BAKER RIVER PROJECT – FERC 2150

Stochastic PMP/ PMF/ IDF Experience & Thoughts

NHA Hot Topics SessionApril 27, 2010

Lloyd Pernela, Manager Dam Safety and Water Resources

Puget Sound Energy

The take away from this presentation:

“How often would that there PMF happen?”

And “is that a reasonable criteria?”

UPPER BAKER DAM

Gravity Dam:On-line in 1959 312’ High 1,200’ Long103 MW Output

Reservoir: 9-Miles, 215 Square Mile Drainage Basin; 184,796 Acre-feet; 4,985 Acres Coverage, Elevation 724-feet.

Mt Baker to West 10, 878 ft, Mt Shuksan to North is 9,131-feet.

[118,640 cfs PMF inflow 1969]

LOWER BAKER DAM Gravity Arch: On-line 1927285’ High 550’ Long80 MW Output

Reservoir:7 miles long82 Square Miles Drainage Area2,278 Acre Surface146,279 Acre-feet

438.6’ Full Pool Elevation

[108,250 cfs PMF inflow, 1969

DEPRESSION LAKE (“pumping pond”)

WEST PASS DIKEDEPRESSION LAKE DIKE

TWO EARTHEN DIKES

West Pass Dike: ‘wing dam’, 64 Feet High, 1200 Feet long;

Depression Lake Dam: 22 Feet High 3000 Feet long.

Depression Lake: 200 Acre Ft.

As FERC licensees we are being asked to determine our Probable Maximum Flood for our projects

(FERC Guidelines Chapter 8 affirmed 2001)

Typical mandate is to use the latest hydrometeorlogical precipitation report These reports are by region and numbered, e.g. HMR 57 and

published by the National Weather Service.

The deterministic FERC Chapter 8 guidelines coupled with latest HMR’s,may result in higher flows than a project design - requiring capital investment.

With current databases, GIS geographic information systems, new computer technology and modeling capabilities,

we are now able to investigate the probabilities or likelihood of an event.We can now ask what is the annual exceedance probability

of a prescriptive PMF and other flows.

HMR 57 (1994) SUPPLEMENTS HMR 43 (1966)

Deterministic PMF Study

• PSE was required to update the Baker PMF from HMR 43 (1966) to HMR-57 (1994)

17.7"

14.0"

9.9"

0

2

4

6

8

10

12

14

16

18

20

100-Year HMR-43 PMP HMR-57 PMP

24-H

r D

ura

tio

n P

reci

pit

atio

n D

epth

(in

ches

)

26% Increase at Baker Project

Consultants

• TetraTech, Inc.• MGS Engineering Consultants• Applied Weather Associates, Inc

Baker Project Modeling

West Pass Dike

Baker River

Depression Lake Dike

Sulphur Creek

Upper Baker Dam

Lake Shannon

Depression Lake

Baker Lake

Lower Baker Dam

Skagit River

Concrete

Baker River

Overland or Channel Flow

Earthen Dike

Concrete Dam

LEGEND

Distributed Hydrologic Modeling Approach

• Precipitation : rain, snow, glaciation, snow-water.

•Soils, surface & bedrock 70% is evergreen forest

• Elevation Zones Mt. Baker is at 10,778 feet.

•Over 5000 zones.

At Mt. Baker, the temperature decreases approximately 3° F with each 1,000 feetincrease in elevation.

Baker Basin

Watershed CharacterizationZones of Mean Annual Precipitation

MGS Engineering

Watershed CharacterizationSoil Zones

MGS Engineering

PMF Deterministic Hydrograph Modeling

Input ParametersSeasonality All months/seasonsStorm Centering Three scenariosStorm Temporal Pattern Three patternsAntecedent Precipitation Average cumulative end of month

value for each monthAntecedent Snow Water Equivalent Iteratively determine return period

resulting in maximum runoff volumeAntecedent Snowpack Density Average end of monthAntecedent UB Reservoir Elevation ACOE flood control rule curve UBKAntecedent LB Reservoir Elevation Normal poolBasin In-Flow Average monthly flowAir Temperature HMR-57 methodologyWind Speed HMR-57 methodology

Model Development

Flow Diagram of Hydrograph Models Used. HEC-5 was used for routing the runoffs through the project.

