Transcript here - Clear Lake City Water Authority

Clear Lake City Water
Authority
Storm Water Detention In
Horsepen Bayou Watershed
September 2009
CLCWA Background
• Created in 1963 by the state legislature at
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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
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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
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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
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Galveston counties
Recycled water facilities at golf courses and UofH/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
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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)
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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
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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
Horsepen Bayou
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Lawrence G. Dunbar, P.E July, 2005
Flooded Areas Along Reseda Road
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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
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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
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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
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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
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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
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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
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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
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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