02-28-11 Drainage and Flooding Committee minutes

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klotz451associates Re- analysis of Drainage Impacts to B106 -02 -00 and B106 -00 -00 August 30, 2010 Page 2 of 2 Stream B106-02-00, which is unstudied, was divided into an upstream reach and a downstream reach for flood routing. The dividing point between the reaches is Old Hickory Drive. In order to define storage - discharge relationships for these reaches, an HEC -RAS model was developed using geometry from LiDAR data. As -built drawings dated February 2, 1982, entitled "Fairmont Park East — Section One," prepared by Gulf Coast Engineering & Surveying were used to define bridge geometry at Old Hickory Drive (and adjacent Humble Pipeline) and the channel geometry upstream from that point. The resulting storage - discharge relationships were used for Modified Pul's routing in HEC -HMS. Results and Conclusion Table 1 shows a comparison of computed flows between pre- and post - project conditions for the 1% storm event. This table shows for 13106 -00 -00 there is no impact on flows between the confluence with B106-02-00 at Junction 2 and the confluence with Armand Bayou (B100- 00 -00) at Node b100 #7d. However, for B106-02 -00 there is an increase in computed flows at Old Hickory Drive. The 1% -event hydrographs for pre - and post - project conditions are shown for these locations on Exhibits 3a thru 3f. Table 2 shows the same comparison for the 10% storm event. This table shows for B106 -00 -00 there is no impact on flows between the confluence with B106 -02 -00 at Junction 2 and the confluence with B 100 -00 -00 at Node b 100 #7d. In conclusion, our re- analysis of impacts for the proposed drainage improvements shows no impacts on flows for the 10% and 1% storm events within B 106- 00 -00. Therefore, for B106-00- 00 the proposed project will cause no impact for events up to and including the 100 -year (1 %) event.