd., Arlington, VA 22230, United States
AU: Vithanage, M
EM: meth@geol.ku.dk
AF: Geological Institute, University of Copenhagan, Copenhagan, Denmark
AU: Jensen, K H
EM: KHJ@geol.ku.dk
AF: Geological Institute, University of Copenhagan, Copenhagan, Denmark
AU: Engesgaard, P
EM: PE@geol.ku.dk
AF: Geological Institute, University of Copenhagan, Copenhagan, Denmark
AU: Obeysekera, J
EM: jobey@sfwmd.gov
AF: Hydrologic & Environmental Systems, South Florida Water Management District 3301 Gun Club Road, West Palm Beach, FL 33406, United States
AU: Villholth, K G
EM: K.VILLHOLTH@CGIAR.ORG
AF: IWMI, International Water Managemen, 127 Sunil Mawatha, Pelawatta, Battaramulla, Sri Lanka
AU: Perera, L
EM: lasanthaperera@hotmail.com
AF: Water Resources Board, 2A, Gregory's Avenue, Colombo, 7, Sri Lanka
AB: The 2004 Indian Ocean tsunami caused extensive contamination of coastal aquifers. Seawater entered the aquifers through open dug wells and also via direct infiltration. In Sri Lanka alone, an estimated 40,000 drinking water wells were either destroyed or contaminated. Based on an initial conceptual model, it was hypothesized that salinity should decrease with recharge from seasonal rains associated with monsoons within a couple of seasons. However, monitoring data collected at some sites for more than two years after the tsunami show that concentrations still have not returned to pre-tsunami levels. This persistence is attributed to a combination of factors that were not taken into consideration in the earlier model. These factors include sub-normal recharge, subsurface heterogeneity, preferential flushing of freshwater through permeable channels, inappropriate cleaning and pumping activities from wells, bathymetry, coastal land topography and local hydrologic and geohydrologic conditions. This paper presents the results from a laboratory study conducted in a 2D intermediate scale test tank to generate both qualitative and quantitative data for preliminary validation of a new conceptual model that takes these factors into account. The focus was to evaluate the effects of heterogeneity on the propagation of an infiltrating salt-water plume and the effectiveness of subsequent flushing with freshwater. Tsunami flooding events were simulated in a large soil tank packed to represent various heterogeneous configurations. Both the tsunami event and flushing from ambient fresh groundwater and infiltrating rainwater were simulated. In addition to qualitative observations, the spatial and temporal variations of salinity were monitored using a set of in-situ electrical conductivity probes. The data strongly suggest that the plume development and persistence is highly controlled by the geological heterogeneity that needs to be characterized using methods other than conventional coring (e.g. geophysical methods).
UR: http:www.cesep.mines.edu
DE: 0466 Modeling
DE: 0468 Natural hazards
DE: 0478 Pollution: urban, regional and global (0345, 4251)
DE: 0496 Water quality
DE: 1831 Groundwater quality
SC: Biogeosciences [B]
MN: 2007 Joint Assembly