Clear Lake City Water Authority Hurricane Harvey Storm Water Analysis

Please review the attached power point presentation from the CLCWA.

The Clear Lake City Water Authority is still looking for survey responses from homeowners who flooded in Hurricane Harvey. There is a reference to the survey at the end of the file, and the survey can also be found on their web site. (www.CLCWA.org, Stormwater Plan and Drainage tab)

This is important because (unlike most utility districts) the Clear Lake City Water Authority owns the storm sewer systems within their jurisdiction. Therefore, they are taking steps to correct flooding issues that resulted from high intensity rainfall that was more than our sewer systems could handle. Options being considered include upsized storm sewer outfall pipes and/or an extreme event sheet flow swale. These options would be used to correct the flooding problems that occurred in Meadowgreen Section 1 and University Green Sections 1-6. These options are only available due to the increased holding capacity provided by the ponds in Exploration Green.

Bay Forest had a different problem…lower elevations in relation to Horsepen Bayou. As a result, the upsized pipes and sheet flow swales will not work for them. Additional holding capacity as development continues in Exploration Green should slow down the flow of water into Horsepen Bayou and assist with those problems. It would also be beneficial if we all continue to work with Harris County Flood Control to desilt our existing flood control ditches in order to restore their original capacity. The more we can hold and slow down the flow into Horsepen Bayou, the more areas will have additional flooding protection, particularly in a high tide and/or high intensity rain situation.

Finally, it was interesting to note on the charts that the flood plain definitions have been expanded due to recent high intensity rain measurements. In addition to 100 and 500 year rainfall standards, we are looking at 1000, 2000, and 5000 year standards. At the bottom of the chart on page 5 there is a line labeled “PMP” for” Possible Maximum Precipitation”. During Hurricane Harvey, the gauge at Clear Creek and I45 hit 95% of the possible maximum precipitation.

 


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