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
Agenda Project Description and Objectives Path to LAMP Benefit Determination Modeling Approach August 2016 Flood Calibration and Results Path Forward Discussion 2
3 Project Location
4 Study Area Focus
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 FEMA LAMP
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
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 Hydrologic & Hydraulic Modeling- Approach
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
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
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
Initial Model Development, 2D Grid SPANISH LAKE 13
Initial Model Development, Surface SPANISH LAKE 14
Initial Model Development, Roughness SPANISH LAKE 15
16 August 2016 Historic Flood
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 August 2016 Historic Flood
2-D Model Calibration: Aug 2016 Event PORT VINCENT SPANISH LAKE INTERIOR LAKE MAUREPAS EXTERIOR 19
2-D Model Calibration: Aug 2016 Event 18.0 RAINFALL 18.0 PORT VINCENT Cumulative Rainfall Depth (in) 16.0 14.0 12.0 10.0 8.0 6.0 4.0 2.0 0.0 8/6 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) 16.0 14.0 12.0 AMITE 10.0 8.0 6.0 4.0 2.0 0.0 8/11 8/13 8/15 8/17 8/19 8/21 8/23 8/25 USGS Stream Gage 07380120 5.0 LAKE MAUREPAS 8.0 MB PUMP STATION Stage (ft) 4.5 4.0 3.5 3.0 2.5 2.0 BLIND RIVER AMITE Stage (ft) 7.0 6.0 5.0 4.0 3.0 EXTERIOR INTERIOR 1.5 2.0 1.0 0.5 0.0 8/11 8/13 8/15 8/17 8/19 8/21 8/23 8/25 USGS Stream Gage 301324090382400 USGS Stream Gage 07380215 1.0 0.0 8/11 8/13 8/15 8/17 8/19 8/21 8/23 8/25-1.0 USGS Stream Gage 073802282, DS USGS Stream Gage 073802282, US 20
2-D Model Calibration: Aug 2016 Event 10.0 BLACK BAYOU DS 12.0 BLACK BAYOU US 9.0 8.0 GAGE MODEL 10.0 GAGE 7.0 6.0 8.0 Stage (ft) 5.0 4.0 Stage (ft) 6.0 MODEL 3.0 4.0 2.0 1.0 2.0 0.0 8/11 8/13 8/15 8/17 8/19 8/21 8/23 8/25 USGS Stream Gage 073802245 HEC-RAS WSE 0.0 8/11 8/13 8/15 8/17 8/19 8/21 8/23 8/25 USGS Stream Gage 0738022395 HEC-RAS WSE 14.0 GRAND GOUDINE 9.0 BAYOU FRANCOIS 12.0 8.0 Stage (ft) 10.0 8.0 6.0 MODEL GAGE Stage (ft) 7.0 6.0 5.0 4.0 MODEL GAGE 4.0 3.0 2.0 2.0 1.0 0.0 8/11 8/13 8/15 8/17 8/19 8/21 8/23 8/25 0.0 8/11 8/13 8/15 8/17 8/19 8/21 8/23 8/25 USGS Stream Gage 0738022295 HEC-RAS WSE USGS Stream Gage 073802273 HEC-RAS WSE 21
22 2-D Model Calibration: Aug 2016 Event
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 110-2-1413 (used as guidance) Over 100 Possible Model Runs Using Different Frequency Event Combinations 27 Critical Combinations Used for Analysis 23
Coincident Event Analysis, Flooding Sources AMITE RIVER SPANISH LAKE INTERIOR LAKE MAUREPAS EXTERIOR MB PUMP STATION 24
25 Coincident Event Analysis - Precipitation
Coincident Event Analysis, Storm Surge 14 Tropical Storm Allison Gage Data Gage Height (ft) 12 10 8 6 4 2 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 14 12 Gage Height (ft) 10 8 6 4 2 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 Preliminary Mapping
28 Preliminary Mapping
29 Preliminary Mapping
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
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 Next Steps
Discussion