Middle Fork Project Project Description and Operations

1
Middle Fork Project Project Description and
Operations

• June 2006

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Presentation Overview

• Water storage delivery facilities water path
  from highest elevation to lowest
• Facilities details and common features
• Supporting and recreation facilities
• Operations overview

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Middle Fork Project Overview

• Developed as a water supply and generation
  project, with initial operation in 1967
• 224 MW Nameplate Generating Capacity
• 120,000 AF Consumptive Water Supply
• Operated by Placer County Water Agency
• Power Purchase Contract with PG E for all
  project electrical output
• Project revenues used for bond defeasance,
  maintenance

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Water Flow Overview

• Major storage is at high elevation in the
  watershed
• Project reservoirs store winter precipitation and
  spring runoff for use through the dry summer and
  fall
• Water released through Project tunnels and
  powerhouses flows downhill to generate power
• Release downstream of the Project are available
  for withdrawals to meet PCWA customer demand

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Upper Diversion Storage Facilities

• Duncan diversion into FM Reservoir
• French Meadows Reservoir
• Hell Hole Reservoir
• North, South Long Canyon Creek
• Collect and store water, total about 340 TAF
• Pattern of collection filling
• Collect in winter spring
• Release in summer and fall

Duncan Diversion inlet in winter
French Meadows Reservoir
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Conveyance and Generationdownstream of storage
facilities
Middle Fork Powerhouse

• Hell Hole MF Tunnel
• Middle Fork Powerhouse
• Interbay Reservoir
• MF Ralston Tunnel
• Ralston Powerhouse
• Ralston Afterbay
• Oxbow Powerhouse

Interbay Reservoir
Ralston Afterbay
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Water Use below Oxbow

• Water released through Oxbow Powerhouse available
  for various uses downstream of the Project
• Stream maintenance flows and recreation below the
  Project
• Consumptive withdrawals at Auburn Pump Station or
  Folsom Reservoir by PCWA and other water rights
  holders

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Supporting Ancillary Infrastructure Facilities

• Access Roads and Trails
• Communication and Power supply lines (not
  Transmission Lines)
• Maintenance and Dormitory Facilities
• Stream Gages

Communications Equipment Building
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Recreation Facilities

• Recreation Plan developed as required by the
  license
• Recreation Facilities include campgrounds, picnic
  areas, boat launch areas, and one scenic vista
• Operated by the Tahoe and Eldorado National
  Forests

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Characteristics Common to Project Facilities
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Large Dams and Storage Facilities

• Rock and gravel fill dams
• Spillways to handle flood flows
• Low level outlets provide stream maintenance flows

French Meadows Outlet to MF
Hell Hole Dam, rock face
French Meadows Spillway Gates
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Two Medium Dams and Reservoirs

• Concrete gravity dams
• Multiple spill gates for flood flow pass-through
• Small reservoirs, little storage turnover in as
  little as 2 hrs (Interbay) to 24 hrs (Afterbay)

Interbay Dam
Afterbay Dam
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Small Dams and Diversion Pools
South Fork Long Cyn Crk

• Ogee crest structures include no storage
• Sized to divert permitted flows but no more
• Minimum flows released through set orifices, to
  ensure flows are met

North Fork Long Cyn Crk
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Tunnels
Duncan Creek Tunnel

• Hard-rock mined tunnels connect various
  facilities of the MF Project
• The MF Project includes a total of 21.28 miles of
  tunnels
• Tunnels have a horse-shoe cross section, are
  partially concrete lined
• Long tunnels include a surge shaft

Ralston Tunnel Surge Shaft
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Inlet, Portal and Penstocks
MF Tunnel Portal

• Tunnel inlets are gated, may include a trash rack
• Tunnel portals include shut off valves
• Flows from tunnel through penstock to powerhouse

MF Penstock
Ralston Tunnel Inlet
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Powerhouses
Switchyard

• Powerhouse and power station facilities include
• Concrete powerhouse structure
• Turbine, generator, controls
• External switchyard interconnection to
  transmission
• All enclosed in a fenced yard

Control Room
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MFP Operations

• Operated to Meet Water Supply Requirements
• Operated to Meet Minimum Instream Flow
  Requirements
• Operated to Optimize Value of Generation
• Operation to undertake maintenance activities

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General Operations Constraints

• Operations Governed By
• MF Project FERC License Conditions
• Water Rights Permits
• Contractual Obligations (Delivery of Water and
  Power)
• Physical Constraints (Size of Tunnels, Capacity
  of Powerhouses)
• Power Market High Value Periods of Operation

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Project Operations Framework for Operations
Non-Variable Constraints
Water Rights Permits
FERC License Terms
Physical Constraints
Window of Operations
Non-Variable Constraints
Non-Variable Constraints
Hydrology Power Market
Variable Factors
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Water/Power Operations Outline

• Major storage is at high elevation in the Project
  watershed
• Project reservoirs store winter precipitation and
  spring runoff for use through the dry summer and
  fall
• Water released through Project tunnels and
  powerhouses flows downhill to generate power
• Withdrawals from the river to meet PCWA customer
  demand are at the bottom (downstream end) of the
  Project

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Seasonal Pattern of OperationsWater Power

• Reservoir Storage
• French Meadows and Hell Hole Reservoirs, 343,000
  Acre-Feet total storage
• Seasonal Pattern of Operations
• Store water during winter and spring
  precipitation and runoff periods (Refill period)
• Releases during the dry summer and fall months
  (Drawdown period)
• Reservoirs are operated to maintain relative
  balance between reservoirs
• Dec. 31 Carry-Over target set to ensure
  sufficient supply for following year

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Reservoir Operations Considerations

• Hydrologic variability
• Inflow Variation
• Spill Avoidance
• Current-year minimum releases consumptive
  demands
• Carry-over to meet following year demands

Avg. inflow to Folsom Variability lt30 to gt240
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Reservoir Operations

• Operations during refill period to meet demands,
  fill reservoirs, avoid spill
• Operations during drawdown to meet demands, hit
  end-of-year storage target
• Reservoir storage targets through the year
• Generally based on historic practice
• Refined during refill period based primarily on
  hydrologic conditions, with some consideration of
  power market conditions
• Storage managed during drawdown period based on
  consumptive obligations and power market trends
• At all times meet minimum release obligations

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Typical Reservoir Storage Curves
Targets - Fill with minimal spill - Carry-over
150TAF total
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Operations for Maintenance

• Maintenance activities requiring coordination
  with operations
• Facility testing (powerhouse equipment testing
  and maintenance, gate and valve testing)
• Debris removal
• Sediment management removal
• Work inside tunnels, penstocks, turbines

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Operations - Generation

• Drivers to generation scheduling
• Water availability
• Reservoir level
• Carryover targets
• Downstream demands
• Power grid needs
• Respond to load and price

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Generation Scheduling

• Watershed provides sufficient water to operate
  about half of the time at full load (50
  capacity factor)
• Full-load operations are most efficient for
  generation
• Project typically operates in peaking mode
  8-16 hours per day, during the most valuable time
  periods
• Annual generation approximately 1 million MW
  hours.

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Peaking Generation
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Key Elements for Peaking Operations

• Available water in Hell Hole reservoir
• Middle Fork and Ralston units operate as one
• Long tunnels and small Interbay mandate closely
  coordinated operations
• Afterbay fluctuates for re-regulation
• MF Ralston may only generate 8 12 hrs/day
• Downstream requirements and minimum flows are 24
  hrs/day
• Afterbay fills during peaking generation
  operations, empties when generation off-line

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Historic Total Generation
Avg generation 1.1M MWhr/yr
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MF Project Facilities