The URL can be used to link to this page

Home My WebLink About190716 2 Stormwater_101_Slidesstormwater basics: hydrology defined Hydrology is the science that encompasses the occurrence, distribution, movement and properties of the waters of the earth and their relationship with the environment within each phase of the hydrologic cycle. stormwater basics: hydrologic parameters Hydrologic parameters refer to model parameters used to calculate the volume and rate at which runoff is generated from a watershed. Watershed data –Watershed area –Land use data -determines the amount of pervious, impervious, and open water area for each subwatershed Rainfall data –“24-hour” storms –Also a 10-day snowmelt event Infiltration data –Soils North Carolina Department of Environment and Natural Resources Major Drainage Areas Land Use Classification Soils Classification Design Storms Used for Stormwater Modeling Design Storm Event Annual Chance of Exceedance 24-hour Storm Depth Peak Intensity2 5-year 20%3.59 inches 5.9 in/hr10-year 10%4.29 inches 7.1 in/hr25-year 4%5.41 inches 8.9 in/hr50-year 2%6.39 inches 10.5 in/hr100-year 1%7.49 inches 12.3 in/hr500-year 0.2%10.5 inches 17.3 in/hr 0 2 4 6 8 10 12 14 0 4 8 12 16 20 24Rainfall Intensity (in/hr)Rainfall Duration (hr) MSE 100-Year (1%-Annual-Chance) 24-Hour Storm stormwater basics: hydraulics the branch of science and technology concerned with the conveyance of liquids through pipes and channels stormwater basics: hydraulic parameters Hydraulic parameters refer to any and all parameters related to conveyance of water through storage areas, pipes, and overland flow channels. Storage in lakes/ponds/wetlands Storm sewer network Tailwater effects (e.g., if Minnehaha Creek is high, it can impact the water levels in the storm sewer pipes that flow into it) Inlet capacity Overland flow network (along streets, along natural areas) stormwater basics: hydraulic parameters Stormwater simulation model has advanced routing capabilities: –Detention (storage) in ponding areas –Backflow in pipes –Surcharging of manholes –Tailwater conditions that affect upstream storage or pipe flows Plan View Pond Pond Profile Viewground stormwater basics: hydraulics Storm sewer network schematic ground Pipe Size & Type Downstream invert Upstream invert Pipe Length Manhole Invert Manhole Rim Elevation stormwater basics: hydraulics •Hard surface areas prevent infiltration of stormwater -Rooftops-Parking Lots-Streets-Driveways-Sidewalks •Less infiltration = More Runoff = More Pollutants Photo by Monroe County, NY Why does imperviousness matter? Effects of Urbanization on Flow Evapo- transpiration Infiltration native conditions (undisturbed) little runoff ~10% land use affects stormwater runoff Flow (cfs)Time (minutes) land use affects stormwater runoff native conditions natural hydrology little runoff ~10% Photo: Minnetonka Mills Flow (cfs)Time (minutes) developed conditions impervious surfaces more runoff >50% land use affects stormwater runoff extra runoff volume Morningside Neighborhood What does underground storage look like? 37th Avenue Greenway, Minneapolis, MN 37th Avenue Greenway, Minneapolis, MN What does large-scale underground storage look like? Towerside District Stormwater System (Minneapolis)https://www.mwmo.org/projects/towerside-district-stormwater-system/ What does large-scale underground storage look like? Towerside District Stormwater System (Minneapolis)https://www.mwmo.org/projects/towerside-district-stormwater-system/ What does large-scale underground storage look like? Towerside District Stormwater System (Minneapolis)https://www.mwmo.org/projects/towerside-district-stormwater-system/ Flood walls Grand Forks, ND Fargo, ND infiltration most common approach –infiltration basins / rain gardens –underground infiltration –tree trenches other volume control methods –pervious pavements –green roofs –stormwater reuse (irrigation, toilet-flushing, industrial) –tree interception part of climate change resiliency Green Line Green Infrastructure, Saint Paul mimicking native hydrology through volume control Before and After storage Green Infrastructure-a new era of stormwater management •Using stormwater management techniques that mimic nature by infiltrating and/or storing rainfall runoff where it lands Examples of Green Infrastructure Rushmore St, Burnsville, MN Rushmore Drive Infiltration Project -Burnsville, MN storage University of Minnesota Duluth City of Minnetonka Civic Center Benefits of City Stormwater Models •Models provide runoff information on an individual subwatershed scale –Detailed nature allows models to be used to evaluate the effects of small or large scale changes within the city Benefits of City Stormwater Models •Models provide flood levels for interior water bodies North Cornelia NWL = 859 Benefits of City Stormwater Models NWL = 859 ft 100-Year Flood Level North Cornelia City models provide flood levels for interior lakes and ponds Benefits of City Stormwater Models •Models identify areas with flooding issues –Identify areas where streets may be flooded –Identify areas where homes may be inundated Lake Edina Benefits of City Stormwater Models •Models provide detailed routing of stormwater to the creek –Timing issues critical when modeling inflows to the Creek –Discuss example of different peak timing Illustration of a storm water catch basin. Storm water carrying debris and organic material flows from above-ground into the grate. Debris settles and excess water is carried out. Water below the inlet/outlet pipe remains in the catch basin. Catch basins often retain water even during dry periods. https://www.chijournal.org/C435 http://www.edcsc.org/wp-content/uploads/2017/01/ECS_Stormwater-House-Illustration.jpg Percent Imperviousness (2011 U of M Dataset)