Canadian Dam Association Bulletin - Summer 2017 - 29

developed is presented in Figure 5,
alongside the interpolated maximum
water level at the dam during Igor.
Routing of the flood hydrographs
is performed with the following
conditions.
* Initial reservoir level at 26.27 m (FSL)
* Spillway with crest level at 26.27 m
and length = 52 m
* Dam as broad crested weir with crest
at 27.77 m and length = 48 m
During Hurricane Igor, the reservoir registered a pool level of
28.23 m, a surcharge of about two
metres (approximately 0.46 m above
the current dam crest) with a total outflow estimated at 284 m3/s which is
approximately 1.7 x Q1,000.
3.2 Hurricane Igor
Flow at Port Union
Simulation of the flood event (Igor)
at Port Union used HEC-HMS to set
up a rainfall - runoff model. There are
some limitations to the model, including a lack of observed hydrometric
and rainfall data in the watershed that
limit model calibration potential and
subsequent validation.
During Hurricane Igor, the nearest
rainfall gauging station at Bonavista
overflowed and the results are considered unreliable. To complete the
model, rainfall from St. Lawrence
climate station is substituted for the
Hyetograph. A temporal distribution
of rainfall on an hourly basis is established based on the pattern of the
storm rain distributions developed
for Canadian East Coast storms (Watt
et al 1989). The resulting approximate
rainfall hyetograph in Bonavista from
Hurricane Igor is presented in Figure 6.
The combined drainage area of the
Halfway Pond sub-basin (63 km2) and
Wells Pond sub-basin (11 km2) at Long
Pond dam constitutes the major part
and is approximately 94% of the total
drainage area (79 km2). The remaining
sub-basins are Whirl Pond sub-basin
(2.7 km2) and Second Pond sub-basin
(2.3 km2) at the system outlet.
Abstractions from rainfall are modeled using the Soil Conservation
Service (SCS) curve number procedure (SCS 1972). The hurricane was
not preceded by an extended period
of rain so CN values corresponding
Canadian Dam Association * Summer 2017

to normal antecedent moisture condition II (AMC-II) are used in the model.
Appropriate CN values are selected
from tables developed by the SCS
which depend on soil type and land
use.
The transformation of rainfall to
runoff is modeled using a SCS dimensionless unit hydrograph method. This
method has only one parameter, lag
time. The parameter was estimated for
each sub-watershed using the corresponding maximum flow lengths, maximum stream lengths, basin slopes
and the approximate average velocities
tables (Chow 1988) for un-concentrated
and concentrated flow conditions
in woodlands.
A flood hydrograph for each
sub-basin is simulated using the
approximate Hurricane Igor hyetograph and respective sub-basin parameters. A base flow of 0.048 m3/s/km2 of
drainage area is assumed for the region
to obtain total runoff. Peak flood
magnitudes and specific discharges
for the sub-basins are presented in
Table 5. There is a lack of observed
hydro-climatic data in the watershed

and calibration and validation of the
model was not possible at the time of
the study.
The estimated peak inflow simulated at Whirl Pond as a result of
Hurricane Igor is 220 m3/s resulting
in a specific discharge of 3.0 m3/s/km2.
Previous flood estimates for the
development (Acres 1999 and Meco
2010) estimated the 1,000 years return
period flood peak as 107 m3/s. The
recent hydraulic frequency analysis
of the WSC gauge at Southern Bay has
nearly doubled the estimated extreme
values, such that at the time of Igor,
the predicted flow was twice the predicted 1,000 year event and now the
predicted flow is approximately equal
to a 1,000 year event.

4. NEWFOUNDLAND
POWER RESPONSE
During the storm, conditions
rapidly deteriorated in the area of the
Lawn and Port Union Developments.
The Whirl Pond structure and Port
Union power house was viewed a
number of times during the event,
with photos provided in Figure 9.

Figure 6: Rainfall hyetograph - Bonavista

TABLE 5: PEAK FLOOD FLOWS AT PORT UNION
Sub-basin

Drainage
Area
(km2)

Halfway sub-basin at Long Pond

63

190.4

3.02

Wells sub-basin at Long Pond

11

46.5

4.23

Whirl sub-basin

2.7

14.4

5.33

Sub-basin at outlet

2.3

14.0

6.09

Peak Flow (m3/s)

Unit Peak
Flow
(m3/s/km2)

29



Table of Contents for the Digital Edition of Canadian Dam Association Bulletin - Summer 2017

