What is stormwater?
Any water running off of the land’s surface after a rainfall or snowmelt event.
Why does stormwater matter?
CWA stated it was no longer acceptable to pollute our country’s water resources and implemented provisions on point sources of pollution or discharges coming from an industrial or municipal wastewater pipe.
What are the problems associated with urbanization?
- changes in landscape
- increased volume of runoff
- quickened manner in which runoff moves
What are the direct impacts on downstream waters and waterways from urban development in a watershed?
- changes to flow behavior and geometry
- degradation of aquatic habitat
- extreme water level fluctuation
What are the changes to stream flow due to urban development?
- alters hydrology rate by disrupting natural water cycle
- increased runoff volumes
- increased peak runoff discharges
- greater runoff velocities
- shorter times of concentration (less time for water to run off the land and reach a stream)
- increased frequency of bank-full and near bank-full events
- increased flooding
- lower dry weather flows
What are the changes to stream geomorphology from developed watersheds?
- increased rate and volume of runoff affects the physical shape and character
- stream widening and bank erosion
- higher flow velocities
- stream downcutting, causing instability in stream profile and triggers further channel erosion
- loss of riparian canopy
- changes in the channel bed due to sedimentation
- increase in the floodplain elevation
How does physical change to urban streams affect aquatic habitat?
- degradation of habitat structure
- loss of pool-riffle structure
- reduced baseflows
- increased stream temperature
- decline in abundance and biodiversity
What is the goal of good runoff management?
To minimize the mobilization of material collected from water flow over urban surfaces and decrease the time the material is delivered to receiving waters.
What are some sources of pollution to stormwater?
construction, roadways, parking lots, farm fields, and the conversion of rural and open space to urban uses.
What are potential water quality concerns resulting from stormwater?
- beach closures and potential illness from bacteria/waste/litter
- nuisance algal growth from nutrient enrichment
- choking of aquatic life and elimination of suitable habitat
- toxicity from contaminants
- oxygen depletion potential or biochemical oxygen demand (BOD) of the water from biodegradable organic material
- temperature changes due to influx of warmer water
- aesthetic impacts from floatable matter and sediments
- contamination of ground water with soluble organic chemicals, metals, nitrates and salt.
What are general principles used for stormwater management?
- evaluate where the water from your land comes from and where it goes
- prevent the potential of pollutants to be washed-off
- try to soak in as much water as possible
- don’t forget about all the snow that will eventually melt and runoff
- a (native) vegetative cover is always better than bare soil
- proper maintenance will prolong the life and sustain on optimum level of pollution removal from a BMP
- each site is unique and will require its own characteristics for stormwater management
- management designs should consider all impacts
What is taken into consideration for managing stormwater in Minnesota?
- climate (rainfall and snowmelt)
- physical features (MN waters, watersheds, ecoregions, geology, soils, topography)
- cultural features
