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Flash Flood Prediction. James McDonald 4/29/08. Introduction - Relevance. 90\% of all national disasters are weather and flood related Central Texas – “Flash Flood Alley” Project Goal – To compare flash flood prediction on multiple scales (NWS, LCRA, City of Austin).

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flash flood prediction

Flash Flood Prediction

James McDonald 4/29/08

introduction relevance
Introduction - Relevance
  • 90% of all national disasters are weather and flood related
  • Central Texas – “Flash Flood Alley”
  • Project Goal – To compare flash flood prediction on multiple scales (NWS, LCRA, City of Austin)
agencies the main players
Agencies – The main players
  • NWS – ultimately responsible for issuing flood warning
  • LCRA – manages flood releases from the Highland Lakes
  • City of Austin – flood monitoring and emergency management
nws west gulf river forecasting center
NWS – West Gulf River Forecasting Center
  • 1 of 13 NWS River Forecasting Centers
  • Also includes in house Meteorological forecasting
nexrad radar
NexRAD Radar
  • 4 km x 4 km grid cell
  • Rain gages across state used to calibrate radar
  • Radar - mean areal precipitation (per hour)
sub basins
Sub-basins
  • Delineated by USGS streamgage
  • Total QPF (Quantitative Precip. Forecast)
    • 6 hr. UH time step
    • Stage height by USGS rating curve
nwsrfs nws river forecast system
NWSRFS - (NWS River Forecast System)
  • Similar to HEC-HMS (good for design)
  • NWSRFS – good for real time flood forecasting
  • Sacramento Soil Moisture Accounting Method (SAC-SMA)
    • Able to adjust soil moisture to tweak model
distributive modeling
Distributive Modeling
  • The Future
  • Finer rainfall distribution instead of mean areal across entire sub-basin
  • Rainfall variation - GIS
the forecast spreadsheet early 1980 s
The Forecast Spreadsheet – early 1980’s
  • Inputs:
    • Colorado River Forecast @ San Saba
    • Time-lagged tributary hydrographs
    • WSEL of Lake Buchanan & Lake Travis
    • Reservoir releases
catchment forecast system cfs
Catchment Forecast System (CFS)
  • Post 1997 flood
  • Integrates HEC programs:
    • PRECIP
    • HEC1
    • UNET
hec s corps water management system cwms
HEC’s Corps Water Management System (CWMS)
  • Integrates the following models:
    • HEC-HMS, Hydrologic Modeling System
      • 289 sub-basins
      • 205 routing reaches
      • 18,340 mi^2
    • HEC-ResSim, Reservoir Evaluation System Simulation
      • 7 reservoirs
    • HEC-RAS, River Analysis System
      • 864 cross-sections
      • 347 river miles
history of austin flooding
History of Austin flooding

November 15, 2001: 8” of rain in 6 hr. (reported up to 15”)

October 17, 1998: 31 deaths

7,000 people evacuated from homes

Property damages ~ $1 billion

454 Austin homes damaged

December 20, 1991: 200 homes in Travis and Bastrop counties were completely under water

May 24, 1981: 13 drowned, $36 million in damages, Shoal Creek 90 gpm -> 6 million gpm

city of austin am i flooding now
City of Austin – Am I flooding now?
  • Flood Early Warning System
  • Emergency Operations Center
austin watersheds time is not our friend
Austin Watersheds – Time is not our friend
  • 7,000 homes in Austin floodplain
  • Tc range 30min. – 6 hr.
  • Lowering arm – low water crossing – marginal success
  • 20 roads close with 5-yr storm
flood early warning system
Flood Early Warning System
  • Components include:
    • ~40 creek and lake gauges
    • ~80 rain gauges
    • Automated data transfer every 15 minutes to the National Weather Service
    • High Hazard Dam Action Plan
special thanks to
Special thanks to:
  • Mike Shultz, National Weather Service, Ft. Worth, TX
  • Matt Ables & Melinda Luna, LCRA
  • Susan Janek, City of Austin, FEWS

Questions?

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