HEC-RAS 2D Modeling in Support of Ascension Parish Levee Certification

Transcription

1 HEC-RAS 2D Modeling in Support of Ascension Parish Levee Certification OFMA 2017 Annual Conference September 19, 2017 Presented by: Jeff Doudrick, PE, ENV SP Project Manager HNTB Corporation

2 Agenda Project Description and Objectives Path to LAMP Benefit Determination Modeling Approach August 2016 Flood Calibration and Results Path Forward Discussion 2

3 3 Project Location

4 4 Study Area Focus

5 Project Objectives Evaluate steps to certify and accredit the existing levee system associated with the Marvin Braud Pump Station Marvin Braud North Marvin Braud West Laurel Ridge Reduce flood risk Reduce flood insurance rates Improve Community Rating System (CRS) rating 5

6 6 FEMA LAMP

7 Collaboration Continuous, collaborative communication with key stakeholders 7 Meetings & Technical Work-Shops with FEMA Region VI, FEMA LOMR, DOTD, and Parish Formal and informal meetings/communications with USACE and CPRA Peer-review available reports and studies Not re-inventing the wheel Incorporated available relevant data & information 7

8 Path to LAMP Determination Interior influenced by Exterior Recommended 2D Model Recommended Coincident Event Analysis 471,640 = 89.3 miles of survey completed Program Implementation Plan H&H Modeling, FEMA LAMP ( Sensitivity Analyses ) Levee & Pump Station Inspection Levee & Channel Surveys Geotechnical Field Data Collection & Analyses Hydrologic & Hydraulic Modeling Data Collection & Develop Plan Recommended LAMP Overall rating of the Marvin Braud Levee System - Unacceptable MB Pump Station Requires updated O&M Manual & updated Operations Procedures Five 80-ft soil borings 8

9 9 Hydrologic & Hydraulic Modeling- Approach

10 Model Formulation: HEC-RAS v5.0 with 2-D Interior Drainage System Modeling Started with current effective FEMA hydraulic model (1-D) Decided on HEC-RAS 2-D to better represent the interconnected flow of the bayous and canals 10

11 Model Formulation: HEC-RAS v5.0 with 2-D Exterior River Modeling Started with update of current effective FEMA hydraulic model (1-D) Backwater impact at Highway 22 Expanded 1-D Modeling to include reach from Diversion to Maurepas 1-D Modeling produced artificially high WSEL at downstream end Decided on full 2-D model for exterior and interior 11

12 Initial Model Development Combined Interior-Exterior Model (~ 400 sq. miles) to provide the best representation of overflow from the Amite River into the interior of the levee system AMITE RIVER SPANISH LAKE INTERIOR LAKE MAUREPAS EXTERIOR MB PUMP STATION 12

13 Initial Model Development, 2D Grid SPANISH LAKE 13

14 Initial Model Development, Surface SPANISH LAKE 14

15 Initial Model Development, Roughness SPANISH LAKE 15

16 16 August 2016 Historic Flood

17 August 2016 Historic Flood Largest flood of record Somewhere between a 100yr and 500yr event Nearly 1/3 of homes within Ascension Parish flooded Happened in the middle of building our model Lots of data collected for model calibration 17

18 18 August 2016 Historic Flood

19 2-D Model Calibration: Aug 2016 Event PORT VINCENT SPANISH LAKE INTERIOR LAKE MAUREPAS EXTERIOR 19

20 2-D Model Calibration: Aug 2016 Event 18.0 RAINFALL 18.0 PORT VINCENT Cumulative Rainfall Depth (in) /6 8/8 8/10 8/12 8/14 8/16 8/18 8/20 8/22 8/24 Cumulative Rainfall (in) RAINFALL RAINFALL RUNOFF Cumulative Rainfall Runoff (in) (SERC SCS CN Method) Stage (ft) AMITE /11 8/13 8/15 8/17 8/19 8/21 8/23 8/25 USGS Stream Gage LAKE MAUREPAS 8.0 MB PUMP STATION Stage (ft) BLIND RIVER AMITE Stage (ft) EXTERIOR INTERIOR /11 8/13 8/15 8/17 8/19 8/21 8/23 8/25 USGS Stream Gage USGS Stream Gage /11 8/13 8/15 8/17 8/19 8/21 8/23 8/ USGS Stream Gage , DS USGS Stream Gage , US 20

21 2-D Model Calibration: Aug 2016 Event 10.0 BLACK BAYOU DS 12.0 BLACK BAYOU US GAGE MODEL 10.0 GAGE Stage (ft) Stage (ft) 6.0 MODEL /11 8/13 8/15 8/17 8/19 8/21 8/23 8/25 USGS Stream Gage HEC-RAS WSE 0.0 8/11 8/13 8/15 8/17 8/19 8/21 8/23 8/25 USGS Stream Gage HEC-RAS WSE 14.0 GRAND GOUDINE 9.0 BAYOU FRANCOIS Stage (ft) MODEL GAGE Stage (ft) MODEL GAGE /11 8/13 8/15 8/17 8/19 8/21 8/23 8/ /11 8/13 8/15 8/17 8/19 8/21 8/23 8/25 USGS Stream Gage HEC-RAS WSE USGS Stream Gage HEC-RAS WSE 21

22 22 2-D Model Calibration: Aug 2016 Event

23 Coincident Event Analysis Questions: What is the 100-year interior event? What is the source of flooding for a 100 year event? Analysis: USACE EM (used as guidance) Over 100 Possible Model Runs Using Different Frequency Event Combinations 27 Critical Combinations Used for Analysis 23

24 Coincident Event Analysis, Flooding Sources AMITE RIVER SPANISH LAKE INTERIOR LAKE MAUREPAS EXTERIOR MB PUMP STATION 24

25 25 Coincident Event Analysis - Precipitation

26 Coincident Event Analysis, Storm Surge 14 Tropical Storm Allison Gage Data Gage Height (ft) LAKE MAUREPAS PORT VINCENT 0 6/2/2001 6/9/2001 6/16/2001 6/23/2001 6/30/2001 Date Amite River at Hwy 22 Near Maurepas Amite River at Port Vincent Hurricane Isaac Gage Data Gage Height (ft) LAKE MAUREPAS PORT VINCENT 0 8/25/2012 0:00 9/1/2012 0:00 9/8/2012 0:00 9/15/2012 0:00 9/22/2012 0:00 Date/Time Amite River at Port Vincent Amite River at Hwy 22 Near Maurepas 26

27 27 Preliminary Mapping

28 28 Preliminary Mapping

29 29 Preliminary Mapping

30 Path Forward to Levee Certification Address Existing Levee Deficiencies Refine HEC-RAS 2D model to include other areas of interest Evaluate projects that could enhance level of protection Full certification Engineering and Design Re-Mapping 30

31 Model Improvements Added Colyell Creek Basin Broke out Henderson Bayou Additional survey Added more bridges and culverts Focused on Exterior (flow, wetland n-values) 31

32 32 Next Steps

33 Discussion