stormwater for solicitors back to basics (bigger pipes are not the answer) tcwa
TRANSCRIPT
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Stormwater for Solicitors
Back to Basics(Bigger Pipes are Not the Answer)
TCWA
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Stormwater is Getting MoreExpensive
For Homeowners
For Municipalities
For Safe Drinking Water Sources and Recreation
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Not More Effective
As development increases, flooding is now occurring where it rarely or never happened before.
Tribune Review
TCWA
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Just One ExampleFamilies live on
municipal border next to golf course.
Course expansion legally destroyed
riparian buffer, filled wetland, and increased runoff.
Despite photos and obvious property damage, letter stated no grass runoff.
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Different Concepts
• Traditional stormwater planning …
considers streams to be little more than “open pipes”
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An AnalogyLeonardo’s Dream
Machines (PBS) Giant Cross Bow Modern version built
using structural engineering principles
Sent a cannonball all of 75 feet
Back to Basics – successful version built according to original drawings
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Underlying Issues• Engineering principles have become
disconnected from real world conditions.• General public has faith in professional
opinions. • Many stormwater engineers recognize
that current standards and methods are only moderately effective.
• Their primary responsibility is to their clients, not to municipalities, and not to those living downstream.
• Consequences shift to other stakeholders.
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Back to Basics
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Back to Basics• The water cycle combines the biology,
chemistry, and physics of water, air, & land in complex inter-relationships.
• Understanding the basic systems and their functions will allow us to model our stormwater systems on effective principles.
• Mimicking natural systems for con-structed BMPs or preserving existing ones affords better chances for success.
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Natural Systems Work for Us
• Our goal has been to defeat nature
• Rainfall runoff = waste product• Understanding the basics shows
how natural systems work to our advantage
• Rain water = valuable resource• Natural infrastructure = high
water quality & flood protection
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Stream Corridor Restoration: Principles, Processes, and Practices
1998 FISWRG
Rainfall Fates & Percentages
Surface runoff
Shallow infiltration
Deep infiltration
Evapo-transpiration
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Basic Components
Rainfall Surface Runoff Overland flow of rainwater Ground surface composition determines rain drop fate Degree of permeability
Soils Vegetative cover Roads Buildings
Extent of infiltration BMPs
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Rainfall Fates
• Sheet drainage to receiving stream• Sheet drainage to storm sewer
inlet• Shallow infiltration to soils• Deep infiltration to water table• Evaporation to atmosphere• Evapo-transpiration from plants
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Runoff in the Stream
Physical Geography.net
Reading a Hydrograph
Rainfall noted in upper left corner
Stream flow following rainfall shown by red line
Stream base flow shown by purple line
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uprct.gov
Runoff in the StreamPre- and Post-
Development red line = pre-dev. higher base flow & more gradual runoff
blue line = post-dev. lower base flow & more abrupt runoff
dotted line = flood post-dev. conditions insure more flooding
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Excess Runoff Effects
Erosion and Sedimentation• Excess runoff erodes soils on
land and from stream banks and channels
• Suspended sediments create water quality problems (TMDL issues)
• Deposited sediments displace available channel volume – making flooding more likely.
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Runoff in the Stream
Erosion Sedimentation
TCWA TCWA
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Runoff in the StreamFloodway and Flood Plain
Floodway is most likely to carry high waters and to be protected by ordinance.
Flood plain will reduce flood damages and is least likely to be protected.
US EPA
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Runoff in the StreamRiparian Area
Slows high water velocity
Protects stream banks and channels
Absorbs excess runoff
Intercepts and collects sediments
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Runoff in the StreamWetlands
Intercept runoff
Store and release stormwater
Filter sediments and nutrients
Protect soils & streambanks
Store carbon
Support recreation industry
Ducks Unlimited
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Runoff in the Stream
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Basic Components Infiltration
Shallow - Can percolate into the top layers of soil
Used by plants and shrubs Deep - Can go all the way down to the ground water table
Used by trees, in wells and springs, or can recharge streams
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Infiltration Diagram
USGS NavGuide
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Increasing Infiltration
Anne Arundel County, MD
Parking Lot Rain Gardens
New or retro-fit, with or without
pervious pavement
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Infiltration – Rain Harvesting
Rain Gardens
Rain Barrels
US EPA
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Basic Components Transpiration
Plants draw water up through their roots, sending vapor out through their leaves Temperature, humidity, and light affect the amount of water used Mature trees transpire between 34 and 100 gallons of water per day
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Transpiration
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Basic Components Fitting things togetherNatural systems incorporate ways
to: reduce surface runoff increase rainwater
infiltration absorb rainfall and slowly release it allow safe stream bank overflow decrease high water velocity reduce erosion and sedimentation deposit sediments on land maintain adequate base flow
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Basic Components Fitting things togetherStormwater ordinances could:
protect existing natural systems encourage use of BMPs that restore natural systems encourage use of BMPs that mimic natural systems reduce construction and maintenance costs afford maximum protection to downstream property owners
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The Endor perhaps …
The Beginning of Sensible, Sustainable
Stormwater Policies and Practices
uva.edu