Preliminary Engineering Drainage Studies Related to Hurricane Harvey Flooding Public Meeting. Thursday, November 29, 2018

Transcription

1 Preliminary Engineering Drainage Studies Related to Hurricane Harvey Flooding Public Meeting Thursday, November 29, 2018

2 Public Meeting Agenda Overview / Background Briefing on the Drainage Investigation & Findings Public Comments from Citizens Written Comments are also Welcome

3 City-Wide Flooding Assessments Immediately following Harvey, the City began assessing drainage issues and started developing a list of areas that would require analysis. Over the course of the next several months, the City began working with Engineering Companies on 6 specific areas for Preliminary Engineering Reports.

4 City-Wide Flooding Assessments In September, Gov. Abbott s office and Representative Bonnen s office asking for a list of priority projects (Rebuild Texas program) to help build a submittal to the Federal Government that outlines high priority projects with estimated costs. In October, the City submitted the paperwork outlining both Regional and City-wide recommendations 21 large projects in total (ranging from the Coastal Spine to infrastructure hardening). The City is actively up-dating our existing City Mitigation Plan to include Harvey-related improvements. On top of up-dating our Mitigation Plan, we are working with the State Mitigation Office to ensure that the maximum number of our projects will be eligible for reimbursement (Texas Hazard Mitigation Grant Program) If funded thru HMGP, the City would be responsible for 25% of the costs. City Staff is also asking Council to consider a General Obligation Bond Election in May 2019.

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8 FEMA Current Flood Zones

9 FEMA Proposed Flood Zones

10 GO Bond Election Timeline & Processes October 23 November 8 November 27 December 11 January 8 January 10 Work Session : Potential Bond Election Town Hall Drainage where we go from here Work Session: Draft list of Bond Program Projects Work Session: Discussion Bond Program Projects Council Finalizes List of Bond Program Projects Town Hall: Bond Program Information 10

11 GO Bond Election Timeline & Processes (Cont.) January 22 February 7 February 12 February 15 March 7 April 4 May 4 First Reading Town Hall: Bond Program Information Second Reading Last day to order the election (Statutory Requirement) Town Hall: Bond Program Information Town Hall: Bond Program Information Election Day 11

12 Magnolia Bayou and Borden s Gully Analysis of Improvements to Existing Detention Area Presented by November 29, 2018 DANNENBAUM

13 Purpose Reduction to Water Surface Elevation By adding storage to existing detention ponds Construction of New Detention Pond (Near Dove Meadows) Eliminating flow constriction at Hughes Ln. and W. Deats Rd. Crossing Flow Diversion to Dickinson Bayou Combination Alternative Cost Estimates 13 DANNENBAUM

14 Background Information Project Location Map 14

15 Background Information Rainfall Gage Stations 15

16 Windshield Damage Survey Flooded Areas Map during Harvey Magnolia Bayou Drainage IH mi 2 Borden s Gully Drainage IH mi 2 16

17 Schematic of Proposed Modifications of Existing Detention Ponds Permanent WSE 17

18 Contributing to Magnolia Bayou Schematic of Proposed Modifications of Existing Detention Ponds Detention Areas Existing Volume at top Proposed Volume at top of Bank (acre-ft) of Bank (acre-ft) 1 BCTC Detention Bay View Detention BCP Detention BCN Detention along Magnolia Bayou Pinnacle Park (PP) Detention along Magnolia Bayou Sub-Total

19 Contributing to Borden's Gully Schematic of Proposed Modifications of Existing Detention Ponds Detention Areas Existing Volume at top Proposed Volume at top of Bank (acre-ft) of Bank (acre-ft) 6 LBC Detention: Dry and Wet MBC Detention West MBC Detention East BCMW West Detention along Borden's Gully BCMW East Detention along Borden's Gully CFL Linear Detention CFL Linear Detention CFL Detention BCP Detention BCP Linear Detention BCP Linear Detention BCP Detention BCPW Detention Combined along Borden's Gully Sub-Total

20 Schematic of Proposed Modifications of Existing Detention Ponds 20

21 Elevation Additional Detention (Near Dove Meadows) 18 Typical Section of Inflow Weir 500yr WSE = Concrete Lining WSE = 14.18' (Prop) 10 ft Station 500-year WSE Source: FEMA Approved LOMR (2014) Top of Bank Weir Invert =10.2 ft Stage-Area-Volume Table Elevation Area Volume Cumlative Volume ft ac ac-ft ac-ft

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23 23 DANNENBAUM

24 Results Detention Volume Gained (Ac ft) Reduction (100-yr) Water Surface Elevation Additional Storage Borden's Gully Tallow Forest St to FM ft 50 Ac ft FM 646 to IH ft Construction Cost (Millions) 1.74 M New Detention Near Dove Meadows Borden's Gully Tallow Forest St to FM ft 115 Ac ft 5.75 M FM 646 to IH ft New Detention Near Dove Meadows + Additional Storage (Borden's Gully) Tallow Forest St to FM ft FM 646 to Hughes Rd 165 Ac ft 0.16 ft 7.49 M Hughes Rd to IH ft Constriction Removed at Hughes Lane and W. Deats Borden's Gully (New Bridges) Tallow Forest St to FM ft 0.92 M FM 646 to Hughes Rd 0.16 ft Channel Improvements along Borden's Gully (TBD) 24 DANNENBAUM

25 Results Detention Volume Reduction (100-yr) Gained Water Surface Construction Cost (Ac ft) Elevation (Millions) Additional Storage Magnolia Bayou 20 Ac ft 0.01 ft 0.71 M Sedona Drainage Study (Magnolia Bayou) Mary s Ln to Tallow Forest St Tallow Forest St to Calder Road 0.29 ft By Developer 0.04 ft By Developer Flow Diversion from Magnolia to Dickinson Bayou-460 Acres Upstream of Mary's Ln 0.15 ft Mary s Ln to Calder Rd 0.26 ft Calder Rd to FM ft FM 646 to IH ft 15 Million (Approx) Bridge IH-45 work by TxDOT No benefits WSE about same By TxDOT 25

26 Recommendations Refine Additional Storage Analysis. Refine analysis for new detention pond near Dove Meadows (Borden s Gully). Refine elimination of removal of constriction at Hughes Lane and W. Deats Road (Borden s Gully). Channel improvements between Hughes Ln. and IH-45. Add Sedona benefits. Detail analysis for flow diversion from Magnolia Bayou. (TBD) Combination Alternatives Analysis. Alternatives benefit analysis /may need some field surveying. 26

27 Contact List City Manager John Baumgartner Assistant City Manager Bo Bass Tonight s Drainage Study Presentation and Slideshow will be posted to: Director of Engineering Christopher Sims, P.E christopher.sims@leaguecitytx.gov Senior Civil Engineer-Drainage Jack Murphy, P.E jack.murphy@leaguecitytx.gov

28 Thank you for attending!