Urban "Karst": The Impacts of Utility/Service Conduits/Ducts on Urban Groundwater Systems

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992899SharpUrban areas are hydrologically similar to karstic settings-they have internal drainage (storm sewers), surface streams (paved drainage ditches) that flow after heavy rains, and a permeability structure that may be dominated by fractures, conduits, and caves (buried utility trenches, abandoned pipes, etc.). Over half the world's population now lives in the urban environment. This is projected to increase both absolutely and as a percentage, and the urban area is increasing at a greater rate than the urban population. Recent studies on urbanization demonstrate signficant impacts on both the rates of recharge and permeability distributions within the shallow subsurface. For example, leakage from water mains and sewerage systems can increase recharge despite increases in "impervious" cover! Urbanization affects groundwater pollution and remediation, water resources, stream flows, and geotechnical projects. The construction and abandonment of subsurface utility systems create an interconnected network in the shallow subsurface with highly contrasting permeabilities (up to 7-10 orders of magnitude in preliminary tests).This project will: (1) examine how urban utility lines, ducts, conduits and their accompanying trenches alter natural permeability structure; (2) compare these changes between carbonate, shale/mudstone, and alluvial environments and with undisturbed settings; (3) predict how such changes affect recharge and urban groundwater contamination; and (4) test chemical tracers (specifically boron) to verify the models and identify the impact of trench networks. We will analyze the effects of these "pathways" on groundwater flow and solute transport using the numerical model FAC3DVS and field studies. We will predict, for representative scenarios, how the construction of trench networks and the leakage from water mains and sewage systems impact on urban groundwater systems. Several tracers will be tested to assess the magnitude of any effects. The research is a joint venture between The University of Texas at Austin, USA, and Royal Holloway College University of London, UK. It will contrast the outcome of urban development in a young and rapidly growing city [Austin] and a more mature urban environment [London] where the long-term effects of urbanization should be more apparent. The work in the UK is the subject of a separate proposal to the British Research Councils.