The Mississippi River: Its Role in Restoration Efforts and Potential Effects of Climate Change

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1 The Mississippi River: Its Role in Restoration Efforts and Potential Effects of Climate Change Clinton S. Willson, P.E., Ph.D. Department of Civil & Environmental Engineering Louisiana State University

2 Acknowledgements LSU Graduate Students: Erol Karadogan, Nathan Dill, Ryan Waldron, Joseph Tsai, Samantha Danchuk, Molly Friedmann Delft Technical University Hydraulic Engineering M.S. Students LSU Undergraduate Students working at SSPM: Kevin Hanegan, Mark Leblanc, Erin Rooney, Paul Leonard, Kyle Breaux, Brett McMann LA Department of Natural Resources CREST Program USACE CHL National Center for Earth surface Dynamics Paola, Parker, Kim LSU Center for Computation & Technology

islands to submerged sand bars; and more Delta is threatened by waves, tides, and

3 River Dominated Delta Sand Sediment Salt (3 S s) & Nutrients Not a static system Natural detail cycle River changes course Solid land to barrier islands Barrier islands to submerged sand bars; and more Delta is threatened by waves, tides, and storm surges Sea level rise and subsidence Changes in sediment loading Coleman & Gagliano, 1964

4 Does this look like a natural Delta?

5 Possible Realignment of Lower Mississippi River The LACPR draft report does not consider this option, stating the alternative was considered to be beyond the scope of the current effort and could not be adequately evaluated within the scope of this effort. NRC recognizes that, while controversial, there needs to be careful study of a major realignment of the lower Mississippi River. An evaluation of how a major realignment of the lower Mississippi River mouth may affect sediment capture and diversion should be conducted 1 st Report from NRC on LACPR Program Review

6 The concept has been around

7 Small Scale Physical Model Pointe a la Hache (~ RM 55) Head of Passes (RM 0)

8 Model Scaling Distorted Scale Movable Bed Model E(L) = 1/12 000, E(H) = 1/500 (HIGH VERTICAL DISTORTION) Limits study to mostly 1D bulk movement in river The model is built according to: Froude similarity law for the hydraulics; and Schield s law for the inception of sediment (sand) transport. also utilize Re scaling to ensure turbulent flow in the river & through diversions Only able to test large scale diversions (~ k cfs) Sediment Time Scale: 1 prototype year = 30 minutes in model time

9 Methodology 1. Run two year hydrograph in one hour period 2. Introduce sediment over identical hydrograph 3. Raise sea level ~1 ft every 30 years Measure stage levels Measure hydrographs Measure dredged material Image to obtain spatial distribution Dye studies to obtain surface velocities and patterns At conclusion of test, spatially collect sediment and measure amount and then sieve

10 SSPM Results Large Diversion #2

11 Impact on Stage Level Relative Sea Level Rise Gauge 2 Water Surface Elevation (ft) Crest LD #2, Gage 2 ws el (ft) 1-2 years Crest LD #2, Gage 2 ws el (ft) 9-10 years Crest LD #2,Gage 2 ws el (ft) years Crest LD #2, Gage 2 ws el (ft) years Crest LD #2, Gage 2 ws el (ft) years Crest LD #2 Gage 2 ws el (ft) years Time Interval (annual hydrogaph)

12 Sediment Deposited

13 Sediment Dredged

14 SSPM Results # of Years % Dredged % Deposited % Out of Model Base Case Large Diversion # Large Diversion #2 (2) Multiple Diversions Multiple Diversions (w/mg) Eastern Navigation Channel DTU Pulsed LD#

15 Land loss by deltaic drowning is neither inevitable nor natural Seismic section: 45 km long, 1.4 km thick 15 cm These low-gradient, low-elevation delta tops are dynamic and self-maintaining

$where H is eustatic sea level, σ spatially averaged subsidence rate, A top the area of the delta top (subaerial wetlands and channels), Q s total volumetric sediment supply, f r the fraction retained$

16 Delta area is set by a balance between sea-level rise + subsidence and deposition of sediment and organic matter:. where H is eustatic sea level, σ spatially averaged subsidence rate, A top the area of the delta top (subaerial wetlands and channels), Q s total volumetric sediment supply, f r the fraction retained in the delta top, and r org the rate of storage of organic matter in the sediment column, expressed as a rate of vertical accumulation (length/time).

17 Desktop Delta Model THE MODEL CAN REPRODUCE THE WAX LAKE DELTA S PAST Yellow: 38 Mt/yr White: 25 Mt/yr (suspended load)

18 VARIATION: SEA-LEVEL RISE = 4 mm/yr, SUBSIDENCE = 10 mm/yr Solid line: variant case Dotted line: base case And extra land-building due to organics is not yet included Worst case : still 701 km 2 of new land

19 Desktop Delta Model SSPM VERY preliminary comparisons Large Diversion w/ 2 medium size diversions 50 years: 440 km 2 from DDM vs km 2 from SSPM 100 years: 620 km 2 from DDM vs km 2 from SSPM Multiple medium size diversions 100 years: 600 km 2 from DDM vs km 2 from SSPM Differences most likely due to assumptions concerning independence of individual diversions and conveyance efficiency using DDM

20 Is there enough sediment? Timing of the sediment?

21 Hydrodynamic Modeling of SSPM Area USACE Adaptive Hydraulics Code - Unstructured FE - Adaptive mesh capabilities - Runs on multiple platforms including HPCs Number of Nodes: 131,042 Number of Elements: 66,468 Total Mesh Area: 3530 km 2 Resolution is down to: 60 m Karadogan, 2008, in progress

22 Model Results vs Observation Data Karadogan, 2008, in progress

23 SSPM Mesh; Water Surface Elevations, 500K, 750K, 1000K cfs Karadogan, 2008, in progress

Channel River Lake Grande Ecaille Bayou Adam s Bay N Bayou Huertes

24 Hypothetical Diversion near Empire, LA Freeport Sulphur Canal Lake Washington Grand Mississippi Bay Lanaux Bay De La Cheniere Diversion Channel River Lake Grande Ecaille Bayou Adam s Bay N Bayou Huertes Bastian Bay Caprien Bay Bay Joe Wise Reference Map Elevations (Dill, 2007)

25 Mesh and Boundary Conditions 1000K cfs Mesh Adaption TAIL WATER ELEVATION of 0.4 m TAIL WATER ELEVATION of 0.4 m TAIL WATER ELEVATION of 1.16 m

26 Water Surface Elevations & Velocities Karadogan, 2008, in progress

critical processes specific to evolution

27 Geophysical processes and geomorphic features control ecological patterns. Thus the structure and function of coastal ecosystems are dependent on critical processes specific to evolution of deltas. Links Delta Evolution to Ecological succession.

28 Final Thoughts Multiple tools are necessary Geological data (historical and current) Physical modeling High resolution numerical modeling Desktop/screening models Land building/ecological Models Accurate elevation data! Need to quantify rates and understand their context (short versus long term)

29 Final Thoughts Sediment Quantity? Occurrence/Frequency? Abandon Lower Mississippi River Delta? Alternative navigation channels? Paired with diversions in upper part? Subsidence rates combined with eustatic sea level rise makes the LMRD a valuable natural lab

The Mississippi River and its Role in Restoration Efforts

The Mississippi River and its Role in Restoration Efforts Clinton S. Willson, P.E., Ph.D. Department of Civil & Environmental Engineering Louisiana State University Acknowledgements LA Department of Natural