Hydrology 101. Impacts of the Urban Environment. Nokomis Knolls Pond Summer June 2008

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1 Hydrology 101 Nokomis Knolls Pond Summer 2002 Impacts of the Urban Environment

2 Hydrologic Cycle; What is it? Geography, Topography, Geology, Land Cover and Climate determine the Amount and Behavior of Excess Precipitation. Point Sources or Non-Point Sources?

3 Hydrologic Cycle: Where is it? How does it move? Clouds Lakes Wetlands Reservoirs Streams Plants and Animals Aquifers Glaciers Oceans Precipitation Stream flow Evaporation Transpiration Watershed runoff Evaporation Infiltration, Percolation Groundwater Flow

4 How do we measure it? Rain gauge Catch basins and storm sewers Shingle Creek Outlet to Mississippi

5 How do we measure it?

6 Natural Hydrograph-Runoff or Stream Flow

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8 Urbanization and Water Quality When land use changes, hydrology changes: Runoff, Peak flows, Infiltration, Pollutant transport

9 Magnified Volume and Flashy Hydrographs Widening, Incising and Bank Slope Failure Within Urban Area Upstream of Urban Area

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13 Impervious Cover Changes the Amount and Behavior of Runoff Predevelopment: 10% runoff 50% infiltration 40% evaporates Urban: 55% runoff (+450%) 15% infiltration (-70%) 30% evaporates Accelerated Pollutant Export Loading = 10 times more 40% evapotranspiration 38% evapotranspiration 25% shallow infiltration 20% shallow infiltration 10% runoff 25% deep infiltration 15% deep infiltration 21% shallow infiltration 10% shallow infiltration Relationship Between Impervious Cover and Surface Runoff (FISRWG 1998 In Low Impact Development Strategies 1999) 21% deep infiltration Natural Ground Cover 10%-20% Impervious Surface 35% evapotranspiration 30% evapotranspiration 30% runoff 35%-50% Impervious Surface 20% runoff 55% runoff 5% deep infiltration 75%-100% Impervious Surface

14 Impacts of Urbanization on Hydrology Increased runoff Decreased infiltration Increased stream flow AND Increased pollutant transport

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16 1. Trash/Debris 2. Suspended Solids 3. Bacteria 4. Road Salt 5. Excess Nutrients Water Quality Key Pollutants in Urban Runoff

17 Phosphorus Phosphorus is an essential cell nutrient An excess of phosphorus excessive plant and algal growth Excessive vegetative growth and decay reduces oxygen in the water, causing fish to die off Severe contact use and public perception impact Algae bloom caused by excess phosphorus (MPCA)

18 Phosphorus Management BMPs Prevention Infiltration/Abstraction Ponds/sediment basins Reduced impervious surface Vegetated buffers Swales & biofilters Rain gardens Wetlands Education

19 Floatable Debris and Sediment Removal -Simple Traps Floatable Material and Sediment Retained in a Structure For Areas < 1 acre Above Ground or Subsurface Inexpensive 60-80% Effective

20 For Large Areas Wet Detention Ponds TSS Effectiveness: %* TP Effectiveness: 40-70% $150K per acre plus land cost $50K Maintenance 3-7 years Can be engineered as amenity Calhoun Ponds ( Bruce Kluckhohn) Calhoun Ponds treats 900 acres 66% TP Removal 85% TSS Removal

21 Typical Stormwater Pond Design MCOG/Metropolitan Council

22 Buffers Effectiveness: stops windblown floatables natural filter for sediment barrier to geese (bacteria) natural filter for particulate phosphorus increases abstraction Implementation: Buffers can be as simple as no mow zones to management areas of native plants Lake Nokomis native plant buffer Calhoun Ponds native plant buffer

23 Rain Garden

24 Burnsville Street Rain Garden

25 Summary Water quality changes in lakes, streams, and wetlands is the product of runoff quality and volume changes driven by: Land use Climate Geology Geomorphic Features Ability of the Receiving Water to Assimilate Stresses Water quality can be changed by engineering BMPs, which change the behavior, volume and pollutant levels of runoff back to its natural state.