Canadian Dam Association Bulletin - Spring 2018 - 13

portions of un-reinforced concrete
tunnel liner in the present design
raised concerns associated with a
translating hydraulic jump dissipating a large amount of energy. These
concerns made apparent the need to
explore alternate arrangements for
restricting downstream releases during the first stage of reservoir filling
up to a reservoir elevation of 440 m.
The second stage of reservoir filling from elevation 440 m to 461.8 m
will utilize the spillway to release
minimum downstream flows. This
paper provides an overview of the
alternatives that were examined
during the definition design phase
and presents the final layout selected
for construction.

2. DESIGN CRITERIA
The following is a summary of
the key requirements, relevant data
and design criteria for the reservoir
filling design:

* The north bank diversion tunnels
must release minimum downstream
flows during the first stage of reservoir filling from an initial reservoir
elevation of approximately 415 m up
to 440 m.
* The spillway will provide downstream flow releases during the
second stage of reservoir filling
from elevation 440 m up to the maximum normal reservoir elevation of
461.8 m.
* Mean annual inflow to Site C is
1,325 m3/s, with mean monthly
inflows varying between 1,060 m3/s
and 1,600 m3/s.
* The minimum discharge from Site C
(including during reservoir filling)
is 390 m3/s for downstream environmental requirements.
* The discharge capacity of the
diversion tunnels during the
diversion period varies from
approximately 400 m3/s (200 m3/s
per tunnel) at minimum headpond

level during construction up to
3,000 m3/s (1,500 m3/s per tunnel)
at the design flood headpond level
of elevation 430 m.
* The reservoir filling rate should
stay within ranges experienced on
other precedent projects including successful BC Hydro facilities.
Reservoir filling rate was considered
more important during the second
stage of reservoir filling above elevation 440 m when greater control
of the filling rate is possible using
the spillway gates.
Seven key criteria were established
as a basis for initial screening of
alternatives and for comparison of
the preferred alternatives. These criteria are summarized in Table 1. In
addition to the criteria below, construction cost and schedule were
secondary considerations that were
included in the evaluation process
at the stage of shortlisting preferred alternatives.

Table 1 - Key Evaluation Criteria
Criteria Name

Description

1. Translating
Hydraulic Jump

The selected design shall not have a hydraulic jump that travels uncontrolled down
the tunnel. If a hydraulic jump is required to dissipate the energy, it must be contained
to a specified location that can be locally strengthened with reinforced concrete
and/or Steel liner.

2. Control Gate
Vibration

The selected design shall not create extreme turbulence or flow velocities which could
cause damaging vibration of the regulating gates in the tunnel inlet.

3. Impact on
The selected design shall not impact the normal diversion operation to an extent that either
Diversion Head Loss the tunnel diameter must be made larger or the cofferdam crest elevation must be raised
due to increased diversion head losses.
4. Constraints
on Upstream
Hydro Plants

The selected design shall not require excessive constraints on the operation of the Peace
Canyon and G.M. Shrum Generating Stations (some short duration constraints may be
permissible during tunnel opening and closing operations).

5. Geotechnical Risk

The selected design shall not significantly increase the pressure inside the tunnel, or the
external pressures on the lining, above levels that will be experienced during diversion;
or subject the tunnel lining to negative pressures or otherwise negatively impact the
geotechnical risk. This was especially important on the downstream end of the diversion
tunnels due to the potential for pressurisation of the rock.

6. Sensitivity

The hydraulics of the selected design shall not be sensitive to parameters that will not be
known with certainty prior to initial operation (e.g. tailwater level, discharge/gate opening
relationship, tunnel hydraulic losses).

7. Total Dissolved
Gas (TDG)

The selected design shall not increase long term total dissolved gas (TDG) levels above
those considered acceptable by fisheries and environmental standards.

Canadian Dam Association * Spring 2018

13



Table of Contents for the Digital Edition of Canadian Dam Association Bulletin - Spring 2018

Board of Directors
President’s Message
Site C Clean Energy Project Diversion Tunnel Orifices for Energy Dissipation During Reservoir Filling
Application for 2018 CDA Scholarships
CDA Presents 2017 Scholarships
ICOLD Corner
CDA Conference 2018
EIC Awards Gala
Buyers’ Guide and Trade List
Canadian Dam Association Bulletin - Spring 2018 - 1
Canadian Dam Association Bulletin - Spring 2018 - cover1
Canadian Dam Association Bulletin - Spring 2018 - cover2
Canadian Dam Association Bulletin - Spring 2018 - 3
Canadian Dam Association Bulletin - Spring 2018 - 4
Canadian Dam Association Bulletin - Spring 2018 - 5
Canadian Dam Association Bulletin - Spring 2018 - 6
Canadian Dam Association Bulletin - Spring 2018 - Board of Directors
Canadian Dam Association Bulletin - Spring 2018 - President’s Message
Canadian Dam Association Bulletin - Spring 2018 - 9
Canadian Dam Association Bulletin - Spring 2018 - Site C Clean Energy Project Diversion Tunnel Orifices for Energy Dissipation During Reservoir Filling
Canadian Dam Association Bulletin - Spring 2018 - 11
Canadian Dam Association Bulletin - Spring 2018 - 12
Canadian Dam Association Bulletin - Spring 2018 - 13
Canadian Dam Association Bulletin - Spring 2018 - 14
Canadian Dam Association Bulletin - Spring 2018 - 15
Canadian Dam Association Bulletin - Spring 2018 - 16
Canadian Dam Association Bulletin - Spring 2018 - 17
Canadian Dam Association Bulletin - Spring 2018 - 18
Canadian Dam Association Bulletin - Spring 2018 - 19
Canadian Dam Association Bulletin - Spring 2018 - 20
Canadian Dam Association Bulletin - Spring 2018 - 21
Canadian Dam Association Bulletin - Spring 2018 - 22
Canadian Dam Association Bulletin - Spring 2018 - 23
Canadian Dam Association Bulletin - Spring 2018 - 24
Canadian Dam Association Bulletin - Spring 2018 - 25
Canadian Dam Association Bulletin - Spring 2018 - Application for 2018 CDA Scholarships
Canadian Dam Association Bulletin - Spring 2018 - 27
Canadian Dam Association Bulletin - Spring 2018 - CDA Presents 2017 Scholarships
Canadian Dam Association Bulletin - Spring 2018 - 29
Canadian Dam Association Bulletin - Spring 2018 - ICOLD Corner
Canadian Dam Association Bulletin - Spring 2018 - 31
Canadian Dam Association Bulletin - Spring 2018 - CDA Conference 2018
Canadian Dam Association Bulletin - Spring 2018 - 33
Canadian Dam Association Bulletin - Spring 2018 - EIC Awards Gala
Canadian Dam Association Bulletin - Spring 2018 - 35
Canadian Dam Association Bulletin - Spring 2018 - 36
Canadian Dam Association Bulletin - Spring 2018 - 37
Canadian Dam Association Bulletin - Spring 2018 - Buyers’ Guide and Trade List
Canadian Dam Association Bulletin - Spring 2018 - cover3
Canadian Dam Association Bulletin - Spring 2018 - cover4
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