Board of Directors
President's Message
Roller Compacted Concrete Buttress at the Site C Clean Energy Project
Hurricane Igor's Impact on Newfoundland Power's Small Hydro
CDA Conference Heads to Kelowna!
CDA Directors & Officers - Call for Nominations
2017 CDA Awards - Call for Nominations
CDA Developing New Ways to Distribute Guidelines
Notice of Annual General Meeting
Time to Renew Your Membership
Buyers' Guide and Trade List
Canadian Dam Association Bulletin - Summer 2017 - intro
Canadian Dam Association Bulletin - Summer 2017 - 1
Canadian Dam Association Bulletin - Summer 2017 - 2
Canadian Dam Association Bulletin - Summer 2017 - 3
Canadian Dam Association Bulletin - Summer 2017 - 4
Canadian Dam Association Bulletin - Summer 2017 - 5
Canadian Dam Association Bulletin - Summer 2017 - 6
Canadian Dam Association Bulletin - Summer 2017 - Board of Directors
Canadian Dam Association Bulletin - Summer 2017 - 8
Canadian Dam Association Bulletin - Summer 2017 - President's Message
Canadian Dam Association Bulletin - Summer 2017 - 10
Canadian Dam Association Bulletin - Summer 2017 - 11
Canadian Dam Association Bulletin - Summer 2017 - Roller Compacted Concrete Buttress at the Site C Clean Energy Project
Canadian Dam Association Bulletin - Summer 2017 - 13
Canadian Dam Association Bulletin - Summer 2017 - 14
Canadian Dam Association Bulletin - Summer 2017 - 15
Canadian Dam Association Bulletin - Summer 2017 - 16
Canadian Dam Association Bulletin - Summer 2017 - 17
Canadian Dam Association Bulletin - Summer 2017 - 18
Canadian Dam Association Bulletin - Summer 2017 - 19
Canadian Dam Association Bulletin - Summer 2017 - 20
Canadian Dam Association Bulletin - Summer 2017 - 21
Canadian Dam Association Bulletin - Summer 2017 - 22
Canadian Dam Association Bulletin - Summer 2017 - 23
Canadian Dam Association Bulletin - Summer 2017 - Hurricane Igor's Impact on Newfoundland Power's Small Hydro
Canadian Dam Association Bulletin - Summer 2017 - 25
Canadian Dam Association Bulletin - Summer 2017 - 26
Canadian Dam Association Bulletin - Summer 2017 - 27
Canadian Dam Association Bulletin - Summer 2017 - 28
Canadian Dam Association Bulletin - Summer 2017 - 29
Canadian Dam Association Bulletin - Summer 2017 - 30
Canadian Dam Association Bulletin - Summer 2017 - 31
Canadian Dam Association Bulletin - Summer 2017 - 32
Canadian Dam Association Bulletin - Summer 2017 - 33
Canadian Dam Association Bulletin - Summer 2017 - 34
Canadian Dam Association Bulletin - Summer 2017 - 35
Canadian Dam Association Bulletin - Summer 2017 - CDA Conference Heads to Kelowna!
Canadian Dam Association Bulletin - Summer 2017 - 37
Canadian Dam Association Bulletin - Summer 2017 - 38
Canadian Dam Association Bulletin - Summer 2017 - 39
Canadian Dam Association Bulletin - Summer 2017 - 40
Canadian Dam Association Bulletin - Summer 2017 - 41
Canadian Dam Association Bulletin - Summer 2017 - 42
Canadian Dam Association Bulletin - Summer 2017 - 43
Canadian Dam Association Bulletin - Summer 2017 - 44
Canadian Dam Association Bulletin - Summer 2017 - 45
Canadian Dam Association Bulletin - Summer 2017 - CDA Directors & Officers - Call for Nominations
Canadian Dam Association Bulletin - Summer 2017 - 47
Canadian Dam Association Bulletin - Summer 2017 - 2017 CDA Awards - Call for Nominations
Canadian Dam Association Bulletin - Summer 2017 - 49
Canadian Dam Association Bulletin - Summer 2017 - CDA Developing New Ways to Distribute Guidelines
Canadian Dam Association Bulletin - Summer 2017 - 51
Canadian Dam Association Bulletin - Summer 2017 - 52
Canadian Dam Association Bulletin - Summer 2017 - Notice of Annual General Meeting
Canadian Dam Association Bulletin - Summer 2017 - Time to Renew Your Membership
Canadian Dam Association Bulletin - Summer 2017 - Buyers' Guide and Trade List
Canadian Dam Association Bulletin - Summer 2017 - 56
Canadian Dam Association Bulletin - Summer 2017 - 57
Canadian Dam Association Bulletin - Summer 2017 - 58
Canadian Dam Association Bulletin - Summer 2017 - 59
Canadian Dam Association Bulletin - Summer 2017 - 60
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