5/25/2017. Overview. Project Background Information. Project Background Information Modeling Approach Model Development Results Next Steps

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1 City of Corpus Christi Downtown 2D Mapping Effort Brandon Hilbrich, PE, CFM Jake Fisher, PE, CFM Curtis Beitel, PE, CFM 2016 HDR, Inc., all rights reserved. Overview Project Background Information Modeling Approach Model Development Results Next Steps Project Background Information 2016 HDR, Inc., all rights reserved. 1

2 Background Corpus Christi has participated in NFIP since 1973 Previous Effective FIRM o July 1985 o Protected area as Zone B Background FEMA started FIS update in 2007 FEMA requested certification from City in March 2012 o Earthen levee on west side (Salt Flats) o Small floodwall on northeast corner Draft FIRM in July 2012 o Protected area as Zone AO w/ (Depth 3 FT) & (Depth 2 FT) o Bay Zone VE (EL 15) o Surge = 8.4 Background FEMA s Levee Analysis & Mapping Procedures (LAMP) o Proposed Approach in December 2011 o Final Approach in July 2013 FEMA Initiated Nueces County LAMP Pilot Study o Initial Documentation o Salt Flats Levee & Museum Floodwall Local Levee Partner Team (LLPT) Meetings o On site and Monthly status calls Submittals to FEMA Review LAMP documents 2

3 Background FEMA and City agreed to show protected area as a Seclusion Area o Allows Preliminary Nueces County FIRMs to become Effective Once LAMP Pilot Study is complete, FEMA will update the FIRM map Purpose Downtown Flood Protection System o Two Storm Water Pump Stations o Complex storm drain network o Variable tailwater Solution = 1D/2D XP-SWMM Model Better understanding of the current level of protection. o Existing Levee and Flood Protection Wall Impacts o Pump Station Effectiveness Identify proposed improvements to the Downtown area o Improvements to existing flood protection system o New drainage infrastructure Downtown Flood Protection System 3

4 Study Area Two Major Watersheds of Inner Harbor Basin o Salt Flats Watershed 2.5 sq mi 81% Urbanized o Downtown Watershed 1.5 sq mi 84% Urbanized 13.9 miles of storm drain system 1.6 miles of open channel Downtown area protected by 3.0 miles flood protection wall o Downtown Elevation: 2 to 7 feet o Flood Protection Wall (top elevation): 12 to 14 feet Project Approach 2016 HDR, Inc., all rights reserved. Scope of Work Update hydrology using latest available data Include Seawall Overflow analysis for current future (50-year and 100- year) sea level rise conditions Develop existing conditions XPSWMM D/2D model Identify 20 structures within Seclusion Area for finished floor survey Develop, model, and evaluate impacts of 4 concept level CIP projects 4

5 Model Design Criteria Conform to City of Corpus Christi Drainage Design Manual and FEMA Mapping Standards Storm surge defined based on USACE sea level rise guidance Existing Conditions Analysis o 9 Annual Chance Event (ACE) conditions o 24-hour storm duration Proposed Conditions Analysis o 1% ACE under current sea level o 4 concept level CIP projects Model Development 2016 HDR, Inc., all rights reserved. Available Data GIS Data o 1-ft Contours and DEM (2011) o SSURGO Soils for Nueces County (2008) o City of Corpus Christi Landuse (2016) o City of Corpus Christ Downtown Building Planimetrics (2012) o City of Corpus Christ Storm Drain Network Data (2016) Concurrent Project o S. Staples St. Improvements (2015) under construction Record Drawings o Storm Drain Systems ( ) o Salt Flats Channel ( ) o Power St. & Kinney St. Pump Stations (1948 & 2008) o Seawall Improvements ( ) Pump Station Operations Previous Studies o City-Wide Storm Water Master Plan (On-going) 5

