Clear Lake City Water Authority Storm Water Detention

Clear Lake City Water Authority Storm Water Detention In Horsepen Bayou Watershed September 2009

CLCWA Background • Created in 1963 by the state legislature at • • • request of the developer to provide water, sewer and drainage service to an unincorporated area. Largest water district in Texas Covers 16, 100 acres, most of which are now in the city of Houston, but also includes most of Taylor Lake Village and parts of Pasadena, Webster and La Porte. Only about 800 acres are still undeveloped Approximately 84, 000 residents live in 30 subdivisions

Background Cont. • 17, 910 water connections • Serves 17, 423 homes; 47 completed multi-family • • complexes which include 10, 726 apartments, townhouses, duplexes, and condominium units; 1, 348 acres of commercial/industrial parks; and JSC through contract. 2007 Taxable Assessed Valuation of $4. 2 billion Annual operating budget of $11 million

Services • Water – provide potable water service to the district; one of the first water districts to switch from ground water to surface water due to subsidence; currently contracted for up to 20. 45 MGD of potable water through the southeast water treatment plant (joint project with City of Houston).

Services – cont. • Waste Water Treatment – plant has the capacity • • to treat 10 MGD Drainage Maintenance – cities are responsible for the street drains; we are responsible from the street drain inlet to the county drainage ditch; and county is responsible for the drainage ditch through the bayou. Other authorization but not utilized – contract for law enforcement, and park/recreation operation

Progressive and Pro-active Actions • • • Consistent Superior water quality rating from state 24 hr emergency response One of lowest water/sewer/tax rates in Harris and Galveston counties Recycled water facilities at golf courses and Uof. H/CL Sponsor water conservation program in CCISD elementary schools One of the few government bodies which allows open comments from the floor at the beginning of every board meeting and before any votes are taken on agenda items

Actions – cont. • One of first governments in Texas to establish a • • continuous infrastructure rehab program to ensure long term reliability Provide adequate fresh surface water capacity at lowest cost to meet future needs Control over increased flooding through realistic storm water detention requirements for new development based on local rainfall, elevation, soil type, etc. and not county averages.

Current Hot Button Flood Control

Flooding Concern in Clear Lake City • TSARP (Tropical Storm Allison Recovery Project) • • study found that the “ 100 year” peak flow rate in Horsepen Bayou watershed increased by 20% during the 1980’s Objective of CLCWA was to: 1. Prevent increased rainwater runoff due to new development, and 2. Reduce current flooding where possible through effective and proven methods Over last 30 years, flooding has grown to be the number one issue for the area

What Is a 100/500 Year Event? • The use of 100 -year and 500 -year event terms • • • are somewhat misleading. A 100 -year event equates to 13. 5 inches of rain within a 24 hour period. There have been 7 of these events since 1976 in CLC. In April 2009, we received over 9 inches in 2 hours !!! A 500 -year event equates to 19 inches of rain within a 24 hour period. There have been 3 of those events since 1979. Markings on the TSARP map only show those areas contiguous to a waterway and does not include depressions (ponding) which are noncontiguous.

TSARP 100 & 500 Year Flood Zone – Horsepen Bayou . Lawrence G. Dunbar, P. E July, 2005 B 1 040200 B 1 04 -0 300 Horsepen Bayou

Flooded Areas Along Reseda Road . Lawrence G. Dunbar, P. E July, 2005

CURRENT FLOODING • This is a photo of a home backing up to the golf course next to the club house and a car in the street. The photo was taken after the water had somewhat subsided, by the home owner who has had water in his house three times and estimated 44 inches of water in the street during that one specific rain event. In addition to the Reseda area, significant other flooding has been recorded in several other areas as illustrated on the map.

Approach • Hired hydrology consultant to better understand flooding in our specific watershed and make recommendations on how to mitigate any future increase and reduce existing problems if possible. Learnings • Flooding is a result of storm water run-off. Flooding increases as • • development covers the ground with impervious surfaces and the ground can no longer soak up the rain. Detention is now becoming recognized as the best method to control flooding along the Texas Gulf Coast versus previous emphasis to make drainage waterways wider, deeper and straighter. Harris County Flood Control District developed their detention requirements several decades ago based on the average county rainfall, soil types, elevations, etc. The Clear Lake area is significantly different in all these conditions than Northwest Harris County. HCFCD currently has their detention criteria under review.

