Canadian Dam Association Bulletin - Summer 2018 - 21

5.2 Statistical Methods
The Hershfield (1961) method is
likely the most common method of estimating PMP using a statistical analysis
approach in Canada. The method is
based on conducting a frequency analysis of the annual maximum rainfall
recorded at a meteorological station
by summing the mean value of maximum rainfall and the standard deviation multiplied by a frequency factor.
Hogg and Carr (1985) present a statistical method of estimating PMP using
a regression equation with isopluvial
maps of 24 hour mean annual extreme
rainfall and standard deviation.

6. SINGLE STATION
AND REGIONAL
FREQUENCY ANALYSIS
CDA (2007) provides engineers and
owners with guidance on good practice for estimating large inflows to
reservoirs and discusses that several
methods should be used to estimate
a reasonable IDF. One of these methods is hydrologic frequency analysis.
Frequency analysis is primarily used
for estimating the magnitude of precipitation or floods of various return
periods based on observed historical
data. Several publications are available
that discuss the use of single station
and regional flood frequency analysis.
Watt et al. (1989) present methodologies and discussions related to the
Canadian Dam Association * Summer 2018

statistical frequency analysis of hydrologic data using single station analysis, regional flood frequency analysis,
and a combination of single site and
regional data. The report discusses the
limitations of statistical analysis and
references a paper by Klemes (1986) that
indicates "a certain degree of scepticism
about the results of elaborate statistical
procedures is warranted." Figure 1 was
taken from Watt et al. (1989) and presents guidance on determining how
many years of single station data are
required for a design interval and
when should a regional analysis be
conducted. The guidance in Figure 1 is
with respect to the stream that the flow
data was measured on. For example,
Figure 1 indicates a design return period of 100 years requires approximately
25 years of data collected on the stream
where the design will be utilized. If less
than 25 years of streamflow data are
available, a regional analysis should
also be completed.
Watt et al. (1989) provide statistical
criteria and tests to be completed on
the hydrologic dataset to determine
if the data is suitable for frequency
analysis. The criterion include randomness, independence, stationarity,

and homogeneity. Of the frequency
analysis studies assessed by the
author in BC and YT, it is rare for the
hydrologist completing the analysis
to mention the above stated criterion. It rather appears the assumption is made, out of practicality, that
the annual time series of maximum
streamflow or daily rainfall data are
random, independent, stationary
and homogeneous. If these criterion
have not been assessed, questions
regarding the suitability of the IDF
estimate are raised. From a practical view, the hydrologist may need
to accept the data for analysis and
convey the uncertainty explaining
if the dataset did not meet any of the
statistical criteria. Cannon (2014) in
a study of annual maximum rainfall
in southern BC, completed all analysis with the assumption the data
series was stationary but indicated
that there is evidence of historical
trends in some daily rainfall maxima
and that there is a need to incorporate non-stationarity in regional frequency analysis.
CDA (2013) provides the following
guidance regarding statistical flood
analysis:

1000

Zone B

DESIGN RETURN PERIOD, Td (years)

5.1 Meteorological Analyses
The method of estimating the probable maximum precipitation utilizing
historical storms as described in WMO
(2009) is:
* Identification of regional historical storms that are relevant to the
catchment area of interest.
* Maximization of the storms.
* Transposition of the storms to the
catchment of interest.
Micovic et al. (2015) list several variables that influence PMP and discuss
that it cannot be calculated directly
but rather must be estimated using a
number of steps which require subjective judgement and describe four
types of meteorological PMP estimation methods.

