Impervious Cover and Erosion: Brushy Creek, Round Rock, Texas

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Impervious Cover and ErosionBrushy Creek, Round
Rock, Texas

• GRG 360-G
• Spring 2004

Beau Barnett Brett Franco
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Erosion and Soil Loss Due to the Increase in
Impervious Cover

• Increase in impervious cover can have
  detrimental effects on soil loss and stream
  erosion.
• Soil Infiltration rate goes down with more
  impervious cover.
• Runoff increases when there is less soil
  infiltration.
• With more runoff, the chance for greater soil
  loss increases

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Area of Study
Williamson County
Round Rock, Texas
Brushy Creek
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Population Boom of Round Rock

• From 1990 to 2000, population of Round Rock has
  more than doubled.
• 1994 Dell Computers moved its headquarters
  from Austin to Round Rock, creating over 10,000
  jobs for the area.
• With an increase in population, rapid
  urbanization occurred.

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Methods Used for Analysis

• Delineation of Brushy Creek and morphometric
  analysis using ArcHydro
• Model soil erosion and soil loss using the
  Revised Universal Soil Loss Equation (RUSLE)
• Digitizing zones of impervious cover and area
  analysis using the Field Calculator

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Sources

• Secondary Data
• 30 meter DEMs from TNRIS
• 2.5 meter DOQQs for Round Rock, Texas
• Annual Rainfall Data for Round Rock, Texas

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Techniques

• Revised Universal Soil Loss Equation (RUSLE)
• A R K LS C P
• A estimated average soil loss in tons per acre
  per year R rainfall-runoff erosivity
  factor  K soil erodibility factor L slope
  length factor S slope steepness factor C
  cover-management factor P support practice
  factor

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RUSLE Factors

• R 94
• Estimated value from tamu.edu
• K 0.5
• Estimated value due to rocky sandy soils
• LS Grid derived from slope and flow
  accumulation
• C 0.75 for West Brushy Creek, 0.35 for East
  Brushy Creek
• Value based on percentage of impervious cover in
  basin
• P 1
• Value constant due to size of study area

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Sources of Error

• More recent DOQQs
• Imprecise soil data for K factor
• C factor is not constant on a landscape
• RUSLE equation is a model, not an exact science!

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Future Research

• Better defined factors for RUSLE equation
• More widely available data
• Study amount of soil deposition downstream
• Development of environmentally sensitive
  construction practices
• Use of newly developed pervious concrete

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Conclusions

• With the relocation of Dell causing a population
  boom in Round Rock the amount of impervious cover
  increased greatly.
• This in turn increased runoff and soil erosion
  in the area and measures need to be taken to
  lessen the impacts of this urban sprawl.

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Works Cited

• http//www.tnris.state.tx.us
• http//www.iwr.msu.edu/rusle/
• http//www.dell.com/
• http//www.ci.round-rock.tx.us
• http//www.utexas.edu/depts/grg/hudson/grg360g/EG
  IS/E_grg360g.htm