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DIFFERENTIAL SEDIMENT CONSOLIDATION ASSOCIATED WITH BARRIER BEACH RESTORATION:

CAMINADA HEADLAND, SOUTH LOUISIANA MARK R. BYRNES1, CHESTER HEDDERMAN2, MICHAEL HASEN, P.E.3, HARRY

ROBERTS4, SYED KHALIL5, AND STEVEN G. UNDERWOOD1

1. Applied Coastal Research and Engineering, 766 Falmouth Road, Mashpee, MA 02649 and 445 North Boulevard, Suite 850, Baton Rouge, LA, 70802, U.S.A. mbyrnes@appliedcoastal.com, sunderwood@appliedcoastal.com.

2. Gahagan & Bryant Associates, 9330 Kirby Drive, Suite 100, Houston, TX 77054 cwhedderman@gba-inc.com;

3. HVJ Associates, 6120 South Dairy Ashford Road, Houston, TX 77072, MHasen@hvj.com. 4. Louisiana State University, Howe-Russell Geoscience Complex, Old Geology Building,

Room 331, Baton Rouge, LA 70803. U.S.A., hrober3@lsu.edu. 5. Coastal Protection and Restoration Authority, 450 Laurel Street, Baton Rouge, LA 70801,

U.S.A. Syed.Khalil@LA.GOV.

Abstract: Consolidation of deltaic sediment associated with overburden from beach restoration is a factor influencing project design elevations. Settlement estimates were determined by sampling subsurface sediment layers and performing geotechnical analyses to assess the potential impact of sediment loading. Calculated settlement is particularly important where project design elevations are critical for habitat restoration success (e.g., maintaining beach width and sand volume on the foreshore by limiting overwash for specific design events). Geotechnical analyses and survey measurements performed as part of this study provided a means of comparing soil-based settlement estimates with high-accuracy elevation measurements for assessing subsurface sediment consolidation associated with beach restoration along the deltaic coast of south Louisiana.

Introduction

Barrier island restoration is a significant component of the wetland restoration strategy in south Louisiana, providing dune and backbarrier habitat for storm surge and wave reduction for interior marsh habitat. A primary question regarding beach restoration in Louisiana relates to subsurface consolidation associated with sediment overburden on compactible deltaic deposits (Rosati et al., 2006). Deltaic sediment has the potential to consolidate significantly under load due to reduction in void space and decay of organic matter. Kuecher (1994) recognized that barrier islands loaded underlying deltaic sediment and caused downwarping. Although greatest compaction is expected within near-surface sediment layers, quantifying differences in compaction at various locations and depths within shallow geologic deposits provides a method for assessing differential sediment consolidation associated with sand fill placement on deltaic

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beaches. This information is beneficial for designing placement elevations to maintain post-construction topography that meets habitat requirements for restoration (Campbell et al., 2005). Also, these data are useful for calibrating/ validating compactional subsidence models for application with future beach restoration projects along barrier island shorelines of south Louisiana (e.g., Rosati et al., 2010).

Presently in south Louisiana, geotechnical analyses of sediment compactibility associated with overburden from beach restoration is estimated using standard consolidation tests for soils beneath planned restoration sites. This information is used to guide beach/dune restoration design elevations relative to expected substrate consolidation (Campbell et al., 2005; Rosati et al., 2006). Although these data provide a foundation for establishing beach restoration design elevations, spatial variability in subsurface sedimentary characteristics may result in underestimated or excessive consolidation estimates (Meckel et al., 2007), potentially limiting the effectiveness of habitat restoration. Direct measurement of settlement in fine-grained deltaic deposits due to sediment overburden from a large beach restoration project provides a method for testing the reliability of standard geotechnical analyses, as well as data for validating consolidation numerical models for predicting effective design elevations. The purpose of this study is to record high-resolution elevation measurements for documenting subsurface sediment consolidation associated with placement of approximately 3.3 million cubic yards (mcy) of sand (about 120 cubic yards per linear foot of beach [275 cubic meters per meter width of beach]) from offshore borrow sites on eroding beaches encompassed by the West Caminada Headland Beach/Dune Restoration Project (BA-45). Figure 1 illustrates the location of sediment cores, survey anchors, and the control benchmark (CMS-BM-01) for monitoring surface and subsurface elevation changes in response to sand fill placement.