SPAS HEC-1 SEFM

HFAM

Snowcourse Data

SNOTEL Data

PRISM Mapping

NEXRAD

Runoff Hydrograph

HEC-5

Hydrologic Model Calibration

November 1990 (1) Hydrographs

0

2,000

4,000

6,000

8,000

10,000

12,000

11/08 00:00 11/09 00:00 11/10 00:00 11/11 00:00 11/12 00:00 11/13 00:00 11/14 00:00

Date

Flow

(CFS

)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

11/08 00:00 11/09 00:00 11/10 00:00 11/11 00:00 11/12 00:00 11/13 00:00 11/14 00:00

Rai

nfal

l (in

)

Model Input Basin Average Precipitation in Low er Baker SubbasinsObserved Total Runoff HydrographSimulated Total Runoff Hydrograph

0

5,000

10,000

15,000

20,000

25,000

30,000

35,000

11/08 00:00 11/09 00:00 11/10 00:00 11/11 00:00 11/12 00:00 11/13 00:00 11/14 00:00

DateFl

ow (C

FS)

0.00

0.10

0.20

0.30

0.40

0.50

0.60

0.70

0.80

0.90

1.00

11/08 00:00 11/09 00:00 11/10 00:00 11/11 00:00 11/12 00:00 11/13 00:00 11/14 00:00

Rai

nfal

l (in

)

Model Input Basin Average Precipitation in Upper Baker SubbasinsSimulated Total Runoff HydrographObserved Total Runoff Hydrograph

Lower Baker Tributary Hydrograph Upper Baker Tributary Hydrograph

Upper Baker PMF HydrographsDeterministic – Pre Global Sensitivity Analysis

700

702

704

706

708

710

712

714

716

718

720

722

724

726

728

730

732

734

736

738

740

742

1/4/2006 0:00 1/5/2006 0:00 1/6/2006 0:00 1/7/2006 0:00 1/8/2006 0:00 1/9/2006 0:00 1/10/2006 0:00 1/11/2006 0:00

Date

Upp

er B

aker

Res

ervo

ir Po

ol (f

eet)

- NA

VD 8

8

0

10,000

20,000

30,000

40,000

50,000

60,000

70,000

80,000

90,000

100,000

110,000

120,000

130,000

140,000

150,000

160,000

170,000

180,000

Flow

Rat

e (c

fs)

Upper Baker Reservoir Elevation

Upper Baker Inflow

Upper Baker Outflow

Max Res. Elev. = 739.84 ft(4.07 feet of overtopping)

Table 8-10. Flood and Reservoir Response Sensitivity to Input Parameters, and Input Parameter Uncertainty

Input Parameter Flood Response

Sensitivity Reservoir Response

Sensitivity Parameter

Uncertainty Seasonality of Occurrence Moderate Moderate Low Centering of Storm Low Low Moderate Storm Temporal Pattern Moderate High Low Antecedent Precipitation Moderate Moderate Low Antecedent Snow Water Equivalent High High Moderate Antecedent Snowpack Density Low Low High Antecedent Reservoir Elevation Lower Baker n/a Low Moderate Antecedent Reservoir Elevation Upper Baker n/a Moderate Moderate

Global Sensitivity AnalysisPer FERC Guidelines.

Table 8-10. Flood and Reservoir Response Sensitivity to Input Parameters, and Input Parameter Uncertainty

Input Parameter Flood Response

Sensitivity Reservoir Response

Sensitivity Parameter

Uncertainty Seasonality of Occurrence Moderate Moderate Low Centering of Storm Low Low Moderate Storm Temporal Pattern Moderate High Low Antecedent Precipitation Moderate Moderate Low Antecedent Snow Water Equivalent High High Moderate Antecedent Snowpack Density Low Low High Antecedent Reservoir Elevation Lower Baker n/a Low Moderate Antecedent Reservoir Elevation Upper Baker n/a Moderate Moderate

PMF Hydrographs - SensitivityGlobal Sensitivity Analysis – Frequency Analysis

728729730731732733734735736737738739740741742

0 10 20 30 40 50 60 70 80 90 100

Percent Non-Exceedance Assuming Full PMP (Based on 10,000 Simulations - All Seasons)

Upp

er B

aker

Res

ervo

ir El

evat

ion

(fee

t N

AVD

88)

Initial PMF Result for Baker Project (739.84 feet ) - 99.4% NE

Final PMF Result for Baker Project (739.19 feet ) - 95.8% NE

PMF Hydrographs - Final

Scenario Peak inflow CFS

Peak outflow CFS

Max Pool Elev. NAVD 88

Depth of overtopping

Upper Baker Reservoir

2 year snow pack

157,800 111,500 739.19 3.42

Lower Baker Reservoir

2 year snow pack

136,800 120,300 458.43 13.86

Stochastic Approach …

1) Use Deterministic Rainfall-Runoff Model (HEC-1)

2) Treat Hydrometeorological Inputs as Variables

3) Stochastically Generate Multi-Thousand Years of Storms and Dates of Storm Occurrence – Use Monte Carlo techniques

4) Select Hydrometeorological Inputs to Accompany Storms and Maintain Seasonal Characteristics and Dependencies Where They Exist

5) Compute Multi-Thousand Flood Annual Maxima using Hydrologic Model and Input Datasets

6) Conduct Frequency Analysis of Model Outputs for: Flood Peak, Runoff Volume, Maximum Reservoir Level

