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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 Quantity
Pipe (18”) 72690 LF
Pipe (24”) 7681.4 LF
Excavation for Pipe
.161 M CY
Excavation for Pond
.078 M CY
Drains 2467
Manholes 243
Quantity Estimates
Object Quantity
Pipe (18”) 72690 LF
Pipe (24”) 6496.4 LF
Excavation for Pipe
.158 M CY
Excavation for Pond
.078 M CY
Drains 2467
Manholes 243
Alternative 1 Alternative 2
Capital Cost Estimate
Alternative 1 Alternative 2Object Total
Cost
Pipe (18”) $ 2.185 M
Pipe (24”) $ .303 M
Excavation for Pipe
$ .597 M
Excavation for Pond
$ .294 M
Dewatering $ 13,185
Drains $ .593 M
Manholes $ .227 M
$4.26 M
Object Total Cost
Pipe (18”) $ 2.185 M
Pipe (24”) $ .496 M
Excavation for Pipe
$ .606 M
Excavation for Pond $ .294 M
Drains $ .593 M
Manholes $ .227 M
$4.45 M
Operating Estimates
Operation Cost
Pipe Maintenance
$ .528M / yr
Operation Cost
Pipe Maintenance
$ .536 M / yr
Alternative 1 Alternative 2
Overall Cost EstimateAlternative 1 Alternative 2Object Total
Cost
Pipe (18”) $ 2.185 M
Pipe (24”) $ .303 M
Excavation for Pipe
$ .597 M
Excavation for Pond
$ .294 M
Dewatering $ 13,185
Drains $ .593 M
Manholes $ .227 M
$4.26 M
Maintenance $ .528 M / yr
Object Total Cost
Pipe (18”) $ 2.185 M
Pipe (24”) $ .496 M
Excavation for Pipe
$ .606 M
Excavation for Pond $ .294 M
Drains $ .593 M
Manholes $ .227 M
$4.45 M
Maintenance $.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?