Bucks Creek Hydroelectric Project, FERC Project No. 619
Proposed Study Plan
WR-S3
STUDY DESCRIPTION WR-S3
DEVELOP UNIMPAIRED AND REGULATED HYDROLOGY FOR PROJECTAFFECTED STREAM REACHES AND EVALUATE WITH INDICATORS OF
HYDROLOGIC ALTERATION MODEL
Revised May 2014
STUDY GOAL AND OBJECTIVE
The Bucks Creek Project (Project) Pre-Application Document (PAD), November 15, 2013,
identified issues associated with water resources for which the existing, relevant, and reasonably
available information is insufficient to address the issues. These issues are:

WR-1
Potential Project effects on water temperature in Project reservoirs and
Project-affected stream reaches

WR-2
Consistency of Project reservoirs and Project-affected stream reaches
with Water Quality Standards

FA-4
species.
Effects of Project operations on common amphibian and aquatic reptile

FA-5
Effects of the Project on instream habitat in Project-affected streams.

RWL-1
Effects of the Project on riparian habitat in tributaries.

RWL-2
Effects of the Project on wetland habitat along reservoir margins.

RTE-1
Effects of Project operations on special-status amphibian and aquatic
reptile species
The goal of this study is to develop the essential additional information to supplement the
existing information, which is necessary to address the identified issues. The specific information
to be developed is the unimpaired and regulated flow regimes for affected reaches of the Bucks,
Grizzly and Milk Ranch creeks and to evaluate against Licensees’ existing Indicators of
Hydrologic Alteration (IHA).
EXISTING INFORMATION
Section 5.2 of the PAD contains extensive information on Project-related hydrology, including
(1) data on the current hydrologic conditions of the Project features and related waterways,
(2) historical records of precipitation, and (3) morphometric characteristics of Project reservoirs.
Appendix E of the PAD contains monthly and annual flow duration curves for stream gages on
the Milk Ranch, Bucks, and Grizzly creek watersheds, and Appendix G contains generation and
outflow records for the two powerhouses at the Project. The Licensees also maintain extensive
streamflow gaging data and reservoir elevation data in its archives.
1
Bucks Creek Hydroelectric Project, FERC Project No. 619
©2014, Pacific Gas and Electric Company and the City of Santa Clara
WR-S3
Bucks Creek Hydroelectric Project, FERC Project No. 619
Proposed Study Plan
Stream gaging information and precipitation records are available from the U.S. Geological
Survey (USGS), California Department of Water Resources (DWR), and Licensees. However,
because the Project facilities have been in place since about 1929, information or evaluation of
the hydrology in the entire Project-affected stream reaches prior to construction of the Project
does not exist. An unimpaired and regulated hydrology was prepared for the Bucks and Grizzly
Creek portion of the Project in an Indicators of Hydrologic Alteration (IHA) study (PG&E
2003). The synthesized record of mean daily streamflows covers a 32-year period from 1970
through 2001. Because of the lack of any accurate streamflow or storage information on Milk
Ranch Creek, streamflows were not synthesized for any points in that basin (PG&E 2003).
NEXUS BETWEEN THE PROJECT AND RESOURCE TO BE STUDIED AND HOW
THE RESULTS WILL BE USED
Project construction, operation, and maintenance activities directly and indirectly affect the Project
stream hydrology. The results of this study will be used in conjunction with the results of other,
resource-specific studies to evaluate potential Project effects and develop management measures
that may be employed to address those effects. The study will address the relevant hydrological
management goals stated within applicable resource management plans (PNF 1988).
STUDY AREA AND STUDY SITES
The Study Area includes (1) Milk Ranch Creek from the inflow to Three Lakes to the North Fork
Feather River (NFFR), (2) Bucks Creek from the inflow to Bucks Lake to Lower Bucks Lake,
(3) Bucks Creek from the inflow to Lower Bucks Lake to the NFFR, and (4) Grizzly Creek from
the inflow to Grizzly Forebay to the NFFR.
Hydrologic records will be compiled so that unimpaired flow can be determined for Three Lakes,
Bucks Lake, and Grizzly Forebay. The Licensees propose using the already developed
unimpaired flow estimates for Bucks Lake and Grizzly Forebay (PG&E 2003). Both regulated
and unimpaired flow will be determined at four points in the Project area used in the IHA
analysis (see below). As part of developing the database, hydrologic records from various
streams in the Milk Ranch, Bucks, and Grizzly creek watersheds, as well as active feeder
streams, will also be reviewed. The anticipated study nodes are as follows:

Milk Ranch Creek (downstream of Three Lakes, USGS Gage 11403300),

Milk Ranch Creek Conduit outlet (USGS Gage 11403450),

Bucks Creek (downstream of Bucks Lake, USGS Gage 11403530),

Bucks Creek (downstream of Lower Bucks Lake, USGS Gage 11403520),

Bucks Creek (near Bucks Lake, USGS Gage 11403500),

Bucks Creek Powerhouse outflow (USGS Gage 11403700),

Bucks Creek Tunnel outlet (USGS Gage 11404100),
2
Bucks Creek Hydroelectric Project, FERC Project No. 619
©2014, Pacific Gas and Electric Company and the City of Santa Clara
Bucks Creek Hydroelectric Project, FERC Project No. 619
Proposed Study Plan

