Current Research
Storm Surge Deposition on Salt Marshes: Impacts of Hurricane Irma from Florida to South Carolina
Funding: National Science Foundation (NSF - RAPID)
Collaborators: Christopher Hein (VIMS), Zoe Hughes and Duncan FitzGerald (BU)
Scientists continue to debate the net impact of hurricanes on wetlands. These events may be considered beneficial because of net sedimentation that occurs during surge inundation, or detrimental due to erosion of the marsh edge and surface excavation by storm waves. While Hurricane Irma tracked over the west coast of Florida, the wind patterns and size of the storm created strong onshore winds along the southeast coast, producing a large storm surge up into South Carolina. The proposed measurements need to be taken swiftly before bioturbation obliterates the new sediment horizon, preventing detection of the boundary, and/or the exact thickness of the deposit is obscured by compaction or subsequent storms (that may erode or deposit sediment). Our study sites range from northern FL to central SC, incorporating the backbarrier marshes behind: Amelia Is., FL; Sapelo Is., GA; Hilton Head Is., SC; Cape Romain, SC. Sites were selected based on their varying physical settings and conditions during Irma. Additionally, we have baseline data at two of the sites.
Mississippi Delta Front Mass Wasting Processes : Observations and Modeling
Funding: Bureau of Ocean Energy Management (BOEM)
Collaborators: Sam Bentley, Kevin Xu, and Navid Jafari (LSU), Jillian Maloney (San Diego State U), Michael Miner (BOEM; now at The Water Institute of the Gulf)
On river deltas dominated by proximal sediment accumulation (Mississippi, Huang He, others), the nearshore region commonly dominated by rapid accumulation of cohesive fluvial sediments is known as the “delta front.” For such river-dominated systems, submarine landslides (referred to generally as “mass wasting”) reshape the seabed, and are important geohazards. Mass transport is preconditioned in sediments by high water content, biogenic gas production, over steepening, and is commonly triggered by strong wave loading and other processes. We have synthesized many industry data sets collected since ca. 1980, and conducted new pilot field and modeling studies of sedimentary and morphodynamic processes. These studies have yielded several key findings that diverge from historical understanding of this dynamic setting. First, delta distributary mouths have ceased seaward progradation, ending patterns that have been documented since the 18th century. Second, despite reduced sediment supply, offshore mass transport continues, yielding vertical displacements at rates of ~1 m/y. This displacement is apparently forced by wave loading from storm events of near-annual return period, rather than major hurricanes that have been the focus of most previous studies. Third, core analysis indicates that this vertical displacement is occurring along failure planes >3 m in the seabed, rather than in more recently deposited sediments closer to the sediment-water interface. These seabed morphodynamics have the potential to destabilize both nearshore navigation infrastructure, and seabed hydrocarbon infrastructure offshore. As well, these findings raise more questions regarding the future seabed evolution offshore of major river deltas, in response to anthropogenic and climatic forcing.
Experimental Modeling of Lateral Migration Dynamics
Funding: Univ. of New Orleans Office of Research and Sponsored Programs
Collaborators: Zoe Hughes (BU) Nick Howes (Previously at Mathworks; now at The Water Institute)
Point bars are areas of high sediment deposition formed in fluvial and tidal meandering systems. In tidal environments, tidal point bars have a distinct evolution that is different from their fluvial counterparts. Barwis (1978) attempted to classify tidal point bars using several geometry-based metrics, including comparing the radius of curvature of the channel to the average width (r/w) along the channel meander. While compelling and intuitive, results from this classification do not explain fully detached tidal bars found in many tidal creeks. We hypothesize that detached bars form as a function of lateral channel mobility, which is a function of bank migration, coupled with the creation of accommodation width along a meander to allow for the bar to detach. The aim of our work was to find how the bed slope and tidal flow influenced the r/w values for meandering creeks. A small-scale physical model was used of a tidal creek with detached bars representing a real creek in the Plum Island Sound, MA. Experiments were run in a stream table and filmed using time-lapse photography on an overhead GoPro camera. A total of 8 experiments were performed with varied flow rate and slope. Final analyses on exact r/w values have not been completed at this stage, but preliminary trends have been identified. High flow seems to have the tendency to straighten out the channel in a lower sloped system, while lower flow in combination with low slope maintains the general morphology of the channel. When high flow and high slope are both affecting the channel migration, a threshold is crossed and the r/w values become difficult to quantify as a broad and sweeping floodplain is created that loses almost all semblance of the original channel.