Methods

A four-phase approach was implemented to document and evaluate changes in subsurface sediment consolidation associated with sand fill placement on the Caminada Headland. Starting April 2012 (Phase 1), continuous geologic borings were obtained from the surface to a depth of 120 ft (36.5 m) at four station locations (A-D on Figure 1) using roto-sonic drilling techniques to record stratigraphic changes. Core logging was completed in the field, and each core section was photographed. During Phase 2, a truck-mounted wet rotary drilling rig was used to sample lithologies identified during Phase 1 for consolidation testing, Atterberg limits, moisture content, specific gravity, and gradation at Stations A, B, and C. Station D was not sampled because lithologies were very similar to those identified at A, B, and C. Laboratory results were used to evaluate natural overburden stress on subsurface deposits and the potential

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magnitude of settlement that may be expected due to placement of sand fill during beach restoration. Based on analyses completed in Phases 1 and 2, subsurface anchors (benchmarks) were installed at specified depths for Stations A, B, and C to measure differential consolidation from sand placement during beach restoration (Phase 3). Phase 4 involved monitoring changes in anchor elevations to document variations in fill-induced consolidation. These direct measurements were compared with consolidation estimates derived from standard geotechnical analyses for estimating habitat design elevations for coastal restoration projects overlying poorly-consolidated deltaic sediment.

Fig. 1. Station locations for sediment borings (A through D) and anchor monuments (A through C) for documenting subsurface sediment characteristics and monitoring elevation changes in response to beach restoration along the Caminada Headland in south Louisiana (Terraserver image 10/22/14).

Campbell et al. (2005) noted that restoration projects in south Louisiana are subject to three kinds of vertical adjustments: 1) initial consolidation of placed hydraulic fill as it dewaters; 2) subsurface consolidation associated with overburden of placed sediment; and 3) relative sea-level rise, which in south Louisiana is dominated by compactional subsidence of poorly-consolidated Holocene deltaic sediment. Survey measurements recorded in this study were designed to focus on subsurface consolidation settlement from beach fill placement; however, natural compactional subsidence was documented as well.

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During study Phase 3, ten subsurface monuments were installed using Borros anchors (Figure 2). Because anticipated changes in subsurface elevations over short periods of time were expected to be relatively small, sub-centimeter survey measurement accuracy was required. To facilitate this requirement, the National Geodetic Survey (NGS) Online Positioning User Service (OPUS) was employed to establish positional information for an installed benchmark used to control all local survey measurements. Based on NGS guidelines, it was determined that at least two 24-hour static observation data sets on a control point separated by a minimum of 48 hours were required. Four static observation periods were performed, and the three with the lowest root mean square (RMS) values were used to determine final position of the control monument in February 2013. The three observations provided repeatable data within project accuracy standards.

Fig. 2. Schematic of Borros anchor used to establish subsurface monuments. This anchor is designed for installation in soft clays like those associated with Holocene deltaic sediment (from http://www.slopeindicator.com/pdf/settlement%20point%20datasheet.pdf).

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This process was repeated in April 2014; a comparison of the two data sets provided a measurement of local natural subsidence. To survey anchor monuments at each of the monitoring stations within the required measurement specification, a high-precision Trimble DiNi digital level was employed with a standard bar staff; maximum one kilometer level loops were performed. All vertical measurements were referenced to the North American Vertical Datum of 1988 (NAVD), Geoid 12A.

Results

Four geologic borings were obtained at or near the beach berm crest to depths of 120 ft (36.5 m) along approximately 3.5 mi (5.6 km) of the Caminada Headland (Figure 1). Eight sedimentary horizons were identified in each of the cores (Figure 3). Sediment layers consisted of fine sand with shells and organics at the surface, underlain by interbedded fine sand and silty clay to clay. Clay content increased with depth. At each of the borings, the upper 25 ft (7.6 m) consisted of fine sand and shell fragments, interbedded with soft silty clay, representing barrier beach and bay deposits. Below these transgressive deposits are progradational sediments of the Lafourche delta complex, ranging from

Fig. 3. Shore-parallel cross-section along the Caminada Headland beach illustrating relatively consistent sediment layers with depth. Blue dots represent geotechnical sample locations.

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distributary mouth bar silty sand to delta front silty sand and silty clay to prodelta silty clay and clay at the base of the sequence. Depositional layers were relatively consistent at all four boring locations, resulting in similar anchor monument depths.