Grizzly Creek (inflow to Grizzly Forebay, USGS Gage 11404250),

Grizzly Creek (downstream of Grizzly Forebay, USGS Gage 11404300), and

Grizzly Powerhouse outflow (USGS Gage 11404240).
WR-S3
Specifically excluded from the Study Area are areas where access is unsafe (very steep terrain or
high water flows) or private property for which Licensees have not received specific approval
from the landowner to enter the property to perform the study. The Licensees will make a good
faith effort to obtain access to private property to conduct the study.
METHODS
To develop the regulated and unregulated hydrological database for the Project, two different
methods will be used: summation and proration. The primary method for synthesizing
streamflow data will use mass balance equations for all points where gaging station records
and/or observer’s reports are available. All available USGS and Licensee data will be used to
compute the unimpaired daily average flows for the study period. For periods of missing data,
the daily flow data may be estimated from previous or following records, by comparison with
other station records from the same or nearby basins and/or by using a rainfall-runoff simulation
model, if necessary. The representative basin(s) will be selected based on similarities in
configuration (e.g., size, climate, topography, elevation, geology). The daily flows may also be
estimated by using flow data at nearby unregulated streams and adjusting its magnitude by
multiplying data by a factor based on the ratio of their respective drainage areas. Summation and
proration are described below.
Summation
Summation uses mass balance equations for all points where gaging station records and/or
observer’s reports were available. For reservoirs, this incorporates the determination of inflows
using the hydrologic water budget equation:
S = I – O
where the change in storage (S) equals inflow (I) minus outflow (O).
The summation method also assimilates stream flow gage data from contributing drainage areas
and accounts for losses from diversion flows.
Proration
The proration method estimates daily, unimpaired flows for a given watershed of interest based
upon unimpaired flow data in a similar (reference) watershed. The unimpaired flow data in the
reference watershed is then prorated to the watershed of interest by applying a drainage area ratio
factor (i.e., drainage area ratio equals drainage area of watershed of interest divided by drainage
area of reference watershed). If the unimpaired flow data for the reference watershed are
accurate, then the proration method is very effective when applied to watersheds with similar
physical characteristics (e.g., climate, topography, elevation, geology). Accretion to the channel
is assumed to be positive and will be estimated based on contributing area.
3
Bucks Creek Hydroelectric Project, FERC Project No. 619
©2014, Pacific Gas and Electric Company and the City of Santa Clara
Bucks Creek Hydroelectric Project, FERC Project No. 619
Proposed Study Plan
WR-S3
As recommended by Richter et al. (1998, 1997, 1996), IHA statistics are normally calculated at
riverine locations where measured hydrology data (mean daily flows) are available for about 20
to 30 years from both the pre-Project and Project period. The Licensees’ approach will differ
from this normal approach in one major way. Because 30 years of pre-Project flow data are not
available for all Project-affected stream reaches, Licensees will utilize the 32-year (1970-2001)
synthesized unimpaired flow developed for the existing IHA analysis (PG&E 2003). Milk Ranch
Creek unimpaired and regulated flow will be developed for the same time period using the above
techniques. The length of hydrologic record developed will ultimately be determined by the
completeness of the data sets available for analysis and simulation. Currently, Licensees intend
to use at least a 30-year period of record, which would include a reasonable range of wet, dry,
critically dry and normal water year conditions.
Water year type classifications may be developed that would be applicable to the Milk Ranch,
Bucks, and Grizzly creek watersheds, depending on review of the hydrologic data and in
consultation with the Relicensing Participants. If water year types are necessary, inflow data for
the period of record would be ranked and broken into four or five categories (e.g., critically dry,
dry, normal, and wet) based on exceedance percentages.
ANALYSIS
The Licensees propose to use the IHA analysis developed in 2003 for this project (PG&E 2003).
This analysis allowed for assessment of changes in the hydrologic condition on the associated
environmental concerns at four sites within the Project area: Bucks Creek at the Lower Bucks
Lake Diversion Dam (Upper Bucks); Bucks Creek at the North Fork Feather River (Lower
Bucks); Grizzly Creek at the Grizzly Forebay Dam (Upper Grizzly); and Grizzly Creek at the
North Fork Feather River (Lower Grizzly). There are 32 statistical metrics that focus on
descriptors of the streamflow regime that are considered to be important to the biological and
physical integrity of the river. The 32 metrics derived in the IHA analysis can be clustered into
five specific groups, which can then be used to assess potential environmental impact. The
ecosystem influence for each of the 32 metrics is well described in the methods. The five groups
for the IHA metrics, which are identified in the IHA protocol as described by Richter et al.
(1996, 1997, and 1998), are listed below:

Magnitude of monthly water conditions,

Magnitude and duration of annual extreme water conditions,

Timing of annual extreme water conditions,

Frequency and duration of high and low pulses, and

Rate and frequency of change in water conditions.
The statistical parameters derived using this method will allow for evaluation of the Projectaffected reaches. The IHA program analyzes the noted metrics using the Range of Variability
Approach (RVA). This analysis determines the statistical variation of each of the 32 metrics in
the pre-development condition. The model then computes the expected frequency values by
4
Bucks Creek Hydroelectric Project, FERC Project No. 619
©2014, Pacific Gas and Electric Company and the City of Santa Clara
Bucks Creek Hydroelectric Project, FERC Project No. 619
Proposed Study Plan
WR-S3
percentile categories for both the pre- and post-development. The IHA factor ((observed
frequency-expected frequency)/expected frequency) is then computed. The analysis assumes that
the two values should be approximately equal.
Annual and monthly flow duration curves of regulated and unimpaired flows will also be
constructed for the Milk Ranch, Bucks, and Grizzly creek watersheds. Flood frequency statistics
will be reviewed and summarized. Sources for flood information could include probable
maximum flood studies and/or studies by federal agencies such as the U.S. Army Corps of
Engineers and USGS.
CONSISTENCY WITH GENERALLY ACCEPTED SCIENTIFIC PRACTICE
The methods used for development of the regulated and unimpaired hydrology database are
widely used for this purpose and accepted in the scientific and engineering communities. For the
IHA evaluation the Licensees’ existing study (PG&E 2003) utilized approaches still in common
practice today. The most recent IHA program (version 7; 2005) has added more metrics and
groupings, but retains the ones evaluated in the PG&E study and both follow Richter et al. (1996,
1997, and 1998).
PRODUCTS
Study products will include a presentation to resource agency personnel and other interested
parties. Study results will be provided to the Relicensing Participants as soon as possible after the
data are collected, tabulated, summarized and checked for quality (i.e., Quality Assurance/Quality
Control); this is anticipated to be in the second quarter of 2016. The Licensees intend to have study
results, to the degree complete, available in sufficient time to allow collaborative development of
possible protection, mitigation, and enhancement (PM&E) measures for inclusion in its
Preliminary Licensing Proposal due on August 3, 2016. A summary of the information and
findings will be included in Exhibit E of the Application for New License. Data gathered as part of
the study will be also included as an appendix to the License Application.
RELATIONSHIP TO OTHER STUDIES
Information developed in this study will also be useful in understanding how Project operations
affect various Project-related resources, including Study Plan GS-S1, Erosion and
Sedimentation; Study Plan FA-S3, Benthic Macroinvertebrates; Study Plan RTE-S1, Specialstatus Amphibian and Aquatic Reptiles; and Study Plan RWL-S1, Riparian and Wetland Survey.
Data developed from this study would also be used in Study Plan WR-S4, Develop Project
Operation Model. The results of this study would allow for precise scoping of these studies.
SCHEDULE
Since the development of the regulated and unimpaired hydrological database is important for
timely considerations by other studies and is based on existing information, Licensees will
commence this study as soon as possible after its review and discussion among resource agencies
and other interested parties. It is anticipated that the hydrological database will be developed by
fall 2014.
5
Bucks Creek Hydroelectric Project, FERC Project No. 619
©2014, Pacific Gas and Electric Company and the City of Santa Clara
WR-S3
Bucks Creek Hydroelectric Project, FERC Project No. 619
Proposed Study Plan
LEVEL OF EFFORT AND COST
The preliminary estimated cost for the study, broken down by major tasks, is as follows:
Office Work ......................................................$ 47,000
Geomorphic Interpretation ................................$ 40,000
Analysis.............................................................$ 13,000
Products.............................................................$ 25,000
Total (2014 dollars) .........................................$ 125,000
REFERENCES
PNF (Plumas National Forest). 1988. Plumas National Forest land and resource management
plan. Department of Agriculture, Quincy, California. August 26, 1988. Available at:
http://www.fs.usda.gov/land/plumas/landmanagement.
Richter, B.D., J.V. Baumgartner, D.P. Braun, and J. Powell, and D.P. Braun. 1996. A method for
assessing hydrologic alteration within ecosystems. Conservation Biology 10:11631174.
Richter, B.D., J.V. Baumgartner, D.P. Braun, and J. Powell. 1998. A spatial assessment of
hydrologic alterations within a river network. Regulated Rivers: Research &
Management 14:329-340.
Richter, B.D., J.V. Baumgartner, D.P. Braun, and R. Wiginton, and D.P. Braun. 1997. How
much water does a river need? Freshwater Biology 37:231-349.
TNC (The Nature Conservancy), Totten Software Design, and Smythe Scientific Software. 2006.
Indicators of hydrologic alteration version 7 users manual. The Nature Conservancy.
July 2006.
6
Bucks Creek Hydroelectric Project, FERC Project No. 619
©2014, Pacific Gas and Electric Company and the City of Santa Clara