20031110 Ver 5_Report_20081210

Draft Minimum Flow Plan
Nantahala Hydroelectric Project
(FERC #2692)
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DRAFT Prepared for:
DUKE ENERGY
CAROLINAS, LLC
P Duke
Energy
December 2008
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Table of Contents
TERMS, ABBREVIATIONS, AND ACRONYMS ....................................................................iii
1.0 INTRODUCTION ...........................................................................................................1
2.0 PROJECT DESCRIPTION ...........................................................................................1
2.1 Nantahala Penstock to Dicks Creek .......................................................................... ..2
2.2 Whiteoak Diversion Dam Bypassed Reach .............................................................. ..2
3.0 PROJECT OPERATION ...............................................................................................4
3.1 General ...................................................................................................................... ..4
3.2 Proposed Operational Changes ................................................................................. ..5
3.3 Whiteoak Creek Penstock ......................................................................................... ..5
3.4 Whiteoak Creek Diversion Dam ............................................................................... .. 5
4.0 SCHEDULE ................................................................................................................... 12
5.0 ENVIRONMENTAL CONSIDERATIONS ............................................................... 12
6.0 CONSULTATION ........................................................................................................ 13
7.0 REFERENCES .............................................................................................................. 13
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List of Figures
• Figure 1 Project Location Map ........................................................................................
Figure 2 Dicks Creek ................................................................................................................. 7
Figure 3 Dicks Creek Minimum Flow Conceptual Design ...................................................... 8
Figure 4 Whiteoak Creek Diversion Dam Bypass ................................................................10
Figure 5 Whiteoak Creek Diversion Dam Gate Section ........................................................ 11
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Duke Energy Carolinas Nantahala Project FERC No. 2692
Minimum Flow Plan
. TERMS, ABBREVIATIONS, AND ACRONYMS
cfs cubic feet per second
FERC Federal Energy Regulatory Commission
FSCD First Stage Consultation Document
msl mean seal level
NCDENR-DWQ North Carolina Department of Environment and Natural Resources -
Division of Water Quality
NCDENR-DWR North Carolina Department of Environment and Natural Resources -
Division of Water Resources
NCWRC North Carolina Wildlife Resources Commission
NPDES National Pollution Discharge Elimination System
PLC Programmable logic controller
• SA Settlement Agreement
USFS United States Forest Service
USFWS United States Fish and Wildlife Service
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Duke Energy Carolinas Nantahala Project FERC No. 2692
Minimum Flow Plan
• 1.0 INTRODUCTION
In 2004, Duke Energy (Duke) filed license applications for its Nantahala Area projects with the
Federal Energy Regulatory Commission (FERC) (Duke Energy 2004). The license application
for the Nantahal Hydroelectric Project (FERC # 2698) (Project) presented the results of
numerous studies of the Project and proposed new license conditions consistent with a negotiated
Settlement Agreement (SA), which was signed on October 29, 2003 by most members of the
Nantahala Cooperative Stakeholder Team (NCST). The SA proposed a License Article 404 to
address minimum flows (Duke Energy 2004) at the Project. This Minimum Flow Plan is a
description of proposed plans and/or options for meeting minimum flow requirements for the
Project. As negotiated in the SA and according to FERC staff recommendations in the Final
Environmental Assessment (FERC 2006), continuous minimum flows will likely be required at
the Whiteoak Creek Diversion Dam and from the Whiteoak Creek Penstock into Dicks Creek.
This Minimum Flow Plan (Plan) is an initial summary of how Duke intends to meet the
minimum flow requirements that are likely to be required by the New License to be issued by the
FERC for the Project. This Plan also considers the Low Inflow Protocol for the Nantahala
Project that was developed as an integral part of the SA (Duke Energy 2003).
2.0 PROJECT DESCRIPTION
Duke Energy Carolinas, LLC (Duke) owns and operates the Nantahala Project, located on the
Nantahala River and its tributaries in Macon and Clay counties, North Carolina. Nantahala Dam
is located at River Mile 23.0, approximately 16 miles from the Town of Franklin, North Carolina
(See Section 401 Application for a Project Location map). The powerhouse is located at River
Mile 13.6. The Project consists of a reservoir, earth and rockfill dam, spillway with four Tainter
gates located on the Nantahala River, Whiteoak Creek concrete gravity dam, and Dicks Creek
concrete gravity dam, connecting tunnels, penstocks, and a common powerhouse with a single
generating unit (Figure 1).
Whiteoak Creek and Dicks Creek dams are small diversion structures with no significant storage
capacity. Nantahala Lake encompasses a surface area of approximately 1,605 acres and is
utilized for the production of hydroelectric power, recreational fishing, and boating. The
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Duke Energy Carolinas Nantahala Project FERC No. 2692
Minimum Flow Plan
watershed covers 108.3 square miles including the drainage from Whiteoak Creek and Dicks
Creek Dams (Duke Energy 2004). This Minimum Flow Plan has been prepared for the two
aforementioned diversion dams within the Nantahala Development (Duke Energy 2004).
