Much of the flooding in Inverness Park and Inverness,
including the flooding of the Inverness Store, could have been prevented
or lessened if culvert clearing had not been stymied by a two-year permit
process requiring the approval of approximately 20 governmental agencies.
Concern about the impact on the creek’s coho salmon and steelhead
trout elongated the process. But blocked culverts and waterways are
just as harmful to fish as to humans.
Marin’s Department of Public Works applied for
permits to clear the culverts and bridges along Sir Francis Drake Boulevard
two years ago.
After the flooding, Public Works went in with backhoes
and a high-pressure water vacuum known as a vactor to remove the silt
deposited by the storm from under the bridge and the two other blocked
culverts in the Inverness area. Because the blockages were determined
to be a risk to life and property, Public Works was able to circumvent
the lengthy process of applying for permits. And because state and possibly
federal funds are forthcoming, there was not the usual concern of finding
a way to pay for the work.
Other culverts and drains in the area are almost certainly
blocked, but because they are not immediately life-threatening, repairs
must wait for the pending permit process.
Why culverts need clearing
When creek beds and culverts become blocked, water
runoff has no where to go but into the surrounding areas and over the
road. This was the case in Inverness and Inverness Park, where blocked
culverts flooded over into nearby homes and businesses.
When a bridge crossing Sir Francis Drake Boulevard
near Inverness Way became blocked, the Inverness Store quickly flooded,
suffering extensive damage. Blockages of a 60-inch culvert at Fish Hatchery
Creek in Inverness Park, as well as another major culvert between Inverness
Park and Inverness, both contributed to further flooding.
County officials say that many of the passages were
already partially obstructed prior to the storm and that routine maintenance
had been impeded by a limited budget and a difficult permitting process.
According to Bob Beaumont, Chief Assistant Director
for Public Works, the culverts and creek beds along this stretch of
Sir Francis Drake had not been cleaned of silt in several years. Public
Works has, for the last two years, been in the process of applying for
a permit to perform routine culvert maintenance in Inverness and Inverness
Park, as well as for other problem areas in West Marin.
Water flow in lower Lagunitas Creek was measured to
have peaked at 18,000 cubic feet per second. For comparison, the rains
of 1982 saw peak flows of 25,000 cfs. And the problem of siltation is
especially prominent in the Inverness area because the soil is composed
primarily of loose decomposed granite. Beaumont of Public Works said
that it was unlikely that even the largest of culverts would have been
able to handle the huge amounts of sediment produced by the rains.
The susceptibility of culverts to blockage from sediment
carried by runoff points to a fundamental limitation of this form of
flood control. According to Gordon Bennet, chair of the Sierra Club’s
Marin chapter, most older culverts are invariably undersized, as they
were initially a technology borrowed from urban situations. In rural
settings, culverts must be oversized in order to handle sedimentation
and to allow the safe passage of wildlife.
"Finding the right size for culverts is like
trying to hit a moving target," Bennet said. Every new paved road,
and every new house adds to the amount of impermeable surface that further
contributes to runoff.
The permitting process
Permits are not always required for culvert maintenance
work. The county can at any point clean out the interior of the culvert
itself, but this does little if the creek is not also cleaned out downstream
of the culvert. Following the recent storms, the repairs to Inverness
area culverts included digging out the filled creaked both upstream
and several hundred feet downstream of the culvert itself. If there
is a clear passage downstream, blockages upstream can generally clean
themselves.
Work of this scale would not normally have been allowed
without a permit, which is required for work in major creek systems
that support sensitive plant and animal populations, most notably coho
salmon and steelhead trout in this case.
Obtaining a permit is laborious and slow work. Depending
on the situation, Beaumont said, there are 15 to 20 different agencies
interested in water course regulation that become involved in the permitting
process. The list is long and includes the Environmental Protection
Agency, The National Oceanic and Atmospheric Administration, The U.S.
Fish and Wildlife Service, and the California Department of Fish and
Game.
Traditionally, permits have been considered on a case-by-case
basis, as each project and site must be individually examined for its
particular environmental impact. Understandably, this produced an overload
of paperwork and slowed Public Work’s ability to keep up with essential
maintenance tasks.
The permit that has been under consideration for the
last two years, and which Beaumont hopes will be approved this summer,
would allow the county to perform routine maintenance on a series of
problematic culverts. Presuming that there is adequate funding for maintenance
projects, clean culverts in the Inverness area should have a better
chance of preventing flooding during all but the biggest of storms.