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PMP/PMF – Stochastic Flood Analysis
Comparison of Methodologies
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Dis
char
ge (c
fs)
Elapsed Time (Hours)
Applegate Dam and Reservoir
Outflow Flood
Inflow Flood
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490R
ESER
VOIR
STA
GE
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t)
ANNUAL EXCEEDANCE PROBABILITY
Extreme Value Type 1 Plotting Paper
Top of Flood Control Pool
1997 Flood
1986 Flood
10-410-2 10-3 10-610-50.5 10-1
Western Hydropower Dam Owners
Workshop July, 2011
Deterministic PMF…
A single flood hydrograph is developed
for assessing the hydrologic and hydraulic adequacy
of a dam and reservoir project
PMF Inflow
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0 24 48 72 96 120 144 168
Dis
char
ge (c
fs)
Elapsed Time (Hours)
Applegate Dam and Reservoir
Outflow Flood
Inflow Flood PMF Sensitivity Analyses
sometimes used
to further assess
project adequacy
Stochastic Flood Analysis…
Multi-thousand flood hydrographs computed to develop
flood-frequency relationships for peak inflow, runoff volume,
maximum reservoir level and maximum spillway releases
based on diversity of storms/floods representative of basin
Robust examination
of reservoir response
to wide range of
flood characteristics 400
410
420
430
440
450
460
470
480
490R
ESER
VOIR
STA
GE
(Fee
t)
ANNUAL EXCEEDANCE PROBABILITY
Extreme Value Type 1 Plotting Paper
Top of Flood Control Pool
1997 Flood
1986 Flood
10-410-2 10-3 10-610-50.5 10-1
Hydrologic Hazard Curve for Max Reservoir Level is Primary Deliverable
Stochastic Flood Analysis… Flood-frequency relationships developed
for any flood characteristics of interest
using flood hydrographs generated from stochastic simulations
Other flood-frequency characteristics can be computed such as:
duration of spillway operation or dam overtopping at certain thresholds
Compare Storm Magnitudes …
PMP can be viewed
as one extreme
storm among
a range of extreme
storms
PMP/PMF Stochastic Flood Analysis
72-Hour PMP
Full Range of Storm Magnitudes Basin-Average 72-hr
Precipitation-Frequency Curve
Compare Storm Seasonality …
PMP/PMF Stochastic Flood Analysis
Month yielding largest flood from PMP
Storm/Flood Dates for full range observed in historical record
American River Watershed
9.0
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NON-EXCEEDANCE PROBABILITY
NU
ME
RIC
AL S
TO
RM
DAT
E
.5 .98.7 .9 .999.99.95
Normal Plotting Paper
.02 .05 .8.6.4.2.1 .3.001 .01
Normal Distribution
72-Hour Extreme Storms
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SEP OCT NOV DEC JAN FEB MAR APR MAY JUN JUL AUG
FREQ
UEN
CY
MONTH
WEST FACE SIERRA MOUNTAINS
Storms exceeding 10-year event
40 Storms 72 Hour Duration
Historical Storms
Normal Distribution
Compare Storm Temporal Patterns …
Suite of Historical Storms (Commonly 12-24 storms)
Each prototype storm has separate temporal pattern
PMP/PMF Stochastic Flood Analysis 1 Synthetic
temporal pattern Suite of temporal patterns based on historical storms