Snap-Tite®
Culvert Retrofit
for
Fish Passageways
What is Snap-Tite? Snap-Tite
is a no-dig solution to culvert lining and rehab challenges. The Snap-Tite®
patented joint and installation system allows replacement of failing culvert
piping without the removal of deteriorated pipe. Most jobs can be completed
with a backhoe, shovels, a come-a-long and chains — without closing a road or
dealing with traffic control. Also providing better flow capabilities than the
CMPs it is replacing. Snap-Tite is made from high density polyethylene (HDPE)
pipe and has a life expectancy of 100 years.
More and more culverts are being
accessed as a crossing by fish and other aquatic organisms; however most
culverts are not fully passable. For a fish on an upstream migration to successfully
negotiate a culvert, it must enter the culvert barrel, traverse the barrel
length, exit at the upstream end and proceed to the first resting area. As
such, many states are implementing recommendations and guidelines for improving
the effectiveness and ecological impact for waterway crossings. Experts tend to
agree that the most effective solution for creating unobstructed fish passages
is to replace problem culverts with new crossing structures such as bridges or
oversized and/or embedded culverts that are able to simulate a natural
streambed bottom. However, many agencies have concluded that due to the number
existing culverts and the limited amount of public funds available, it is
unlikely and/or impractical that every culvert that impairs fish passage will
be removed and replaced with an adequate design. In situations where
replacements are not practical or sensible, retrofitting a culvert with baffles
may be a reasonable measure to provide some passage improvements. Culvert
retrofits are modifications to an existing culvert and/or stream channel in an
attempt to reduce barriers and improve fish passage. Baffle retrofits are not
considered by many to be long-term solutions, but rather are viewed as a
temporary solution until replacement can be logistically and financially
viable.
For many years, Snap-Tite has made its
mark as an excellent option for rehabilitating culverts that are failing
structurally, where replacement would be costly, untimely, and very disruptive
to the surroundings. Snap-Tite with factory installed baffles can become a
culvert retrofit option that provides the same construction advantages and cost
saving benefits, while also providing improvements for aquatic passage. Most
culverts with fish passage problems were designed with a focus on the culvert
diameter required to pass a high flow event. As a result they are undersized
because they were designed for stream flow only, without regard to velocity
impact on fish passage and other aquatic organisms.
Corner Baffle Design
Baffles are placed off center from the invert or flowline of the
culvert and remain on one side of the culvert and do not alternate.
The notched weir baffle design and corner baffle designs are
recognized by Fed Highway Administration along with many state transportation
and environmental agencies.
Baffles are used to solve depth and
velocity problems within a culvert during flow extremes. In low flow
situations, most baffles act like weirs to create small pools of standing
water. As the flow increases, the water rises up on the baffle and the baffles
act as roughness elements that decrease the flow velocity, creating resting areas
for fish to escape high velocity water streaming through the culvert. Again it
should be noted that baffles are not recommended by leading research
organizations for new installations or complete replacement of culverts where
fish passage is of concern.
When adding baffles to a retrofitted
culvert, the culvert now becomes more prone to become blocked or clogged. It is
imperative that a regular schedule inspection and maintenance program is developed;
otherwise the crossing has exchanged one fish passage problem with another.
Inspections and maintenance are typically important during and immediately
after high flow events, especially as fish migration occurs in these events.
Baffles (and culvert retrofits) are
considered part of the Hydraulic Design Option for design methods used in fish
passage analysis. Baffles are typically recommended for culverts with a maximum
slope of 2.5%-3.5%. (Corner baffles are typically used for slopes less than 2.5%
while notched weir baffles are used between 2.5
%and 3.5%) It is acknowledged that
while the goal is to optimize culvert capacity, limit sediment deposition and
debris accumulation, limit maximum velocity and maximum turbulence; each
criterion will have to be balanced against each of the others for a compromise in
the overall design. Culvert retrofits are not expected to be able to satisfy
all the requirements of the Hydraulic Design option. The retrofit design should
also be analyzed in conjunction with inlet and outlet control features such as
tailwater control measures. The design engineer should consider and evaluate
these conditions when specifying the baffle criterion to Snap-Tite for
fabrication. For further information contact your local Snap-Tite representative
or visit: www.culvert-rehab.com
Is Erosion Control a Problem?
Erosion control is a major concern when rehabbing an existing
culvert. Snap-Tite is your no-dig solution to lining failing culverts, and is
also your answer to erosion control challenges. Not only does Snap-Tite rehab
the culvert, it provides erosion control for the areas surrounding the culvert.
It maintains a constant elevation,thus making it easier for fish to enter the
culvert. Snap-Tite pipe is made from HDPE pipe, which can be made to fit any of
your culvert needs. Talk to your Snap-Tite representative for more details.
GRECOR-LLC
TEL: (360) 789-5029
FAX: (360) 438-1932
439 DUTERROW RD SE
SUITE 9
OLYMPIA WA 98513
E-Mail: Grey@Grecor-LLC.com