The Mississippi River and its Role in Restoration Efforts

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

2 Acknowledgements LA Department of Natural Resources Brown, Cunningham & Gannuch Forte & Tablada CREST Program USACE CHL National Center for Earth surface Dynamics LSU Center for Computation & Technology

3 Acknowledgements LSU Graduate Students: Erol Karadogan, Nathan Dill, Ryan Waldron, Samantha Danchuk, Molly Friedmann DTU Hydraulic Engineering M.S. Students LSU Undergraduate Students working at SSPM: Kevin Hanegan, Mark Leblanc, Erin Rooney, Paul Leonard, Kyle Breaux CE 4260 (Spring 2008) Hydrologic Design Class

4 Outline Background Sediment Studies Small Scale Physical Model (SSPM) Studies Modeling Desktop Delta Model HEC RAS Hydraulic Modeling High Performance Hydrodynamic & Sediment Transport Modeling Conclusions & Path Forward

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

6 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

7 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

8 The concept has been around

9 General Goals of Small River Diversion Reduce saltwater intrusion in historically fresh areas Reestablish favorable salinity levels Reduce the rate of land loss Improve fish and wildlife habitat

10 Larger River Diversion West Bay

11 Study of Diversions Field Tests monitor a process in a similar place Computer Modeling inexpensive, but discretization error and ability to incorporate all physical processes Physical Modeling model complex situations, but scale effects

12 Sediment Budget A 2006 NRC report questioned the viability of maintaining the current extent of coastal land areas saying Achieving no net loss is not a feasible objective because the social, political, and economic impediments are extensive; the sediment supply is limited; and the affected area is large If a LA coastal system wide sediment budget shows that there are not sufficient resources to sustain the existing landscape then proposed structural and nonstructural projects may be only partly feasible, or even infeasible. 1 st Report from NRC on LACPR Program Review

13 Sediment Sources for Restoration Divide the lower river into three parts Old River Control Structure to Baton Rouge Baton Rouge to below New Orleans Head of Passes to the Gulf Renewable sediment loads million tons ( ) million tons (70 s 90 s) 124 million tons (current) The fraction of sand has not changed much over time (~ 20%) Allison, 2006, CREST Presentation Nittruoer et al., 2008, JGR

14 Sediment Sources for Restoration Of the 124 million tons (current) 22.3 million tons is suspended sand (St. Francisville) At Belle Chase, the suspended sand load is only about 10 million tons At Head of Passes, the suspended sand load is only about 4 6 million tons Probable loss in suspended sand load may be bed aggradation More comprehensive measurements and long term monitoring is needed Since so little of the sand is found as bed load (? Maybe 0.1 million tons?), diversions that could carry suspended load may be the best way to deliver sand to the wetlands Allison, 2006, CREST Presentation Nittruoer et al., 2008, JGR

15 Sediment Sources for Restoration Lower river survey to identify sedimentary facies of Mississippi River channel bed (Nittrouer & Allison) Sections of river bottom at depths > ~35 m water depth are typically composed of exposed older substrate Sections of river bottom at depths ~ m water depth are commonly mantled with sandy dunes Sections of river bottom at shallow depths, < ~15 m are mantled by recent mud deposit Below New Orleans ~ 25% of riverbed is exposed substrate Where there is sand it is ~ 7m thick (average) Allison, 2006, CREST Presentation Nittruoer et al., 2008, JGR

16 Sediment Sources for Restoration Most of the sand is moved down the river during high flow events (~5 10% of time) Most of the sand moves in suspension It appears that there are regions of aggradation upstream of New Orleans where sand is stored until released during high flow events Allison, 2006, CREST Presentation Nittruoer et al., 2008, JGR

17 Small scale Physical Model Vincent A. Forte Coastal and River Engineering Research Laboratory Small Scale Physical Model

18 Movable Bed Modeling loose boundary flow rivers, streams, coastal zones and estuaries Large scale MBM study bed morphology Micro MBM education/outreach

19 Common techniques used in movable bed modeling Distorted Scales Necessary for modeling larger domains Limits ability to model bed morphology Lightweight Sediment Necessary for proper scaling of incipient motion and Re numbers There can be issues related to buoyant and cohesive effects Exaggerated Froude # Necessary for creating necessary gradients & velocities for sediment transport

20 Categorizing MBMs (CSS Categories) 1. Demonstration, education, and communication 2. Screening tool for alternatives to reduce maintenance and dredging of the navigation channel 3. Screening tool for alternatives of channel and navigation alignments 4. Screening tool for environmental evaluation of river modifications, side channel modifications, notches in dikes, etc 5. Screening tool for major navigation problems, around structures such as lock approaches, bridge approaches, confluences, etc.

