Silt Accumulations in the Wintersburg Channel
Last updated June 26, 2003
Since I live near the Wintersburg Channel, I have ample opportunities for
viewing it both on foot and while driving over various area bridges. I've
noticed that substantial silt deposits are visible in the lower reaches of
the channel (Graham to Springdale) at low tide. In the nearly 4 years
that I've lived here, I have never seen these lower reaches dredged.
I asked Bob Righetti of the Huntington Beach Public Works Department about
whether or not the Shea Parkside flood study (FEMA CLOMR case #01-09-393R)
accounted for the presence of any silt when the flood potential of the Wintersburg
Channel was being evaluated. He said no, the flood study does not account
for any silt -- it assumes the original as-built invert capacity of the channel
with no silt accumulation. He went on to say that what I had observed
was likely not silt at all, but rather channel bottom that had been redistributed
by currents.
I have learned to never take anything at face value regarding Shea Parkside,
so I made several photographic surveys of the Wintersburg Channel at low
tide conditions from the Graham Street bridge all the way upstream to the Gothard
Street bridge. These surveys show irrefutably that the Wintersburg Channel
does indeed have large accumulations of silt which in certain reaches has
resulted in large accumulations of vegetation. If the Shea Parkside
flood study has not accounted for this silt and vegetation, then it understates
the flood risk to Huntington Beach and needs to be revised.
Since one picture is worth a thousand words, let's take a photographic
tour of the Wintersburg Channel. All of these photographs were taken
on April 20, 2003 at approximate morning low tide as visually observed from
current flow under the Graham bridge. Each subsequent photograph was
taken upstream of the photograph before it. Click on each thumbnail
photograph for a full-res version. The complete set of several hundred
raw photographs from several surveys is available in CD-ROM format upon request
from the photographer.
Looking Northeast (Upstream) from Graham Street
Substantial silt accumulation is visible on the far bank, with a little bit of vegetation.
Looking Southwest (Downstream) from Warner Avenue
Major silt accumulation along the near bank, crossing the full width
of the channel to the far bank in the distant background. Note the
fairly thick vegetation along the near bank.
Looking Northeast (Upstream) from Warner Avenue
Silt clogs nearly half the width of the channel at this location.
Looking Southwest (Downstream) from Springdale Street
Two strips of silt attempt to cross from the left bank to the right bank.
Looking East (Upstream) from Springdale Street
Substantial silt accumulations with continuous riparian vegetation along
both banks. The Edwards Street bridge is barely visible in the far background.
Looking West (Downstream) from Edwards Street
The silt and the vegetation are getting thicker. Vegetation is now
visible growing in the middle of the channel. The Springdale Street bridge
is visible in the far background.
Blocked Flap Gates at Edwards Street Bridge
Two pairs of flap gates feed into the channel at each end of the Edwards
Street bridge. All four flap gates are blocked by accumulated silt. This
poses a flooding risk to the adjacent drainage areas served by these flap
gates.
Looking East (Upstream) from Edwards Street
A lush, densely vegetated wetland dominates this reach. Major silt
accumulations form areas of dry land in the middle of the channel.
A Few Hundred Feet East of Edwards Street
There is so much dry land in the middle of this part of the channel
that at least one coyote calls it home. Who would have thought -- coyotes
in the middle of residential/commercial Huntington Beach!
Looking East (Upstream) Between Edwards Street & Goldenwest Street
There is more dry land than water here. The channel transitions from
earthen to concrete in the far background behind the post office.
Looking West (Downstream) from Near Goldenwest Street
The channel bottom is made of concrete in this reach, therefore any soil
in the channel MUST be accumulated silt. The transition to an earthen
channel is visible in the far background behind the post office.
Looking West (Downstream) Between Goldenwest Street & Gothard Street
Have I convinced you yet that the channel is full of silt & vegetation?
The Goldenwest Street bridge is visible in the background.
Looking East (Upstream) from Gothard Street
Instead of appreciable silt in this reach, we just see a bunch of small to
moderately-sized rocks. Water velocities must be fairly high in this
reach to have pushed these rocks downstream.
Conclusions
These photographs prove that certain reaches of the Wintersburg Channel
between Graham and Gothard in Huntington Beach have substantial amounts of
silt and vegetation. Any flood study that assumes an as-built invert
capacity of these reaches is assuming more capacity than exists in reality.
Therefore the Shea Parkside flood study apparently underestimates the
risk of flooding in the adjacent areas of Huntington Beach.
FEMA and various local, county, and state officials have been notified
about these findings. The FEMA response acknowledges that the Shea flood study may need to be revised at LOMR time.
Webmaster: Mark Bixby