Based on textural characteristics of subsurface deltaic sediment layers, 12 samples were obtained for geotechnical analyses to estimate consolidation settlement within each layer (Figure 3). Settlement estimates for Stations A, B, and C due to fill placement and ongoing settlement were determined for periods ranging from 6 months to 20 years (Table 1). These estimates represent the primary geotechnical information used to assist with design of project elevations to account for settlement over the life of a project.

Table 1. Estimated subsurface compaction from fill placement and ongoing settlement (ft) by station based on geotechnical properties of soils.

Station 6 Months 2 years 4 years 20 years

A 0.29 0.67 0.86 1.61

B 0.24 0.54 0.70 1.30

C 0.46 0.86 1.13 1.94

After analyzing core data, ten subsurface anchor monuments were installed at Stations A, B, and C to monitor elevation changes within specific sedimentary facies. Target layers were determined based on lithology and geotechnical settlement analyses associated with subsurface clay layers (Strata II, IV, VI, VIII in Figure 3). Prior to sand fill placement, anchor monument locations for Station A were installed at -19.1, -41.1, and -62.1 ft NAVD. Monuments for Station B were installed at -18.8, -48.3, -64.3, and -87.8 ft, and monuments for Station C were installed at -23.6, -41.4, and -85.1 ft (Figure 4). Figure 5 documents monument conditions at Station A prior to and after sand fill placement. Precautions were taken to ensure no monument disturbance during sand placement at all stations.

A settlement plate also was installed at each station prior to sand fill placement. Settlement measurements at each plate recorded total elevation change resulting from sediment consolidation beneath the fill plus natural subsidence due to Holocene sediment compaction. Elevation measurements associated with subsurface anchors recorded sediment consolidation for layers beneath each anchor, providing a means of differentiating variations in sediment compaction with depth. Furthermore, high-accuracy elevation measurements at the control benchmark provided data on local natural subsidence (Table 2). These data were used to remove the effect of natural subsidence when determining consolidation

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settlement associated with sand fill placement. Although the length of record between control point observation periods for this study was only 410 days, the estimated local subsidence rate (9.35 mm/yr) is greater than relative sea-level rise recorded at the Grand Isle water level gage (9.24 mm/yr [1947-2006] of which 2 mm/yr is due to eustatic sea-level rise), 28 km (17.5 mi) east of the study area, emphasizing the observation that subsidence is the primary driver for relative sea-level rise in south Louisiana.

Fig. 4. Anchor monument locations relative to subsurface sediment layers at Stations A, B, and C.

Fig. 5. Anchor monument locations for Station A prior to sand fill placement (left image) and after beach restoration (right image).

A-1 A-2 A-3

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Table 2. Control Benchmark Observations: CMS-BM-01

Observation From To X (ft) Y (ft) Z (ft)

Opus 1-1 02/05/13 02/06/13 3,646,877.00 221,734.96 4.5800

Opus 1-2 02/13/13 02/14/13 3,646,876.98 221,734.95 4.5702

Opus 1-3 02/17/13 02/18/13 3,646,876.97 221,734.98 4.5899

Average 3,646,876.98 221,734.96 4.5800

Opus 4-1 03/31/14 04/01/14 3,646,876.99 221,734.93 4.5571

Opus 4-2 04/03/14 04/04/14 3,646,877.00 221,734.93 4.5341

Average 3,646,876.99 221,734.93 4.5456

Elevation Change (ft)

-0.0344

Subsidence Rate (ft/yr)

0.0307

Subsidence Rate (mm/yr)

9.35

Nine of twelve survey data sets have been completed, documenting elevation change at settlement plates and anchors for Stations A, B, and C to assess the rate at which consolidation has occurred since February 2013 (Table 3). Stations A and B illustrated greater than 0.5 ft settlement since sand fill was placed (9/30/2013 for Station A; 12/8/2013 for Station B). However, sand fill was not completed at Station C until 10/8/2014, resulting in settlement of 0.33 ft for the first 101 days of measurements. As a comparison, settlement of this magnitude took 186 days at Station A and approximately 120 days at Station B, indicating greater rates of consolidation settlement where the barrier beach has migrated landward onto bay bottom clays of Bay Champagne and adjacent marshes of the Lafourche delta complex.

Survey data for Station A illustrates consolidation settlement has occurred at all monitored depths within the subsurface. However, settlement below about -41 ft NAVD appears to have stopped since October 2014, approximately one year after sand fill was placed at this location (Figure 6). Conversely, sediment layers shallower than -41 ft continued to consolidate through January 2015, with greatest settlement occurring between -19 and -41 ft in a 20-ft thick clay layer. Sediment layers between the settlement plate and -19 ft have contributed significantly to overall consolidation, but these primarily sand layers are less compactible than deltaic silt and clay layers deeper than -41 ft.