Hydrodynamics and Sediment Transport in the Great Marsh system, Plum Island, MA
Funding: National Fish and Wildlife Foundation (NFWF)
Collaborators: Duncan M. FitzGerald, Christopher Hein, Zoe Hughes
Field hydrodynamic data were acquired and used to validate a hydrodynamic and sediment transport model of the Plum Island Sound/Merrimack River Estuarine system. Fifteen tripods were deployed and recovered in 2015 with velocity profile data, tides, salinity, sediment concentration proxy and offshore waves. In addition, sediment cores were collected at 15 locations throughout the Great marsh for the purpose of determining vertical accretion rates. These cores have all been processed and Pb-210 and Cs-137 profiles have yielded reliable accretion rates. Grab samples were obtained along all the major channels in the Great Marsh. These samples have been sieved and grain size statistics determined. Taken together, field, laboratory and modeling results are used to assess the marsh resiliency to sea level rise, sediment transport trends within the sound and to identify chief mechanisms for sediment transport and sedimentation throughout the Great Marsh.
Coupled Barrier Islands, Shoreline and Shoreface Dynamics
Funding: Coastal Protection and Restoration Authority (CPRA)
Collaborators: Michal Miner (BOEM), Darin Lee (CPRA)
Barrier island and tidal inlet systems along the Mississippi River Delta Plain (MRDP) are undergoing rapid morphological change due to shoreface retreat and increasing bay tidal prism, driven by high rates of relative sea-level rise (RSLR) (1 cm/yr) and interior wetland loss. Protection and restoration of barrier habitats, sea-grass beds, and marshes are common (CPRA 2012). Here we analyse shoreline, seafloor, wave and sediment data, and corroborate the role of the shoreface in driving barrier island trajectory at both the regional (barrier chain) and local (~100 m) scales. We extend the analysis to include cross-shore profiles backed by marsh and those that are primarily sandy, thereby determining differential erosion mechanisms, and we focus on locations that restoration or nourishment took place previously, to determine whether the fate of nourished barriers exhibits comparative response to under-nourished barriers by comparing shoreface characteristics (migration rates, slope, barrier island slope) and provide insights into shoreface dynamics.
Hydrodynamics of multiple inlet systems: Observations from Raccoon Pass and East Timbalier Pass, Louisiana
Raccoon Pass is a wave-dominated tidal inlet and part of a transgressive shoreline encompassing East Timbalier Island and the Caminada-Moreau headland. During the past century, the inlet has undergone significant morphological changes and has migrated onshore due to reduced sand availability that has caused the ongoing transgression of the barrier arc. Moreover, human modifications completely altered the updrift longshore sediment transport system, initially facilitating the transgression, widening of the tidal inlets, opening of new tidal inlets, and restricting inlet sediment bypassing. To determine sediment transport trends in the vicinity of Raccoon Pass we (1) conducted hydrodynamic observations during winter storms and fair weather conditions, (2) analyzed historic shorelines and bathymetric profiles, and (3) assessed hydrodynamic data in terms of regional and local bathymetric controls. Our analyses highlight multiple regimes and pathways of sediment transport at this inlet, which is dominated by high-energy events such as winter storms when backbarrier basins exchange larger volumes of water. During these events, water exchange results in subtidal water levels in the backbarrier basin imposing critical controls on local fluxes at the inlet, and at times diminish flood-tidal currents altogether. This response, coupled with large waves and strong currents along the upper shoreface and through the inlet, have significant influence on the sediment budget of this system. Finally, geometric analyses of bathymetric profiles and shoreline positions over long time scales, underscore the upper and lower shoreface response compared to the shoreline migrational trends, indicating different pathways of barrier migration and associated geomorphic environments (inlets, spit platforms, flood/ebb deltas, etc.). Regionally tropical cyclones are suggested as the primary mechanisms of coastal change, whereas this work highlights the cumulative effect of changes induced on a more seasonal and frequent basis.
Effects of Sediment Properties on Barrier Island Morphology and Processes
Funding: Bureau of Ocean Energy Management (BOEM)
Collaborators: Rex Caffey (Louisiana State University Ag. Center), Daniel Petrolia (Mississippi State University), Michael D. Miner (BOEM)
Barrier island restoration and nourishment are necessary actions for sustaining coastal systems worldwide. In the Mississippi River Delta Plain (MRDP), the lack of sediment supply and ongoing transgression promotes rapid degradation of barriers, which can contribute to mainland storm impacts. Barrier island restorations that utilize higher quality sediment (Outer Continental Shelf – OCS) are expected to exhibit higher resiliency withstanding erosion during storms and the ongoing transgression, compared to lower quality near shore (NS) sands. Additionally, use of OCS sediments help offset low sediment supply by adding material to the system, and are expected to increase barrier longevity compared to their NS counterparts. We forecast, using a modeling framework, the barrier geomorphic trajectory nourished with OCS and NS sands and compare resulting morphology over time.
