Stormwater for Solicitors

Back to Basics(Bigger Pipes are Not the Answer)

TCWA

Stormwater is Getting MoreExpensive

For Homeowners

For Municipalities

For Safe Drinking Water Sources and Recreation

Not More Effective

As development increases, flooding is now occurring where it rarely or never happened before.

Tribune Review

TCWA

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.

Different Concepts

• Traditional stormwater planning …

considers streams to be little more than “open pipes”

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

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.

Back to Basics

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.

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

Stream Corridor Restoration: Principles, Processes, and Practices

1998 FISWRG

Rainfall Fates & Percentages

Surface runoff

Shallow infiltration

Deep infiltration

Evapo-transpiration

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

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

 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

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

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.

Runoff in the Stream

Erosion Sedimentation

TCWA TCWA

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

Runoff in the StreamRiparian Area

Slows high water velocity

Protects stream banks and channels

Absorbs excess runoff

Intercepts and collects sediments

Runoff in the StreamWetlands

Intercept runoff

Store and release stormwater

Filter sediments and nutrients

Protect soils & streambanks

Store carbon

Support recreation industry

Ducks Unlimited

Runoff in the Stream

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

Infiltration Diagram 

USGS NavGuide

Increasing Infiltration

Anne Arundel County, MD

Parking Lot Rain Gardens

New or retro-fit, with or without

pervious pavement

Infiltration – Rain Harvesting

 

 

Rain Gardens

Rain Barrels

US EPA

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

Transpiration

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

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

The Endor perhaps …

The Beginning of Sensible, Sustainable

Stormwater Policies and Practices

uva.edu