Mapping the River as it Reconnects with Its Delta: Field Studies in Big Mar and Bohemia

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1 Mapping the River as it Reconnects with Its Delta: Field Studies in Big Mar and Bohemia Ezra Boyd, John Lopez, Andy Baker, Theryn Henkel Lake Pontchartrain Basin Foundation Coastal Sustainability Program

2 Outline Introduction & Context: Isolated cases of landgain in Mississippi Delta Caernarvon / Big Mar: Significant landgain from engineered diversion Cypress tree planting in emergent marsh Bohemia: Signs of a resilient ecosystem 2011 hydro study Mardi Gras Pass: The river re-writes the map

3 Introduction & Context: Traditional Landloss Map

4 Introduction & Context: Isolated Cases of Land Gain Big Mar Pond Bohemia Spillway

5 Caernarvon / Big Mar

6 Caernarvon Diversion Big Mar Pond Caernarvon Terre aux Boeufs Estuary

7 Big Mar: Landchange Assessment via Sonris Used SONRIS AOI tool to draw polygons around marsh land masses and to get areas

8 Summary: 500 acres of emergent marsh Landmass 1998 Area 2004 Area 2005 Area 2010 Area Difference ( ) Difference ( ) Difference ( ) A B C D E F G H I J K L M N 7.46 Difference ( ) O P Q R 3.62 Total Area acres acres acres acres Number of Landmasses New Landmasses acres / yr Rate of Land Growth 156 acres / yr 64 acres / yr acres / yr

9 Big Mar: Landchange Assessment via USGS

10 Summary of Raster Statistics within Big Mar Boundary Class Name Pixel Count Area (acres) (*) Rate (acres/year) (**) Change (acres) New Land Area Gain Gain Gain Gain Gain Gain Gain Gain Gain Gain Gain (*) Area = 0.22 acres/pixel x Pixel Count, based on 7,810 pixels covering 1718 acres (**) Assumes the stated time periods from Jan 1 to Jan 1. So spans 1 year, while spans 2 years

11 Big Mar: Sept 2011 Field Survey B Used handheld GPS and airboat to obtain tracks for marsh perimeter C A 2011 Landmass Area (Acres) A 723 B 86 C 68 Total 877

Aerial Photo of Emergent Marsh in SW Corner Shallow Water Outside of Polygon Flow Channels Shallow Water Shallow Water Approximate GPS Track Because we

12 Aerial Photo of Emergent Marsh in SW Corner Shallow Water Outside of Polygon Flow Channels Shallow Water Shallow Water Approximate GPS Track Because we only surveyed the perimeter of the landmass, we have no data on water areas within the landmass. Because of this our estimate of the land area is probably high.

Aerial Photo of Emergent Delta in NE Corner Mississippi River Flow Channel Approximate GPS Track Lagoons We originally went around the entire landmass.

13 Aerial Photo of Emergent Delta in NE Corner Mississippi River Flow Channel Approximate GPS Track Lagoons We originally went around the entire landmass. On the way out, Howard took us through the central flow channel. Howard says that it will stay as a permanent channel, so I used our track through the channel to divide the land mass into two masses. Land mass Additionally, five notable lagoons are within the perimeter, but they to not seem to add up to more than 30% of the total area. There is also a landmass on the SE quadrant that is outside of our perimeter. For these reasons, we think our estimate here is more accurate.

14 Caernarvon / Big Mar: Cypress Tree Planting 60+ volunteers 3 day planting mission 600+ trees planted Partnered with Coalition to Restore Coastal Louisiana

15 Bohemia Spillway

16 Mississippi River flood protection and back Levees Breton Sound Bayou Lamoque

17 Bohemia: Signs of a resilient ecosystem

18 Results: USGS Data Landloss Land gain Net Change Area Area Time Period (Sq. Miles) (Sq. Miles) Sq. Miles Total Loss Total Gain Total Net Change Modest Net Gain

19 2010 Elevation Survey of Spillway Road Whenever river stage is greater than elevation, sediment laden fresh water discharges into the spillway Survey completed by Luis Martinez of Innovative Mapping Solutions Using Trimble GNSS-RTK System mounted on 4-Wheeler September 11, 2011

20 Historic high water in spring 2011 created opportunity to observe the spillway in action LPBF teams completed hydrologic survey along the road Measured depth, velocity, and direction every ~500 ft Used data to estimate peak discharge rate into spillway Bohemia: 2011 hydro study

21 River Stage at West Pointe A La Hache Pre-High water LPBF survey March 3, 2011 High water surveys (LPBF & UNO) May 17 through June 7, 2011 Post-High Surveys July 10 17,and 24, 2011

23 Calculating Flow Rate Data Points Data points sampled flow per foot of road Water Surface Q Per foot of road Road Surface Depth x Velocity = CFS per foot of road Combined depth and velocity, then studied distributions of our samples

24 Overbank Flow: Results First Order: 38,731 cfs Second Order: 35,492 cfs Interpretive Analysis: 43,893 cfs Additional Flow: 4,553 cfs 585 cfs from culverts 3,967 cfs from blowouts => Total Flow: 40,045 48,446 cfs

blowout remained high Investigated sandbar along the riverbank.

25 Mardi Gras Pass May 21, 2011 First observed as a road blowout on May 21, 2011 When we returned on July 10, the river stage was lower but the flow through the blowout remained high Investigated sandbar along the riverbank. Observed that flow over the sandbar was eroding potential channels through the bar July 10, 2011

26 July 10, 2011 Water flowing over the sand bar and into the blowout channel

28 Because the pass connected with the river around Mardi Gras Day 2012, we have dubbed it Mardi Gras Pass

30 Mardi Gras Pass & State Master Plan

31 Conclusion The river is reconnecting with the Delta On the eastbank: An engineered diversion An unengineered spillway An emerging distributary channel In general, we have observed positive impacts in terms of land gain and resiliency.

Measurements of lateral flow from the Mississippi River at Mardi Gras Pass in the Bohemia Spillway using synoptic ADCP

Measurements of lateral flow from the Mississippi River at Mardi Gras Pass in the Bohemia Spillway using synoptic ADCP A Technical Report Submitted to: The Lake Pontchartrain Basin Foundation Submitted