Pájaro River Watershed Flood Protection Plan - The Pajaro River ...

parkway system that can be implemented with no or minimal outside funding.
Graniterock has already demonstrated a willingness to propose such action
and assisted our study through their generous sharing of their aerial survey
data. If conservation easements or land trust arrangements can be
implemented for parts of the upper Pájaro watershed in conjunction with
these major landholders, this may facilitate faster completion of potential
storage volumes. We can help to facilitate such planning and
implementation.
Suggested Enhancement Options for Upper Pájaro River:
The Upper Pájaro River, along the Santa Clara-San Benito County line is
fundamentally different than the San Benito River. Here a channel is incised
up to 25 feet below the Lake San Benito lakebed, but because the riverbed
has historically carried a reliable supply of influent groundwater, a dense
finger of riparian forest characterizes most of the channel. This mature
riparian forest of cottonwood, alder, maple, and willow has a dense woody
instream fabric of logs and mid-channel growth, with a diverse pool structure.
Although only 100 m wide in places, this riparian corridor provides high
quality wildlife habitat and, apparently, allows anadromous fish passage into
Llagas and Uvas creeks.
Because the riparian forest is so dense and woody debris so prevalent, flood
stages rise rapidly and go overbank onto the old San Benito lakebed. Local
landowners report that flooding reaches the old lakebed level at a frequency
of 10 years or less. Because of the high regional groundwater levels that
seasonally saturate up to the lakebed silt cap, the soils of the area are
classed as hydric and, unless cropped continually, revert to wetland
conditions with emergent wetland plants. Farmers have constructed drainage
channels across these lands to carry shallow groundwater and rainfall into
the Pájaro.
We were able to meet with local landowners and/or farm leaseholders. We
learned that this Soap Lake area, just south of Gilroy, and situated along
Highway 25 between Gilroy and Hollister, may be a target for extensive
development. An ongoing effort sponsored through the Pájaro River
Watershed Flood Prevention Authority and AMBAG seeks to establish flood
or conservation easements for the Soap Lake basin. Our sources suggest
that the opportunity costs for development are so great that contiguous
easements may be very difficult to obtain. While the site looks like marginal
agricultural land used for little more than growing hay or grazing with small
areas of row crops, it is in fact being leased back to local farmers and kept in
agriculture as an interim holding pattern while development options are
considered. If some of these lands would be wetlands were it not for
continual agricultural use, then federal regulations will make it necessary to
maintain agricultural uses or raise the lands or protect them with dikes and
levees to permit non-agricultural uses. Should this be the case, a need for
local fill may provide an opportunity to encourage landowners to excavate the
3-foot deep lake-silt cap immediately adjacent to the river. This could
increase the flood storage.
DRAFT 7/22/03
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Pajaro Watershed Flood Management