The new paradigm for stormwater management

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

[email protected]

Jennifer Welch

Ankeny FO

515-964-1883 x 3

[email protected]

Wayne Petersen

Wallace Building, Des Moines

515-281-5833

[email protected]

Derek Namanny

Spirit Lake FO

712-336-3782 x 3

[email protected]

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




• Extreme Flood Protection -> 6 -7 in/24 hrs


WQv

Unified Sizing Criteria

and Managing for Channel Protection




• Extreme Flood Protection -> 6 -7 in/24 hrs


CPv

Best Management Practices

• Green Roofs / Green Walls

• Rainater Harvesting

• Soil Quality Restoration

• Native Landscaping

• Porous Pavement

• Bioretention

• Bioswales

• Planter boxes

• Stream Corridor Stabilization

The new paradigm for stormwater management

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