06-11-18 Drainage and Flooding Committee Meeting

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REQUEST FOR DRAINAGE COMMITTEE AGENDA ITEM Agenda Date Requested: June 11, 2018 Requested By: L. Wingate/D. Pennell Department: Public Works Report: �*, Resolution: C-Ordinance: C- Exhibits : Appropriation Source of Funds: Account Number: Amount Budgeted: Amount Requested: Budgeted Item: 4, YES C-NO SUMMARY Harris County Flood Control District's (HCFCD) F101-06-00 Channel system conveys storm water runoff from the Lomax area and ultimately outfalls into Lower San Jacinto Bay. The downstream section of the channel has been improved to ultimate capacity. An existing pipeline corridor, containing several pipelines located at depths ranging from approximately 2' to 18', cross the channel, limiting the depth of potential channel improvements. Moderate/heavy rain events, compounded with backwater conditions from this section of the channel, contributes to wide -spread flooding within the Lomax Area. Harris County Flood Control staff has informed Public Works staff that survey data has been collected on this most upstream section. Construction drawings are being prepared in-house, by HCFCD staff, to provide direction on clearing overgrowth, trees, and obstructions; minor erosion control and slope stabilization; and desalting. Construction is projected to begin late 4th quarter 2018 or early 1st quarter 2019 (calendar year). A high level delineation by KSA found the watershed to be about 310 acres, versus the 583 acres used in the 1987 masterplan. Unit F101-06-00 has a capacity of less than 200 cfs, currently, before it rises out of its banks. The following options were included within the preliminary draft of the feasibility study prepared by KSA: 1) Full excavation of existing 60-ft ROW to construct a concrete channel that will maximize capacity of current ROW, providing approximately 700 cfs, without deepening the channel. 2) Construct concrete channel from Valley View to the existing drop structure; widen the channel beyond the ROW to convey the 100-year event (1,326 cfs) by maintaining existing flow line of the channel. 3) Construct concrete channel from Valley View to the pipeline corridor and deepen the existing grass lined channel, by one foot, from the pipeline corridor to the existing drop structure. Action Re quire d: Approved for Drainage Committee Agenda Corby D. Alexander, City Manager Date