The Pontchartrain Maurepas Surge Consortium (LPMSC) Lake Sloshing Effect Preliminary Findings Lake Pontchartrain Basin Foundation John A. Lopez, Ph.D. with contributions from Dr. Joe Suhayda, Dr. Hal Needham, and Dr. Ezra Boyd workshop held Feb. 20 2015 April 16, 2015 South Louisiana Flood Protection Authority East Board Meeting Kenner, La SaveOurLake.org
Pontchartrain Maurepas Surge Consortium Mission The LPMSC mission is to leverage local expertise with additional technical resources in a regional collaboration that will promote a broader understanding of storm surge dynamics in the lakes, and abetter informed storm surge risk reduction strategies for all communities around the Lakes to bolster the environmental sustainability, community resilience, and safety of residents through enhancement of storm surge risk management.
Regional Authorities Participating CPRA NWS LPBF LSU Climate Center La DHS
Presentation of surge data is often the maximum surge during storm passage and so is a composite over time masking the actual storm surge movement details including model data and observed storm surge elevations.
20 18 16 14 12 10 8 6 4 2 0 Water Surface Elevation Profile - North Transect 100-Year Event 400-Year Event 1000-Year Event Feet Interstate 10 Lake Pontchartrain Shoreline Lake St. Catherine Shoreline Lake St. Catherine Shoreline Lake Borgne Shoreline Lake Pontchartrain East Orleans Land Bridge Lake Borgne
Composite maximum surge Incoming surge Outgoing surge
Empirically Derived Storm Surge Return Levels Image: Time News Feed How often does a surge of this magnitude occur? Contact info: Hal Needham hal@srcc.lsu.edu
Empirical Storm Surge Return Levels around Lake Pontchartrain Location 50 yr 100 yr 200 yr 500 yr New Orleans 10.2 12.0 13.7 16.1 Lakefront Frenier 10.3 12.6 14.9 18.0 Mandeville 9.2 10.6 12.0 13.8 Slidell 12.3 15.2 18.1 21.9 Units: Feet above Mean Sea Level (MSL) Hal Needham hal@srcc.lsu.edu
High Water Records around Lake Pontchartrain Location Storm Year Water Level Datum Year Event New Orleans Katrina 2005 11.9 NAVD88 98 Lakefront Frenier Betsy 1965 13.1 Unknown 115 Mandeville Katrina 2005 10.0 NAVD88 78 Slidell Katrina 2005 15.7 NAVD88 114 Hal Needham hal@srcc.lsu.edu
Links/ Contact Info SCIPP www.southernclimate.org SURGEDAT http://surge.srcc.lsu.edu Contact info: Hal Needham hal@srcc.lsu.edu
The Lake Pontchartrain sloshing effect is principally due to wind stress, wind driven waves and surge flux, which vary during storm Passage. The Variables Influencing Wind Driven Waves: Wind Speed Fetch Width of area affected by a wind field, i.e. open water that the wind is blowing Wind duration Water depth
30 Lake Maurepas Maurepas Landbridge Lake Pontchartrain East Orleans Landbridge Mississippi Sound 20 10 0 10 0 10 20 30 40 50 60 70 80 20 30
30 Lake Maurepas Maurepas Landbridge Lake Pontchartrain East Orleans Landbridge Mississippi Sound 20 10 0 10 0 10 20 30 40 50 60 70 80 20 30 Direction and Length of Maximum Fetch ESE >75 SSW to SE 25 WSW 29 W 52 ENE 45 WNW 43 N 25
Surge Transmission Potential function of cross section area and boundary resistance IHNC closed Positive surge head
Surge Transmission Potential function of cross section area and boundary resistance IHNC closed Negative surge head
SE 16 SSE 15 SW 14 ENE 22 WNW 10 NNE 10
LP Soft and Equidistant Hard and Convergent
