Stormwater Management

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StormwaterManagement

• Sandhills Water Resources Conference
• Southern Pines Civic Club Building
• 2007 November 08
• Thomas S Blue

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What is Stormwater?
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Stormwater is precipitation that has reached a
surface.
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The surface can be a variety of things...

• Soil
• Vegetation
• Roofs
• Pavement
• Creeks
• You!

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What is Stormwater Runoff?
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Whatever amount of stormwater doesn't1) go
into a surface (usually the ground)or2) get
held on a surface (such as small
depressions)becomes stormwater runoff.So,
changing the landscape (building, timbering,
farming, etc) changes the amount of stormwater
runoff (both the amount and the rate).
What is Stormwater Runoff?
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What is a Stormwater System?
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What is a Stormwater System?
Any combination of constructed or natural
features that directs the path of, treats the
pollutants in, or modifies the rate of stormwater
flow

• Channels and Ditches
• Curbs and Gutters
• Creeks and Streams
• Culverts and Pipes
• Lawns and Yards
• Ponds and Lakes
• Structural Management Measures

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What is a Stormwater System?
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Stormwater Systems are completely separate
from Sanitary Sewer Systems (some older systems
were not like this)
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What are Stormwater Structural Management
Measures?

• Purposely designed and constructed to manage
  stormwater in some manner (flow rate, volume,
  pollutants)
• Are usually not hard structures (only portions
  of the structure - if any - are concrete, metal,
  etc)
• Often include vegetation (grasses, shrubs,
  trees)
• Sometimes called Best Management Practices
  (BMPs), though not always the best management

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Common Stormwater Structural Management Measures
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Bioretention Cell
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Wet Detention Basin
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Grass Filter Strip
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Infiltration/Retention Basin
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Constructed Wetland
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Sand Filter
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Vegetated Swale
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Dry Detention Basin
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What can happen when we don't properly manage
stormwater?
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Public Safety
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Soil Erosion
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Water Recreation
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Community Aesthetics
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Commercial/Recreational Fisheries
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Structures Protection
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Water Supply
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Wastewater Discharge
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Water Quality
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Why do we manage stormwater?

• Public Safety
• Soil Erosion
• Water Recreation
• Community Aesthetics
• Commercial/Recreational Fisheries
• Structures Protection
• Water Supply
• Wastewater Discharge
• Water Quality

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Stormwaterbefore and afterreal estate
development
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Stormwater before typical real estate development
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Stormwater after typical real estate development
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Stormwater after typical real estate development
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(No Transcript)
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• Stormwater alterations to the hydrologic cycle
  following typical real estate development
• By the numbers
• Recharge reduction 50 (15 to 80)
• Runoff volume increase 550 (200 to 700)
• Runoff peak rate increase 600 (200 to 900)

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That is a Problem
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To safeguard (protect and sustain) our water
resources, we need to focus on infiltration of
stormwater
The Solution
...which will recharge aquifers and streams while
reducing runoff and removing pollutants
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Stormwater in hydrologic cycle before and after
real estate development
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Infiltration, infiltration, infiltration
Rain
Pervious Surface
Runoff
Percolation
Predevelopment lots of water goes into the
ground, little runs off
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Infiltration, infiltration, infiltration
Rain
Impervious Surface (paved)
Runoff
Percolation 0
and lack of it.
Postdevelopment little water goes into the
ground, lots runs off
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Infiltration, infiltration, infiltration
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Infiltration, infiltration, infiltration
Turf grasses have shallow root systems
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Infiltration, infiltration, infiltration
Vegetation native to our area has deeper roots
which improves infiltration non-native
vegetation, especially turf grasses, has
shallower roots
Native vegetation has root systems that promote
better infiltration
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Infiltration, infiltration, infiltration
Pervious pavements (asphalt, concrete, other)
seem like a great solution!
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Infiltration, infiltration, infiltration

