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

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

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)

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

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 1 am to 8 am 3 am

Highest Rainfall Measured 5 min 1.0” Cypress Crk at SH 249 15 min 2.2” Greens Bayou at North Belt 30 min 3.4” Cypress Crk at SH 249 1 hour 4.7” Greens Bayou at Knobcrest 2 hour 7.3” Langham Crk at Longenbaugh 3 hour 8.3” Little Mound Crk at Mathis Rd 6 hour 13.9” Little Mound Crk at Mathis Rd 12 hour 16.7” 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

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

Natural Cypress Creek Overflow

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 5-19-16, 17,000 people signed up requesting Individual Assistance.

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

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 9,840* *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

Katy Hockley Cut-off @ U102 Katy Hockley at Sharp Rd Cypress Creek Overflow Location April 2016 April 2009 Oct 1998 Oct 1994 Katy Hockley Cut-off @ U102 160.8 158.7 158.6 159.1 Katy Hockley at Sharp Rd 166.8 166.7 157.9 N/A U102-14 @ Katy Hockley 166.9 159.0 160.7 Addicks Cypress Creek

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

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

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

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

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)

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

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

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.

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

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.

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

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

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.

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?

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?

Questions? Russ Poppe, P.E. – Executive Director www.hcfcd.org 713-684-4070

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

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

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

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.

8-12 inches in 12 hours

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

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!

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