WATER SUPPLY PLANNING
COMMITTEE
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ITEM: |
ACTION
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2. |
Develop Recommendation to the Board of Directors on Receipt of Los
Padres Dam and Reservoir Long-Term Strategic and Short-Term Tactical Plan |
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Meeting
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April 18, 2014 |
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From: |
David
Stoldt, |
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General
Manager |
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Prepared
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Larry
Hampson |
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SUMMARY: At their February 4, 2014 meeting, the Committee provided comments on the draft “Los Padres Dam and Reservoir Long-Term Strategic and Short-Term Tactical Plan” (Shibatani Plan) and requested that the Shibatani Group revise the report to include: 1) a plan for decommissioning Los Padres Dam and construction of off-stream storage; 2) a timeline for completion; 3) a cost estimate; 4) a focus on the need to regulate the Carmel River; 5) a solution for regulation of the river should Los Padres Dam remain intact; and 6) a description of flood control measures needed on the Carmel River with and without off-stream storage. The revised report was sent to Committee members under separate cover. Tasks 1, 2, 3, and 6 are not within the existing scope of work and are discussed below.
As described to the Committee at its August 14, 2013 meeting, in its 2015-17 General Rate Case application to the California Public Utilities Commission, Cal-Am is requesting $4.2 million to improve downstream fish passage at Los Padres Dam and $1 million to complete a detailed feasibility study to determine the ultimate fate of the dam. District staff intend to cite portions of the final Shibatani Plan to argue in favor of MPWMD taking the lead in developing a long term strategy for the dam.
RECOMMENDATION: The Committee should review the final version of the Shibatani Plan and consider providing a recommendation to the Board and staff concerning: 1) additional tasks that were not within the original scope of work for the Shibatani Group; and 2) the preferred strategy that the District should adopt concerning Cal-Am’s Los Padres Dam requests in the 2015-17 Cal-Am General Rate Case testimony.
DISCUSSION: In April 2013, the National Marine Fisheries Service (NMFS) directed California American Water (Cal-Am) to resolve fish passage issues and aquatic habitat degradation associated with Los Padres Dam. Subsequently, Cal-Am filed two requests in its 2015-17 General Rate Case to address these issues. The proposed schedule is to award contracts for both the fish passage improvement project and the Los Padres Dam feasibility study in mid-2015. The District will support Cal-Am’s request for funds to improve fish passage, although there are concerns about the estimated cost of the improvement, which has steadily climbed since passage improvements were first discussed.
Concerning the proposed long-term feasibility study, Mark Schubert, a Cal-Am manager, states in his direct testimony that “California American Water only wants to propose a project that best addresses the concerns of NOAA Fisheries.” In its 2013 Final Recovery Plan for steelhead, one of the critical recovery actions for steelhead in the Carmel River is to:
“Remove or physically modify San
Clemente, Los Padres, and Old Carmel River Dams* to provide natural rates of
steelhead migration to upstream spawning and rearing habitats;”
* Note: Prior to the removal or
modification of these dams appropriate investigations and environmental review
should be completed to address regional water supply and environmental issues,
including, but not limited to any effects on the existing steelhead resources
of the Carmel River watershed.
Cal-Am’s proposal for the feasibility study focuses on two alternatives – dam removal and restoration of reservoir capacity (partial or full) with additional habitat and fish passage improvements. A preliminary cost estimate for sediment removal is provided, which ranges from $52 million to remove about 500 acre-feet of sediment to $100 million to remove all the accumulated sediment (i.e., about 1,250 acre-feet). No costs associated with constructing upstream fish passage improvements, dam spillway modifications, or habitat enhancement activities downstream of the dam are provided. Cal-Am described in its testimony that a strategy would need to be developed for working with the District on how to best manage the Carmel River under either option, because of on-going environmental programs.