2.1 Nantahala Penstock to Dicks Creek
The Dicks Creek Diversion Dam impounds water in a 0.2-acre reservoir at surface elevation of
3,030 above feet mean sea level (msl) and is formed by a concrete gravity dam 109 ft long and
16 ft in height. The dam crest, at Elevation 3,027.6 ft msl, functions as a spillway and is topped
with 3 ft high flashboards. A small concrete gravity dam, 39 ft long and 4 ft high, diverts
additional drainage (Diamond Valley) into the Dicks Creek Pond via an 18-inch-diameter culvert
measuring 320 ft long (Duke Energy 2004).
2.2 Whiteoak Diversion Dam Bypassed Reach
The Whiteoak Creek Diversion Dam (Creek Mile 2.3) impounds water in a 1.1-acre reservoir
formed by a concrete gravity dam 115 ft long and 16 ft high. The dam crest at Elevation 3,025.2
ft msl functions as a spillway and is topped with 7 ft high flashboards. Water from the Whiteoak
Creek Pond is directed to the Nantahala penstock via a 2,045 ft long section of tunnel and a
section of steel pipe measuring 52 inches in diameter and 9,400 ft long
(Duke Energy 2004).
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Nantahala Hydroelectric Project
FERC No. 2692
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Project Location Map
December 2008
Source: ESRI 9.2 Dataset series, 2006.
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Duke Energy Carolinas Nantahala Project FERC No. 2692
Minimum Flow Plan
• 3.0 PROJECT OPERATION
3.1 General
Water used for the production of hydroelectric power is supplied to the powerhouse via
connecting tunnels and penstocks from two sources: Nantahala Dam and Whiteoak Creek
Diversion Dam. On May 5, 1999, the FERC issued the "Order Approving Settlement and
Amending Licenses." This license order requires that flows are no longer diverted from Dicks
Creek to the main power tunnel upstream of the powerhouse. Flows impounded by the Dicks
Creek Diversion Dam are allowed to pass downstream from the dam into the Nantahala River
(Duke Energy 2004).
To support and enhance downstream recreational activities, the Nantahala Hydro Station
normally generates at least 8 hours per day, 7 days a week, from May to Labor Day of each year.
The normal operational schedule is shortened to 5 to 6 hours per day during the months of
March, April, and October. The average flow from generation is 500 cubic feet per second (cfs).
The average annual runoff (river inflow) into the Project with Dicks and Whiteoak creeks is 350
cfs with highly variable seasonal flows (Duke Energy 2004).
Dicks Creek is maintained as free flowing with outflow from the base of Dicks Creek Diversion
Dam being equal to inflow into Dicks Creek Pond, thus providing additional flow in the
Nantahala River Bypassed Reach downstream of Dicks Creek. As required by the Order
Approving Settlement and Amending Licenses (issued May 5, 1999), a seasonal minimum now
of 8 cfs is released from the Whiteoak Creek Penstock into Dicks Creek. This provides flow to
the downstream reach below Dicks Creek Diversion Dam and the Nantahala River Bypassed
Reach annually from July 1 to November 15 for protection and enhancement of aquatic habitat,
as well as maintenance of water quality (Duke Energy 2004). No other continuous minimum
flows are required in the Existing License.
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Duke Energy Carolinas Nantahala Project FERC No. 2692
Minimum Flow Plan
3.2 Proposed Operational Changes
The SA and Final Environmental Assessment for the Project (FERC 2006) recommended normal
year-round continuous minimum flows of 8 cfs from Whiteoak Creek Diversion Dam into the
Whiteoak Creek Bypassed Reach and an additional normal continuous minimum flow of 8 cfs
from the Whiteoak Creek Penstock into Dicks Creek annually from June 1 to October 31. Duke
is planning to modify the Project in order to address these normal minimum flow requirements,
which will likely be required when the New License is issued and accepted. These modifications
are described in the following sections:
3.3 Whiteoak Creek Penstock
Duke will continue to maintain the existing minimum flow valve capable of releasing up to 8 cfs
from the Whiteoak Creek Penstock into Dicks Creek to provide flows into the Nantahala River
• Bypassed Reach. Duke is planning the installation of an another minimum flow valve capable of
releasing an additional 8 cfs from the Nantahala Penstock into Dicks Creek and downstream to
the Nantahala River Bypassed Reach.
To accomplish this requirement, a new manual V-ball valve will be installed on the new
discharge pipe to regulate the amount of flow entering Dicks Creek. This valve will be manually
set and adjusted as required during the year. To monitor the flow, a magnetic flow tube will be
placed in line with the discharge pipe and incorporate a flow transmitter (See Figures 2 and 3).
