Consider Contract with CSUMB for Bathymetric Survey at Los Padres Dam


Meeting Date:

May 8, 2017





David J. Stoldt,


Augment Water Supply


General Manager

Line Item No.:

1-1-1 A Los Padres Reservoir Expansion Simulation


Prepared By:

Larry Hampson




General Counsel Review:  N/A

Committee Recommendation:  The Administrative Committee reviewed this item on May 8, 2017 and recommended __________.

CEQA Compliance:  This action does not constitute a project as defined by the California Environmental Quality Act Guidelines section 15378.


SUMMARY:  MPWMD is currently cooperating with Cal-Am to carry out a set of studies related to developing a long-term management plan for Los Padres Dam and Reservoir.  A key piece of information related to these studies and selection of management alternatives is the long-term sedimentation rate at the reservoir.  The School of Natural Sciences at California State University Monterey Bay has provided a proposal to conduct a bathymetric survey of the reservoir as described in Exhibit 3-A.  This survey would use the same equipment and methods as was used by CSUMB in their 2008 reservoir survey.


RECOMMENDATION:   Staff recommends authorizing the General Manager to enter into an agreement with University Foundation for a Not-to-Exceed amount of $16,000.  Staff requests an additional $4,000 in contingency funding for unforeseen conditions.  If this item is approved with the Consent Calendar, the General Manager would be authorized to expend up to $20,000 for this work.


DISCUSSION:  CSUMB surveyed Los Padres Reservoir in August 2008 immediately after the Basin Complex fire had burned through the watershed contributing to Los Padres Reservoir.  At the time, the Burned Area Emergency Response (BAER) team set up to review the effects of the fire had predicted that up to about 300 acre-feet of sediment could enter the reservoir in the years following the fire.


In August 2017, during the Soberanes fire, HDR completed a bathymetric study of Los Padres Reservoir that showed reservoir storage had not changed between 2008 and 2016.  However, the period after the 2008 fire was hydrologically quiet, with four straight years of drought including a couple of years of extreme drought. The Soberanes fire in 2016 followed by the extremely wet winter of 2016-17 may have resulted in additional siltation in the reservoir.  The BAER report for this fire predicted about 250 acre-feet of siltation from a 10-year rainfall event.  Observations of portions of the Carmel River watershed showed that rainfall events in January and February 2017 caused significant slides and debris flows; however, there are no data on what has happened in the watershed above Los Padres Dam as the National Forest and Ventana Wilderness has remained closed since the fire.


The effects of the 1977 Marble-Cone fire and resulting loss of storage at Los Padres Reservoir may be an outsized influence on the long-term siltation rate and expected life of reservoir storage.  The M-C fire occurred after an extreme two-year drought in areas with a high fuel load.  The fire was extremely hot and burned very completely (almost 90% of vegetation was burned in many areas) and was followed by the extremely wet winter of 1977-78.  Bathymetric surveys were completed by the USGS in 1977 and 1978 and showed that 555 acre-feet of silt entered the reservoir in a single winter.


Another bathymetric survey at this time will inform the choice of alternatives for sediment management in the future at the reservoir and could confirm whether the 1970s series of events was an outlier or not.


California Environmental Quality Act Compliance (CEQA): Guidelines Excerpt



A project involving only feasibility or planning studies for possible future actions which the agency, board, or commission has not approved, adopted, or funded does not require the preparation of an EIR or Negative Declaration but does require consideration of environmental factors. This section does not apply to the adoption of a plan that will have a legally binding effect on later activities.



2-A      PRE-PROPOSAL—April 25, 2017