Memorial Day Flood May 25-26, 2015 Harris County, Texas

4/29/2016
Memorial Day Flood
May 25-26, 2015
Harris County, Texas
TDEM Conference
April 6, 2016
Jeff Lindner, Flood Operations Manager/Meteorologist
Jeremy Justice, Hydrologic Analyst
Recent Major Flooding Events
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May 1989
June 1989 (TS Allison # 1)
March 1992
October 1994
September 1998 (TS Frances)
October 1998
November 1998
June 2001 (TS Allison # 2)
October 2002
November 2003
June 2006
October 2006 (2)
August 2007 (TS Erin)
September 2008 (Hurricane Ike)
April 2009 (2)
January 2010
July 2012
May 2015 (2)
October 2015
5 of 22 (23%) Tropical Cyclone
10 of 22 (45%) (Fall: Sept, Oct, Nov)
Harris County Watersheds
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4/29/2016
A Wet Spring
Month
Rainfall Departure
April
6.10
+ 2.79
May
14.17
+ 9.08
Prior Harris County Events
April 16-17
2-3” widespread
4-6” max
street flooding
40 homes flooded
30-Day Rainfall Prior to Memorial Day
May 12-13
1-3” widespread
8-10” max
Sig. street flooding
300 Apts. flooded
1 death
Average Rainfall: 7.0-17.0 inches
Antecedent Conditions - April 2015
April 2015 Rainfall 150% to 500% of normal for Harris County
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4/29/2016
Wimberley Warning – Blanco River
Wimberley – The Mixed Message
Meteorologists
Confirmation of the capability of the air mass to produce
extreme short term rainfall and dangerous flooding.
Non-Meteorologists
A central TX concern. Not much rainfall Sunday morning.
E-mail 7:21 am (5/25)
“While models have been good with their forecasted rainfall
amounts…they have been off on the placement (mainly across central
TX). Even though the air mass has dried some since yesterday I am still
leery of the potential for excessive rainfall in a short period of time on
top of saturated grounds.”
E-mail 4:28 pm (5/25)
“Will need to watch trends very closely over the next few hours as
this line approaches as this is the type of setup with these kind of
rainfall rates that will get the area into trouble very quickly.”
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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4/29/2016
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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4/29/2016
NWS Chat Log – May 26
02:01 <media-brooks.garner> Jeff, please let us know especially if there's anything more than
the typical low-land stuff. Thanks!
02:02 <HCFCD-Jeff Lindner> 2.04 inches in 1 hr Spring Creek
02:02 <HCFCD-Jeff Lindner> Brooks: really worried about the SW/W side with cell mergers.
03:31 <HCFCD-Jeff Lindner> HGX: any consideration for FF emergency wording.
Have several watersheds nearing bankfull
03:32 <nws-joshua.lichter> Jeff- Yes. We have been discussing.
03:34 <HoustonOEM Michael Walter> Talked with safety folks at Toyota Center They're holding people in their seats until the storms clear.
03:43 <nws-joshua.lichter> Looking at FFW emergency for southwest Harris into
northern Fort Bend. This area has taken the brunt of it and still more rain coming.
03:47 <nwshgx-melissa.huffman> Flash Flood Emergency coming shortly for SW
Harris, Northern Ft. Bend
03:48 <nwshgx-melissa.huffman> This will include Spring Branch, Sugar Land,
Stafford, Mission Bend
03:50 <HCFCD-Jeff Lindner> Nearing 7 inches on Buffalo
03:56 <HCFCD-Jeff Lindner> HCFCD is advising all residents to remain at their
current location. Avoid all travel.
03:57 <HCFCD-Jeff Lindner> Overbanks on Brickhouse...homes are flooding
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.
THIS IS AN EXTREMELY
DANGEROUS AND LIFE THREATENING SITUATION. DO NOT ATTEMPT
• PRECAUTIONARY/PREPAREDNESS ACTIONS...