3.4 Whiteoak Creek Diversion Dam
In order to meet the SA and FERC recommended flow requirements of 8 cfs into the Whiteoak
Creek Bypassed Reach from the Whiteoak Creek Diversion Dam; Duke intends to modify the
existing spillway gate to pass the normal minimum flow requirement of 8 cfs. A small
pneumatically operated inflatable gate will be used to regulate the amount of flow cresting over
the spillway. The gate will be automated to follow changing pond elevations so that the
minimum flow release will be maintained. A small equipment house will be located along side
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Duke Energy Carolinas
Nantahala Project FERC No. 2692
Minimum Flow Plan
0 of the dam to shelter the pneumatic controls and devices used to operate the gate. Duke will
calibrate the flow measuring devices within 60 days following installation and at least once every
two years thereafter.
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Figure 3 Dicks Creek Minimum Flow Conceptual Design
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SECTION B-8
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Duke Energy Carolinas Nantahala Project FERC No. 2692
Minimum Flow Plan
0 A permanent flow transmitter will be installed on the existing Whiteoak Creek Penstock
minimum flow release system where a flow orifice and flange set are currently in place. Both
flow transmitters will be hardwired in rigid conduit back to the valve house for monitoring and
data storage. Inside the valve house, a monitoring box will store flow rate data for specific
periods of time and will provide a continuous readout of flow at each monitoring location.
The existing head gate into the Whiteoak Creek Penstock will be modified to allow the required
water flow into Whiteoak Creek. An actuator will control water flow into the penstock by
raising and lowering the head gate depending on the pond level. As inflow into the pond
changes, the adjustable head gate will raise or lower and pass more or less water over the
inflatable gate. A pond level transmitter will be employed to monitor and transmit data to a
programmable logic controller (PLC), which will adjust the head gate and inflatable gate. The
gate modification includes replacing the seals and roller mechanisms while upgrading the
existing cable operator with a rising stem actuator (Figures 4 and 5).
0 In order to install the gate, the pond must be drawn down in compliance with Nantahala
Settlement Agreement: Attachment C - Hydro Project Maintenance & Emergency Protocol
(HPMEP) for the Nantahala Project, Section B. l.a.
The engineering concepts presented in this Minimum Flow Plan may need to be modified
subsequent to further engineering discussions and agency consultations.
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Duke Energy Carolinas
4.0 SCHEDULE
Nantahala Project FERC No. 2692
Minimum Flow Plan
The continuous minimum flow requirements for the Project were negotiated and proposed to the
FERC in the SA (Duke Energy 2003), which was filed with FERC on January 8, 2004. Proposed
License Article 404 in the SA contains the negotiated minimum flows for the Project along with
a proposed implementation schedule, as follows: Within 6 months of license acceptance, Duke
will file the Plan for FERC approval to modify the Project facilities as outlined in the Plan. This
filing will take place after consultation with the North Carolina Wildlife Resources Commission
(NCWRC), North Carolina Department of Environment and Natural Resources - Division of
Water Resources (NCDENR-DWR), North Carolina Department Environment and Natural
Resources - Division of Water Quality (NCDENR-DWQ), United States Fish and Wildlife
Service (USFWS), and the United States Forest Service (USFS). Within one year following
FERC approval of the Plan, Duke will complete the modifications of Project facilities identified
in the plan and begin providing the minimum flows as specified in Article 404. Duke will
calibrate the flow measuring devices within 60 days following installation and at least once every
two years thereafter.
5.0 ENVIRONMENTAL CONSIDERATIONS
Water quality, fisheries, and other environmental effects of these modifications were described in
the Section 401 Water Quality Certification Application filed for the Nantahala Project. None of
these proposed modifications will degrade water quality. The modifications will also provide
enhanced aquatic habitat in the Nantahala River Bypassed reaches. The proposed operation
changes will have no impacts any RTE species documented in the Project area.
Construction associated with the minimum flow release structure will occur in a previously
disturbed area that is immediately adjacent to the existing flow release structure. Project
modifications are not anticipated to adversely affect the cultural or recreational resources within
the Project boundary. Duke will obtain all necessary environmental permits prior to
commencing with Project modifications.
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Duke Energy Carolinas
0 6.0 CONSULTATION
Text to be inserted upon agency consultation
7.0 REFERENCES
Nantahala Project FERC No. 2692
Minimum Flow Plan
Duke Energy Corporation. 2003. Nantahala Hydroelectric Project FERC #2692 Settlement
Agreement Notebook.
2004. Nantahala Hydroelectric Project FERC #2692 License Application Volume I.
2006.Final Environmental Assessment for Hydropower Licenses Natahala West Projects.
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