Westerly Creek, A Poster Child for Understanding the
Benefit of Stormwater Investment
Presented at the ASFPM Annual Conference Atlanta, GA June 1 – June 5 2015
Jon Villines, EIT, CFM – Aurora Water Alan Turner, PE, CFM – CH2M
What is this project about? – Westerly Creek
Two UDFCD Major Basins:
– Upper (9.0 sq. mi., upstream of Westerly Creek Dam)
– Lower (7.0 sq. mi. Westerly Creek Dam to Sand Creek)
City of Aurora and Denver
CH2M Updating MDP and FHAD for Upper Westerly Creek (2014)
Lower Westerly last studied in 2010
Major detention areas: Jewell Wetlands, Utah Park, Expo Park, Westerly Creek Dam, Kelly Road Dam (all 100-year)
What is this project about? – Westerly Creek
Denver International Airport City of Longmont City of Boulder Downtown DenverWhat is this project about? – Westerly Creek
Kelly Road Dam
Westerly Creek Dam
Expo Park
Utah Park
Why Westerly Creek? – September, 2013 Storms
Aurora and Westerly Creek Watershed were one of the hardest-hit areas
11.76 inches of rain over 7-days
Peak of 5.96 inches of rain on September 12, 2014
Historic levels of rain and runoff, but minimal damage
$2.5 million in known damages to COA assets
But it could have been much worse…
$48.8M investment (2014 $) in detention facilities over 56 years
Why Westerly Creek – Peoria St, Downstream of
Utah Park
Why Westerly Creek – Peoria St, Downstream of
Utah Park
Why Westerly Creek – Peoria St, Downstream of
Utah Park
What’s the Objective? – Describe Benefit of Detention
During/after storm, citizens said “Parks and streets are flooding!”
Detention & conveyance functioned as-designed
COA fared surprisingly well
Multi-use detention facilities not well understood
Gov. Hickenlooper expressed interest in quantifying benefit
CH2M contracted to study
benefit/cost of Westerly Creek detention facilities
APPROXIMATESEPTEMBER
2013 FLOODEXTENTS
Expo Park Kelly Road Dam
Westerly Creek Dam
Utah Park
1
st: What Facilities Did we want to look at?
1
st: What Facilities Did we want to look at?
Expo Park Utah Park
2
nd: Update Hydrology to Remove Detention
With Detention Hydrograph at
Westerly Creek Dam
Without Detention Hydrograph
at Westerly Creek Dam
0 2000 4000 6000 8000 10000 12000 14000 16000 0 50 100 150 200 250 300 F low ( c fs ) Time (Minutes)
Flow Without Detention 0 5 10 15 20 25 30 35 40 45 50 0 50 100 150 200 250 300 F low ( c fs ) Time (Minutes
3
rd: Develop 2-D models for Upper and Lower Basin
Manning’s N
3
rd: Develop 2-D models for Upper and Lower Basin
Lastly: Determine Impacted Structures
Used Data from a variety of Sources
– City of Aurora Building Shapefile – City of Aurora Parcel Data
– City of Denver Building Shapefile
Three Categories of Structures Identified
Commercial Structures
Multi-Family Residential
Single Family Residential
Structure Value Determined from Zillow
Cost Benefit Analysis Of Westerly Creek Detention
Structures
Cost Development – Construction Costs of Dams
Dams were constructed and improved over a 56 Year period
Records of Construction cost not always available
Accurate costs found for:
– Jewell Wetlands – Expo Park
– Utah Park
– Westerly Creek Dam
An estimate for Kelly Road dam was done based on other ponds in basin
Cost Escalated to 2014 Costs
y = 6996.2x + 2E+06 R² = 0.9854 $5,000,000 $10,000,000 $15,000,000 $20,000,000 $25,000,000 $30,000,000 $35,000,000 0 1000 2000 3000 4000 5000 Cost of Construction (2014 $) versus Detention Volume for
Westerly Creek Detention Facilities
Cost Development – Construction Costs of Dams
Dams were constructed and improved over a 56 Year period
Records of Construction cost not always available
Accurate costs found for:
– Jewell Wetlands – Expo Park
– Utah Park
– Westerly Creek Dam
An estimate for Kelly Road dam was done based on other ponds in basin
Cost Development – Construction Costs of Dams
Detention Facility Year
Constructed Constructed Cost ($) Volume (Ac-Ft) 2014 Cost ($) Jewell Wetlands 2001 $1,110,000 85 $1,484,000 Utah Park 2009 $5,400,000 158 $5,960,300 Expo Park 1999 $2,341,097 226 $3,325,400
Westerly Creek Dam 1987 $15,124,000 4,150 $31,508,300
Kelly Road Dam* 1953 $329,000 130 $2,910,000
Kelly Road Dam Exp.* 1979 $1,108,000 360 $3,609,000 *Cost estimated from other ponds.
