10/5/2015
Memorial Day Flood May 25-26, 2015 Harris County, Texas
Texas Floodplain Management Association September 4, 2015
Jeff Lindner, Flood Operations Manager/Meteorologist
A Wet Spring
Month Rainfall Departure April 6.10 + 2.79 May 14.17 + 9.08
Antecedent Conditions - April 2015
April 2015 Rainfall 150% to 500% of normal for Harris County
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Prior Harris County Events
April 16-17 30-Day Rainfall Prior to Memorial Day 2-3” widespread 4-6” max street flooding 40 homes flooded
May 12-13 1-3” widespread 8-10” max Sig. street flooding 300 Apts. flooded 1 death
Average Rainfall: 7.0-17.0 inches
Harris County Watersheds
Memorial Day Activation Timeline
645 pm: Activate HC EOC at 800pm – Level 3… increased readiness
740 pm: Some staff in place at EOC
8:00 pm: Initial staff briefing (S.O., HCFCD, HCFMO, HCOEM)
8:17: Move HCFCD staff to Monitor mode
8:33: Flash Flood Warning issued for Harris County (53 min)
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May 25 Radar – 800 pm
30-40mph moist inflow
May 25 Radar – 900 pm
Cell Mergers and Training over SW/W Harris Co
Memorial Day Activation Timeline 9:57 pm: HCFCD staff to flood mode (1hr 40 min)
10:00 pm: EOC Level 2…high readiness
10:04 pm: Flood Warning Rummel Creek (W156) (2hr 24min)
10:52 pm: Flash Flood Emergency (NWS)
11:00 pm: EOC Level 1…maximum readiness (1st time since Ike)
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NWS Chat Log – May 25 02:01
BULLETIN - EAS ACTIVATION REQUESTED FLASH FLOOD WARNING NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX 1052 PM CDT MON MAY 25 2015 ...
FLASH FLOOD EMERGENCY FOR SOUTHWEST HARRIS COUNTY...
• UNTIL 1245 AM CDT *
• AT 1047 PM CDT...DOPPLER RADAR INDICATED A THUNDERSTORM PRODUCING HEAVY RAIN ACROSS THE WARNED AREA. 5 TO 7 INCHES OF RAIN HAVE FALLEN.
• THIS IS A FLASH FLOOD EMERGENCY FOR AREAS FROM SUGAR LAND...MEADOWS PLACE...SPRING BRANCH...BUNKER HILL VILLAGE TO MEMORIAL.
• ADDITIONAL RAINFALL AMOUNTS OF 2 TO 4 INCHES ARE POSSIBLE IN THE WARNED AREA.
• PRECAUTIONARY/PREPAREDNESS ACTIONS... THIS IS AN EXTREMELY DANGEROUS AND LIFE THREATENING SITUATION. DO NOT ATTEMPT TO TRAVEL. BE ESPECIALLY CAUTIOUS AT NIGHT WHEN IT IS HARDER TO RECOGNIZE THE DANGERS OF FLOODING. TURN AROUND...DONT DROWN WHEN ENCOUNTERING FLOODED ROADS. MOST FLOOD DEATHS OCCUR IN VEHICLES.
May 25 Radar – 1100 pm
30-40mph moist inflow
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Memorial Day Activation Timeline
Midnight: 10 channels involved (3hrs 30 min)
1:00 am: City of Stafford suspended 911 service
3:00 am: 16 channels involved 10 overbanks 6 near bankfull
6:00 am: City of Houston declares State of Emergency
Highest Rainfall Amounts
15 min 2.1” Little White Oak at Tidwell 30 min 3.3” Little White Oak at Tidwell 1 hour 4.8” Little White Oak at Tidwell 3 hour 8.0” Brays at West Belt 6 hour 10.1” Buffalo at West Belt 12 hour 11.0” Brays at West Belt
Harris County average for 12 hours: 5.3 inches = 162 billions gallons
May 25-26, 2015 (6-hr Rainfall)
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Flood Event Rainfall Comparison
Date 1-hr 3-hr 6-hr 12-hr 24-hr
6/8/01 (Allison) 6.3 13.5 21.2 28.3 28.5
6/26/07 6.8 13.4 17.8 17.8 17.8 (Marble Falls, TX)
4/18/09 6.9 9.2 9.9 10.0 11.0
5/26/15 4.8 8.0 10.1 11.0 11.0
Flood Event Rainfall Comparison
Date 1-hr 3-hr 6-hr 12-hr 24-hr 4/17/15 4.0 4.3 4.8 4.9 5.5 5/13/15 3.3 6.2 7.8 8.2 8.4 5/13/15 (Bay Knoll Sub) 11.98 13.58 5/26/15 4.8 8.0 10.1 11.0 11.0 Maximum gage recorded rainfall in inches
Date 1-hr 3-hr 6-hr 12-hr 24-hr 4/18/09 6.9 9.2 9.9 10.0 11.0 4/24/09 3.8 6.8 7.6 7.6 7.6 4/28/09 4.8 7.0 7.1 10.4 11.3 Maximum gage recorded rainfall in inches
Return Period: 10year 25year 50year 100year 500year
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Brays Bayou • Ship Channel to US 59: 10% (10-yr) and 2% (50-yr) • Upstream US 59: below 10% (10-yr)
Event Date HWM 5/26/15 52.9 9/19/83 52.5 10/18/94 51.5 11/17/03 51.0 Allison (01) 50.4 Peak: 52.8 ft, 5-6 am 1/9/12 50.3
Brays Bayou Channel – May 26 am
Chimney Rock Rice Ave
Texas Medical Center SH 288
Brays Bayou near Loop 610 – May 26 am
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Keegans Bayou • Entire channel: at or above 1% (100-yr) • Keegans to Dairy Ashford: near .2% (500-yr)
