1. West Houston Association
Flood Forum
September 15, 2016
Russ Poppe, P.E.
Executive Director

2. Agenda Tax Day 2016 Flood Overview Cypress Creek Overflow
New Criteria and Plan 5
Corps Partnerships
Funding

3. Recent Major Flooding Events
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
April 2016
May 2016
Background Option
5 of 24 (21%) Tropical Cyclone
10 of 24 (42%) (Sept, Oct, Nov)
10 of 24 (42%) (Apr, May, June)

4. Antecedent Conditions – March 2016
200% to 400% of normal for NW Harris County (average 6-8 inches)

5. April 17-18 Radar 1st Round 7 pm to 1 am 2nd Round 1 am to 8 am 11 pm
Optional Slide for previous “Activation Timeline” slides and radars”
2nd Round am to 8 am
3 am

6. Highest Rainfall Measured
5 min 1.0” Cypress Crk at SH 249
15 min ” Greens Bayou at North Belt
30 min ” Cypress Crk at SH 249
1 hour ” Greens Bayou at Knobcrest
2 hour 7.3” Langham Crk at Longenbaugh
3 hour ” Little Mound Crk at Mathis Rd
6 hour ” Little Mound Crk at Mathis Rd
12 hour ” Little Mound Crk at Mathis Rd
24 hour 17.4” Little Mound Crk at Mathis Rd
Steve’s version
23.5” in 14.5 hours in Pattison, Waller County

7. Rainfall Comparison Recent Flood Events
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
4/18/09
6.9
9.2
9.9
10.0
11.0
5/26/15 (Memorial Day)
4.8
8.0
10.1
4/18/16 (Tax Day)
4.7
8.3
13.9
16.7
17.4
Steve’s version – Harris County only

9. Natural Cypress Creek Overflow

10. Flood Facts
Due to extremely intense rainfall rates, 40,000 + cars/trucks flooded Significant overland flooding Nine fatalities related to the flooding (No one died in their home or work place) Federal disaster declaration April 25 for Individual Assistance; Public Assistance added June 3 As of , 17,000 people signed up requesting Individual Assistance.

11. HCFCD Facilities Conditions
8/24/2015
HCFCD Facilities Conditions
No major blockages prior to event & flow not impeded by vegetation growth
Channels and detention basins functioned as designed & helped reduce flood levels
Where rainfall was 1% (100-yr) and higher, the channels & basins were overwhelmed
Debris & damages are extensive along Buffalo Bayou, Cypress Creek, Little Cypress Creek, and Addicks/Barker tributaries.
Problems are fallen trees, slope failures, bank erosion, outfall pipe damage

12. Structure Flooding Estimates
Watershed
Structure Count
White Oak Bayou
2,080
Willow Creek
240
Cypress Creek
1,680
S Mayde Creek
220
Brays Bayou
1,380
Bear Creek
130
Buffalo Bayou
950
Cane Island Branch
120
Langham Creek
810
Barker Reservoir 90
Greens Bayou
600
San Jacinto Bayou
Horsepen Creek
510
Sims Bayou 50
Little Cypress
430
Spring Creek 40
Halls Bayou
370
Other
TOTAL ,840*
*FEMA flood insurance claims account for 4,030
Harris County: 2700 apartment units + 50 commercial properties
Waller County: 430 homes + 27 commercial properties
Montgomery County: 55 homes along Spring Creek

13. Katy Hockley Cut-off @ U102 Katy Hockley at Sharp Rd
Cypress Creek Overflow
Location
April 2016
April 2009
Oct 1998
Oct 1994
Katy Hockley U102
160.8
158.7
158.6
159.1
Katy Hockley at Sharp Rd
166.8
166.7
157.9
N/A
Katy Hockley
166.9
159.0
160.7
Addicks
Cypress Creek

14. Cypress Creek Overflow into Addicks Tribs
Bear Crk
FM 529
SH 99
Dinner Crk

15. South Mayde Creek at Greenhouse Rd. Cypress Creek Overflow Arrives
Event Date
HWM
10/19/98
109.2
Ike (08)
110.4
4/28/09
111.5
7/12/12
108.5
4/18/16
111.4
Cypress Creek Overflow Arrives

16. Addicks Reservoir Top 5 Pool Elev. Apr 2016 102.65 Mar 1992 97.64
Date
Elevation
Apr 2016
102.65
Mar 1992
97.64
Apr 2009
97.08
Nov 2002
96.63
Nov 1998
95.88
Precinct 3 Park
SH 6
N. Eldridge Pkwy

17. Barker Reservoir Top 5 Pool Elev. Date Elevation Apr 2016 95.22
Buffalo Bayou
Fry Road
Date
Elevation
Apr 2016
95.22
Mar 1992
93.60
Nov 2002
93.24
Nov 1998
92.31
Jul 2007
91.85
Westheimer Parkway
Precinct 3 Park

