EXHIBIT 24-A

                                                                             

MONTEREY PENINSULA WATER MANAGEMENT DISTRICT

 

MEMORANDUM

 

 

DATE:            April 7, 2008

 

TO:                 Darby Fuerst, General Manager

 

FROM:           Andrew M. Bell, District Engineer

 

SUBJECT:     Report on Factors to Consider in Determining the Feasibility of Raising Los Padres Dam, or Otherwise Increasing the Storage Capacity of Los Padres Reservoir

 

BACKGROUND

 

At the February 28, 2008 Board meeting, the Board approved a request by Director Bob Brower to direct staff to prepare, for review at a future Board meeting, a report regarding the feasibility of increasing the height of the existing Los Padres Dam.  The stated purpose of the project is to create additional storage capacity in the reservoir so that stored water could be released to increase streamflow in the Carmel River to benefit the river and its associated environment.  This Memorandum is written in fulfillment of that request.

 

The existing Los Padres Dam, constructed in 1948 and 1949 by California Water and Telephone, predecessor of California American Water, is an embankment dam (zoned earthfill) approximately 150 feet high.  It is located on the Carmel River at River Mile 24.8, approximately 12 miles southeast of Carmel Valley Village near the settlement of Princes Camp.  When built, the reservoir had a capacity of 3,030 acre-feet, but due to accumulation of sediment, the storage capacity has been decreased by more than half. 

 

DISCUSSION

 

Some important questions to consider in determining a project description for raising Los Padres Dam are as follows:

 

1.  How much additional storage is desired (and therefore how much would the height of the dam need to be increased)? 

One set of inputs to this decision is what benefits in terms of increased streamflow are desired.  This would require a hydrologic analysis of streamflow, combined with biological input on the needs for different animal and plant species that are intended to benefit from the project.

 

2.   Can all or any of the existing structures be kept as part of the ultimate project? 

It is most likely that the existing dam is not capable of being built upon, and that in order to have a higher spillway at the same location would require removing the existing dam, spillway, and outlet works and replacing them with newly-engineered structures.  See further discussion below under “Determining Whether the Existing Dam Could Be Built Upon” for additional information.

 

3.  When full, would the new reservoir extend into the Ventana Wilderness? 

If so, a land exchange similar to that proposed for MPWMD’s New Los Padres Dam and Reservoir Project and CAW’s Carmel River Dam and Reservoir Project, or other arrangement acceptable to the U.S. Forest Service and other entities with interests in wilderness areas, would be required.  An increase in the elevation of the existing spillway of five feet or more would cause the reservoir to extend into the Ventana Wilderness along Danish Creek near its mouth.  Attachment 1 is a figure from the 1998 Draft Supplemental EIR for California American Water’s proposed Carmel River Dam and Reservoir Project, which was a new, higher concrete gravity dam to be located approximately one-half mile downstream of the existing dam and a reservoir with a capacity of 24,000 acre-feet.  This figure shows the “Existing Wilderness Boundary” and the “Proposed Los Padres National Forest Boundary Adjustment,” which would be an addition of approximately 140 acres (Parcel B) to the Ventana Wilderness in exchange for removing approximately 23 acres (Parcel A).

 

4.  Would the existing fish passage facilities be adequate, or would improved fish passage be a requirement of the project? 

Steelhead passage facilities at Los Padres Dam are considered by some to be inadequate.  Upstream migrants must find a fish ladder that leads to a holding tank.  During the upstream migration season, the tank is checked daily by a California American Water (CAW) employee, and if steelhead are in the tank, the CAW employee transports them to the reservoir.  Downstream migration is achieved only via the spillway, resulting in significant mortality to migrants.  If the dam were raised or replaced, California Department of Fish and Game and National Marine Fisheries Service would likely call for significant improvements to the existing methods of fish passage for both upstream and downstream migrants.  One potential method of providing improved passage would be to install a fish ladder.

 

5.   How would access to upper Los Padres Reservoir, the Ventana Wilderness, and private parcels upstream of the dam be maintained, both during construction and once the new project facilities are in place? 

Existing access is provided by a road across the dam face and extending approximately one-half mile upstream along the west side of the reservoir.  From there, trails suitable for hikers, fishermen, backpackers, horses, and other pack animals extend southerly and westerly into the Ventana Wilderness.  These access paths would need to be maintained during and after any construction.

 

6.  What routes would be used for construction access? 

Existing public road routes are (1) Carmel Valley Road to Cachagua Road, southerly and southeasterly on Cachagua Road to Nason Road in Princes Camp, then southerly on Nason Road to the existing dam; and (2) Carmel Valley Road to Tassajara Road in Jamesburg, southwesterly on Tassajara Road to Cachagua Road, westerly on Cachagua Road to Nason Road in Princes Camp, then southerly on Nason Road to the existing dam. Cachagua Road is narrow and curvy, with steep sections west of Nason Road. Construction equipment, materials, and workers would need to have access to the construction areas. Deliveries of large equipment and materials could be scheduled well in advance.  Construction workers would likely commute to and from the construction site daily.

