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RELATED
LINKS
For more information
on habitat issues, please contact the WDFW Habitat Program.
habitatprogram@dfw.wa.gov
Phone: 360-902-2534
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| Mitigation
for Water Withdrawal
Introduction
Growth happens
…
At least two
impacts are of concern for impacts to freshwater ecosystems:
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Growth
requires water, and |
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Growth
occurs on the landscape of a watershed,
affecting hydrological, geomorphological, and ecological processes.
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Residential
and industrial growth results in impermeable surfaces that alter
hydrology, yielding flashy high flows and reduced low flows. Riparian
habitat is modified, impacting lateral connectivity and water quality. |
| Mitigation
Goals
Retain or
restore watershed functions and processes that maintain aquatic
habitats.
| Key
functions and processes include: |
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Hydrology
– timing and quantity and quality of water |
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Connectivity |
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Sedimentation |
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Erosion |
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Large woody
debris recruitment |
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Thermal
flux |
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Mitigation
Strategies
Control land
use in headwaters and riparian areas.
Headwater
land area is where precipitation hits surface and enters soil.
Headwater interception determines quality, quantity and timing
of flow through the remainder of the stream. Maintaining natural
vegetation, topography, and degree of soil disturbance and compaction
will retain rates of water movement to stream headwaters.
Riparian vegetation,
together with hydrology and hydraulic conditions, controls rates
of bank erosion and sedimentation. It determines the rate of woody
debris input and the type and amount of other terrestrial organic
input, including insects.
Eliminate
or reduce longitudinal barriers to maintain or restore longitudinal
connectivity.
Eliminate
or reduce lateral barriers to restore lateral connectivity. Stream
interactions with floodplain are key to stream function and restore
or maintain rates of processes such as erosion and sedimentation.
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Implementation
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Get a seat
at the table. |
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Being effective
means getting others to give you authority so that your opinions
carry weight. |
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Find allies.
Who has goals that are at least partly consistent with yours?
Embrace the common interests. Discard traditional animosities. |
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Public
water supply utilities have some common interests:
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Clean
water |
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Abundant
water |
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Flood control
interest also have some common interests: |
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| Techniques
Headwater
land protection – Mitigate for every acre-foot annual
withdrawal with protection (purchase/conservation easement/dedication)
of 2 acre-foot equivalents. Where annual headwater precipitation
is 36 inches, this would require protection of >2/3 acre, depending
on rates of evapotranspiration and other causes of water loss.
Calculations are standard for hydrologists. Doubling acreage mitigates
for some of loss of lower basin land function due to development
as well as direct flow loss.
Riparian
land protection – Mitigate for every acre-foot annual
withdrawal with 2 acres of riparian protection, where width from
stream bank includes whole floodplain width, including old or
secondary channels.
Artificial
barrier (lateral or longitudinal) removal – Removal
or setback of dikes contributes to more natural interaction of
the stream and its watershed. Removal or reduction of dams or
other artificial stream blockage restores movement of organisms
and nutrients through the watershed.
Stream
shading – Riparian trees provide shade to keep water
temperatures cooler. They also provide bank stability, cover in
the form of roots, eventual input of large woody debris, and ongoing
source of insects as food for fish. Establishing riparian trees
can be useful mitigation, but determining an appropriate amount
of tree establishment can be difficult. Successful establishment
will require a number of years of effort and monitoring and response
to monitoring.
Pump-and-dump – Recharging streams from groundwater
is a popular mitigation strategy whose efficacy remains to be
clearly demonstrated. It may have merit, but it modifies natural
processes and benefits need to be shown.
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Sixteen
Mile Creek and Mill Creek confluence,
Milton, Ontario.
Photo
by Lorne Fitch, Alberta Sustainable Resource Development,
Fish and Wildlife Division – from IFC 2004 (Instream
Flows for Riverine Resource Stewardship),
Fig. 1-5c. |
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| Summary
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It’s
not just the water in the stream. It’s how the water interacts
with its watershed and channel. |
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Successful
protection of fish and wildlife habitat requires a broad view
and taking advantage of any option that is available. |
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Water in
a concrete channel has minimal habitat value. Habitat is a product
of climate, watershed, banks, channel, and water. |
Contact
Hal Beecher Washington Department of Fish and Wildlife
Phone: (360) 902-2421 E-mail: beechhab@dfw.wa.gov
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Asotin
Creek in SE corner of Washington
has headwaters in Umatilla National Forest
and flows into Snake River. |
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