Canadian Dam Association Bulletin - Winter 2018 - 12

1. GENERAL
Applied Weather Associates (AWA)
has completed a Probable Maximum
Precipitation (PMP) study for the Elbow
River Basin-Springbank Off-Stream
Storage Project (Springbank) located
near Calgary, Alberta. The purpose of
the study was to determine PMP values
specific to the watershed, taking into
account topography, climate, and storm
types that affect the region.
The approach used in this study
was consistent with those used in
numerous PMP studies AWA has completed, including several in similar
meteorological and topographical settings. Recommendations provided in
"Guidelines of Extreme Flood Analysis"
(Alberta Transportation, 2004) were
addressed. AWA employed a stormbased approach similar to the methods and processes employed by the
National Weather Service (NWS) and
recommended by the Canadian Dam
Association to the extent that the data
and current understanding of meteorological processes supports those previous methods. The World Meteorological
Organization (WMO) manual for PMP
determination recommends this stormbased approach when sufficient data
are available. This approach identified extreme rainfall events that have
occurred over a wide region from the
Continental Divide of the Rockies eastward to the High Plains, from northern
Alberta through the northern United
States. Storms in these regions have
meteorological and topographical characteristics similar to extreme rainfall
storms that could occur over the basin.
The largest of these rainfall events were
selected for detailed analyses and
PMP development.
Twenty-one storm events were identified as having similar characteristics
to PMP-type events that could potentially occur over the basin and could
potentially influence the PMP values.
Storms were categorized as either general storms (greater than 6-hours and
greater than 500-square kilometres)
or local storms (6- hours or less and
less than 500-square kilometres). PMP
values were derived separately according to each storm type. Each storm
was analyzed by AWA for this study
12

using the Storm Precipitation Analysis
System (SPAS). Some storms had more
than one Depth-Area-Duration (DAD)
zone analyzed by SPAS. A total of 22
unique DAD zones were used in the
final PMP development for this study.
The general concepts employed to
derive the PMP values included rainfall
maximization, storm transposition, and
topographic adjustments. These PMP
development processes were consistent
with those used in the numerous PMP
studies completed by AWA in regions
that were similar to this basin. New
techniques and databases were used
in the study to increase accuracy and
reliability, while adhering to the basic
approach used in the HMRs and in
the WMO Manual for PMP. Updated
analysis methodologies were utilized
in this study. The first analysis method
used was the Orographic Transposition
Factor (OTF), which objectively quantifies the effects of terrain on rainfall
enhancement and depletion. This process replaces the NWS Storm Separation
Method as employed in HMR 55A. Use
of the OTF allows the unique and highly
variable topography at both the in-place
storm location and the Springbank
basin to be properly represented in
the development of PMP values and
subsequent Probable Maximum Flood
(PMF) modeling. The second analysis
method used was the HYSPLIT trajectory model, which evaluates the location of moisture source regions over
the Pacific Ocean. These regions were
identified using a National Oceanic and
Atmospheric Administration (NOAA)
model reanalysis interface. Updated
climatological maximum dew point
data were developed for the regions of
Canada that were analyzed for in-place
storm maximization and used in
this study.
Storm maximization factors were
computed for each storm using an
updated dew point climatology,
HYSPLIT, and an updated evaluation of
the storm representative dew point for
each storm event. Each historic extreme
rainfall event used for PMP development was maximized, transpositioned,
and orographically adjusted to a series
of grid cells covering the entire basin.
The procedure used methods consistent

with HMR 55A and previous AWA PMP
studies modified to work on a gridded
basis. The governing equation used
for computation of the Total Adjusted
Rainfall (TAR) is shown in Equation 1.
The PMP becomes the maximum TAR
for all analyzed storms at each grid cell
at each duration.
TARxhr = Pxhr * IPMF * MTF * OTF (1)
where:
TAR xhr is the Total Adjusted Rainfall
value at the x-hour duration for the
specific grid cell at each duration at
the target location;
P xhr is the x-hour precipitation
observed at the historic in-place storm
location (source location) at the basinarea size;
In-Place Maximization Factor (IPMF)
is the adjustment factor representing
the maximum amount of atmospheric
moisture that could have been available
to the storm for rainfall production;
Moisture Transposition Factor (MTF)
is the adjustment factor accounting for
the difference in available moisture
between the location where the storm
occurred and each grid cell in the basin;
Orographic Transposition Factor
(OTF) is the adjustment factor accounting for differences between orographic
effects at the historic in-place storm
location and the Springbank basin.
A total of 318 grid cells, at a resolution of .025° decimal degrees x .025°
decimal degrees (4.92-square kilometres), were analyzed over the basin.
The resulting values were analyzed
over a total of 48-hours and provided
by sub-basin averages for the 11 subbasins above Glenmore Dam for use
in PMF modeling. Use of the 48-hour
maximum duration was chosen based
on the rainfall accumulation period
of the storms used for PMP development, prior use as a standard duration
in previous PMP studies in the region,
and discussions with the review board
regarding requirements for proper
Probable Maximum Flood modeling.
These data were distributed spatially
using both the precipitation climatology developed for this study and historic rainfall events, which occurred
over the basin. The temporal distribution of the hourly PMP were accumulated following standard PMP patterns,