Quote From Golf Course Development Impact Study • “As one would expect, peak flow rates within these ditches resulting from this proposed development would increase considerably from those computed for existing conditions. Even though these ditches have capacity to handle additional flow before reaching their banks, any increase in water levels within these ditches would adversely impact the local storm drainage system that is connected to these ditches. Also, any increase in flow rates entering Horsepen Bayou from these ditches would aggravate the flooding along Horsepen Bayou. ”

Recommendations • Develop a detention criteria based on specific conditions • • within our watershed. The 1 acre foot per acre requirement is not any more restrictive than policies put into place in Fort Bend and Brazoria Counties. Acquire additional land at headwaters of Horsepen Bayou (end of runway at EFD) for detention ponds. Acquire the available 178 acres in OB/OBW (former golf club) to retro-fit the older developed areas with detention

OB/OBW Area Detention Pond • 178 acres available for detention pond • 1, 727 acre feet of storage capacity available at elevation of 17 feet • • • (assuming 20 ft maintenance berms, 3: 1 side slopes, and an average depth of 11 feet) 2, 047 acres would drain into the ponds and bring the old subdivisions with no detention ponds up to 85% of the 2005 CLCWA requirements for new development. Peak discharge entering Horsepen Bayou for 100 -year flood event would be reduced from approx. 3, 000 cubic feet per second down to 300 cfs. Reduces 100 -year flood levels in Horsepen Bayou downstream of El Dorado Blvd. by 20% or the equivalent of around 1. 5 feet.

EFD Area Detention Pond • Acquire around 170 acres for detention ponds • 2, 000 acre feet of storage capacity available at elevation of 22 to 24 • • feet. 4, 365 acres would drain into the ponds Peak discharge along Horsepen Bayou at ponds for 100 year flood event would be reduced from approx. 5, 000 cfs to 3, 000 cfs Reduces 100 year peak flows in Horsepen Bayou downstream of Space Center Blvd. by approx. 2, 000 to 3, 000 cfs (around 40%) Reduces 100 year flood levels in Horsepen Bayou downstream of Space Center Blvd. by approx. 4 feet.

Combined Detention Ponds • Reduces peak discharges along Horsepen Bayou for 100 year event • • by 2, 000 to 5, 000 cfs Reduces maximum flood levels along Horsepen Bayou for 100 year event by 2 to 4 feet Reduces peak discharges in Armand Bayou for the 100 year event by approx. 4, 500 cfs (around 15%) Virtually shrinks the 500 year event floodplain down to the existing 100 year event floodplain level Would remove approximately 4, 000 homes in Clear Lake City from the 500 year flood plain

Multi-use For Taxpayer Value • Single use does not maximize taxpayer value • Detention pond areas can be used for a wide variety of recreational activities • Pledge to work jointly with County, City and local citizens to develop a plan for designing multi-use amenities into the detention facilities

Status of Recommendations • New storm water detention policy put into place in Nov. 2005 which • • applies to all new development Jury in state district court golf course condemnation court hearing in November 2008 ruled that they believed that the condemnation was about blocking development and not storm water detention. Ruling has been appealed by the CLCWA and is expected to be reviewed in Spring of 2010. Land value was set in the lower court at $5. 1 million. EFD area ponds have been discussed with HCFCD and City of Houston. Since development in that area is not eminent, concentration of efforts is centered on the OB/OBW property at this time. Will take the cooperation of Exxon Mobil, Harris County, and City of Houston to put into place.

Storm Surge Study • CLCWA approached in Spring of 2009 by Rice University with a • • proposal to conduct a storm surge study for the Clear Lake area. Study would take studies already done on rainfall events and overlay with various storm surge scenarios. Maps would show actual water depth by address. Interactive map would be posted on web site so that residents could access and determine the impact on their home as part of their emergency planning. Map would also be useful in emergency response planning with a better understanding of how deep water would be in streets. Total cost would be $65, 000. CLCWA agreed to fund half of the cost and Houston Endowment will fund the other half – study to be complete by May 2010.

Impact Fee Instituted • Current sewer plant capacity has been committed and • • any future capacity due to new development will require that the sewer plant be expanded. Additional development along Space Center Blvd would also require building an addition water tower to ensure adequate water pressure in the area. In the Spring of 2009, the CLCWA implemented a new impact fee policy. Any new development would be required to pay a fee of around $3, 000 per SFRE. These funds would be used to pay for any bond money required to expand the sewer plant and build new water towers.

What Can Be Done Now • Continue to bring up the flooding issue to every • level of elected officials – CLCWA, city, county, state, and federal Remember that the elevation increases to the west – as they increase storm water run-off, where do you think it drains? All area governments need to work together.

Thank You For the opportunity to serve you and to explain how the CLCWA impacts the quality of life in the Clear Lake area