The Pontchartrain Maurepas Surge Consortium (LPMSC) Lake Sloshing Effect Preliminary Findings

Transcription

1 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 April 16, 2015 South Louisiana Flood Protection Authority East Board Meeting Kenner, La SaveOurLake.org

2 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.

3 Regional Authorities Participating CPRA NWS LPBF LSU Climate Center La DHS

4 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.

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7 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

8 Composite maximum surge Incoming surge Outgoing surge

9 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

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11 Empirical Storm Surge Return Levels around Lake Pontchartrain Location 50 yr 100 yr 200 yr 500 yr New Orleans Lakefront Frenier Mandeville Slidell Units: Feet above Mean Sea Level (MSL) Hal Needham

12 High Water Records around Lake Pontchartrain Location Storm Year Water Level Datum Year Event New Orleans Katrina NAVD88 98 Lakefront Frenier Betsy Unknown 115 Mandeville Katrina NAVD88 78 Slidell Katrina NAVD Hal Needham

13 Links/ Contact Info SCIPP SURGEDAT Contact info: Hal Needham

14 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

15 30 Lake Maurepas Maurepas Landbridge Lake Pontchartrain East Orleans Landbridge Mississippi Sound

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18 30 Lake Maurepas Maurepas Landbridge Lake Pontchartrain East Orleans Landbridge Mississippi Sound Direction and Length of Maximum Fetch ESE >75 SSW to SE 25 WSW 29 W 52 ENE 45 WNW 43 N 25

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20 Surge Transmission Potential function of cross section area and boundary resistance IHNC closed Positive surge head

21 Surge Transmission Potential function of cross section area and boundary resistance IHNC closed Negative surge head

22 SE 16 SSE 15 SW 14 ENE 22 WNW 10 NNE 10

23 LP Soft and Equidistant Hard and Convergent

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25 Lake Maurepas Lake Pontchartrain Track East of New Orleans Eye far southeast of LP Pre wind surge Mississippi Sound Eye East of LP Wind & Surge effect Eye northeast of LP Wind & Surge discharge effect

26 Lake Maurepas Lake Pontchartrain Track East of New Orleans Eye far southeast of LP Pre wind surge Mississippi Sound Eye East of LP Wind & Surge effect Eye northeast of LP Wind & Surge discharge effect

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28 All storms East Track only e.g. Katrina West track only e.g. Isaac All storms

29 LP WEST LP LP LP SOUTH LP NORTH LP EAST LP

30 E>S>W E>N>W

31 E>W E>S>W E>N>W

32 Easterly Passage, such as Hurricane Katrina

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34 LP LP LP

35 ENE 45 SW 15

36 SE 16 N 25 NNE 10

37 WNW 43 WNW 10

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39 W 52 SW 15

40 W 52 SW 15 Lower Surge Transmission

41 Westerly Passage, such as Hurricane Isaac

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43 EARLY Hurricane Isaac CERA Model LATE

44 LP LP LP

45 LP LP wet side rainfall LP

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47 ENE 45 SW 15

48 SSW to SE 25 SE 16 S 12 SW 15 SW 15 NNW 10 WNW 10

49 WSW 29 S 12

50 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

51 Lake Passage, such as 1915 Hurricane

52 E>W E>S>W E>N>W

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54 So what is the worst track scenario for Pontchartrain Maurepas Surge? Different tracks put different areas at most risk

55 LP Westerly Passage E>S>W wind rotation worst case surge Frenier to Mandeville LP LP LP

56 Easterly Passage E>N>W wind rotation worst case surge NO east to Slidell LP LP LP LP

57 Lake Passage E>W wind shift worst case surge Frenier & Slidell

58 All worst case surges of the three conceptual tracks

59 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

60 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.