In order to provide additional water supply to the Monterey Peninsula and develop a long-term strategy for Los Padres Dam, the Committee requested an investigation by the Shibatani Group. The first draft of the Shibatani Plan was reviewed by the Committee with Robert Shibatani on February 4, 2014 (see the Committee minutes). The Committee’s requests from that meeting are discussed below.
1) A plan for decommissioning Los Padres Dam and construction of
off-stream storage; 2) a timeline for completion; and 3) a cost estimate;
The scope of work for the Shibatani Plan was to develop a guidance document that would identify short-term tactical actions and a long-term strategic plan. Selection of an alternative for further development was not included in the scope, although the Shibatani Group notes the dam removal coupled with new off-main stem storage meets all of the planning criteria. In order to develop a solution further, the Committee and Board should provide guidance for the preferred alternative(s) and a proposal for completing the work should be obtained.
4) A focus on the need to regulate the Carmel River;
The Shibatani Group agreed to address this in the final draft plan.
5) A solution for regulation of the river should Los Padres Dam remain intact;
This task was not within the scope for development of the Shibatani Plan. An answer to the regulation of the river if Los Padres Dam remains intact depends on several factors including: what action is taken at the dam (e.g., no action, partial dredge, full dredge, dam raise); how Cal-Am changes its downstream diversions in the future; and desired instream flow conditions. District staff are currently developing a linked surface-groundwater model and an instream flow model that, together, will have the capability of modeling different alternatives and their outcomes on water availability, habitat, and flows. The models should be completed in 2015.
6) A description of flood control measures needed on the Carmel River with and without off-stream storage.
Several flood control alternatives for the main stem were studied in detail by the Corps of Engineers in a 1981 document entitled “Feasibility Report on Water Resources Development, Carmel River, Monterey County.”
Carmel River channel capacity to pass floods: The 1981 study estimated that channel capacity downstream of the Robles del Rio gage on Esquiline Road in Carmel Valley Village (the Village) was 3,500 to 10,000 cfs. Since then, the January 10, 1995 flood event (about 10,000 cfs) inundated homes in the vicinity of the Esquiline Road Bridge in the Village and in the Mission Fields area. The March 10, 1995 event (16,000 cfs) flooded the same areas, as well as many others along the river; however, because the 1995 floods scoured vegetation out of the active channel and improvements were made in the wake of the flood, the February 6, 1998 flood event (14,700 cfs) caused far less flooding and many areas that were flooded in 1995 were not inundated in 1998. Since that time, channel capacity of the river in the lower 16 miles has been affected by both vegetation encroachment, which works to reduce capacity, and downcutting, which works to increase capacity. Currently, channel capacity may be somewhat reduced from the 1998 condition, but is probably somewhat greater than 10,000 cfs in most areas.
Flood storage requirements: The table below shows information on the required storage and effectiveness of dams at four main stem locations that would attenuate a 100-year flood at the Near Carmel gage (see Exhibit 2-A for locations) to a flow that would be contained within the existing channel. The 100-year flood estimates contained in the 1981 Corps report are somewhat higher than the current Flood Insurance Study estimates.[1] Nevertheless, the 1981 analysis of main stem alternatives using the 50-year flood event is fairly close to the current (2006) estimates for the 100-year flood event. Using the San Clemente location as an example, a main stem dam with 28,000 acre-feet of storage would be required. In other words, flow in the main stem from upstream of the present-day Los Padres Dam together with flows from Cachagua Creek, Pine Creek, and San Clemente Creek would need to be reduced to no more than 3,500 cfs at Robles del Rio in order to reduce the 100-year flood to a flow that could be contained within the existing channel downstream of the Village.
Using the 1981 Corps report estimate of the 50-year flood event (which seems to correspond to the more recent 100-year flood estimates), a 100-year flood event at Los Padres Dam would be about 8,500 cfs. Presuming that a main stem dam for flood control is not an option, even reservoirs on all the upper watershed tributaries would probably not be able to attenuate a flood peak at the Near Carmel gage to the point where flooding does not occur.