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

BOARD OF DIRECTORS
PRESIDENT’S MESSAGE
UPDATING PMP FOR THE ELBOW RIVER: COMPLEX TERRAIN, UNIQUE SOLUTIONS
KELOWNA 2017
CDA AWARDS
ANNUAL GENERAL MEETING 2017
YOUNG PROFESSIONALS UPDATE
DAMS AND DIKES, WIKI STYLE
2017 FINANCE REPORT
CDA 2018 CONFERENCE: THE MANAGEMENT OF AGING DAMS
CDA NEWS BRIEF
BUYERS’ GUIDE AND TRADE LIST
Canadian Dam Association Bulletin - Winter 2018 - Intro
Canadian Dam Association Bulletin - Winter 2018 - cover1
Canadian Dam Association Bulletin - Winter 2018 - cover2
Canadian Dam Association Bulletin - Winter 2018 - 3
Canadian Dam Association Bulletin - Winter 2018 - 4
Canadian Dam Association Bulletin - Winter 2018 - 5
Canadian Dam Association Bulletin - Winter 2018 - 6
Canadian Dam Association Bulletin - Winter 2018 - BOARD OF DIRECTORS
Canadian Dam Association Bulletin - Winter 2018 - PRESIDENT’S MESSAGE
Canadian Dam Association Bulletin - Winter 2018 - 9
Canadian Dam Association Bulletin - Winter 2018 - UPDATING PMP FOR THE ELBOW RIVER: COMPLEX TERRAIN, UNIQUE SOLUTIONS
Canadian Dam Association Bulletin - Winter 2018 - 11
Canadian Dam Association Bulletin - Winter 2018 - 12
Canadian Dam Association Bulletin - Winter 2018 - 13
Canadian Dam Association Bulletin - Winter 2018 - 14
Canadian Dam Association Bulletin - Winter 2018 - 15
Canadian Dam Association Bulletin - Winter 2018 - 16
Canadian Dam Association Bulletin - Winter 2018 - 17
Canadian Dam Association Bulletin - Winter 2018 - 18
Canadian Dam Association Bulletin - Winter 2018 - 19
Canadian Dam Association Bulletin - Winter 2018 - 20
Canadian Dam Association Bulletin - Winter 2018 - 21
Canadian Dam Association Bulletin - Winter 2018 - 22
Canadian Dam Association Bulletin - Winter 2018 - 23
Canadian Dam Association Bulletin - Winter 2018 - 24
Canadian Dam Association Bulletin - Winter 2018 - 25
Canadian Dam Association Bulletin - Winter 2018 - KELOWNA 2017
Canadian Dam Association Bulletin - Winter 2018 - 27
Canadian Dam Association Bulletin - Winter 2018 - CDA AWARDS
Canadian Dam Association Bulletin - Winter 2018 - 29
Canadian Dam Association Bulletin - Winter 2018 - ANNUAL GENERAL MEETING 2017
Canadian Dam Association Bulletin - Winter 2018 - 31
Canadian Dam Association Bulletin - Winter 2018 - YOUNG PROFESSIONALS UPDATE
Canadian Dam Association Bulletin - Winter 2018 - 33
Canadian Dam Association Bulletin - Winter 2018 - DAMS AND DIKES, WIKI STYLE
Canadian Dam Association Bulletin - Winter 2018 - 35
Canadian Dam Association Bulletin - Winter 2018 - 2017 FINANCE REPORT
Canadian Dam Association Bulletin - Winter 2018 - 37
Canadian Dam Association Bulletin - Winter 2018 - 38
Canadian Dam Association Bulletin - Winter 2018 - 39
Canadian Dam Association Bulletin - Winter 2018 - CDA 2018 CONFERENCE: THE MANAGEMENT OF AGING DAMS
Canadian Dam Association Bulletin - Winter 2018 - 41
Canadian Dam Association Bulletin - Winter 2018 - CDA NEWS BRIEF
Canadian Dam Association Bulletin - Winter 2018 - 43
Canadian Dam Association Bulletin - Winter 2018 - 44
Canadian Dam Association Bulletin - Winter 2018 - BUYERS’ GUIDE AND TRADE LIST
Canadian Dam Association Bulletin - Winter 2018 - 46
Canadian Dam Association Bulletin - Winter 2018 - cover3
Canadian Dam Association Bulletin - Winter 2018 - cover4
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