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8 1D Model Hydrology & Hydraulics SWMP Inner Harbor Basin subdivided into 136 subbasins o Major SD > 30 inch o Minor SD > 24 inch outfalls directly to Corpus Christi Bay along Seawall o Major SD Junctions o Open channels throughout system Delineated using ft LiDAR data Hydraulic systems defined using City network dataset, LiDAR, and as-builts o Size, length, material o Inverts, spill crests Assumptions o SD not inlet controlled o Does not include entire SD network (manholes, bends, and lateral systems) 8

9 2D Model Application 1D Components linked to 2D Surface Rainfall runoff, wave overtopping, and storm surge o Overland areas o Undefined open channels 2D Model Data Input Data o 2011 LiDAR DEM o Breaklines o 2D Landuse Roughness One grid extents for entire model (30 cell) Seawall Overtopping Analysis Calculated RSLR for nearest NOAA station o 50-year = +1.3 feet o 100-year = +3.0 feet Used peak WSELs from FEMA FIS (2012); Applied RSLR to peak WSELs for future conditions Determined peak overtopping flow per foot of Seawall Storm surge stage and Overtopping flow hydrographs used in model as boundary conditions 9

10 System Boundary Conditions Tailwater Storm Surge Initial Depth Consideration o Sea Level Condition o Backflow Prevention o Initial pump station depths Wave Overtopping Flow Levee Gates closed Photo of SFL gate on Broadway St. Results 2016 HDR, Inc., all rights reserved. Existing Conditions 10% and 1% ACE inundation depths mapped for entire study area Overland flow transfer between watersheds Local system inefficiencies 10

11 Existing Conditions Max WSELs (CSL conditions) determined for all storm events within Seclusion Area System assessment summarized by specified Zones Source of flooding for 1% ACE identified Existing Conditions Wave overtopping accounts for 10% flood volume in Power and Kinney Street watersheds Depths increased by along Shoreline Blvd Increases less than 0.5 in Downtown low areas FEMA LAMP Study Comparison XPSWMM 1% ACE inundation mapping compared to FEMA LAMP FLO-2D results developed in September

12 FEMA LAMP Study Comparison Design Constraints Workshop held with City to discuss existing conditions 20 Buildings selected for finished floor survey Design constraints set based on priority area identified by City Proposed Improvements Evaluated 4 scenarios o Existing Blucher-Arroyo System failure and improvements o Proposed Hughes St. Pump Station (Design completed) o Two additional project improvement scenarios to meet Design Constraints Simulated for 1% ACE under current sea level conditions only Cost Estimates not developed for improvement options 12

13 Blucher-Arroyo System Failure Oct Event Road failure 10 wide Rainfall data not available 1% ACE Results o 70 min. surcharge duration o Peak flow = 85 cfs o Flood depth near 1 in area o Did not impact Downtown system near Power St. Pump Station System Breach Location Blucher-Arroyo System Failure System Breach Location Blucher-Arroyo System Failure 13

14 Hughes St. Pump Station Acquired 2009 Design Plans SD Improvements o N. Mesquite St. o Hughes St. o Chaparral St. Relieve Salt Flats ditch New pump station 2-6 x5 (in) 1-9 x6 (in) 1-48 (in) Hughes Street Pump Station 2-8 x6 (out) Option 1 Improvements Salt Flats Lift Station Channel Improvements x3 (in) Option 2 Improvements Upsize to 48 RCP along Lawrence St. Results: o Max 0.7 flood depth reduction o Flooding eliminated at Education Service Center Region 2 (Bldg No. 5) o Localized benefit

15 Moving Forward City of Corpus Christ to provide existing conditions floodplain mapping to FEMA for consideration in mapping the Seclusion Area. Use holistic model to evaluate CIP projects selected for the recent City Bond program. Contact Information Curtis Beitel, PE, CFM D M brandon.hilbrich@hdrinc.com Brandon Hilbrich, PE, CFM D M brandon.hilbrich@hdrinc.com Jake Fisher, PE, CFM D jake.fisher@hdrinc.com Questions? Questions 15