100

Td = 4N

Zone C

Zone
A

10
N = 10

Zone A: use regional analysis alone
Zone B: use combination of single station
and regionl analysis
Zone C: use single station analysis alone

1

0

10

20

30

40

50

60

70

PERIOD OF RECORD, N (years)
Figure 1: Empirical guidance for reliance on single station and/or regional estimates
of design flood. Taken from page 47 of Watt et al. (1989).
21



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

Board of Directors
President’s Message
Inflow Design Flood Estimation for Reservoirs in British Columbia and Yukon Territory
ICOLD 2018: Canadian Expertise on the World Stage
ICOLD Corner
CDA Will Be Meeting in Quebec City!
CDA Directors & Officers – Call for Nominations
2018 CDA Awards – Call for Nominations
Notice of Annual General Meeting
Time to Renew Your Membership
Clean Energy B.C.'s Operational Excellence Award for Corra Linn Dam
Buyers’ Guide and Trade List
Canadian Dam Association Bulletin - Summer 2018 - Intro
Canadian Dam Association Bulletin - Summer 2018 - cover1
Canadian Dam Association Bulletin - Summer 2018 - cover2
Canadian Dam Association Bulletin - Summer 2018 - 3
Canadian Dam Association Bulletin - Summer 2018 - 4
Canadian Dam Association Bulletin - Summer 2018 - 5
Canadian Dam Association Bulletin - Summer 2018 - 6
Canadian Dam Association Bulletin - Summer 2018 - Board of Directors
Canadian Dam Association Bulletin - Summer 2018 - President’s Message
Canadian Dam Association Bulletin - Summer 2018 - 9
Canadian Dam Association Bulletin - Summer 2018 - Inflow Design Flood Estimation for Reservoirs in British Columbia and Yukon Territory
Canadian Dam Association Bulletin - Summer 2018 - 11
Canadian Dam Association Bulletin - Summer 2018 - 12
Canadian Dam Association Bulletin - Summer 2018 - 13
Canadian Dam Association Bulletin - Summer 2018 - 14
Canadian Dam Association Bulletin - Summer 2018 - 15
Canadian Dam Association Bulletin - Summer 2018 - 16
Canadian Dam Association Bulletin - Summer 2018 - 17
Canadian Dam Association Bulletin - Summer 2018 - 18
Canadian Dam Association Bulletin - Summer 2018 - 19
Canadian Dam Association Bulletin - Summer 2018 - 20
Canadian Dam Association Bulletin - Summer 2018 - 21
Canadian Dam Association Bulletin - Summer 2018 - 22
Canadian Dam Association Bulletin - Summer 2018 - 23
Canadian Dam Association Bulletin - Summer 2018 - 24
Canadian Dam Association Bulletin - Summer 2018 - 25
Canadian Dam Association Bulletin - Summer 2018 - 26
Canadian Dam Association Bulletin - Summer 2018 - 27
Canadian Dam Association Bulletin - Summer 2018 - ICOLD 2018: Canadian Expertise on the World Stage
Canadian Dam Association Bulletin - Summer 2018 - ICOLD Corner
Canadian Dam Association Bulletin - Summer 2018 - CDA Will Be Meeting in Quebec City!
Canadian Dam Association Bulletin - Summer 2018 - 31
Canadian Dam Association Bulletin - Summer 2018 - 32
Canadian Dam Association Bulletin - Summer 2018 - 33
Canadian Dam Association Bulletin - Summer 2018 - CDA Directors & Officers – Call for Nominations
Canadian Dam Association Bulletin - Summer 2018 - 2018 CDA Awards – Call for Nominations
Canadian Dam Association Bulletin - Summer 2018 - Notice of Annual General Meeting
Canadian Dam Association Bulletin - Summer 2018 - Time to Renew Your Membership
Canadian Dam Association Bulletin - Summer 2018 - 38
Canadian Dam Association Bulletin - Summer 2018 - Clean Energy B.C.'s Operational Excellence Award for Corra Linn Dam
Canadian Dam Association Bulletin - Summer 2018 - 40
Canadian Dam Association Bulletin - Summer 2018 - Buyers’ Guide and Trade List
Canadian Dam Association Bulletin - Summer 2018 - 42
Canadian Dam Association Bulletin - Summer 2018 - cover3
Canadian Dam Association Bulletin - Summer 2018 - cover4
Canadian Dam Association Bulletin - Summer 2018 - outsert1
Canadian Dam Association Bulletin - Summer 2018 - outsert2
Canadian Dam Association Bulletin - Summer 2018 - outsert3
Canadian Dam Association Bulletin - Summer 2018 - outsert4
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