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Table 3. Measured Elevation Changes for Settlement Plates and Anchors, 2/17/2013 to 1/17/2015.

Station Day 0 101 255 297 327 411 598 635 699

SP-A Elev.

10.79 10.60 10.57 10.47 10.30 10.27 10.23

Change

-0.19 -0.22 -0.32 -0.49 -0.52 -0.56

Consol.

-0.18 -0.21 -0.30 -0.46 -0.49 -0.52

A-1 Elev. -19.10 -19.11 -19.24 -19.28 -19.30 -19.35 -19.48 -19.49 -19.51

Change

-0.01 -0.14 -0.18 -0.20 -0.25 -0.38 -0.39 -0.41

Consol.

0.00 -0.12 -0.16 -0.17 -0.22 -0.33 -0.35 -0.35

A-2 Elev. -41.10 -41.09 -41.17 -41.21 -41.20 -41.21 -41.28 -41.28 -41.28

Change

0.01 -0.07 -0.11 -0.10 -0.11 -0.18 -0.18 -0.18

Consol.

0.02 -0.05 -0.09 -0.07 -0.08 -0.13 -0.13 -0.12

A-3 Elev. -62.10 -62.10 -62.17 -62.21 -62.19 -62.19 -62.25 -62.25 -62.25

Change

0.00 -0.07 -0.11 -0.09 -0.09 -0.15 -0.15 -0.15

Consol.

0.01 -0.05 -0.09 -0.06 -0.06 -0.10 -0.10 -0.09

SP-B Elev.

12.23 11.96 11.70 11.67 11.62

Change

-0.27 -0.53 -0.56 -0.61

Consol.

-0.26 -0.51 -0.53 -0.58

B-1 Elev. -18.80 -18.79 -18.83 -18.94 -18.99 -19.10 -19.30 -19.32 -19.36

Change

0.01 -0.03 -0.14 -0.19 -0.30 -0.50 -0.52 -0.56

Consol.

0.02 -0.01 -0.12 -0.16 -0.27 -0.45 -0.47 -0.50

B-2 Elev. -48.30 -48.29 -48.30 -48.40 -48.44 -48.54 -48.73 -48.75 -48.80

Change

0.01 0.00 -0.10 -0.14 -0.24 -0.43 -0.45 -0.50

Consol.

0.02 0.02 -0.08 -0.11 -0.21 -0.38 -0.40 -0.44

B-3 Elev. -64.30 -64.29 -64.30 -64.36 -64.39 -64.41 -64.47 -64.48 -64.49

Change

0.01 0.00 -0.06 -0.09 -0.11 -0.17 -0.18 -0.19

Consol.

0.02 0.02 -0.04 -0.06 -0.08 -0.12 -0.13 -0.13

B-4 Elev. -87.80 -87.80 -87.80 -87.85 -87.88 -87.89 -87.94 -87.95 -87.96

Change

0.00 0.00 -0.05 -0.08 -0.09 -0.14 -0.15 -0.16

Consol.

0.01 0.02 -0.03 -0.05 -0.06 -0.09 -0.10 -0.10

SP-C Elev.

13.96 13.81 13.62

Change

-0.15 -0.34

Consol.

-0.15 -0.33

C-1 Elev. -23.60 -23.60 -23.64 -23.66 -23.67 -23.70 -23.77 -23.85 -23.91

Change

0.00 -0.04 -0.06 -0.07 -0.10 -0.17 -0.25 -0.31

Consol.

0.01 -0.02 -0.04 -0.04 -0.07 -0.12 -0.20 -0.25

C-2 Elev. -41.40 -41.38 -41.39 -41.40 -41.39 -41.39 -41.41 -41.48 -41.50

Change

0.02 0.01 0.00 0.01 0.01 -0.01 -0.08 -0.10

Consol.

0.03 0.03 0.02 0.04 0.04 0.04 -0.03 -0.04

C-3 Elev. -85.10 -85.08 -85.09 -85.08 -85.09 -85.09 -85.10 -85.15 -85.15

Change

0.02 0.01 0.02 0.01 0.01 0.00 -0.05 -0.05

Consol.