Cost Development – Structure Value Assumptions
Structure Values were based on Neighborhood Averages from Zillow
Assumptions for Categories
– Single Family
• 1 or 2 Story Structure w/basement
– Multi-Family
• 6 units per a structure
• Structure is multi-story with no basement
• Value based on neighborhood sales
– Commercial
• Structure is multi-story with no basement
• Average Commercial Value is $1.75 million dollars
Neighborhood Avg. Value
Structure
East Colfax $199,900 1-Story With Basement Lowry Field $534,000 2-Story w/ basement Expo Park $200,000 2-Story w/
basement Utah Park $230,000 2-Story w/
basement Windsor $475,000 2-Story w/
basement Village East $350,000 2-Story w/
basement East Ridge $300,000 2-Story w/
Cost Development – Damage Assumptions
Damage based on U.S. Army Corps of Engineers Depth Damage Tables
Both Structure Damage and Contents Damage Considered
Assumption of 1’ depth of water
Results –Flood Plains for Upper Westerly Creek
Without Detention
With Detention (Existing)
Expo Park Kelly Road Dam
Westerly Creek Dam
Utah Park Jewell Wetlands Expo Park Kelly Road Dam Westerly Creek Dam Utah Park Jewell Wetlands
Results –Structures Impacted with Existing Detention
Structures Affected
– 69 Commercial Buildings – 99 Multi-Family Buildings – 389 Single Family Buildings
Cost of Damage – Structure damage = $56,590,000 – Contents Damage = $33,510,000 – Total Damage = $90,100,000 Expo Park Kelly Road Dam Westerly Creek Dam Utah Park Jewell Wetlands
Results –Structures Impacted without Existing
Detention
Structures Affected
– 204 Commercial Buildings – 282 Multi-Family Buildings – 1,657 Single Family Buildings
Cost of Damage
– Structure damage = $195,075,000 – Contents Damage = $115,415,000 – Total Damage = $310,490,000
Expo Park Kelly Road Dam
Westerly Creek Dam
Utah Park
Jewell Wetlands
Cost Benefit Analysis
Costs
Benefits
Detention Facility 2014 Cost
(Million $)
Jewell Wetlands $1.48
Utah Park $5.96
Expo Park $3.33
Westerly Creek Dam $31.51 Kelly Road Dam $2.91 Kelly Road Dam Exp. $3.61
Total Cost = $48.80
Damage Type Damage
(Million $) Without Detention Structure Damage $195.08 Contents Damage $115.42 Total Damage $310.50 With Detention Structure Damage $56.59 Contents Damage $33.51 Total Damage $90.10 Net Benefit = $220.40
Cost Benefit Analysis
Benefit Cost Ratio =
4.5
Expo ParkKelly Road Dam
Westerly Creek Dam
Utah Park
Jewell Wetlands
Summary – Value goes beyond Health and Safety
The Benefits of Master Planning and implementation of drainage improvements are huge.
Benefits go beyond Structure Damage
– Improved water quality
– Environmental Enhancement – Recreational Enhancement – Increased Park Space
– Enhanced Property Values – Reduction in Flood Insurance
Costs
– Additional Developable Land – Increased Tax base for City
Jewell Wetlands
Conclusions – Take Away from September 2013
Total Damages seen in 2013 = $2.5 Million Dollars
– Most Damage was Sediment and Debris removal
– Peoria Street Reconstruction – Handful of Structures Damaged
Without Improvements
– Approximately $8.6 Million Dollars in Damage
– Approximately 60 Structures Damaged
