Transcript "Economics of LID" (PP), David Peters, P.E. CFM, D.WRE

Houston Land/Water Sustainability Forum
David W. Peters, P.E., CFM, D.WRE
February 6, 2008
Summary
 The Private – Public – Private Responsibility Shift
 EPA Case Studies
 Local Church Revision to LID
 Final Notes
The Private – Public – Private
Responsibility Shift
 Agricultural Beginnings – prior to 1940
 Farmers Objective – Capture and retain as much
moisture as possible
The Private – Public – Private
Responsibility Shift
 Subdivisions developed rapidly form 1950 through
1985
 Homeowners Objective – Drain and remove rainfall as
quickly as possible
The Private – Public – Private
Responsibility Shift
 Through the decades the responsibility for the rain has
shifted from the private land owner to the public
agencies (City, County, Flood Control)
 Economic Question to ponder is which is less costly:
 Private Owner handling the raindrop where it falls
 Private Owner passing the raindrop to Public Entity to
handle
EPA Case Studies
 The EPA presented 17 case studies in a report titled
“Reducing Costs through Low Impact Development
(LID) Strategies and Practices”
 Report is available online at:
 http://www.epa.gov/owow/nps/lid/costs07/
 Primary LID Techniques are:
 Bioretention
 Grassed Swales
 Reduced Impervious Area
 Cluster Building
EPA Case Studies
 Auburn Hills Subdivision, Wisconsin
 Overall Savings 32%
 56% of savings was in storm water management using
bioswales and vegetated swales
 Development used cluster development with 40 percent
open space
 Savings reduction were also realized in water and sewer
installation and are not including in the 32% LID
savings
EPA Case Studies
 Mill Creek Subdivision, Illinois
 1,500 acre mixed use community with overall savings of
30%. Savings was $3,500 per lot.
 70% of savings was in storm water management using
vegetated swales
 Development used cluster development with 40 percent
open space
 In addition to savings on development, the lots near
amenities with view of open space and bike trails were
sold at $3,000 to $17,000 premiums
EPA Case Studies
 Somerset Subdivision, Maryland
 80 acre residential community with 200 homes on 0.25
acre lots. Overall savings of 32%. Savings was $4,000
per lot.
 Half of subdivision was conventional and half was LID
 Each 10,000 sq. ft. lot had a 400 sq. ft. bioretention cell.
 LID runoff was 20 percent less and metals showed an
average of 30 percent reduction
Local Church Revision to LID
 Church construction required a 10 ac-ft detention
pond to meet County standards.
 Pond location at rear of property required piping to
rear and then back to discharge at front.
 Shallow outfall required shallow pond or pumped
discharge
Local Church Revision to LID
 LID Options Considered
 Add grass strip filter to parking areas and allow parking
areas to flood to 6 inches during extreme events (> 10
year recurrence)
 Convert grassed areas near front and side of church to
depressed rain gardens
 Flooding of parking lot and rain gardens controlled by
regulated outlet at discharge from property
 Church Site Layout
POND DISCHARGE LINE
RAIN
GARDEN
OPTION
DETENTION
CHURCH
PARKING
POND
LOT
STORM DRAIN LINE
STREET
BUILDING
RAIN
GARDEN
OPTION
Final Notes
 Project overall objectives need to be examined when LID




options are considered
Economic benefits may not only be in initial construction
cost savings, but increased values of LID developed
properties
The closer to the source that storm water can be mitigated
the lower the transmission costs will be
Creativity and flexibility needs to be applied to each project
based on final objectives
Shifting storm water maintenance to the private
homeowner may be problematic unless legally encumbered
into the property deed requirements