Airborne radar imaging of subaqueous channel evolution in Wax Lake Delta, Louisiana, USA

Shaw, John; Ayoub, F.; Jones, Cathleen E.; Lamb, Michael P.; Holt, Benjamin; Wagner, R. Wayne; Coffey, Thomas S.; Chadwick, J. Austin; Mohrig, David

doi:10.1002/2016gl068770

Cited by 30 publications

(41 citation statements)

References 22 publications

(30 reference statements)

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“…In total, the subaerially exposed portion of WLD accumulated 6.7 × 10 5 m 3 during the study period. For scale, volumetric change calculated between 2011 [ Shaw and Mohrig , ] and 2015 [ Shaw et al ., ] for the 70.3 km 2 subaqueous front of WLD was 1.9 × 10 6 m 3 . Subaerial deposition was 35% of subaqueous deposition for these partially overlapping 4 year periods.…”

Section: Resultsmentioning

confidence: 99%

Elevation change and stability on a prograding delta

Wagner

Lague

Mohrig

et al. 2017

Geophysical Research Letters

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Coastal wetland systems are among the most dynamic landscapes on Earth's surface; however, interrelated processes create wetland platforms that are relatively constant in space and time. Theoretically, “stable” elevations should maintain themselves through time if the balance of processes creating that elevation remains unchanged. At Louisiana's prograding Wax Lake Delta, we measure landscape change between 2009 and 2013, quantifying volumetric changes to the delta, subaerial slope adjustment, and an equilibrium elevation of 0.56 m North American Vertical Datum of 1988 (where elevation change, on average, is zero), around which elevations fluctuate. We calculate a system average “equilibrium time scale” of 16 years to describe how long locations will take to approach the stable elevation. This time scale increases as a function of distance from channel edge. Peaks in elevation probability density functions can form for multiple reasons and do not require stability; e.g., peaks can temporarily form at elevations where elevation change rate is locally minimum.

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Section: Resultsmentioning

confidence: 99%

Elevation change and stability on a prograding delta

Wagner

Lague

Mohrig

et al. 2017

Geophysical Research Letters

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“…The apex of this flow expansion is at 29.471°N, 91.487°W (Figure 1b). Distances from the apex to the crest of these three shoals are measured in bathymetric maps collected in June 2010, August 2011, and February 2015 (Shaw, Ayoub, et al, 2016;Shaw & Mohrig, 2014). Flood Table 1 Key Boundary Conditions and Measurements (Bold) From Experimental and Field Data Used in This Experiment discharge to this site has been measured to be about 360 m 3 /s (Hiatt & Passalacqua, 2015;Shaw, Mohrig, et al, 2016).…”

Section: Field Datamentioning

confidence: 99%

Island Formation Resulting From Radially Symmetric Flow Expansion

2018

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Island formation and distributary channel branching are important processes in prograding river deltas. We develop and test a new theory predicting the distance to islands and channel bifurcations based on fluid mass conservation and radially symmetric transport conditions. We analyze channelization and island formation using nine new and five existing delta experiments as well as four field deltas. The new experiments were designed to produce islands from initial deposition of a mouth bar. Before island formation, each bar evolved into a radially symmetric deposit with unchannelized flow over its top previously described as a topographic flow expansion. This morphology was stable to topographic perturbations, and its distal limit prograded basinward while maintaining a characteristic flow depth. Island formation and channel branching occurred on top of this deposit. We hypothesize that this distance (Ψ) is set by the location where boundary shear stress applied by expanding, radially averaged flow falls below the threshold of sediment motion. The model predicts that the distance to the first island scales with water discharge, scales inversely with flow depth, and scales with the inverse square root of median grain diameter. From experiment to field scales, distances to island locations are predicted within a factor of two.

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“…Our analysis found that streaklines were difficult to measure in Landsat 1 and Landsat 2 imagery, but possible in some cases. Streaklines have also been observed in imagery flown from planes and in SAR imagery (Shaw et al, 2016a). This means that the FD2C method can be used to monitor the decadal change of deltas, ranging from the Wax Lake Delta presented here to other sites such as the West Bay diversion of the main stem Mississippi River where land building and sediment retention are explicit goals (Allison et al, 2017;Andrus and Bentley, 2007;Kolker et al, 20 2012).…”

Section: Each Of the δL Distributions Have Significant Standard Deviamentioning

confidence: 69%

“…However, most deltas are far larger than their sub-aerial portions. For instance, the subaerial area of the Wax Lake Delta in 2015 was 50 25 km 2 (Olliver and Edmonds, 2017) while the subaqueous area was an additional 82 km 2 (Shaw et al, 2016a). The difference arises because the Wax Lake Delta has an extensive delta front deposit that lies below low tide.…”

Section: Introductionmentioning

confidence: 99%

Measuring Subaqueous Progradation of the Wax Lake Delta with a Model of Flow Direction Divergence

Shaw¹,

Estep²,

Whaling³

et al. 2018

Preprint

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Abstract.Remotely sensed flow patterns can reveal the location of the subaqueous distal tip of a distributary channel on a prograding river delta. Morphodynamic feedbacks produce distributary channel tips that become shallower over their final reaches before becoming deeper over the unchannelized foreset. The flow direction field over this morphology tends to diverge 10 and then converge providing a diagnostic signature that can be captured in flow or remote sensing data. Twenty-one measurements from the Wax Lake Delta (WLD) in coastal Louisiana, and 317 measurements from numerically simulated deltas show that the transition from divergence to convergence occurs in a distribution that is centered just downstream of the channel tip, on average 132 m in the case of the WLD. With these data we validate the Flow Direction to Channel tips (FD2C) inverse model for remotely estimating subaqueous channel tip location. We apply this model to 33 remotely sensed images of 15 the WLD between its initiation in 1974 and 2016. We find that the distributaries grew unevenly, 6 of the primary channels grew at rates of 60-80 m/yr while one grew at 116 m/yr. We also estimate the growth rate of the total area enclosed by the subaqueous delta platform to be 1.83 km 2 /yr with no obvious rate changes over time.

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Airborne radar imaging of subaqueous channel evolution in Wax Lake Delta, Louisiana, USA

Cited by 30 publications

References 22 publications

Elevation change and stability on a prograding delta

Elevation change and stability on a prograding delta

Island Formation Resulting From Radially Symmetric Flow Expansion

Measuring Subaqueous Progradation of the Wax Lake Delta with a Model of Flow Direction Divergence

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