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Final Environmental Modeling

Final Environmental Modeling

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CSpryFinal5 Presentation Transcript

  • 1. Storm Water Modeling using the Curve Number Runoff Method Town Creek Watershed - Salisbury NC Presented by: Chris Spry 12.17.10
  • 2. Context of Problem
    • Land use change alters the hydrology of an area and can increase storm water runoff and flooding hazards.
    • Increasing impermeable surfaces (parking lots, roads, and buildings) has an additive effect.
    • Decreasing natural areas such as forests, open grassy areas, and misuse of flood plains also increase risk
    • The Town Creek Watershed (part of the Yadkin River basin), located in Salisbury, NC is a prime example of these changes.
  • 3.  
  • 4. Project Objectives
    • Model land use change between the years of 1978 and 2010 within the study boundaries.
    • Determine the percentage of land uses (forest, open space, and urban space) in this area within these time periods.
    • Calculate the change in land uses and storm water runoff over this time period.
    • Evaluate the usefulness of this method for use in an urban area
  • 5. Methods (Data Collection)
    • DEM (Digital Elevation Model) obtained from City of Salisbury GIS Division
    • Soil Data obtained from Rowan County
    • Aerial Imagery from 1978 obtained from City of Salisbury GIS Division
    • Satellite Imagery from 2009 obtained from City of Salisbury GIS Division
    The following data was required to complete the project:
  • 6.  
  • 7. 1978 Aerial vs. 2009 Satellite Imagery Zoomed
  • 8. Methods (Incorporate data into GIS)
    • DEM was used to create data involving flow direction , and flow accumulation to create stream channels.
    • Imagery was digitized and clipped to create two land cover maps for 1978 and 2009.
    • Soil Data was clipped for the study area and grouped in to Hydro groups ( A-D ) (A = low runoff potential and D = higher runoff potential.)
    • 4 inch Rainfall map was created using flow direction and accumulation techniques.
    • The Curve Number Runoff ( CNR) Equation was used to show runoff totals for both time periods
    • The higher the CN , the higher potential for runoff
  • 9. Methods: (CRN) Equation
    • Q = (P - I a ) 2
    • P - I a + S
    • Q = runoff
    • P = precipitation
    • S = potential maximum soil moisture retention after runoff begins
    • I a = initial abstraction, basically the amount of water before runoff , such as infiltration , or interceptance by vegetation.
    • I a is the percentage of S: I a = 0.2S
    • Q is then:
    • Q = (P - 0.2S ) 2
    • (P + 0.8S)
    • The Curve Runoff Number , CN is then related:
    • S = 1000 - 10
    • CN
  • 10. Results Land Use Statistics for the year (1978) Forest = 53% Open Space = 40% Urban = 7% Flow Accumulation at Innes St. point from a 4 inch rainfall: 78,592 Land Use Statistics for the year (2009) Forest = 50 % Open Space = 35% Urban = 15% Flow Accumulation at Innes St. point from a 4 inch rainfall: 92,131 Land Use Change between 1978 and 2009 Forest = -3% Open Space = - 5% Urban = +8%
  • 11. Project Significance and Encountered Issues
    • Projects like this one can be significant because they reinforce what is already known about the impacts of urbanization on storm water runoff.
    • Knowledge has been used in the development of storm water retention ponds.
    • From this example, downstream development which is near the floodplain has been removed over the years and discouraged .
    • This next slide shows a couple issues I encountered: My evaluation is that the CNR Method would work better for areas with greater change in elevation and less urbanized environments.
  • 12.  
  • 13. Thanks for your attention! Questions?