18. Addicks and Barker Stormwater
Detention Reservoirs
Record water levels in both; No homes flooded from water rising in reservoirs
Subsequent rainfall events kept water levels up while trying to empty
Primary roads closed
Clay Road – 21 days
N. Eldridge Pkwy – 28 days (twice)
State Highway 6 – 33 days (twice)
Westheimer Pkwy – 21 days
Both emptied July 6-7 (~ 80 days)

19. Cypress Creek Overflow is Real and Complex
Overflow involves a large volume of overflow that occurs for long duration
Lack of a well defined, uniform flow path – the overflow tends to spill out over a large region in the upper Addicks Reservoir watershed that provides substantial attenuation before overflow drains into the Addicks system
Path and depth of the overflow is sensitive to topographic conditions
Need to maintain consistency in modeling approach in order to maintain a comprehensive set of models for impact analyses in the overflow

20. Overflow - Challenges
Avoid downstream impacts to Cypress Creek due to “blocking” of overflow
Ensure overflow is conveyed without expediting it toward Addicks Reservoir or pushing it onto neighbors.
Traditional 1-D models are more appropriate for flow in a channel

21. Supplemental Criteria Needed
Performing drainage impact analyses for projects within the overflow region.
Dedication of overflow conveyance facilities.
Stormwater runoff volume control (retention).
Revised Site-Runoff Curve equations for the upper Cypress Creek watershed.
Revised minimum detention requirements.

22. Criteria Adopted March 29, 2016
Revised Site Runoff Curves to account for ponding in the upper Cypress Creek watershed
Revised minimum detention requirements for upper Cypress Creek watershed 0.65 ac-ft per acre
Overflow impact analyses using the results from HCFCD’s current 1-D/2-D Coupled XP-SWMM model for the Cypress Creek overflow as the best available data
Overflow conveyance facilities to be located within public drainage easements

23. Cypress Creek Overflow – Supplemental Criteria
General Region of Application
Service area includes those portions of the upper Cypress Creek and Addicks Reservoir watersheds located in Harris County.
While the draft criteria area proposed in Harris County at this time, I’d like to point out that the District plans to reach out to our neighboring counties as well to discuss adoption in Waller County and Fort Bend County as well.
In addition to the those two watersheds, some of the supplemental criteria will also be applied in the Barker Reservoir watershed within Harris County, which is shown in green on the map.

24. Retention - General Strategy
Require developments to manage the increase in runoff volume, just as they do the increase in flow rate.
Options
Retention of first 2” of runoff (avg. 1x per year)
Prairie restoration
Re-use of first 2” of runoff
Low Impact Development
Other, subject to HCFCD approval

25. Katy Hockley N - Cypress Reservoir “Plan 5”
Katy Hockley N– Cypress Storage, or Plan 5
The second concept, would build a shallow berm across Cypress Creek to create a large-scale storage facility that straddles the divide between the Cypress Creek watershed and the Addicks Creek watershed. Water would be allowed to flow both down Cypress Creek and down Bear Creek.
A conveyance channel along Bear Creek, similar to Plan 3, will be constructed. Bear Creek would be enlarged upstream of the existing development. The channel would look similar to the wide conveyance channel I showed previously. The combination of the storage area, collection area, and wide channel will provide sufficient storage and attenuation to ensure that flows along Bear Creek through the existing neighborhoods will not be increased.
No diversion of overflow volume
Outfalls to Cypress Creek (5,300 cfs) and Bear Creek (2,000 cfs)
Equalization channel with backflow preventer
Katy-Hockley N. Cypress Storage Area – requires about 11,300 acres of land (includes PMP volume)
5,155 private land; 5,725 ac conservation land; 390 ac hcfcd land
1% (100-yr) event - storage: 26,500 ac-ft; inundation: 7,400
Additional detention in John Paul’s Landing
Bear Creek – 500’ Corridor
Natural channel design, “stream corridor” concept
Convey 4,500 cfs (2,000 cfs outfall, 4,500 cfs from local)
Additional development criteria in Addicks and upper Cypress Watersheds would be required