0.03 0.03 0.04 0.04 0.04 0.05 0.00 0.00

Elev. - monument elevation; Change - elevation change relative to initial survey; Consol. - consolidation settlement (elevation change minus natural subsidence).

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Fig. 6. Differential settlement trends associated with sand fill placement at Station A. Greatest consolidation occurred between -19 and -41 ft NAVD in a deltaic clay layer.

Station B illustrates consolidation settlement trends similar to those identified at Station A, except greatest settlement was associated with a clay layer between -48 and -64 ft NAVD (Figure 7). Since sand fill placement (about 400 days), the clay layer between -19 and -48 ft NAVD documented relatively minor consolidation (0.06 ft), but the clay layer directly below this layer recorded net consolidation of 0.31 ft (Table 3). Geotechnical analyses of sediment samples from this sedimentary deposit indicate it is the layer with highest predicted settlement capacity; however, this does not explain the lack of measured consolidation in the same layer at Station A. Variations in sediment texture and layering within deltaic sedimentary facies illustrated in Figure 4 may account for localized variations in consolidation settlement within the same layer. Similar to Station A, settlement deeper than 64 ft below the beach surface illustrates no significant change since November 2014, approximately one year after sand fill was completed at Station B.

Sand fill placement at Station C did not occur until October 10, 2014; therefore, only 101 days of survey measurements are available for documenting consolidation settlement trends associated with sand fill. However, elevation measurements were recorded since the initial survey in February 2013. Two primary observations were documented: 1) the elevation change curve associated with the settlement plate is steep compared with stations to the west and 2) although sand was not hydraulically placed at Station C until October 2014, >0.1 ft of consolidation was recorded in the clay layer between -23

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and -41 ft NAVD in response to sand deposition from erosion and longshore transport of fill placed west of this station (Figure 8). Field observations indicated that approximately 1 ft of sand had deposited adjacent to the anchor monuments, with increasing deposition between October 2013 and October 2014. Once sand fill was hydraulically placed at Station C, the magnitude of consolidation increased rapidly due to overburden associated with the fill quantity (0.13 ft in 101 days). Subsurface consolidation recorded at the settlement plate documented 0.33 ft of change over this short period, whereas only 0.04 ft of settlement was recorded for sediment deposits deeper than -41 ft.

Fig. 7. Differential settlement trends associated with sand fill placement at Station B. Greatest consolidation occurred between -48 and -64 ft NAVD in a deltaic clay layer.

Although consolidation settlement is expected to continue at all three stations, the magnitude of elevation change at Station C should be greatest over the final three survey periods once the long-term impact of fill overburden translates to subsurface clay layers with largest propensity for settlement.

Discussion

Beach and barrier island restoration is a major component of wetland restoration activities in south Louisiana. Millions of cubic yards of sand and silty sand are used to restore beaches and backbarrier habitat in an effort to fortify the first line of defense for interior wetlands and infrastructure against storm waves and surge. Natural subsidence encompasses approximately 80% of the relative sea level rise signal near the Caminada Headland (González and Törnqvist, 2006),

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illustrating the significance of Holocene sediment compaction on wetland change. Measurements of consolidation settlement associated with beach and barrier islands restoration indicate that subsurface sediment layers are compacting at least an order of magnitude greater than natural subsidence rates, albeit for a shorter length of time. These significant changes in elevation must be considered when designing the functional life expectancy of restoration projects.

Fig. 8. Differential settlement trends associated with sand fill placement at Station C. Consolidation settlement prior to sand fill placement occurred between -23 and -41 ft NAVD due to longshore transport and deposition of sand eroded from fill placed west of Station C.

Geotechnical properties of soils are used to estimate settlement associated with sediment placement during restoration, but prior to this study, no independent measurements of elevation change were available to verify the reliability of estimated elevation changes. As predicted by geotechnical analyses, elevation changes occurred at all depths, with greatest settlement in clay layers between 25 and 75 ft below the surface. However, settlement was not consistent at all anchor locations within these clay layers. Local variations in sediment composition and water content, not recognized in discrete sediment samples, likely resulted in consolidation settlement variations within specific layers. Unlike discrete sediment samples, high-accuracy elevation measurements at specific sediment horizons record the cumulative impact of loading for the entire sediment sequence below the anchored horizon. Therefore, a more realistic profile of differential changes in consolidation settlement can be determined from elevation measurements where variable sediment characteristics are encountered. Alternatively, increasing the number of geotechnical samples may provide better estimates of variability.