Caminada Headland Dune and Beach Restoration: Sediment Change Analysis
Funding: Coastal Protection and Restoration Authority, LA
Collaborators: Darin Lee (CPRA)
The purpose of this report is to present and evaluate sediment characteristic changes using grain size statistics along the Caminada Headland post beach and dune restoration. Results show that with the exception of lower and middle shoreface, both restoration projects (increment 1 and 2) increased the median grain size along the entire headland. Dune and berm sediments increased in size by 6 - 17μm, while beach face and upper shoreface sediments increased in size by 10 - 43μm. The restoration project has also changed sediment characteristic along the headland as evident by the sediment statistics; for instance, dunes became less sorted, exhibited a slight shift towards positive skewness although remained symmetrical, and gradually shifted from mesokurtic to leptokurtic. Berms equally changed from very well sorted to well sorted, although remained similar in terms of skewness (symmetric) and kurtosis (mesokurtic). Beach face sediments did not exhibit much change between pre- and post-project construction, however did demonstrate small oscillations in sorting, skewness and kurtosis. Finally, shoreface sediments exhibited the least change resulting from project construction, although we note that many of the shoreface samples contained less than 70% sand and therefore were not analyzed.
Barrier Island Comprehensive Monitoring Program (BICM): Chenier Plain Sediment Sampling: Sabine River to Marsh Island
Funding: Coastal Protection and Restoration Authority, LA
Collaborators: Mark A. Kulp (UNO), Jim Flocks (USGS) Darin Lee (CPRA)
Development and morphology of point bars in tidal rivers, observations from Sapelo and the Altamaha River, GA
Many tidal creeks and rivers exhibit bars associated with meander bends. However, hydrodynamic and morphodynamic studies of these point-bars are scarce, compared with the extensive studies of fluvial-point bars. The few studies that have been undertaken suggest significant differences between tidal bars and their fluvial counterparts, including low rates of channel migration, a unique planform morphology resulting from the bi-directional tidal flows and tidal asymmetry, and variation in stage-discharge behavior. We examine point-bars in two closely situated estuaries on the Georgia coast: the Altamaha and Sapelo. Both sites are meso-tidal; however, the Altamaha has significant fluvial input, whereas the Sapelo creeks have minimal fluvial input. Both sites exhibit mixed sand-mud point bars of various sizes. However, sites dominated by fluvial processes are coarser-grained and contain a higher percentage of sand. Velocity measurements from vessel-mounted and moored acoustic Doppler current profilers record the separation of flood and ebb flows to either side of the tidal bars, which results in a residual circulation over their surface. Large bedforms with opposing migration directions are observed on either side of the bar, suggesting that each side of the channel experiences a separate sediment transport regime. Shallow seismic data at two resolutions (Boomer and Chirp) indicate that the internal architecture of the tidal bars consists of lateral accretion surfaces with multi-directional strike orientations and dips, suggesting a more complex pattern of growth and development. We compare and contrast the hydrodynamics and the resulting morphologies of the bars and identify differences between fluvially-influenced and purely tidal environments. This data set also allows us to examine the hypothesis that these forms are scale invariant by examining a wide range of bars in both large and small channels.
Funding: Shell Clastics Research
Collaborator(s): Zoe Hughes (BU), Nick Howes (Shell Clastics Research, now at Mathworks)
Modeling exchange processes in the Lower Mississippi River; saltwater intrusion dynamics and flow distribution changes in response to constructed sediment diversions upriver
Large sediment diversion structures constructed to build land in coastal Louisiana need fully assessment in terms of design and operation, and a full analysis of the impacts to receiving basin ecosystems are required. An aspect of the analysis is the lower Mississippi River and its response to changes in discharge (flow) in the river will after saltwater instruction in the lower delta, and compromise freshwater intakes in the Orleans and Plaquemines parishes. Three-dimensional hydrodynamic and salinity transport models were used and validated for present conditions without the implementation of projects, and were then used to simulate future conditions with project (diversions) implementation. Several scenarios were simulated some of which include climate change driven sea level rise.
