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Impervious Cover and Erosion:Brushy Creek, Round Rock, Texas
GRG 360-G
Spring 2004
Beau Barnett
Brett Franco
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
Population Boom of Round Rock
• From 1990 to 2000, population of Round Rock has more than doubled.
• 1994 Dell Computers moved it’s headquarters from Austin to Round Rock, creating over 10,000 jobs for the area.
• With an increase in population, rapid urbanization occurred.
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
Sources
Secondary Data:
• 30 meter DEMs from TNRIS
• 2.5 meter DOQQs for Round Rock, Texas
• Annual Rainfall Data for Round Rock, Texas
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
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
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!
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
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.
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/EGIS/E_grg360g.htm