Id Gaffe

451 Term Project:Storm Water Design

Hilary BruggerStephen KellyAnastasia NugentJoseph Roberts

• Design storm water runoff system for a 1 hour, 100 year storm as specified by the College Station Unified Development Ordinance.

• Using the Rational Method to determine a conservative calculation for the excess runoff:• Design intensity for a 1 year, 100 year storm is

4.41 in/hr• Design runoff coefficient for undeveloped and

grassy areas is .355• Design runoff coefficient for impervious surfaces

is .945

Level of Service Measures

Estimate DemandRunoff

Pre-Development 193398 cy

Post-Development

271496 cy

Change (Storage needed)

78098 cy

• 78098 cy is equivalent to 48.4 acre-feet.

• A pond with a maximum depth of 6 feet would be a 10 acre pond.

Alternative 1: Enlarge Spearman Lake

Alternative 2: Creation of a Storm Water Detention Pond

Object QuantityPipe (18”) 72690 LFPipe (24”) 7681.4 LFExcavation for Pipe

.161 M CY

Excavation for Pond

.078 M CY

Drains 2467Manholes 243

Quantity Estimates

Object QuantityPipe (18”) 72690 LFPipe (24”) 6496.4 LFExcavation for Pipe

.158 M CY

Excavation for Pond

.078 M CY

Drains 2467Manholes 243

Alternative 1 Alternative 2

Capital Cost EstimateAlternative 1 Alternative 2Object Total

CostPipe (18”) $ 2.185

MPipe (24”) $ .303 MExcavation for Pipe

$ .597 M

Excavation for Pond

$ .294 M

Dewatering $ 13,185Drains $ .593 MManholes $ .227 M

$4.26 M

Object Total Cost

Pipe (18”) $ 2.185 M

Pipe (24”) $ .496 MExcavation for Pipe

$ .606 M

Excavation for Pond $ .294 MDrains $ .593 MManholes $ .227 M

$4.45 M

Operating Estimates

Operation CostPipe Maintenance

$ .528M / yrOperation CostPipe Maintenance

$ .536 M / yr

Alternative 1 Alternative 2

Overall Cost EstimateAlternative 1 Alternative 2Object Total

Cost

Pipe (18”) $ 2.185 M

Pipe (24”) $ .303 MExcavation for Pipe

$ .597 M

Excavation for Pond

$ .294 M

Dewatering $ 13,185Drains $ .593 MManholes $ .227 M

$4.26 MMaintenance $ .528

M / yr

Object Total Cost

Pipe (18”) $ 2.185 MPipe (24”) $ .496 MExcavation for Pipe

$ .606 M

Excavation for Pond $ .294 MDrains $ .593 MManholes $ .227 M

$4.45 MMaintenance $.536

M / yr

• We will be paying for this via municipal bonds and grants.

• The grants that we believe we can receive will cover 20% of the capital cost.

• The other 80% will be covered using bonds with a 7% interest rate.

How Will We Pay For It?

Alternative B Alternative AInterest: 0.07 0.07Terms: 20 20Present Value $4,693,800 $4,260,000

Payment: $443,062 $402,114

Net Taxable Property Value (College Station, calculated using .43 per $100 tax rate) ~$25,000,000

Alternative B Alternative ATax Rate: $437.99 per $100K valueTaxable Value With Alternatives:

$25,443,062 $25,402,114

Net Tax Increase Per Household (per $100k value of land) $9.83 $9.50

Cost Per Household

Questions?