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Storm Water Modeling using the Curve Number Runoff Method Town Creek Watershed - Salisbury NC Presented by: Chris Spry 12.17.10

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Environmental Modeling Final

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Page 1: Chris Spry

Storm Water Modeling using the Curve Number Runoff Method

Town Creek Watershed - Salisbury NC

Presented by: Chris Spry12.17.10

Page 2: Chris Spry

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.

Page 3: Chris Spry
Page 4: Chris Spry

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

Page 5: Chris Spry

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:

Page 6: Chris Spry
Page 7: Chris Spry

1978 Aerial vs. 2009 Satellite Imagery

Zoomed

Page 8: Chris Spry

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

Page 9: Chris Spry

Methods: (CRN) Equation

Q = (P - I a ) 2

P - Ia + SQ = runoffP = precipitationS = potential maximum soil moisture retention after runoff

beginsIa = initial abstraction, basically the amount of water before

runoff, such as infiltration, or interceptance by vegetation.Ia is the percentage of S: Ia = 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

Page 10: Chris Spry

ResultsLand Use Statistics for

the year (1978)Forest = 53%

Open Space = 40%Urban = 7%

Flow Accumulation at Innes St. point from a 4 inch

rainfall: 78,592Land Use Statistics for

the year (2009)Forest = 50 %

Open Space = 35%Urban = 15%

Flow Accumulation at Innes St. point from a 4 inch

rainfall: 92,131Land Use Change

between 1978 and 2009Forest = -3%

Open Space = - 5%Urban = +8%

Page 11: Chris Spry

Project Significance and Encountered Issues

• Projects like this one can be significant because they reinforces 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 I the CNR Method would work better for areas with greater change in elevation and less urbanized environments.

Page 12: Chris Spry
Page 13: Chris Spry

Thanks for your attention!Questions?