Using HEC-1 for Subdivision Runoff Detention Pond Design

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Using HEC-1 for Subdivision Runoff Detention Pond
Design

• Stacie Kato
• April 26, 2004

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Project Background

• A detention pond is needed for a developing
  subdivision in the town of Cicero located in the
  Jackson Township in Indiana
• The site is currently a farm field bordered by a
  fire station, wastewater treatment plant, park,
  church and residential lands.
• There is an existing storm sewer that is located
  north of the site that the detention ponds will
  be routed to
• The subdivision will have an average lot size of
  ¼ acres

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Project Goal

• To design two detention ponds on the west side of
  the site (one in north portion, the other in the
  south portion)
• To meet the maximum release rate into the
  existing storm sewer set by the Town of Cicero
• To design a storm sewer system to route runoff to
  the detention ponds
• To design an emergency spillway channel that will
  be routed to Warehams Pond (northwest of site)

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Model Description

• HEC-1 generates hydrographs from rainfall data
  and routes them to reaches and reservoirs
• Uses the continuity equation (inflow outflow
  change of storage rate), inflow information from
  design storm hydrograph ordinates, and
  storage-outflow relationship to calculate flood
  flow routing

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Methods

• Determined watershed area from a survey map
  located from the Hamilton county website
• Determined basin areas from the slope of site
• Determined curve number for a residential area
  with an average lot size of ¼ acres
• Calculated the time of concentration for each sub
  basin using a figure from SCS National
  Engineering Handbook

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• Derived a rainfall intensity equation for the
  project area and calculated intensities for each
  sub basin and for the total watershed
• Calculated the peak flow for each sub basin to
  determine the pipe diameter for the storm sewer
• Varied detention pond area and outlet pipe
  diameter to obtain the best design to meet the
  maximum release rate into the storm sewer
• Designed an emergency spillway using the maximum
  probable storm

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Results

• South Detention pond size 0.5 acres and north
  detention pond size 0.75 acres, both having a 9
  diameter outlet pipe

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• South storm sewer system pipe diameter 36 to 42
  to 48, North storm sewer system pipe diameter
  36 to 42

42 pipe
36 pipe
North East and West Sub basin runoff
North East Sub basin runoff
To pond
48 pipe
42 pipe
36 pipe
To pond
Sub basin 1 runoff
Sub basin 1 2 runoff
Sub basin 1, 2 3 runoff
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• Emergency spillway from south detention pond to
  north detention pond at least 6.4 feet deep, from
  north detention pond to Warehams Pond at least
  10.1 feet deep

10 ft
10 ft
10.1 ft
6.4 ft
South Detention pond spillway rectangle channel
North Detention pond spillway rectangle channel
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Sensitivity Analysis

• Most parameters were highly sensitive. Lag time,
  pond depth, and spillway characteristics were not
  sensitive.
• Parameters were not as sensitive for maximum
  stage output as they were for the peak flow

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Recommendation for HEC-1 Use

• HEC-1 is easy to use
• Model parameters are sensitive to peak flow
  output
• Good model to use for designing detention ponds

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Conclusion

• Two detention ponds were designed using HEC-1
• A storm sewer system was designed
• An emergency spillway was designed using HEC-1
  and FlowMaster

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Questions?