• Unfortunately, were a long way from using these
  surfaces in general applications
• high maintenance (including vacuuming)
• surface sealing / pore clogging from oils,
  greases, fine particles (dust, clay, silt)
• subsurface utility maintenance patching
• more expensive than conventional pavements
• money better spent on other options

clogging/sealing
Pervious pavements (asphalt, concrete, other)
seem like a great solution!
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Case Example Existing Stormwater
System Commercial Retail Shopping Center Old
and New Construction Fairly Flat
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Existing Stormwater System commercial retail
shopping center
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Existing Stormwater System commercial retail
shopping center
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Existing Stormwater System commercial retail
shopping center
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Existing Stormwater System commercial retail
shopping center
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Existing Stormwater System commercial retail
shopping center
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Existing Stormwater System commercial retail
shopping center
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Existing Stormwater System commercial retail
shopping center
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Case Example Sustainable Stormwater
System Single Family Home Residential
Subdivision Community 190/- Lots Rolling Hills
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Sustainable Stormwater System single family home
residential subdivision community
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Sustainable Stormwater System single family home
residential subdivision community
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Sustainable Stormwater System single family home
residential subdivision community
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Case Example Sustainable Stormwater
System Senior Care Facility 40/- Impervious
Surface Fairly Flat
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Sustainable Stormwater System senior care
facility
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29,189 sf Building
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3.3 ac Watershed
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5,622 sf Bioretention
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Stormwater flow
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Complete site stormwater infiltration
three months after construction
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Looking towards bioretention area
eighteen months after construction
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seven years after construction (three years ago)
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CommonStormwater ManagementMisconceptions
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Common Stormwater Management Misconceptions
I thought that Providing naturally vegetated
stream buffers prevents degradation of the
surface water. But actually the case is Only in
relatively flat terrain and rural areas with
diffuse flow (spread out) do vegetated buffers
provide significant water quality benefit. In
rolling or hilly terrain and urbanized areas, the
stormwater short-circuits through the buffer area
without much treatment.
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Common Stormwater Management Misconceptions
I thought that All stormwater runoff is treated
(pollutants removed) before it enters streams,
ponds, and other surface waters. But actually
the case is Most all stormwater runoff in North
Carolina (and the Sandhills) is not treated
before entering streams, ponds, and other surface
waters after construction is completed.
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Common Stormwater Management Misconceptions
I thought that Regulations require that
stormwater runoff must be treated (pollutants
removed) before it enters streams, ponds, and
other surface waters. But actually the case
is Most areas of North Carolina (and the
Sandhills) do not have regulations which require
stormwater runoff to be treated before entering
streams, ponds, and other surface waters after
construction is completed.
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Common Stormwater Management Misconceptions
I thought that Regulations require that
stormwater runoff from real estate development
projects must not increase downstream
flooding. But actually the case is Most areas
of North Carolina (and the Sandhills) do not have
regulations which require real estate development
projects not to increase downstream flooding.
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Common Stormwater Management Misconceptions
I thought that Regulations require that
stormwater runoff from real estate development
projects must not erode creeks downstream. But
actually the case is Most areas of North
Carolina (and the Sandhills) do not have
regulations which require real estate development
projects not to erode creeks downstream.
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Common Stormwater Management Misconceptions
I thought that The project erosion and
sedimentation control plan/permit addresses
stormwater management at a site. But actually
the case is The project erosion and
sedimentation control plan/permit addresses
stormwater management only during the span of
active construction, not thereafter unless
erosion becomes an issue.
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Common Stormwater Management Misconceptions
I thought that Those basins at the edge of
construction sites are for stormwater
management. But actually the case is Most of
those basins are for temporary sediment control
during active earthwork construction and are not
intended for permanent stormwater management
except sometimes in those areas that have
postconstruction stormwater regulations.
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Common Stormwater Management Misconceptions
I thought that Those green stormwater
management systems increase the cost of land
development projects. But actually the case
is With almost all projects, stormwater
management systems which focus on infiltration
directly reduce the initial and long term project
costs.
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There are a lot of resources available to help
you address these issuessee your
registration packet and the Sustainable Sandhills
web site.
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If you remember nothing else, please remember
Infiltration Infiltration Infiltration