Addressing Stormwater Impacts on Hawaiian Streams · 20/5/2008 · Microsoft PowerPoint -...
Transcript of Addressing Stormwater Impacts on Hawaiian Streams · 20/5/2008 · Microsoft PowerPoint -...
Stephen Blanton, PEMay 20, 2008
Addressing Stormwater Impacts on Hawaiian Streams
Mr. Stephen Blanton, PE14 years experience focusing on water resources, geomorphology, environmental science, civil engineering and planning.
Currently working for ENTRIX, Inc, conducting stream restoration projects aimed at restoring natural function to impacted river/stream systems.
Hawaii work included; TMDL for Nawiliwili, Pearl Harbor, and Kaukonahua. Dam failure analysis for Reservoir 24, Maui. Maui County hydrologic study (West Maui Mountains), and various water quality studies on Maui and Oahu.
Natural Function of a Healthy Stream-
A natural functioning stream has the ability to dissipate energy from normal high flow event without excessive erosion, sediment transport, and channel adjustment. To achieve this, a stream must have functioning riparian area and floodplain.
Functioning Floodplain
Not so much
Healthy Riparian Area and Floodplain
Improves water qualityfilters sediment
Controls rates and volume of erosionattenuates flood peakstreambank stability
Aquifer Rechargedry season streamflow
The key is to keep the water on the land
Typical Stream Profile
Stormwater Impacts A healthy naturally functioning stream has developed a dynamic equilibrium based on the hydrologic characteristic of the watershed.
Changes to the drainage area’s hydrology due to land use changes alter this equilibrium and the stream then starts to adjust to accommodate the conditions.
Typical land use changes are: residential/commercial/industrial development, timber harvest, agriculture, fire, and diversions.
Residential Development
Agricultural Development
Typical Impacts to a Watershed
Increased runoff volumes
Increased peak runoff rates
Increased flow velocities
More frequent channel forming flows
Lower baseflow
Less groundwater recharge
Water Quality
Hydrologic Analysis
North slope of Haleakala
Mostly Agricultural land – Sugar
Small Residential area in upper region
Impacts of Impervious Area
0
20
40
60
80
100
120
140
160
3/1/19960:00
3/1/199612:00
3/2/19960:00
3/2/199612:00
3/3/19960:00
3/3/199612:00
3/4/19960:00
3/4/199612:00
3/5/19960:00
3/5/199612:00
3/6/19960:00
Date
Flow
Rat
e, c
fs
Residetial 38% ImperviousAgriculture 7% Impervious
Runoff Increase
0
2000000
4000000
6000000
8000000
10000000
12000000
14000000
12/17/1995 0:00 2/5/1996 0:00 3/26/1996 0:00 5/15/1996 0:00 7/4/1996 0:00 8/23/1996 0:00
Date
Acc
umul
ated
Run
off V
olum
e, ft
3
Agriculture- 7% Impervious
Residential- 38% Impervious
Water Quality Issues
Increase in:
Nutrients- Nitrogen, Phosphorus.
Sediment load- TSS
Herbicides & Pesticides
Metals- copper, zinc, lead, chromium
Temperature
Adverse Impacts
Native Species of Fish, Shrimp, and Snails
Habitat Impacts Native Survival and Allows Invasive (more tolerant) Species to gain presence and displace natives.
Concrete Channels lack of riparian vegetation create barriers for the amphidromous species to complete natural life cycle.
Lack of natural stream functions impacts coral reef health.
Stream Health Related to Impervious Area
Non-Supporting Urban Drainages
Change so all zones are sources………
Typical Impacted Stream
Extreme Event
Stormwater Regulations in The State of Hawaii
Counties address stormwater from development using Counties address stormwater from development using design standards. design standards.
The State addresses stormwater quality through the The State addresses stormwater quality through the NPDES and TMDL programs associated with the Clean NPDES and TMDL programs associated with the Clean Water Act.Water Act.
Future of Stormwater and Stream Health
Low Impact DevelopmentLow Impact Development-- The goal is to maintain The goal is to maintain historic/natural hydrologic conditions.historic/natural hydrologic conditions.
Restoration OpportunityRestoration Opportunity-- Add natural function back to impacted Add natural function back to impacted streams.streams.
Mother Nature Conducting Stream Restoration