Characterization of an Internal Drainage Basin Cave Using

ArcGIS

Brian Cowan

Study Area

• In the Recharge Zone of the Edwards Aquifer – Barton Springs Segment

• Flint Ridge Cave– City of Austin Water Quality Protection Land– Somewhere in South Austin

Study Area

University of Texas

Study Area

Importance of Study Area

• Flint Ridge is one of the largest recharge features in the South Austin area

• Internal Drainage Basin– Cave is only outlet for basin– Large amount of recharge– Discrete Flow: Over-land flow

• Relatively large portion of aquifer recharge from internal drainage basins

Importance of Study Area

• Home to the Cicurina cueva cave spider

• Impacts Barton Springs– Barton Springs Salamander– Flow– Quality

• Impacts the Edwards Aquifer– Pollution can travel long distances in karst aquifers

City of Austin

Original Plan

• Use ArcHydro to automatically delineate basin area– Basin area too small!– 50 acres in size

• Relief of basin may also play a roll in difficulties

Original Plan

• Flow accumulation in basin based on “fake” rainfall– Again, not able to delineate basin with ArcGIS– Theory: Apply “fake” rainfall data to

delineated basin area to determine total amount of precipitation landing in basin. By subtracting known values of infiltration and evapotranspiration at the site I could calculate total volume of discrete recharge

Original Plan

• After proving that the recharge values could be calculated, apply actual data to the model – NEXRAD data would be used

• Compare model output with actual measured values

Frustration sets in…

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Benefits of Proposed Plan

• Remotely measure discrete recharge of internal drainage basins (and other geological settings).– Characterize the “normal” percentage

infiltration for area of interest– Obtain evapotranspiration and precipitation

data for study area…

Benefits of Proposed Plan

For an Internal Drainage Basin…

Discrete Recharge = Precip - ET - Infiltration

A New Direction

• Determine area of study site in the field

• Artificially create a basin of the same size in the same location

• Apply NEXRAD data to the model

• Compare with measured results to determine feasibility

If Successful…