21 SSPM Model Area Pointe a la Hache Head of Passes The total model platform dimension is 8.46 m x 7.41 m = m 2 reproducing a prototype surface area of about 9,027 km 2 equivalent to 3,526 square miles.

22 Model Scaling The following type of scales must be defined: geometric scales; E(L) = 1/12 000, E(H) = 1/500 (HIGH VERTICAL DISTORTION) dynamic scales; and sediment scales; The model is built according to: Froude similarity law for the hydraulics; and Schield s law for the inception of sediment transport. We do also utilize Re scaling to ensure turbulent flow in the river & through diversions

23 Sediment Transport Scaling Particle Reynolds Number Ratio of inertial to viscous forces on sediment grains Shields Number Ratio shear stress on bed to submerged weight of a particle Ratio of depth a grain size Surface tension effects Ratio of sediment density to water density Buoyant force on the sediment

24 Sediment Material Scale combining yields: Based on a model sediment with S.G. of 1.05 E(d) = 3.2 NOTE: this scale makes it practically impossible to simulate fine sediments along with sand

25 Hydraulic Time Scale The SSPM hydraulic time scale is determined from Fr scaling Hydraulically 1 day of prototype (river) time equals 161 seconds in the SSPM OR 1 year in river time equals ~ 16 hours in the SSPM

26 Sediment Time Scale Empirical Law derived by SOGREAH (Parthiot, 1988, Hamm et al., 2004) for use with Seine River Estuary Model E(ts) = This means that from a sediment transport time scale, 1 river year equals ~ 30 minutes in the SSPM

27 Water Surface Profiles The water surface profile, also known as the Hydraulic Gradient Line (HGL) of flow in an open channel, or simply Gradient is the elevation of the water s free surface plotted against the length of the channel Because of different horizontal and vertical scales, it is particularly important in distorted scale modeling for the gradient to be accurate

28 Waldron, 2008, M.S. Thesis

29 Waldron, 2008, M.S. Thesis

30 Hydraulic Time Scale Analysis Determine travel time/velocity Measure of Froude Number similarity Two Techniques Dye Confetti

31 Stretch 1 Stretch 2 Waldron, 2008, M.S. Thesis

32 Velocity & Froude # Analysis Waldron, 2008, M.S. Thesis

33 Discharge, Stage Level, and Sediment Data Discharge: The Mississippi river discharge, measured at Tarbert Landing, for the period , has been used as flow input at the head of the model near Point a la Hache,La. Stage Levels: Mississippi river upstream of Head of Passes West Pointe a la Hache Port Sulfur Empire Venice Head of Passes South West Pass Southwest Pass at Mile 9.2 Southwest Pass at East Jetty South Pass South Pass at Port Eads Particle Sizes: the particle size distribution of bottom material from the Mississippi river is estimated according to available data, mainly at Belle Chasse.

34 Model Verification Observation of the energy gradients in the Mississippi River for various discharges. Representation of the general model roughness. Observation of the flow characteristics of the discharge diverted from the river. Observation of the sediment movement and the nature of sedimentation in the Mississippi River and the various river arms (i.e., incipient motion, suspended load, etc ). Observation of the sedimentation at outlets of the above mentioned Passes.

