Generating Flow Frequencies – Generating Flow Frequencies – Updating NOAA Atlas Precipitation Updating NOAA Atlas Precipitation

Frequency for CaliforniaFrequency for California

by: John High, Hydrologistby: John High, Hydrologist Sacramento DistrictSacramento District U.S. Army Corps of EngineersU.S. Army Corps of Engineers

Precipitation Frequency CurvesPrecipitation Frequency Curvesalso calledalso called

““Depth Duration Frequency (DDF) Curves”Depth Duration Frequency (DDF) Curves”

Q: What are they used for??Q: What are they used for?? A: A: Input to Rational Equation or Rainfall-Runoff ModelInput to Rational Equation or Rainfall-Runoff Model

* Calculate peak discharge* Calculate peak discharge- channel design- channel design- levee design- levee design- culvert design- culvert design- floodplain mapping - floodplain mapping

* Calculate a runoff volume for a storage area or a dam * Calculate a runoff volume for a storage area or a dam

Streamgage

Watershed Map

Damage reach

streamgage

1. Create Rainfall-Runoff Model & Calibrate to Historic Storm Event

Damage reach

Concentration point

RAINFALL IN INCHES PER HOUR

PEAK = 53,500 CFS

1983 FLOOD

streamgage

2. Input “design storm” into model and adjust parameters to match flow frequency curve.

Damage reach

Concentration point

hydrograph

Flow Frequency Curve

streamgage

Damage reach

Concentration point

100-yr design hydrograph

Existing Depth-Duration Frequency CurvesExisting Depth-Duration Frequency Curvesfor Californiafor California

-- NOAA ATLAS 2 “Precipitation NOAA ATLAS 2 “Precipitation Frequency Atlas of the Western United Frequency Atlas of the Western United States”, Vol XI- California, 1973States”, Vol XI- California, 1973

- Department of Water Resources- Department of Water Resources Rainfall Analysis for Drainage DesignRainfall Analysis for Drainage Design Bulletin 195, 1976Bulletin 195, 1976 (regional frequency analysis by Jim Goodridge and staff)(regional frequency analysis by Jim Goodridge and staff)

NOAA Atlas 2NOAA Atlas 21. Covers 11 Western States1. Covers 11 Western States2. Regional Frequency Analysis2. Regional Frequency Analysis3.3. Gumbel Extreme Value DistributionGumbel Extreme Value Distribution4.4. Isopluvial Maps for 6-hr and 24-hr Isopluvial Maps for 6-hr and 24-hr

duration, 2 – 100 yr return periodsduration, 2 – 100 yr return periods5.5. Use formulas/charts to derive otherUse formulas/charts to derive other durations/return periodsdurations/return periods6. GIS maps recently available in raster 6. GIS maps recently available in raster

format (cells)format (cells)

NOAA Atlas 2

DWR Bulletin 195DWR Bulletin 195

1. Covers California1. Covers California2. Regional Frequency Analysis2. Regional Frequency Analysis3.3. Pearson Normal DistributionPearson Normal Distribution4.4. Hard-copy maps of 2-yr thru 10,000 yr, short Hard-copy maps of 2-yr thru 10,000 yr, short

and long-duration valuesand long-duration values5.5. Analyzed ~2,000 gagesAnalyzed ~2,000 gages

Note: DWR will update Bulletin 195 near future. Note: DWR will update Bulletin 195 near future. GIS map layers available within a couple yearsGIS map layers available within a couple years

- David Rizzardo of DWR- David Rizzardo of DWR

WHY HASN’T NOAA ALTAS 2 BEEN UPDATED?WHY HASN’T NOAA ALTAS 2 BEEN UPDATED?

1.1. NOAA Atlas updates are NOAA Atlas updates are NOTNOT in the Weather Service’s Mission in the Weather Service’s Mission StatementStatement

2.2. U.S. Congress provides no fundingU.S. Congress provides no funding

3.3. Funding must come from other federal or state agenciesFunding must come from other federal or state agencies

UPDATED PORTIONS OF THE COUNTRY

WHO DOES THE UPDATE?WHO DOES THE UPDATE?

National Weather ServiceNational Weather Service    Hydrometeorological Design Studies Center    Hydrometeorological Design Studies Center    Silver Spring, MD    Silver Spring, MD      Geoff Bonnin, ChiefGeoff Bonnin, Chief

• Small, top-notch team of scientists.Small, top-notch team of scientists.

• Future funding uncertain, so staff may be Future funding uncertain, so staff may be laid off.laid off.

Funding to Finish NOAA14 for CaliforniaFunding to Finish NOAA14 for California

Total Cost = $305,000 -or- moreTotal Cost = $305,000 -or- more

1. 1. CALTRANS: CALTRANS: $100,000$100,000

Glenn Decou, Chief of Highway Drainage DesignGlenn Decou, Chief of Highway Drainage Design

2. 2. CA Department of Water Resources:CA Department of Water Resources: $100,000$100,000

3. 3. NWS, Sacramento OfficeNWS, Sacramento Office (Coastal Storms (Coastal Storms Program) – Program) – maybe maybe $50,000$50,000??

4.4. U.S. Army Corps of Engineers: U.S. Army Corps of Engineers: $55,000$55,000 or or moremore

COMPLETED PRODUCT IN 2 – 3 YEARSCOMPLETED PRODUCT IN 2 – 3 YEARS

LOCATION ON EAST SIDE OF LAKE TAHOE:

90% Confidence Interval Upper Bound = 5.53 inches

100YR, 24-HOUR DEPTH = 4.93 inches

90% Confidence Interval Lower Bound= 4.32 inches

SUMMARY

1. The National Weather Service will start work on NOAA14 for the rest of California within a few months.

2. Completion will be in 2 – 3 years

3. Study will incorporate state-of-the-art methods and technology

4. Includes quality control and screening – not all gages will be used

5. Study will include review and comment period of draft product

Concern: NWS used calendar year analysis of data for Semi-Arid region. Not appropriate for California – annual data should be separated by Water Year.

Weblink for NWS NOAA14 Precipitation:

http://hdsc.nws.noaa.gov/hdsc/pfds/index.html

Points of Contact: Dave Rizzardo, DWR 916-574-2617John High, USACE 916-557-7136

THE END