Water Management

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Water Management
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Water Management Affects
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Dewatering
Dewatering is the removal of water from the work
area.
The purpose is to prevent water from interfering
with the work, and to prevent the discharge of
contaminants such as suspended sediment and
concrete.
Dewatering may include damming, stream bypass,
pumping, and/or draining the site.
The dewatering of an adromous fish stream must be
conducted in consultation with the Department of
Fish and Game and NOAA Fisheries.
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DewateringRemoval of water from the work site

• Permitting California Dept. of Fish Game
  requires a Streambed Alteration Agreement
• Consult with Fish/Aquatic Biologist.
• Intakes and outlets designed to minimize
  turbidity.
• Intakes should be screened with wire mesh not
  larger than 5 millimeters to prevent amphibians
  from entering pump system.
• Filtration/settling system must be included to
  reduce downstream turbidity.

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Dewatering Options
Cofferdams Sand Bag and Gravel Berm
Gravel Berm Cofferdam
A cofferdam is a temporary structure built into a
waterway to enclose a construction area and
reduce sediment pollution from construction work
in, or adjacent to water.
Cofferdams may be made of rock, sandbags, wood,
or aqua barrier.
The most common method used in small streams is
gravel berms made from river run rock (uniformly
graded no fines) wrapped in plastic or sandbags.
More information on cofferdams is located in
FishNet Roads Manual Appendix A-BMPs Toolbox
Water Management BMPs (page A-151).
Illustrations courtesy of FishNet 4C
Sand Bag Cofferdam
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Sand Bag Cofferdams
Examples of cofferdams made of sandbags with
plastic sheeting.
The top photo is from the mainstem Trinity River
while the lower photo is a small creek in coastal
Humboldt County.
Water collected behind the dam is pumped around
the construction site, filtered for sediment, and
put back into the river/stream.
Photo courtesy of Caltrans
Photo by Michael Love
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Dewatering Options
Aqua Barrier

• Applications Benefits
• Used for water damming, water diversion, and silt
  containment
• Portable, re-usable, and comes in a variety of
  sizes

• Limitations
• May need permit
• Need abundant water
• Not for steep gradients

Illustration courtesy of FishNet 4C
Aqua barriers are temporary, re-usable
water-filled plastic tubes installed as dams.
They come in a variety of sizes and are easily
transported when drained. More information on
Aqua Barriers is located in FishNet Roads ManuaL
Appendix A-BMPs Toolbox Water Management BMPs
(page A-149).
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Examples of Shallow Trench Dewatering System
Here are simple dewatering systems for shallow
trenching.
The drawing at left shows the use of a perforated
drum and pipe dropped at the low spot in the
trench to dewater. The fabric around the pipe
will act as filtration.
The drawing on right shows perforated pipe
wrapped with fabric and surrounded by rock
aggregate about a half inch in diameter. The
rocks and fabric will act as filtration to remove
fine particles.
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Examples of Large Scale Dewatering System
For large dewatering of groundwater, the
dewatering system will consist of above ground
tanks to settle sediment before it is discharged
into an authorized drain or creek.
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Media Filtration Units
Here is a two-step filtration unit which uses
both a sand filter and a finish filter to remove
sediment from water before releasing it to the
environment.
Sand filter
For fine sediment removal from dewatering
operations, advanced treatment will be required.
Media (e.g., sand, flocculants and filter cloth)
Filtration Units are used for treating small
particulates such as silt. Some are able to treat
various bacteria, oils, etc.
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Dirt bag may not be effective filtration
initially because it takes time for the water to
swell the fibers of the bag enough for the
filtering of small particles to begin.
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Water Diversion Options
Diversion Berm

• Applications Benefits
• Berm used to direct water away from unstable
  slope
• Made from sandbags or aggregate material/plastic
• Temporary use
• Inexpensive

BERM
Unstable Slope

• Limitations
• Not for fast flowing water
• Not for replacement of failing roadway or shoulder

ROAD
Illustration by Tyler Ledwith
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Water Diversion Options
Slope Drain
(Temporary, Overside, Swale)

• Applications Benefits
• Used to direct water away from unstable slope
• Made from PVC, ABS, or corrugated metal.
• Temporary use

• Limitations
• Gully erosion if fails
• Could be tricky to install

Illustration courtesy of FishNet 4C
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Temporary Run-on Diversion

• Divert upland drainage flow from work site
• Stabilize all disturbed areas prior to rainy
  season with spray-on application. Mulch,
  tackifier, Bonded Fiber Matrix (BFM) etc.
• Control site drainage by installing appropriate
  combination of BMPs.
• Good house keeping and maintenance of BMPs.
• Inspect weekly and document all observations and
  corrective measures.

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• Temporary
• Diversion of Run-on
• using plastic pipe

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Example of Diversionof Run-on
Erosion Control Blankets are keyed in under fiber
rolls to mitigate erosion and sediment.
This will allow for clean run-on.
Fiber rolls are also used as check dams to
control the velocity of run-on. Fiber rolls work
as check dams in this situation because they can
be properly anchored with stakes.
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In this example of run-on diversion BMPs, we see
that source control was first addressed in the
form of Bonded Fiber Matrix covering on the left
side, mulch and silt fence on the right, and
erosion control blanket in the middle of the
channel to transport clean run-on.
Diversion of Run-on
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This run-on BMP is good, but which BMP might
complete this scenario?

• Erosion Control Blankets
• Mulch
• Hydro-seeding
• Any of the above

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It pays to do it right the first time!
Temporarily Divert Run-on
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Environmental Barricades
Environmental barricades come in various shapes,
sizes and materials, from sand or gravel bags to
manufactured systems such as the one in this
photo.
These manufactured barricades have a variety of
advantages over sand or gravel bags in that they
may be used for
Other advantages are
Rental Options Recyclable Replaces Sandbags Labor
Saving
Spill Containment Flood Control Erosion
Control Water Filtration
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Environmental Barriers such as this one are
modular and may be configured to fit almost any
situation. Each module is a hollow plastic mold
that weighs 45 to 50 pounds. When filled with
water each module will weigh more than 400 pounds.
Environmental Barricade
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Portable Dewatering Unit using an Environmental
Barrier
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Environmental Barricade used for a sediment
holding tank
Notice the plugs that allow for gradual release
of water.
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For more information onWater ManagementRefer to
the Fishnet Roads Manual

• Chapter 6 Working in and Around Stream Channels
• Dewatering
• Appendix A BMP Toolbox Water Management BMPs