Groundwater dynamics and surface water–groundwater interactions in a prograding delta island, Louisiana, USA

O’Connor, Michael T.; Moffett, Kevan B.

doi:10.1016/j.jhydrol.2015.02.017

Cited by 30 publications

(27 citation statements)

References 39 publications

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“…[] for details). Wind (±0.20 m), tides (±0.3 m), river flow (±0.2 m), and storms all affect water‐level changes on Wax Lake Delta [ O'Connor and Moffett , ], leading to large changes in area of exposed land due to the low relief of the system [ Geleynse et al ., ]. These factors led to more subaerial delta area surveyed in 2009 than in 2013, despite continuing delta progradation.…”

Section: Methodsmentioning

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: Methodsmentioning

confidence: 99%

Elevation change and stability on a prograding delta

Wagner

Lague

Mohrig

et al. 2017

Geophysical Research Letters

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“…This method relies upon knowing the water levels at the remote sensing imaging times, however, which is difficult for long or old imagery time series and in ungauged field locations. It is particularly difficult to know the water level imaged at an arbitrary time for the typical ungauged coastal wetland field site because wind, storm, and synoptic effects often strongly modify the background harmonic tidal prediction and may make water levels appear surprisingly stochastic [265,266].…”

Section: Landsat Records Of Topographic State Bifurcation In the Wax mentioning

confidence: 99%

Multiple Stable States and Catastrophic Shifts in Coastal Wetlands: Progress, Challenges, and Opportunities in Validating Theory Using Remote Sensing and Other Methods

et al. 2015

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Multiple stable states are established in coastal tidal wetlands (marshes, mangroves, deltas, seagrasses) by ecological, hydrological, and geomorphological feedbacks. Catastrophic shifts between states can be induced by gradual environmental change or by disturbance events. These feedbacks and outcomes are key to the sustainability and resilience of vegetated coastlines, especially as modulated by human activity, sea level rise, and climate change. Whereas multiple stable state theory has been invoked to model salt marsh responses to sediment supply and sea level change, there has been comparatively little empirical verification of the theory for salt marshes or other coastal wetlands. Especially lacking is long-term evidence documenting if or how stable states are established and maintained at ecosystem scales. Laboratory and field-plot studies are informative, but of necessarily limited spatial and temporal scope. For the purposes of long-term, coastal-scale monitoring, remote sensing is the best viable option. This review summarizes the above topics and highlights the emerging promise and challenges of using remote sensing-based analyses to validate coastal OPEN ACCESS Remote Sens. 2015, 7 10185 wetland dynamic state theories. This significant opportunity is further framed by a proposed list of scientific advances needed to more thoroughly develop the field.

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“…Both simplifications lead to underestimating rates of surface water‐groundwater exchange. Empirical observations from Pintail Island in Wax Lake delta show that tides and storms significantly enhance surface water‐groundwater interactions, particularly along island perimeters [ O'Connor and Moffett , ]. Nevertheless, our models capture prevailing flow patterns observed in Pintail Island: groundwater tends to flow basinward across island bars because surface water elevations are higher in upstream channels than interior island lagoons.…”

Section: Resultsmentioning

confidence: 99%

“…Simulations represent steady, long‐term average groundwater flow in mature deltas. We do not simulate tides or flooding, which enhance surface water‐groundwater interactions [ O'Connor and Moffett , ]. We also assume surface water and groundwater are fully fresh.…”

Section: Methodsmentioning

confidence: 99%

Surface water‐groundwater connectivity in deltaic distributary channel networks

Sawyer

Edmonds

Knights

2015

Geophysical Research Letters

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Delta distributary channel networks increase river water contact with sediments and provide the final opportunity to process nutrients and other solutes before river water discharges to the ocean. In order to understand surface water‐groundwater interactions at the scale of the distributary channel network, we created three numerical deltas that ranged in composition from silt to sand using Delft3D, a morphodynamic flow and sediment transport model. We then linked models of mean annual river discharge to steady groundwater flow in MODFLOW. Under mean annual discharge, exchange rates through the numerical deltas are enhanced relative to a single‐threaded river. We calculate that exchange rates across a <10 km2 network are equivalent to exchange through ~10–100 km of single‐threaded river channel. Exchange rates are greatest in the coarse‐grained delta due to its permeability and morphology. Groundwater residence times range from hours to centuries and have fractal tails. Deltas are vanishing due to relative sea level rise. River diversion projects aimed at creating new deltaic land should also aim to restore surface water‐groundwater connectivity, which is critical for biogeochemical processing in wetlands. We recommend designing diversions to capture more sand and thus maximize surface water‐groundwater connectivity.

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Groundwater dynamics and surface water–groundwater interactions in a prograding delta island, Louisiana, USA

Cited by 30 publications

References 39 publications

Elevation change and stability on a prograding delta

Elevation change and stability on a prograding delta

Multiple Stable States and Catastrophic Shifts in Coastal Wetlands: Progress, Challenges, and Opportunities in Validating Theory Using Remote Sensing and Other Methods

Surface water‐groundwater connectivity in deltaic distributary channel networks

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