Funding: The Water Institute of the Gulf , through Coastal Protection and Restoration Authority (CPRA)
Chandeleur Islands Post-Berm Physical Processes and Restoration Plan
The Chandeleur Islands were once a much larger and robust barrier island chain that has experienced severe erosion and degradation by more than a decade of intense hurricanes that began with Hurricanes Ivan in 2004 and Georges in 1998. In addition these islands were heavily oiled from the MC 252 Oil Spill in 2010. As part of the oil spill response, 6.1 miles sand berm were constructed along the north end of the islands. The objective of this study was to assess the physical impact of the berm, evaluate options to modify the berm to enhance the ecologic function and longevity of the Chandeleur Islands, and develop a long-term coastal restoration plan for the Chandeleur Islands.
Funding: Lake Pontchartrain Basin Foundation
Collaborator(s): Mark A. Kulp, Duncan M. FitzGerald, Michael Miner
Barrier Island Comprehensive Monitoring Program (BICM): Central Coast and Chandeleur Islands Sediment Sampling
Funding: Coastal Protection and Restoration Authority, LA
Collaborators: Mark A. Kulp (UNO), Jim Flocks (USGS) Darin Lee (CPRA)
Hydrodynamic and Geomorphic Controls of Mouth Bar Evolution
While river deltas are one of the major repositories for sediments and carbon on Earth, there exists a paucity of field data on the formation of distributary mouth bars, one of their key features. Here we present results from an experiment that tested a model of mouth bar development using hydroacoustic, optical, sedimentary, and geochemical tools on a mouth bar in a crevasse splay near the mouth of the Mississippi River. Our results validate an existing model for mouth bar development, which we extend to explain mouth bar stratigraphy. We propose that changes across a hydrological cycle are important for mouth bar development, resulting in a stratigraphy that has alternating fine and coarse grain sediments. Results also indicate that sand is carried up to 6 km from the main stem of the Mississippi River, despite repeated channel bifurcations, which has important implications for our interpretation of the rock record, understanding of coastal sedimentary systems, and the restoration of large deltas.
Funding: USGS Northern Gulf of Mexico Program (NGOM)
Collaborator(s): Chris Esposito (WI), Alexander Kolker (LUMCON)
Delta allometry digitized from Wolinsky et al. (2010) (blue, gray, and green dashed lines and red circles), with delta allometry metrics for six SDC (purple; a-c), LD12 (dark blue), and LD13 (light blue; d-f).
Collaorators: Kyle Straub, Tulane University Sediment Dynamics Lab
Growth laws for crevasses in the modern Mississippi River Delta; Do crevasse splays obey delta laws?
Using a populated database of a few large deltas from Edmonds and Slingerland (2007), and adding twelve crevasses created by the U.S. Fish and Wildlife Service in the Delta National Wildlife Refuge (DNWR) in the modern Mississippi river Delta (MRD), as well as data from the well-established crevasse Brant’s splay within the Cubits Gap subdelta, we test the hypothesis that small crevasses channel network laws similar to those of large and laboratory scale deltas. Data were obtained using a combination of geospatial tools such as ArcGIS and Google Earth® followed by image analysis to obtain planform metrics (such as channel length and width), while channel depths where obtained from crevasse project data reports provided by CPRA and bathymetric datasets from Esposito et al., (2013). The data sets were supplemented additionally by Boyer et al., (1997) data, updated to reflect more recent land gain. While the large delta dataset was later supplemented by laboratory scale deltas as well as deltas produced using numerical models, there exist a paucity of similar analysis for deltas that are smaller than the Wax lake Delta (WLD) in Louisiana, which is a bayhead delta that is approximately 5 to 10 times larger in size than active crevasse splays within the MRD. Results show that these smaller deltas (crevasses) do in fact obey general deltas growth laws, as well as area and perimeter scaling laws and can good analogs for sediment diversions aimed at building land in the MRD.
Geomorphic evolution and sedimentary framework of the coupled Raccoon Pass and West Belle Pass barrier spit
The objective of this study is to develop a conceptual sedimentary framework and budget of the eastern end of the Timbalier barrier arc system, specifically including West Belle Pass and the associated flood tidal delta near Racoon Pass. The characteristics of this systems’ sediment budget, sedimentary facies, and barrier lithosome evolution are of particular interest to the long-term morphodynamics of the system, barrier restoration perspective, and the fundamental geologic framework of a highly transgressive barrier arc systems.
Funding: The Water Institute of the Gulf
Collaborator(s): Mead Allison and Mark A. Kulp
