Clear Lake City Water Authority. Presentation to Space Center Rotary July 14, 2008. 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
Presentation to Space Center Rotary
July 14, 2008
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.
A 500-year event equates to 19 inches of rain within a 24 hour period. (19.33 in Allison ‘02)
Markings on the TSARP map only show those areas contiguous to a waterway and does not include depressions (ponding) which are non-contiguous.
Lawrence G. Dunbar, P.E. July, 2005
Lawrence G. Dunbar, P.E. July, 2005
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 44inches 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.
Hired hydrology consultant to better understand floodingin our specific watershed and make recommendations on how to mitigate any future increase and reduce existing problems if possible.
Flooding is a result of storm water run-off.
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.
“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.”
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
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
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.
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.
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
New storm water detention policy put into place in Nov. 2005 which applies to all new development
Golf course condemnation court hearing reset to begin the first week of Sept. 2008. Motion for Summary Judgment on validity of deed restrictions was upheld at a hearing on April 24, 2008
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.
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.
For the opportunity to serve you and to explain how the CLCWA impacts the quality of life in the Clear Lake area