Storm Seasonality

0.000.020.040.060.080.100.120.140.160.180.20

AUG AUG SEP SEP OCT OCT NOV NOV DEC DEC JAN JAN FEB FEB MAR MAR APR APR MAY MAY JUN JUN JUL JUL

MONTH

PRO

BA

BIL

ITY

Smoothed

• Database of 132 extreme storms (rarer than 20-yr event)• Windward Puget Sound Lowlands and West Slope of

Cascades

MGS Engineering

Uses:

• Effectiveness of current flood control rule curveMGS Engineering

Flood Frequency Curves

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

160,000

ANNUAL EXCEEDANCE PROBABILITY

MA

X 24

-HO

UR

INFL

OW

(cfs

)

Top Historical Peaks from 78Year Period of Record

Extreme Value Type 1 Plotting Paper

10-1010-9.5 10-810-610-510-410-310-210-1

Stochastic Model Results

PMF Estimate107,100 cfs

10-7

Upper Baker Project Frequency Curve

• Stochastic model verified using historical record

• Stochastic results are therefore extension of historical record

Table ES-1. Estimated Annual Exceedance Probabilities Associated with PMF Hydrograph for Upper Baker Dam

Flood Characteristic Magnitude

Annual Exceedance Probability

Peak Inflow 157,800 cfs 5.1 x 10-9

Maximum 24-Hour Inflow 107,100 cfs 7.2 x 10-8

Maximum 72-Hour Inflow 59,200 cfs 4.5 x 10-7

Maximum Reservoir Elevation 739.19 feet a 1.0 x 10-8

Notes:a.Elevation referenced to North American Vertical Datum of 1988 (NAVD 88)

Table ES-2. Estimated Annual Exceedance Probabilities Associated with PMF Hydrograph for Lower Baker Dam

Flood Characteristic Magnitude

Annual Exceedance Probability

Peak Inflow 136,800 cfs 2.8 x 10-8

Maximum 24-Hour Inflow 113,200 cfs 5.4 x 10-8

Maximum 72-Hour Inflow 67,000 cfs 9.5 x 10-7

Maximum Reservoir Elevation 458.43 feet a 5.3 x 10-8

Notes:a.Elevation referenced to North American Vertical Datum of 1988 (NAVD 88)

PMF ANNUAL EXCEEDANCE PROBABILITIES

Flood Frequency CurvesUpper Baker Max Elevation

700

705

710

715

720

725

730

735

740

745

750

ANNUAL EXCEEDANCE PROBABILITY

MA

X R

ESER

VOIR

STA

GE

- U

PPER

B

AK

ER (f

t NA

VD88

)

Extreme Value Type 1 Plotting Paper

Stochastic Model Results

10-1010-9.5 10-810-610-510-410-310-210-1

PMF Estimate739.19 ft NAVD88

Top of Dam735.77 ft NAVD88

Top of Flood Control Pool727.77 ft NAVD88

10-7

Upper Baker Project Regulated Frequency Curve

Flood Frequency Curves• Lower Baker Max Elevation

410

415

420

425

430

435

440

445

450

455

460

465

ANNUAL EXCEEDANCE PROBABILITY

MA

X R

ESER

VOIR

STA

GE

- LO

WER

B

AK

ER (f

t NA

VD88

)

Extreme Value Type 1 Plotting Paper

Stochastic Model Results

10-1010-9.5 10-810-610-510-410-310-210-1

PMF Estimate458.43 ft NAVD88

Overtopping Elevation 444.57 ft NAVD88

Normal Full Pool Elevation442.35 ft NAVD88

10-7

Lower Baker Project Regulated Frequency Curve

History of Stochastic Event Flow Model

Development started in 1996 for USBRInitial Public Domain Model Completed in 1998

Used by USBR for Hydrologic Risk Assessments since 1998

Bumping Lake Dam – Bumping River, WA

Cle Elum Dam – Cle Elum River, WA

Keechelus Dam – Yakima River, WA

Minidoka Dam – Snake River, ID

Whiskeytown Dam – Clear Creek, CA

Trinity Dam – Trinity River, CA

A.R. Bowman Dam – Crooked River, OR

MGS Engineering Solutions

History of SEFM …

BChydroMica Dam, Upper Columbia River, BC

Received International Peer Review 2001

US Corps of EngineersFolsom Dam, American River, CA

SEFM Accepted by USCOE for Analysis of Extreme Floods and PMF

Puget Sound EnergyBaker River Project, Baker River, WA

FERC Licensed ProjectMGS Engineering Solutions

Summary

• FERC guidelines require a deterministic solution to define PMF.

• PSE has showed both Lower and Upper Baker Dams are stable under the PMF loading.

• FERC guidelines require that a project must safely pass the PMF. 1:190,000,000 likelihood for PSE.

• What is appropriate FERC AEP?

• What is appropriate PMF approach deterministic vs. stochastic? Or weighted?

• Consider using stochastic criteria as in FERC anticipated Maximum Credible Earthquake likelihood for an Maximum Credible Flood?

• “How often would that there PMF happen?”

• And “is that a reasonable criteria?”