the new paradigm for stormwater management
TRANSCRIPT
Low Impact Development and Green Infrastructure 101
The new paradigm for stormwater management
Wayne Petersen Urban [email protected]
IDALS’s Urban Conservation Team
Amy Bouska,
Iowa City FO
319-337-2322 x 3
Jennifer Welch
Ankeny FO
515-964-1883 x 3
Wayne Petersen
Wallace Building, Des Moines
515-281-5833
Derek Namanny
Spirit Lake FO
712-336-3782 x 3
The Water Cycle
Historic Hydrology vs. Modern Hydrology
(the native ecosystem model)
50%0-10%
15%
55%
The Native Ecosystem Model and The Historic Hydrology
• Prairie
• Savanna/Woodland
• Surface waters (wetlands/streams/rivers/lakes)
The Tallgrass Prairie
Iowa Vegetative History 1850’s
Iowa Vegetative History 1990’s
• Dominated by row crop agricultural
• Grassland and degraded savanna in the southern portions is dominated by non-native species
The roots / The soil
Historic Landscapes• Prairie soils had 8-10% organic matter (OM)
and 45% pore space.
• Now soils have 2 - 4% OM.
• Often less OM where development has occurred (topsoil exported).
• Bulk density has increased – less pores space
Historic Landscapes
• Soils have lost 60-80% of their ability to absorb and infiltrate rainfall events
• Landscapes initiate runoff sooner; shed more runoff
• Fashier hydrology - more runoff - water quality degradation
• Compounded with impervious and compacted urban landscapes
Hydrologically Dysfunctional Soils
Water runs off this
compacted turf
grass after a storm
Savanna/Woodlands
“Drive a wagon with a team of horses through the woods”
• Open Forest Canopy• Light Hits Forest Floor• Floor Covered with
Native Species
Bill & Sybilla BrownA Case Study in Ecosytem Restoration
Wetlands
• Vital Habitat for Migratory Bird Species
• Breeding areas for many different kinds of aquatic young
• “Kidneys of the Environment”
Farmed Wetland
Restored Wetland
Stormwater Wetlands
Iowa’s Changing Land Use
• High OM to Low OM
• High porosity to higher bulk density
• Pervious to impervious
• Effects include:• Less infiltration
• Less groundwater recharge
• More runoff
• Flashy stream flows
• More erosion
• Water quality degradation
• Increased flooding
Examples
Slide provided by Lori McDaniel, DNR
Adding Imperviousness
1990
2009
Q
T
Hydrograph Scenarios
2
1 Existing
Developed, conventional CN, no control.
Pre-developmentPeak Runoff Rate
1
2
Presently…detention for flood control
Wet Detention
D.A. = 48. 3 acresResidential = 34 acAg = 14. 3 acP. Surface= 2.4 ac
Q
T
Hydrograph Scenarios
2
3
1 Existing
Developed, conventional CN, no control.
Developed, conventional CN and control.
Pre-developmentPeak Runoff Rate
1
23
Unified Stormwater Sizing Criteria and
Traditional Stormwater Management
(Flood Control)
• Water Quality Volume - 1.25 in/24 hrs
• Channel Protection Volume - 2.38 in/24 hrs
• Overbank Flood Protection - 4 in/24 hrs
• Extreme Flood Protection -> 7 in/24 hrs
Rainfall Data 1948 - 2004
Flood Control
Unified Sizing Criteria
and Managing for Water Quality
• Water Quality Volume - 1.25 in/24 hrs
• Channel Protection Volume - 2.38 in/24 hrs
• Overbank Flood Protection - 4 in/24 hrs
• Extreme Flood Protection -> 6 -7 in/24 hrs
Rainfall Data 1948 - 2004
WQv
Unified Sizing Criteria
and Managing for Channel Protection
• Water Quality Volume - 1.25 in/24 hrs
• Channel Protection Volume - 2.38 in/24 hrs
• Overbank Flood Protection - 4 in/24 hrs
• Extreme Flood Protection -> 6 -7 in/24 hrs
Rainfall Data 1948 - 2004
CPv
Best Management Practices
• Green Roofs / Green Walls
• Rainater Harvesting
• Soil Quality Restoration
• Native Landscaping
• Porous Pavement
• Bioretention
• Bioswales
• Planter boxes
• Stream Corridor Stabilization