26. Plan Details Plan 5 Land Area 11,300 ac Managed Storage Volume
(Addicks Reservoir Manages 200,800 ac-ft over 16,400 ac)
26,500 ac-ft
100-yr Event
Inundation Depth
8’ Max
Drain Time
7 days
Land where Overflow Removed
18,000 ac
Here are some key metrics associated with each plan. They both occupy a lot of land – Plan 3 occupies 5,400 ac and Plan 5 occupies 11,300 ac. For a point of reference, Addicks Reservoir occupies 16,400 acres. However, Addicks manages a much greater volume of water. Plan 3 manages 15, 700 ac-ft. An acre-foot is a lot of water – about 325,000 gallons. So Plan 3 manages about 5 billion gallons. Plan 5 manages 26,500 ac-ft, almost twice as much as Plan 3. While this is a lot, it is not nearly as much as Addicks Reservoir – which manages 200,800 acre feet. So while these plans are almost as big in area as Addicks Reservoir, Addicks manages much more water because the dam is much higher.
During a 100-year event, Plan 3 will have a maximum depth of 13’ feet, although most of the reservoir will see depths smaller than this. It will drain in about 3 days – very fast. Plan 5 has a maximum depth of 8 feet. It will drain in about 7 days.
Both plans remove the overflow from about 18,000 acres of land.

27. Absent a Regional Management Plan
Development will address and manage overflow on a case-by- case basis.
Land will need to be provided on a parcel by parcel basis to store and manage the overflow.
Lose opportunity for a predictable, comprehensive overflow management system for both large and small tracts of land in the Addicks Reservoir watershed will be lost.
Sequence of surrounding development patterns may impact overflow management designs.
Construct new roads at existing grade or mitigate overflow impacts.
Cost and Timeline Challenges
If you are surrounded by undeveloped land – is there an outfall? If development proceeds from downstream up – will there be drainage facilities in place to tie in with?
If you construct overflow facilities and then someone builds upstream of you – what happens? Are there obsolete drainage facilities on-site? Do they still function?

28. Remaining Topics Funding Corps Partnerships Wetlands Mitigation Bank
Brays, White Oak and Hunting Bayou = HCFCD Led
Greens, Sims and Clear Creek = Corps Led
Section 408 Plan reviews
Draft list of Categorical Permissions
Under Review, requires public notice
Wetlands Mitigation Bank
Greens Bayou Bank, adding others
Funding
If you are surrounded by undeveloped land – is there an outfall? If development proceeds from downstream up – will there be drainage facilities in place to tie in with?
If you construct overflow facilities and then someone builds upstream of you – what happens? Are there obsolete drainage facilities on-site? Do they still function?

29. Questions? Russ Poppe, P.E. – Executive Director www.hcfcd.org

30. Brays Bayou Corps Project
8/24/2015
Brays Bayou Corps Project
$310M spent of $480M total cost estimate
12.6 of 21.0 miles of channels conveyance improvements from the mouth to Fondren
10 of 30 bridge replacements/modifications
Four excavated detention basins stored 2.1 billion gallons of stormwater (3.5 billions at 1% design)
~ 1,500 homes flooded in Brays watershed
Completed segments prevented about 1,500 homes from flooding along Brays Bayou

31. 7-9 inches in 12 hours Channel Work Near Complete
Channel Work Left to Complete
Four Detention Basins Near Complete

32. Brays Project Detention Basins
8/24/2015
Brays Project Detention Basins
Eldridge looking east
Old Westheimer
looking north
Arthur Storey Park looking south

33. White Oak Bayou Regional, Corps, and FEMA Projects
8/24/2015
White Oak Bayou Regional, Corps, and FEMA Projects
9.5 of 15.3 miles of channels conveyance improvements from Cole Creek to FM 1960
Multiple bridge replacements/modifications
Ten excavated detention basins (1.9 billion gallons so far ~ 5,800 ac-ft)
~ 2,200 homes flooded in the watershed
Completed segments/projects prevented about 1,800 homes from flooding along White Oak Bayou
400 home buyouts – not there to flood.

34. 8-12 inches in 12 hours

35. Other Beneficial HCFCD & Partnered Projects (partial list)
8/24/2015
Other Beneficial HCFCD
& Partnered Projects (partial list)
Greens Bayou – Six regional & one Corps partnered detention basin
Halls Bayou – Two City of Houston partnered regional detention basins
Vogel Creek channel conveyance improvements
Willow Creek – Two regional detention basins & channel conveyance improvements on M125
Cypress Creek, Mason Creek, Langham Creek, & Horsepen Creek – Regional detention basins

36. Brays Bayou Federal Funding
Each Federal fiscal year unknown - so far, so good
All reimbursement requests have been made
Expenditures to-date $308M ($141M HCFCD, $167M Corps)
Additional Federal costs ±$50M (additional HCFCD cost ±$60M)
Benefit Cost Ratio reevaluated, changed 2.2 to 3.5!

37. Brays Bayou Federal Funding
Last 10 Years Only
Fed. Fiscal Year
Amount
2005
$8,884,000
2006
$11,682,000
2007
$15,387,000
2008
$13,453,000
2009
$5,011,000
2010
$7,777,000
2011
$23,239,000
2012
$5,004,000
2013
$37,247,000
2014
$8,975,000
2015
$21,036,000