Low Impact Development and Green Infrastructure 101 The new paradigm for stormwater management Wayne Petersen Urban Conservationist 515-281-5833 Wayne.Petersen@iowaagriculture.gov
IDALS s Urban Conservation Team Wayne Petersen Wallace Building, Des Moines 515-281-5833 Wayne.petersen@iowaagriculture.gov Derek Namanny Spirit Lake FO 712-336-3782 x 3 Derek.namanny@ia.nacdnet.net Jennifer Welch Ankeny FO 515-964-1883 x 3 Jennifer.welch@ia.nacdnet.net Amy Bouska, Iowa City FO 319-337-2322 x 3 Amy.bouska@ia.nacdnet.net
The Water Cycle
Historic Hydrology vs. Modern Hydrology (the native ecosystem model) 0-10% 50% 55% 15%
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 Brown A 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 Examples 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
Adding Imperviousness 1990 2009 Slide provided by Lori McDaniel, DNR
Hydrograph Scenarios 1 Existing Developed, conventional CN, no control. 2 Q Pre-development Peak Runoff Rate 2 1 T
Presently detention for flood control
Wet Detention D.A. = 48. 3 acres Residential = 34 ac Ag = 14. 3 ac P. Surface= 2.4 ac
Hydrograph Scenarios 1 Existing 2 3 Developed, conventional CN, no control. Developed, conventional CN and control. Q Pre-development Peak Runoff Rate 2 3 1 T
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