Chris Spry


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Final Presentation for Environmental Modeling

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Chris Spry

  1. 1. Storm Water Modeling using the Curve Number Runoff Method Town Creek Watershed - Salisbury NC Presented by: Chris Spry 12.17.10
  2. 2. Context of Problem <ul><li>Land use change alters the hydrology of an area and can increase storm water runoff and flooding hazards. </li></ul><ul><li>Increasing impermeable surfaces (parking lots, roads, and buildings) has an additive effect. </li></ul><ul><li>Decreasing natural areas such as forests, open grassy areas, and misuse of flood plains also increase risk </li></ul><ul><li>The Town Creek Watershed (part of the Yadkin River basin), located in Salisbury, NC is a prime example of these changes. </li></ul>
  3. 4. Project Objectives <ul><li>Model land use change between the years of 1978 and 2010 within the study boundaries. </li></ul><ul><li>Determine the percentage of land uses (forest, open space, and urban space) in this area within these time periods. </li></ul><ul><li>Calculate the change in land uses and storm water runoff over this time period. </li></ul><ul><li>Evaluate the usefulness of this method for use in an urban area </li></ul>
  4. 5. Methods (Data Collection) <ul><li>DEM (Digital Elevation Model) obtained from City of Salisbury GIS Division </li></ul><ul><li>Soil Data obtained from Rowan County </li></ul><ul><li>Aerial Imagery from 1978 obtained from City of Salisbury GIS Division </li></ul><ul><li>Satellite Imagery from 2009 obtained from City of Salisbury GIS Division </li></ul>The following data was required to complete the project:
  5. 7. 1978 Aerial vs. 2009 Satellite Imagery Zoomed
  6. 8. Methods (Incorporate data into GIS) <ul><li>DEM was used to create data involving flow direction , and flow accumulation to create stream channels. </li></ul><ul><li>Imagery was digitized and clipped to create two land cover maps for 1978 and 2009. </li></ul><ul><li>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.) </li></ul><ul><li>4 inch Rainfall map was created using flow direction and accumulation techniques. </li></ul><ul><li>The Curve Number Runoff ( CNR) Equation was used to show runoff totals for both time periods </li></ul><ul><li>The higher the CN , the higher potential for runoff </li></ul>
  7. 9. Methods: (CRN) Equation <ul><li>Q = (P - I a ) 2 </li></ul><ul><li>P - I a + S </li></ul><ul><li>Q = runoff </li></ul><ul><li>P = precipitation </li></ul><ul><li>S = potential maximum soil moisture retention after runoff begins </li></ul><ul><li>I a = initial abstraction, basically the amount of water before runoff , such as infiltration , or interceptance by vegetation. </li></ul><ul><li>I a is the percentage of S: I a = 0.2S </li></ul><ul><li>Q is then: </li></ul><ul><li>Q = (P - 0.2S ) 2 </li></ul><ul><li>(P + 0.8S) </li></ul><ul><li>The Curve Runoff Number, CN is then related: </li></ul><ul><li>S = 1000 - 10 </li></ul><ul><li>CN </li></ul>
  8. 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%
  9. 11. Project Significance and Encountered Issues <ul><li>This project is significant because it reinforces what is already known about the impact of urbanization on storm water runoff. </li></ul><ul><li>Knowledge has been used in the development of storm water retention ponds. </li></ul><ul><li>Downstream development which is near the floodplain has been removed and discouraged . </li></ul><ul><li>Issues Encountered: CNR Method would work better for areas with greater change in elevation and less urbanized environments. </li></ul>
  10. 13. Thanks for your attention! Questions?