 

Determining Whether the Existing Dam Could Be Built Upon

Primary in determining the feasibility of “raising” the existing dam is to determine the condition of the foundation and abutment formation materials in the area of the damsite.  Some of this type of exploration work was done prior to building the existing dam, but it would be necessary to do additional testing, including  foundation coring and possibly exploration of nearby seismic faults.  Deciding factors in determining whether all or part of the existing dam could be preserved include whether proposed structures would be capable of withstanding seismic and flooding standards of the California Department of Water Resources, Division of Safety of Dams (DSOD).  In order to learn whether the new structures would be approved by DSOD typically requires conducting geotechnical and engineering field studies and analyses, and presenting the results of those studies along with a proposed design as part of a permit application to DSOD. 

 

It would be necessary to determine what types of construction (e.g., embankment, concrete gravity, concrete arch) would be appropriate.  In the event DSOD would allow adding to the height of the existing dam, the appropriate method of new construction may be earthfill, the same category as the existing structure.  However, DSOD no longer allows spillways to be incorporated in large embankment dams on streams with the potential for significant streamflow.  Alternative spillway types include a tunnel separated from the embankment.  This means that either a different type of spillway than the current concrete-lined channel built into the embankment would be required, or else the existing dam would need to be removed and replaced with a different type of dam construction. 

 

Flood and Seismic Safety

Current DSOD standards require a dam to safely resist forces that would occur during significant flood and seismic events.  The basic requirements are to safely pass the peak streamflow during what is termed the Probable Maximum Flood, and to safely resist the Maximum Credible Earthquake.  Hydrologic, seismologic, and structural analyses must be conducted to determine to the satisfaction of DSOD that a proposed structure will meet these requirements.

 

Environmental Review and Permitting Requirements

Environmental review would likely require completion of state (CEQA) and federal (NEPA) environmental review processes.  Permits for  a major revision or reconstruction of Los Padres Dam would at minimum require the following permits:

 

US Army Corps of Engineers Section 404 Permit (brings in NMFS and USFWS)

California Department of Fish and Game Stream Alteration Agreement

Monterey County grading or use permit

 

It may also be necessary to obtain a change to CAW’s water rights license for Los Padres Dam and Reservoir.  In conducting the studies needed to bring the New Los Padres Dam and Reservoir Project to a vote in 1995, the District learned that there are a host of other requirements, including mitigations for potential impacts to steelhead, California red-legged frogs, riparian, wetland, and upland habitats,  historical and cultural resources, and other  resources

 

Rights of Way

Los Padres Dam and Reservoir and much of the surrounding land belong to CAW.  It would be necessary to obtain either ownership of some or all of the facilities and land, or agreement by CAW to allow any proposed modifications to their property.  In addition, if the spillway elevation were raised five feet or more, the new reservoir would extend into the Ventana Wilderness along Danish Creek near its mouth.   In this case, some property arrangement acceptable to the U.S. Forest Service and other entities with interests in the Ventana Wilderness, and wilderness areas in general, would be required. 

 

ALTERNATIVES THAT COULD BE CONSIDERED

 

Staff is aware of two alternatives to raising the existing dam that would increase the storage capacity of the reservoir.   These are described below.

 

Remove Accumulated Sediment from the Existing Reservoir

A significant amount of sediment has become deposited in Los Padres Reservoir since it was created by the construction of Los Padres Dam in 1948 and 1949.  MPWMD has periodically looked at the potential for removing the sediment.  The most recent MPWMD report on this topic, dated July 28, 2000 and titled “Preliminary Draft, MPWMD Issue Paper 2000-001, Assess Potential Feasibility of Dredging Existing Reservoirs on the Carmel River,” is attached as Attachment 2.  In 1996, CAW consultant Moffatt & Nichol issued a report titled “San Clemente Reservoir Dredging Feasibility Study, Carmel Valley, California,” but MPWMD staff is not aware of more recent reports conducted by or for CAW regarding removal of sediment from Los Padres and/or San Clemente Reservoirs.

 

Install an Inflatable Dam in Los Padres Spillway

An inflatable dam could be installed in the spillway to raise the reservoir elevation during periods when it is considered safe to do so without adversely affecting the spillway’s ability to safely pass flows.  To determine this would require confirming with DSOD the dates when the reservoir level could be raised.

 

CONCLUSION

 

Increasing the height of Los Padres Dam, or otherwise increasing the storage capacity of Los Padres Reservoir, would require extensive engineering, geotechnical, environmental review, and project planning efforts.  In order to evaluate the technical feasibility of this project, the District would need to retain expertise in dam construction and rehabilitation, in environmental impacts of such a project, and most likely in fish passage biology and engineering.  MPWMD staff members are not qualified to make such determinations.  The timelines and costs for such studies would require staff to developing scopes of work for the desired studies, obtain proposals from consultants, and analyze the proposals.

 

Attachments

1.         Figure 2-2. Location Map - Proposed Carmel River Dam and Reservoir.  From Jones & Stokes Associates, November 13, 1998, Draft Supplemental EIR for the Carmel River Dam and Reservoir Project

2.         Preliminary Draft, MPWMD Issue Paper 2000-001, Assess Potential Feasibility of Dredging Existing Reservoirs on the Carmel River, July 28, 2000, prepared by Andrew Bell, District Engineer, and Henrietta Stern, Project Manager

 

 

 

 

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