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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4/29/2016
Memorial Day Activation Timeline
Midnight: 10 channels involved (3hrs 30 min)
1:00 am: City of Stafford suspends 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
Highest Rainfall - Brays Bayou at Beltway 8
6.4 inches/2hrs
Brays Bayou average rainfall
8.6 inches or 18.9 billion gallons
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4/29/2016
May 25-26, 2015 (6-hr Rainfall)
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
(Marble Falls, TX)
6.8
13.4
17.8
17.8
17.8
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
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4/29/2016
Brays Bayou
• Ship Channel to US 59: 10% (10-yr) and 2% (50-yr)
• Upstream US 59: below 10% (10-yr)
Event Date
Peak: 52.8 ft, 5-6 am
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
1/9/12
50.3
Brays Bayou – May 26 am
Chimney Rock
Texas Medical Center
Rice Ave
SH 288
Brays Bayou near Loop 610 – May 26 am
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4/29/2016
Brays Bayou – May 26 am
Lawndale
Idleywood
Upstream South Main
South Main
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
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4/29/2016
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
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)
Peak: 35.7 ft, 540 am
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
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4/29/2016
Buffalo Bayou – May 26 am
Memorial Dr
Downtown
Downtown - Milam
Allen Pkwy
White Oak Bayou
• Downtown to Heights: just above 10% (10-yr)
Event Date
HWM
Allison (01)
45.5
3/4/92
40.1
Frances (98)
37.6
5/26/15
36.6
Ike (08)
36.3
Peak: 36.6 ft, 4 am
White Oak Bayou – May 26 am
I-45 & N. Main
Heights Blvd
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4/29/2016
Brickhouse Gully
Entire Channel: 10% (10-yr) to 2% (50-yr)
Base flow to
flood in 2 hrs
Peak: 64.1 ft, 1230 am
Event Date
HWM
Allison (01)
68.9
5/26/15
65.5
5/10/07
64.7
Ike (08)
64.4
10/29/02
63.7
4/28/09
63.3
Other Channels
Overbank flooding
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Greens Bayou
Halls Bayou
Greens Bayou
San Jacinto River
Clear Creek
Cypress Creek
Little Cypress Creek
Little White Oak Bayou
Many tributaries
Garners Bayou
House Count Estimate
1,185
245
295
270
335
485
495
3,015
Brays Bayou
Keegans Bayou
Willow Waterhole
Buffalo Bayou
Spring Branch
White Oak Bayou & Tributaries
Other Watersheds
(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 4000 and 7000
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4/29/2016
House Count Comparison
Jurisdiction
House Flooding
Estimate
May 25, 2015 Flood
currently ranks as 4th most
number of homes flooded
City of
Houston
2,660
City of
Bellaire
160
Unicorp.
Harris County
110
The Villages
65
10-18- 94
City of
Pasadena
Total
Flood
Event
House Flooding
TS Allison
73,000
6-19-06
3,370
3,248
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5-25-15
3,015 w/o FEMA
6,335 w/ FEMA
3,015
4-28-09
2,305
90% flooded homes in City of Houston
Memorial Day Rainfall and House Flooding
Floodplains and House Flooding Memorial Day
57% flooded structures outside
floodplains
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4/29/2016
HCFCD Actions
Flood Watch team activated (HCFCD + HCOEM)
May 23, 6 pm until May 30, 10 pm
Clear Creek 2nd Outlet Channel Gates opened twice
- May 23 and May 27 (5 times in 2 months)
Two helicopter recon flights
HCFCD Actions
60 media interviews + news conferences
Partner press releases
HCFCD press releases
HCFCD Actions
115 high water marks identified and surveyed at
bridges on seven channels
High water marks taken in houses along Brays
Bayou and HCFCD detention basins
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4/29/2016
Addicks & Barker Reservoirs – Peak on June 1
Addicks
Peak: 95.51 ft
7th highest
Barker
Peak: 91.87 ft
5th highest
Lessons
Integrated Warning Team works well
HCOEM Twitter Feed
(NWS, EM, HCFCD, media)
Issuance of properly worded
products to elevate threat
FFE, messaging, social media
Monday Night after Game
Lessons
• Urban floods quickly overwhelm
• Multiple watersheds
• Sheetflow/ponding (where/how bad)
• Must work fast on warnings and messages
• Situational awareness
• Trust and believe data
• Previous water levels (comparison)
• Every flood is different (rainfall never the same)
• Secondary event (Wednesday morning)
• Turn Around Don’t Drown
• Stop driving into high water!