35 Methodology 1. Run two year hydrograph in one hour period 2. Introduce sediment over identical hydrograph 3. Raise sea level ~1 ft every 25 years 1. Measure stage levels 2. Measure hydrographs 3. Measure dredged material 4. Image to obtain spatial distribution 5. Dye studies to obtain surface velocities and patterns 6. At conclusion of test, spatially collect sediment and measure amount and then sieve

36 SSPM Results Base Case

37 SSPM Results Large Diversion #2

38 SSPM Results Multiple Diversions

39 SSPM Results Eastern Navigation Channel (Hang a left)

40 Sediment Deposited

41 Sediment Dredged

42 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#

43 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)

44 Dye Studies Flourescent dye is injected at the head of model Time lapsed photos are taken Surface velocities and areas can be calculated from images Useful for estimating transport of silts and clays

45 Advantages & Limitations of SSPM Advantages of this model study are : Visualization and semi quantification of sedimentation process along and around the selected diversion channel arrangements. Model sedimentation time scale enables reproduction of one year s evolution in 30 minutes. Thus it is possible to reproduce fairly long term sedimentation process within a few hours testing (100 years sedimentation process in 50 hours testing) and asses the validity of a project concept, possibility of improvement, help to take decisions on site selection and/or design studies, etc. Due to large vertical distortion, the model should be thought of as reproducing the bulk 1D movement of water and sediment

46 Desktop Delta Model Developed by team of engineers & geologists Excel based model runs on a PC Based on hydraulics & sediment transport principals Can account for subsidence, sea level rise, sediment/sand fraction Able to simulate delta growth over decades

47 Desktop Delta Model DELTA MADE BY HUMANS: TAILINGS BASIN OF AN IRON MINE, LABRADOR, CANADA Sediment disposal rate: ~ 24 Mt/yr

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

49 Desktop Delta Model VERY preliminary comparisons LD2 50 years predicts 440 km 2 vs km 2 from SSPM 100 years predicts 620 km 2 vs km 2 from SSPM MD 100 years predicts 600 km 2 vs km 2 from SSPM Differences most likely due to assumptions concerning independence of individual diversion using DDM

The present Caernarvon diversion, while helpful, delivers mostly mud.

50 Diversion Structures IN ORDER FOR THE DIVERSIONS TO BE SUCCESSFUL, CONTROL STRUCTURES AND SHORT GUIDE CHANNELS, NOT OVERFLOW POINTS, ARE NEEDED We need to get as much sand as possible into the new deltas. The present Caernarvon diversion, while helpful, delivers mostly mud. We know how to build the control structures that divert sand as well as mud, because we built the Old River Control Structure to regulate flow into the Atchafalaya River.

51 Numerical Modeling 1D modeling Steady and unsteady; with and without sediment transport Simulate long timescales 2D modeling Steady and unsteady; with and without sediment transport Time scales are much shorter (days to weeks) 3D modeling Probably steady; with and without sediment transport Simulate complex hydrodynamics and sediment transport in and around diversion structures

52 1D Computer Model Hydraulic Engineering Center River Analysis System (HEC RAS) Steady flow solves 1D energy equation Geometry Data same as SSPM ~ 1 XS/mi Same Discrete flow steps as SSPM; downstream WSL set using river gage data Simulations performed by Spring 2008 CE 4260 Hydrologic Design class

53 Account for flow out Bohemia Relief Three scenarios modeled: 1.Base Case 2.LD#2 3.Multiple Diversion

54 HEC RAS Results

55 HEC RAS Results

Hydrodynamic Modeling of SSPM Area Number of Nodes: 131042 Number of Elements: 66468

56 Hydrodynamic Modeling of SSPM Area Number of Nodes: Number of Elements: Total Mesh Area: 3.53 x 10 9 m 2 Resolution is down to: 60 m Karadogan, 2008, in progress

57 Alliance West Pointe A La Hache All of the gages shown in here are Army Corps Gages Port Sulphur Underlined Stations: Rating Curves are available in Sogreah Report Empire Venice Head of Passes Southwest Pass At Mile 9.2 Additional data is available for all gages for 1994 and 1997 floods together with current data (Southwest Pass) At East Jetty South Pass At Port Eads

58 BOUNDARY CONDITIONS INFLOW DISCHARGE TAIL WATER ELEVATION of 0.4 m Karadogan, 2008, in progress

59 Karadogan, 2008, in progress

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

61 SSPM Mesh; Velocity Magnitudes, 500K, 750K, 1000K cfs Karadogan, 2008, in progress

Medium SSPM Area w/ and w/o diversion # of Elements: 42133 # of Nodes: 21892 Total Mesh Area: 5.