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Overall, measured changes in anchor monument elevations are greater than those predicted using geotechnical analyses (Table 4). At Station A, predicted settlement six months after placement of the fill was slightly less than that recorded by surveys, but by two years after placement, predicted changes are greater than those derived from survey measurements. However, survey elevation changes are only estimates based on extrapolation of recent change trends because our longest survey record for any station since fill was placed is 474 days (Station A). At Stations B and C, six month and two year estimates exceeded both geotechnical-based predictions. Although elevation change estimates are based on extrapolation of recent change trends documented at Stations B and C, settlement estimates suggest that increased fill design elevations may be needed to compensate for elevation trends.

Table 4. Comparison of estimated settlement (ft) by station for geotechnical and survey data.

Station 6 Months 2 years

Geotechnical Survey Geotechnical Survey

A 0.29 0.30 0.67 0.54

B 0.24 0.40 0.54 0.88

C 0.46 0.60 0.86 1.20

Conclusions

An evaluation of localized sediment consolidation associated with placement of a 3.3 mcy sand restoration project along the Caminada Headland in south Louisiana was initiated in February 2012. Prior to placement of ten subsurface monuments, geologic borings were collected at four locations along a 3.5-mile segment of barrier beach to document subsurface sediment characteristics to a depth of approximately 120 ft. At each of the borings, the upper 25 ft consisted of fine sand and shell fragments, interbedded with soft silty clay, representing barrier beach and bay deposits. Below these transgressive facies are progradational silty sand and silty clay deposits of the Lafourche delta complex. Predicted settlement rates based on standard geotechnical analyses were determined for comparison with changes in monument elevation measurements.

Ten subsurface anchor monuments at three stations were surveyed periodically since February 17, 2013 as sand fill was placed on the Caminada Headland beach. Elevation changes were recorded at all depths, with greatest settlement occurring in clay layers between 25 and 75 ft below the surface. However, settlement was not consistent at all anchor locations within these clay layers. Measured changes in anchor monument elevations generally were greater than those predicted using geotechnical analyses, indicating that fill design elevations could be slightly higher to compensate for elevation trends documented to date.

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At least three additional data acquisition surveys will be conducted to document continued subsurface sediment consolidation since fill placement. These data are expected to refine elevation change trends for comparison with geotechnical predictions. Ideally, anchor monument surveys should be continued until elevation changes are within measurement uncertainty.

Acknowledgements

All authors on this paper contributed significantly to design and implementation of this data acquisition effort. Chester Hedderman was the primary person responsible for data collection, analysis, and report preparation. Mike Hasen was responsible for geological and geotechnical data collection and analyses. Mark Byrnes, Harry Roberts, and Syed Khalil designed the study to better understand the impact of sediment loading on consolidation settlement associated with texturally variable deltaic deposits. Steve Underwood assisted with field survey data collection. This study was sponsored through the Louisiana Coastal Protection Restoration Authority (CPRA) with funding from the U.S. Fish and Wildlife Service, Coastal Impact Assistance Program (CIAP).

References

Campbell, T., Benedet, L., and Thomson, G. (2005). “Design considerations for barrier island nourishments and coastal structures for coastal restoration in Louisiana,” Journal of Coastal Research, Special Issue 44, 186-202.

González, J. L., and Törnqvist, T. E. (2006). “Coastal Louisiana in crisis: subsidence or sea level rise?,” EOS, Transactions, American Geophysical Union, 87(45), 493-508.

Kuecher, G. J., 1994, Geologic framework and consolidation settlement potential of the Lafourche Delta, Topstratum Valley Fill: Implications for wetland loss in Terrebonne and Lafourche Parishes, Louisiana: PhD Dissertation, Department of Geology and Geophysics, Louisiana State University, Baton Rouge, Louisiana, 346p.

Meckel, T. A., Ten Brink, U. S., and Williams, S. J. (2007). “Sediment compaction rates and subsidence in deltaic plains: numerical constraints and stratigraphic influences,” Basin Research, 19(1), 19-31.

Rosati, J. D., Stone, G. W., Dean, R. G., and Kraus, N. C. (2006). “Restoration of barrier islands overlying poorly-consolidated sediments, South-Central Louisiana,” Gulf Coast Assoc. Geological Societies Trans., 56, 727-740.

Rosati, J. D., Dean, R. G., and Stone, G. W. (2010). “A cross-shore model of barrier island migration over a compressible substrate,” Marine Geology, 271(1-2), 1-16.

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