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Estimating Anthropogenic Recharge to the Barton Springs Segment of the Edwards Aquifer (Austin, Texas) Michael Passarello Jackson School of Geological Science The University of Texas at Austin 11/30/10
More than 50% of global population live in urban areas • This percentage, total urban population, and urban sprawl are increasing • Urbanized areas are more vulnerable to pollutants and are more prone to flooding • Groundwater is often an underutilized resource in urban areas • Urban areas supplant critical environmental areas • Effects of artificial recharge sources Why StudyUrban Hydrogeology?
Case study: Barton Springs segment / Edwards Aquifer N ~5mi • Well studied karst aquifer • Rapidly growing urban area • History of community conflict • Approved GAM for allocation • Hydrogeological modeling based on the GAM Austin Barton Springs Contributing Zone Recharge Zone Artesian Zone About 25% of the world’s population depends on karstic water supply 40% of the United States uses water from karstic areas.
Anthropogenic Sources • Leaky water distribution and wastewater lines • Excess irrigation of lawns and agriculture • Leaky stormwater management structures • Impoundments built to enhance recharge Sources of Additional Recharge
This Research • Objective: Model recharge to the Edwards Aquifer without relying on historical discharge from Barton Springs • Demonstrate that continued increases in discharge from Barton Springs are from anthropogenic sources • Develop a model framework that utilizes precipitation, land use, and anthropogenic data sets
Methodology • Determined total monthly recharge amounts for each cell of Texas’ state approved Groundwater Availability Model (GAM) • The GAM for the Barton Springs segment of the Edwards Aquifer consists of a grid of 7,038 ModFlow cells • Each cell is 500,000 ft2 with ~1/2 overlaying the Recharge Zone south of downtown Austin, TX • Total recharge for each ModFlow cell is defined as: • Direct recharge from precipitation based on land use type (Impervious vs Pervious) • Anthropogenic recharge from leaking water distribution and wastewater lines as well as irrigation return flow
Required Data Sets Direct Recharge Average monthly precipitation for each GAM cell from 1999 - 2010 (Nexrad). Total area of Impervious and Pervious cover for each GAM cell for each year from 1999 – 2010 (City of Austin land use surveys). Percentage of precipitation that contributes to direct recharge for Impervious and Pervious land cover within Austin, TX. (Wiles, 2007 and Hauwert, 2008). graphics from Tom Wiles
Required Data Sets Anthropogenic Recharge – Leaky Utility Lines Average leakage rates for water distribution and wastewater lines in Austin, TX (Austin Water Utility and Garcia-Fresca, 2004). Monthly volumes of water distributed and treated within Austin, TX from 1999 – 2010 (Austin Water Utility) Total length of water distribution and wastewater lines for each GAM cell for each year from 1999 – 2010 (City of Austin). Leakage volumes were evenly distributed over the entire pipe network (ft3/month per foot of pipe)
Required Data Sets Anthropogenic Recharge – Irrigation Return Flow Irrigation (I) = (Water Distributed – Water Treated) – Pipe Leakage Irrigation Return Flow = I – Plant Water Requirement satisfied by irrigation Average monthly precipitation for each GAM cell from 1999 – 2010 Average monthly Palmer Drought Index for the Austin area Total area of Austin’s water service area for each GAM cell