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4/29/2016
Comparison of 2015 Harris County
Rainfall Events
Countywide Comparison of 2015 Floods
1-hr
3-hr
6-hr 12-hr 1-day 2-day
Memorial Day (avg)
2.5
4.3
5.4
5.5
5.5
6.5
Oct. 24-25 (avg)
1.1
2.2
3.6
5.5
7.1
7.7
Halloween (avg)
1.9
2.9
3.6
5.3
5.3
5.9
Memorial Day (B gal)
76.4 131.8 165.5 170.1 170.8 199.6
Oct. 24-25 (B gal)
33.6
68.7 112.0 168.9 220.4 237.4
Halloween (B gal)
58.6
90.6 112.0 162.2 164.1 182.4
(avg) = average rainfall in inches
(B gal) = Billions of gallons of water
Memorial Day Rainfall and House Flooding
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4/29/2016
Oct 24-25 Rainfall and House Flooding
Halloween Rainfall and House Flooding
Brays Bayou
1-hr
3-hr
6-hr
12-hr
1-day
2-day
House
Memorial Day (avg)
2.5
5.7
7.8
8.4
8.4
8.6
1800
Oct. 24-25 (avg)
1.2
2.5
3.7
6.0
7.6
8.1
0
Halloween (avg)
2.6
3.9
4.4
6.3
6.3
6.7
90
Memorial Day (B gal)
5.5
12.5
17.2
18.5
18.5
18.9
Oct. 24-25 (B gal)
2.5
6.0
8.2
13.3
16.7
17.8
Halloween (B gal)
5.7
8.6
9.7
13.9
14.0
14.6
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4/29/2016
Brays Bayou
Brays Bayou @ Rice Avenue
Brays Bayou at Rice
60
55
Stage (ft)
50
45
Memorial Day
40
Oct. 24th
35
Halloween
30
Top of Bank
25
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0
5
10 15 20 25 30 35 40 45 50
Hours from Start of Event
HCFCD Flood Forecasting Effort
Real-time Gage Data
Discharge & Rating Curve
Accurate and Timely Flood Forecasts
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4/29/2016
Mission Statement
Measure discharge at determined gage
locations and create and maintain
accurate rating curves to be utilized by
HCFCD and partners for flood forecasting
and calibration of hydrological models.
Discharge
Discharge (flow) is the volume of water moving down a
stream or river per unit of time. We express this in cubic
feet per second.
Q=VxDxW
Q = Discharge
V = Velocity
D = Depth of water
W = Width
1 cubic foot water = 7.48 gallons and weighs 62.42lbs .
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4/29/2016
Discharge Measurements
Langham Creek at W. Little York
Little White Oak at Tidwell
Cedar Bayou at SH 146
Rating curves are determined by taking discharge
measurements at different stages.
Site Selection
65 HCFCD potential rated locations
40 USGS rated locations
Rating Curves
• Stage/Discharge Rating Curve is the relationship between
water level (stage) and volumetric rate of flow (discharge).
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4/29/2016
Flood Forecasting Effort
• Develop accurate rating curves for most HCFCD
gage sites
• Determine best forecasting methods for Harris
County watersheds (gage locations)
• Test and verify methods
• Develop and implement categorical flood levels at
all HCFCD gage sites (minor, moderate, major)
Questions?
Jeff Lindner
Harris County Flood Control District
Jeff.lindner@hcfcd.org
Jeremy Justice
Harris County Flood Control District
Jeremy.justice@hcfcd.org
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