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
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
Introduction & Context: Traditional Landloss Map
Introduction & Context: Isolated Cases of Land Gain Big Mar Pond Bohemia Spillway
Caernarvon / Big Mar
Caernarvon Diversion Big Mar Pond Caernarvon Terre aux Boeufs Estuary
Big Mar: Landchange Assessment via Sonris Used SONRIS AOI tool to draw polygons around marsh land masses and to get areas
Summary: 500 acres of emergent marsh Landmass 1998 Area 2004 Area 2005 Area 2010 Area Difference (1998-2004) Difference (2004-2005) Difference (2005-2010) A 5.7 6.33 5.08 6.24 0.63-1.25 1.16 0.54 B 38.61 43.69 99.74 104.7 5.08 56.05 4.96 66.09 C 5.91 9.74 15.31 26.65 3.83 5.57 11.34 20.74 D 17.18 18.83 23.13 80.31 1.65 4.3 57.18 63.13 E 1.95 3.43 11.85 65.5 1.48 8.42 53.65 63.55 F 2.74 2.85 4.31 18.78 0.11 1.46 14.47 16.04 G 15.1 19.36 16.95 22.38 4.26-2.41 5.43 7.28 H 1.63 0.92 4.35-0.71 3.43 I 15.21 45.53 30.32 J 37.81 33.55-4.26 K 24.22 81.26 57.04 L 7.2 14.68 7.48 M 13.17 N 7.46 Difference (1998-2010) O 13.99 P 13.99 Q 27.13 R 3.62 Total Area 87.19 105.9 261.7 583.3 18.67 acres 155.87 acres 321.56 acres 496.1 acres Number of Landmasses New Landmasses 7 8 12 18 1 5 6 3.11 acres / yr Rate of Land Growth 156 acres / yr 64 acres / yr 1998-2010 41 acres / yr
Big Mar: Landchange Assessment via USGS
Summary of Raster Statistics within Big Mar Boundary Class Name Pixel Count Area (acres) (*) Rate (acres/year) (**) Change (acres) 2009-2010 New Land Area 103 23 23 2006-2010 Gain 181 2008-2009 Gain 389 85 85 2006-2008 Gain 337 74 37 1998-2004 Gain 2004-2006 Gain 639 140 70 23 2002-2004 Gain 38 8 4 1998-2010 Gain 1999-2002 Gain 58 13 4 344 1998-1999 Gain 11 2.41 2.41 1995-2010 Gain 1995-1998 Gain 2 0.44 0.15 345 (*) 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 2008-2009 spans 1 year, while 2006-2008 spans 2 years
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 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. 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.
Caernarvon / Big Mar: Cypress Tree Planting 60+ volunteers 3 day planting mission 600+ trees planted Partnered with Coalition to Restore Coastal Louisiana
Bohemia Spillway
Mississippi River flood protection and back Levees Breton Sound Bayou Lamoque
Bohemia: Signs of a resilient ecosystem
Results: USGS Data Landloss Land gain Net Change Area Area Time Period (Sq. Miles) (Sq. Miles) Sq. Miles 1932-1956 1.5430 0.6357-0.9073 1956-1973 0.3615 0.0207-0.3408 1973-1975 0.2724 0.0046-0.2678 1975-1977 0.3250 0.0491-0.2759 1977-1985 0.1615 0.0025-0.1590 1985-1988 0.1457 0.0007-0.1450 1988-1990 0.2499 0.0035-0.2464 1990-1995 0.3008 0.0158-0.2850 1995-1998 0.1597 0.0200-0.1397 1998-1999 0.1274 0.0021-0.1253 1999-2002 0.0621 0.0158-0.0463 2002-2004 0.1229 0.0256-0.0972 2004-2006 0.0828 0.1836 0.1007 2006-2008 0.0793 0.0769-0.0025 2008-2009 0.0179 0.0126-0.0053 2009-2010 0.0418 0.0197-0.0221 Total Loss Total Gain Total Net Change 4.0537 1.0888-2.9649 Modest Net Gain 2004-06
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
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
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
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
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
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
July 10, 2011 Water flowing over the sand bar and into the blowout channel
Because the pass connected with the river around Mardi Gras Day 2012, we have dubbed it Mardi Gras Pass
Mardi Gras Pass & State Master Plan
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.