Event Date HWM 5/26/15 80.8 1/9/12 78.9 5/12/12 77.8 4/28/09 75.9 Ike 75.6
Peak: 80.7 ft, 4 am
Keegans Bayou – May 26 am
Huntington Park Sub
Keegans Rd
Huntington Park Sub
Willow Waterhole
Entire channel: 2% (50-yr) to 1% (100-yr)
Event Date HWM 5/26/15 51.7 4/27/13 48.1 1/9/12 49.1 Ike (08) 47.8 4/28/09 43.2
Peak: 51.5 ft, 4 am
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Willow Waterhole – May 26 am
Willowbend Willowbend
Westbury Area
Buffalo Bayou • Downtown to Shepherd: near 2% (50-yr) • Woodway to Gessner: 2% (50-yr) to 1% (100-yr) • Upstream Gessner: 10% (10-yr) to 2% (50-yr)
Event Date HWM Allison (01) 40.5 5/26/15 34.0 Frances (98) 33.9 3/4/92 31.6 Ike (08) 31.0 4/28/09 28.0 Peak: 35.7 ft, 540 am
Buffalo Bayou – May 26 am
Downtown Memorial Dr
Downtown - Milam Allen Pkwy
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House Count Estimate 1,185 Brays Bayou 245 Keegans Bayou 295 Willow Waterhole 270 Buffalo Bayou 335 Spring Branch 485 White Oak Bayou & Tributaries 495 Other Watersheds 3,015 (3,540 multi-family + 92 businesses) FEMA Flood Insurance Claims 4,630 total 3,320 not in house count above Total flooded homes likely between 3000 and 6000
House Count Comparison
House Flooding May 25, 2015 Flood Jurisdiction th Estimate currently ranks as 4 City of most number of 2,660 Houston homes flooded City of Flood 160 House Flooding Bellaire Event Unicorp. 110 TS Allison 73,000 Harris County 6-19-06 3,370 The Villages 65 10-18- 94 3,248 City of 20 3,015 w/o FEMA Pasadena 5-25-15 6,335 w/ FEMA Total 3,015 4-28-09 2,305 90% flooded homes in City of Houston
Concentrated House Flooding Areas
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House Damage
• 1900s – Drainage Districts: “4” – 4 feet deep, 4 feet wide • 1930s – Corps of Engineers “Standard Project Flood” • 1940s – Public Petition: “4 inches of rain in 24 hours” • 1960s – Comprehensive Studies: Sliding scale based on drainage area, maximum 25-year level of protection. Corps changes in project development – economics and environment • 1970s – Introduction of the National Flood Insurance Program (NFIP) and the 100-year flood(plain) • 1980s – First detailed floodplain studies, design criteria, hydrologic methodology, general application of stormwater detention, extensive stream and rainfall gage network developed • 2000s – Tropical Storm Allison Recovery Project (TSARP), LiDAR technology
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Hindsight’s 20-20
“Studies have found that one of the most effective ways to reduce flood damage are building codes requiring that new structures be at least a couple feet above the expected flood level.”
“And we know that now. I really wish we’d known that a hundred years ago,”
Curtis Beitel, P.E. President, Texas Chapter of ASCE July 20, 2015
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May 2015 Rainfall
IAH: 14.17 in (+ 9.08 in) – 5th wettest Hobby: 14.0 in (+ 9.65 in) – 2nd wettest Sugar Land: 20.40 in (+ 15.77 in) – 1st wettest Huntsville: 14.93 in (+ 10.93 in) – 1st wettest
May 2015 Rainfall Ten Wettest Months in Texas History (1895-Present) May 2015 8.93 June 2004 6.66 May 1914 6.62 September 1936 6.55 May 1929 6.45 Rainfall (in) May 1935 6.38 September 1974 6.32 October 1919 6.26 April 1957 6.19 November 2004 6.18
May 2015 wettest month ever since 1895. Surpassed previous record by 2.27 inches! May 2015 rainfall = 35 trillion gallons across TX!
Questions?
Jeff Lindner Harris County Flood Control District [email protected]
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Harris County Flood Warning System Performance • 89 rainfall alarms (1’ in 15 minutes) 69 water level alarms (3 ft from bankfull) • No obvious loss of data due to contention during peak of event • Rainfall & stage data real-time & accurate • Record # of hits on public FWS website (no overloading problems) • One radar sensor destroyed by flood flow
Lessons Learned
• When to activate and staff onsite at HCOEM and Flood Operations Center? • Working flood from multiple locations hinders communications and coordination • Working floods after many years of little to no flood activity a challenge – new people, new tools, new versions. • Need to improve flood forecasting
Test
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Test
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