Additional studies needed
There are several component studies that should be carried out in order to fully evaluate options for Los Padres Dam. These include:
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Flow analyses associated with alternatives
– several flow analyses involving different levels of diversions would be
required in order to evaluate alternatives including: existing conditions and
Cal-Am operations; future Cal-Am operations as proposed in the Monterey
Peninsula Water Supply Project; partial reservoir dredging; full reservoir
dredging; reservoir enlargement; and dam removal (with future Cal-Am
operations). It is likely that a change
petition to SWRCB involving Permit 20808B would result in a permit that
includes maintaining minimum instream flow requirements (see next bullet).
·
Updated instream flow study – NMFS
completed recommendations for maintaining instream flows in 2002. A modified version of those recommendations
is currently being attached by SWRCB to all new permits issued for the Carmel
River. The 2002 NMFS study does not accurately
reflect significant changes in river habitat conditions and Cal-Am operations
over the past 25 years. District staff
is currently working with a consultant to develop an updated instream flow
analysis using the Instream Incremental Flow Method (IFIM). A workshop to discuss the IFIM study is
scheduled for April 23, 214. The study
will likely take one to two years to complete.
The IFIM can be
used to evaluate how changes in flow affect steelhead habitat and fish
passage. Alternatives being considered
at Los Padres Dam would have significant effects on the flow regime in the dry
season and could affect the flow regime in the “shoulder” seasons of late
fall/early winter and late spring/early summer.
·
Steelhead habitat evaluation of the Carmel
River watershed – MPWMD’s 2004 evaluation of steelhead habitat in the
watershed estimated that 50% of the spawning habitat in the watershed was
upstream of Los Padres Dam. Similarly,
MPWMD estimated that 42% of the suitable rearing area in the watershed was
above Los Padres Dam and that it was of exceptional quality due to its location
within the Ventana Wilderness. These
estimates were based on habitat conditions between the 1980s and early 2000s
and included the effects of unauthorized diversions.
The value of steelhead habitat both upstream and downstream of Los Padres Dam should be re-evaluated in the context of improvements to habitat in the main stem due to the removal of San Clemente Dam, stream restoration in the lower 15 miles of the river, proposed reductions in Cal-Am diversions, and any proposed gravel replenishment projects associated with sediment management at Los Padres Reservoir. A combination study using IFIM and habitat suitability index assessments should be used to better understand the value of each reach of the river and each tributary and the potential for improvements downstream of Los Padres Dam.
·
Yield and cost/benefits analysis –
increasing storage capacity at Los Padres Reservoir can be achieved through
dredging, increasing the spillway elevation, or a combination. Each alternative has different economic and
environmental costs as well as benefits.
·
Sediment management – Los Padres
Reservoir is a more difficult and expensive site to address sediment issues
than at the San Clemente Reservoir, where a unique situation allowed sediment
to remain in place. A fundamental issue with
Los Padres Dam that needs to be addressed with any proposed project is both
short term and long term management of sediment. The long term average sediment inflow is
about 20 AFY or the equivalent of about 2,200 tandem truckloads of sediment
annually. Sediment starvation downstream
of the dam continues to degrade the river through the armoring effect
(winnowing of spawning gravel) and downcutting into the riverbed. Failure to address this degradation will
compromise efforts to reduce diversions and may lead to further destabilization
of streambanks in the lower 15 miles of the river.
A recent paper entitled “Sustainable Sediment Management in Reservoirs and Regulated Rivers: Experiences from Five Continents” suggests that for certain locations, a tunnel around a reservoir can be used to successfully bypass most of the bedload traveling through the river, thus significantly extending the life of a reservoir in a high sediment load drainage. This alternative could be evaluated for Los Padres Reservoir. The paper was authored in part by Prof. G. Mathias Kondolf, who has been involved with Carmel River projects since writing his Master’s Thesis on streambank erosion in 1980.
EXHIBITS
2-A Location of Damsites Studied
U:\staff\Board_Committees\WSP\2014\20140418\02\item2.docx