62 Medium SSPM Area w/ and w/o diversion # of Elements: # of Nodes: Total Mesh Area: e+08 m 2 # of Elements: # of Nodes: Total Mesh Area: e+08 m 2 Karadogan, 2008, in progress

63 Elevation Close Up View Diversion Channel 240 m wide 9 m deep

64 Mesh and Boundary Conditions 1000K cfs 0.4 m 1.16 m Karadogan, 2008, in progress

65 Water Surface Elevations Karadogan, 2008, in progress

66 Velocity Magnitudes Karadogan, 2008, in progress

67 Velocity Magnitudes Karadogan, 2008, in progress

68 Karadogan, 2008, in progress

Freeport Sulphur Canal Grand River Adam s Bay Bayou Bastian

69 Lake Grande Ecaille Hypothetical Diversion Mississippi Bay Lanaux N Bay De La Cheniere Diversion Channel Lake Washington Freeport Sulphur Canal Grand River Adam s Bay Bayou Bastian Bay Caprien Bay Bayou Huertes Bay Joe Wise Reference Map Feature Map

70 Empire Mesh Elevation Contours Karadogan, 2008, in progress

Area: Resolution is down to: 14517 28818 291

71 Empire Mesh - Adaption Initial Mesh Number of Nodes: Number of Elements: Total Mesh Area: Resolution is down to: km2 30 m Adapted Mesh Karadogan, 2008, in progress

72 INPUT CONDITIONS 100k cfs input discharge 0.3 m Tail Water Elevation 3 grain sizes: 0.08 mm (%10), 0.13 mm (%80) and 0.25 mm (%10) No cohesive properties Equilibrium Input Boundary Condition Karadogan, 2008, in progress

73 Concentration Contours for 0.08 mm (upper left), 0.13 mm (upper right) and 0.25 mm (bottom)

74 Bed Displacements for 0.08 mm (upper left), 0.13 mm (upper right) and 0.25 mm (bottom) Karadogan, 2008, in progress

75 Karadogan, 2008, in progress

76 Karadogan, 2008, in progress

77 Karadogan, 2008, in progress

78 Model Application (ADCIRC & RMA2) ADCIRC linear triangles 12,328 nodes, 24,457 elements RMA2 quadratic triangles or quadrilaterals 16,070 nodes, 7173 elements Dill, 2007, M.S. Thesis

79 Flow Distribution (ADCIRC) Overall nincrease Baseline Dill, 2007, M.S. Thesis

80 % Particles Remaining in Domain Baseline Overall n Increase Shallow n Increase RMA Days 100 Different residence times Impact of mesh & resolution Impact of wetting/drying routines % Particles Remaining in Domain Baseline Overall n Increase Shallow n Increase ADCIRC Days Dill, 2007, M.S. Thesis

81 Nutrients When nutrient levels are high enough to promote nuisance algal blooms, marsh plants can rapidly remove dissolved nitrogen; The added nutrients act to stabilize marshes though creation of new organic matter, particularly as part of their root systems Nuisance algae can also be controlled by pulsing flow through the diversion so that the temperature structure of the water column is not stable Day, 2006, CREST Presentation

critical processes specific to evolution

82 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.

83 Next Step Add ecological models to the land building models Requires inputs of Sand Sediment Salinity nutrients

84 Conclusions & Where to Go From Here There is sand available for land building A majority of it is suspended load Very punctuated delivery of sand SSPM can be used to qualitatively and semi quantitatively investigate the bulk downstream transport of sand and the transport through diversions Tradeoffs between number of diversions, diversion sizes, pulsing, & dredging requirements Distorted scale limits application to design of actual diversions and impact on bed morphology Desktop Delta Model appears to be a very useful took for estimating land building capabilities of diversions Decent agreement between DDM & SSPM for LD#2 scenario (? Forced conveyance?) Easy to tie in ecological/habitat models

85 Conclusions & Where to Go From Here Simple HEC RAS model shows that diversion structures will have an impact on river gradients and velocities Advanced hydrodynamic & sediment transport models along with high performance computing allows for high resolution spatial & temporal modeling Improved understanding of velocities and currents Detailed numerical studies of sediment transport Study impact of eustatic sea level rise Need better bathy/topo data of potential diversion sites Better understanding of most effective diversion structures We have some good students we need more!

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

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