30 20 10 Lake Maurepas Lake Pontchartrain Track East of New Orleans Eye far southeast of LP Pre wind surge Mississippi Sound 0 10 0 10 20 30 40 50 60 70 80 20 30 30 20 Eye East of LP Wind & Surge effect 10 0 10 0 10 20 30 40 50 60 70 80 20 30 30 20 Eye northeast of LP Wind & Surge discharge effect 10 0 10 0 10 20 30 40 50 60 70 80 20 30
30 20 10 Lake Maurepas Lake Pontchartrain Track East of New Orleans Eye far southeast of LP Pre wind surge Mississippi Sound 0 10 0 10 20 30 40 50 60 70 80 20 30 30 20 Eye East of LP Wind & Surge effect 10 0 10 0 10 20 30 40 50 60 70 80 20 30 30 20 Eye northeast of LP Wind & Surge discharge effect 10 0 10 0 10 20 30 40 50 60 70 80 20 30
All storms East Track only e.g. Katrina West track only e.g. Isaac All storms
LP WEST LP LP LP SOUTH LP NORTH LP EAST LP
E>S>W E>N>W
E>W E>S>W E>N>W
Easterly Passage, such as Hurricane Katrina
LP LP LP
ENE 45 SW 15
SE 16 N 25 NNE 10
WNW 43 WNW 10
W 52 SW 15
W 52 SW 15 Lower Surge Transmission
Westerly Passage, such as Hurricane Isaac
EARLY Hurricane Isaac CERA Model LATE
LP LP LP
LP LP wet side rainfall LP
ENE 45 SW 15
SSW to SE 25 SE 16 S 12 SW 15 SW 15 NNW 10 WNW 10
WSW 29 S 12
The future of the region and New Orleans hinges on Coastal restoration. Emergence of Coastal Louisiana s Vulnerability to Hurricane Surges Eye over lake but west of Orleans 21 deaths West passage 58 deaths Hurricane Betsy West Passage 12 deaths East Passage 986 to 1,440 deaths Hurricane Katrina Pontchartrain & Vic. Decision Chronology (Woolly and Shabman, 2008) Mortality added by LPBF 3
Lake Passage, such as 1915 Hurricane
E>W E>S>W E>N>W
So what is the worst track scenario for Pontchartrain Maurepas Surge? Different tracks put different areas at most risk
LP Westerly Passage E>S>W wind rotation worst case surge Frenier to Mandeville LP LP LP
Easterly Passage E>N>W wind rotation worst case surge NO east to Slidell LP LP LP LP
Lake Passage E>W wind shift worst case surge Frenier & Slidell
All worst case surges of the three conceptual tracks
Typical Expected Characteristics to the Pontchartrain Maurepas Basin Relative track Westward Passage of LP Eastward Passage of LP Central Passage LP Example storms tracks Isaac, Gustav, Bill, Betsy Katrina, Isidore, Camille, Georges 1915 hurricane? Wind field shift (origin) East>South>West East>North>West E>W Surge max rotation Clockwise Counter clockwise Symmetrical west to east Local Rainfall Wet storm Dry storm?? Local Runoff significant, may add to surge less significant?? Location Maximum lake surge NW quadrant NE Quadrant NE Quadrant Approaching "Slosh" location LaBranch/Frenier LaBranch/Frenier Frenier Departing "Slosh" Location NW Quadrant NE Quadrant NE Quadrant
Preliminary conclusions of Lake surge sloshing Primary Factors Surge flux, i.e. surge head Waves, i.e. run up Secondary Factors Shoreline geometry e.g. leeward/windward or convergence Natural Shoreline type e.g. shallow /steep, vegetation Surge transmission potential e.g. cross sectional area, roughness Levees, e.g. reducing storage, deflecting surge In all except a for direct strike, Sloshing is actually a rotation of maximum surge around the lake perimeter, but typically more pronounced on eastern and western shores. The rotation of the max surge is counter clockwise for an east passing storm and clockwise for a westerly passing storm. For Lake passage surge would likely slosh symmetrically west to east.