Advancements in FloodFlash Flood Forecasting Using the Site Specific SACSMA Headwater Model

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Advancements in Flood/Flash Flood Forecasting
Using the Site Specific SAC-SMA Headwater Model
Ohio Severe Weather Symposium April 7,
2006 Jim Noel Ohio River Forecast Center
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Optimizing Flood Forecasting with the Site
Specific Headwater Predictor
Reservoir Releases
Satellite Data
River Gage Data
Precipitation Estimates
Radar Data
Snow Cover/ Melt Data
Precipitation Forecasts
RFC/Probabilistic
WFO Site Specific
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Where does SSHP fall within the NOAA/NWS
Hydrologic Services
WFO Flash Flood Monitor and Prediction
RFC NWSRFS/ESP/Probabilistic
WFO Site Specific Flood and Flash Flood
Application
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AHPS
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Site Specific Model Recent Historic Overview

Headwater Tables
SSHP API-MKC
SSHP SAC-SMA
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Site Specific Model Overview

• Designed to replace headwater guidance
• - Mainly for basins 200 sq miles or less
• - Mainly for time-to-crest of 12 hours or less
• - Not designed for routed water basins
• - Visually-oriented product
• Improves headwater crest timing through higher
  temporal resolution.

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Site Specific Model HeadWater Guidance
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Site Specific Model Applications

• Allows for graphical look at hydrograph
  forecasts
• Quick headwater forecasts
• Integrate into NWS RiverPro for WFO FLWs/FFWs
• Integrate into Advanced Hydrologic Prediction
  Service (AHPS)
• Integrate into WFO Flood Watches

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Site Specific Model AHPS
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Site Specific Model AHPS
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Site Specific Model Text FLW from RiverPro
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Site Specific Model API Strengths/Weaknesses

• Development time is fast!
• Requires much more WFO interaction with FFG
• 1-hr FFG values tend to cause over-forecast
  crests, sometimes significantly (minor versus
  major)
• Must select FFG value from beginning of first
  event for multiple rainfall events
• Knowledge of other hydrologic parameters
• RFC staff that continues losing knowledge of API
  in operational setting
• API based on Kansas City API model parameters
  that are not as applicable to other basins.

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Site Specific Model SAC-SMA Strengths/Weaknesses

• More accurately forecasts crests of flood events
• Requires little WFO interaction except for
  rainfall QC
• RFC staff that is very knowledgeable on SAC-SMA
• SAC-SMA model parameters based on RFC
  calibrations for each specific basin modeled.
• Requires slightly more development time per SSHP
  site when using RFC 6-hr SACSMA parameters (less
  than 5 person hours)

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Site Specific Model SAC-SMA Development Process

• 1-hr unit hydrograph
• Basin boundary
• Rating Curve
• SAC-SMA parameters (NWSRFS/OFS)
• SAC-SMA states (OHRFC script)
• Flood Stage WFO requirement

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SSHP SAC-SMA Basins
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Site Specific Model Case Studies from OHRFC

• Looked at 30 events from June 2005 to March 2006
• All but one crest forecast better in SAC-SMA
  version
• Several crests differ by more than 5 feet (minor
  versus moderate/ major flood forecasts
• Recession forecast better in most cases by
  SAC-SMA
• API version reasonably close to SAC-SMA version
  if hydrologic parameters are modified to reflect
  event (manual intervention and requires
  hydrologic knowledge)

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Site Specific Model Comparison of
SAC-SMA/API-MKC Some very recent
examples LRHI3/WYNI2/DEPI3/SBVI3

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Site Specific Model March 7-13 Heavy Rain Event

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Site Specific Model SACSMA LRHI3

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Site Specific Model API LRHI3

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Site Specific Model SACSMA WYNI2

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Site Specific Model API WYNI2

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Site Specific Model API WYNI2

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Site Specific Model SACSMA DEPI3

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Site Specific Model SACSMA DEPI3

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Site Specific Model SACSMA ALPI3

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Site Specific Model SACSMA SBVI3

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Site Specific Model Summary

• SSHP huge advancement from old text product and
  tables to graphical based forecasts for fast
  responding streams and small rivers.
• Able to fully integrate SSHP into end-to-end
  process from forecasts to warnings.
• Without any manually intervention, SSHP SAC-SMA
  usually produces better results than API-MKC
  version.
• Both SAC-SMA and API-MKC forecast timing of
  headwaters basins better than RFC NWSRFS
• SAC-SMA forecasts crest height more accurately
• SAC-SMA is more hands-off allowing for more time
  at WFO for other operational needs

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