HomeMy WebLinkAboutMINUTES - 03121985 - X.17 TAE BOARD OF SUPERVISORS OF CONTRA COSTA COUNTY , CALIFORNIA
i
I
I
Adopted this Order onl March 1.2, 1985 , by the following vote:
AYES: SupervisorslPowers , McPeak, Torlakson, Fanden
i
NOES: None
ABSENT: Supervisor Schroder
ABSTAIN: None
-------------------------------------------------------------------- -
--------------------------------------------------------------------
SUBJECT: Delta Subsidence and Seismicity Studies
The Problem
Subsidence is a recognized occurrence in the Delta. It affects the adequacy of levee
systems and other flood protection measures, the longevity of Public Works projects, and
the stability of private-sector developments. Along with seismicity, subsidence is
becoming an issue in Eastern Contra Costa Countyas more private-sector projects and
public programs (including levee rehabilitation programs ) are proposed in the Delta.
Background
The Delta area has two geological problems that must be considered in planning, design,
and construction of waterways, water transfer, and land-based facilities; (1) subsidence of
up to 21 feet, much land that lies below normal water levels; and (2) levees that fail under
stresses of high water but have not yet been severely tested by added forces of an
earthquake. The seismicity of the delta is poorly understood and the seismic record is too
short to make broad conclusions. Furthermore, the causes of subsidence are only known in
a general and area-wide way; the causes are not the same everywhere in the Delta; and
the causes of shallow settlement have not been separated from deep-seated (over 50 feet)
causes that may contribute significantly to the overall subsidence in some places.
Recommendations
The Contra Costa County Board of Supervisors should take the following actions:
1) Request that the U.S. Department of Commerce, National Geodetic Survey An
cooperation with the California Department of Water Resources, resurvey the
Delta, utilizing precision elevation surveys, and to the extent possible, correlate
elevation changes on bench marks set to depths of up to 100 feet, by Federal surveys
during the 1960's.
2) Request that the California Department of.Water Resources and. federal agencies,
including the U.S. Bureau of Reclamation, the U.S. Army Corps of Engineers and the
U.S. Geological Survey, locate and segregate all the significant factors contributing
to subsidence in the Delta.
3) Request that the U.S. Geological. Survey and the State Geologist in the Department
of Conservation re-evaluate Delta seismicity and its effect on all Delta facilities by
State-of-the Art geological, seismological, and earthquake engineering studies, and
present recommendations for implementation in future Delta facilities by all
Federal, State and local agencies.
And
4) Request that member counties of .the Delta Advisory Planning Council support the
foregoing studies by actions of their respective governing bodies, and by follow-up
letters to the following Federal and state agencies: the U.S. Department of
Commerce, the U.S. Bureau of Reclamation, the U.S. Geological Survey, the U.S.
Army Corps of Engineers, the California Department of Water Resources and the
State geologist in the California Department of Conservation.
I
I
i
I
It is intended that the results of these studies would be
applied during the planning and design of Federal , State , and local
government facilitiesiand in the exercise of these governments '
regulatory programs .
As requested by Supervisor Tom Torlakson, IT IS BY THE
BOARD ORDERED that the recommendations as set forth above are
APPROVED .
i
cc: Director of Planning
Agencies as noted
County Administrator
I hereby certify that this Is a true and correctcopy of
an action taken and entered on the minutes of the
Board of Supervisors on the date shown.
ATTESTED:
PHIL BATCHELOR, Clerk of the Board
of Supervisors and County Administrator
By Deputy
i
i