A perfect storm: An archaeological management crisis in the Mississippi River Delta

Engineered projects resulting in unintended consequences, coastal erosion, subsidence, and sea-level rise are rapidly destroying archaeological sites in the Mississippi River Delta (MRD). The processes of site obliteration are intensifying and accelerating due to anthropogenic transformation of the environment, including cumulative engineered alterations of the landscape and climate change. Combined with increased inundation and erosion from storm surges, hundreds of terrestrial sites formerly located on natural levees, barrier islands, and other coastal landforms are progressively eroded, redeposited, deeply buried, and submerged. These include thousand-year-old earthen mounds and shell middens constructed by Native Americans, as well as centuries-old fishing communities along the coast. These irreplaceable cultural properties can provide crucial information on the unique history and ecology of the MRD. Ongoing studies include consulting with interested parties and implementing data sharing agreements. Re- searchers have formed a consortium of universities and state and federal agencies, and are partnering with culturally affiliated Native American tribes, descendant groups, and coastal communities. The consortium is developing a robust GIS-enabled risk matrix for analyzing threats and effects to endangered sites. It is using the risk matrix to select 30 sites for monitoring, assessment, aerial photogrammetry, and recording environmental data on water table fluctuations. Analysis of action-based scientific data on these imperiled and rapidly disappearing places is urgently needed and will provide the impetus and baseline for future studies. Otherwise, ongoing site destruction will erase any remaining opportunities for learning about Louisiana’s deep history and diverse cultural heritage

Three-dimensional flow structure and bed morphology in large elongate meander loops with different outer bank roughness characteristics

© 2016. American Geophysical Union. All Rights Reserved. Few studies have examined the three-dimensional flow structure and bed morphology within elongate loops of large meandering channels. The present study focuses on the spatial patterns of three-dimensional flow structure and bed morphology within two elongate meander loops and examines how differences in outer bank roughness influence near-bank flow characteristics. Three-dimensional velocities were measured during two different events—a near-bankfull flow and an overbank event. Detailed data on channel bathymetry and bed form geometry were obtained during a near-bankfull event. Flow structure within the loops is characterized by strong topographic steering by the point bar, by the development of helical motion associated with flow curvature, and by acceleration of flow where bedrock is exposed along the outer bank. Near-bank velocities during the overbank event are less than those for the near-bankfull flow, highlighting the strong influence of the point bar on redistribution of mass and momentum of the flow at subbankfull stages. Multiple outer bank pools are evident within the elongate meander loop with low outer bank roughness, but are not present in the loop with high outer bank roughness, which may reflect the influence of abundant large woody debris on near-bank velocity characteristics. The positions of pools within both loops can be linked to spatial variations in planform curvature. The findings indicate that flow structure and bed morphology in these large elongate loops is similar to that in small elongate loops, but differs somewhat from flow structure and bed morphology reported for experimental elongate loops

Analysis of shallow turbulent flows using the Hilbert-Huang transform: a tool for exploring the characteristics of turbulence and coherent flow structures

The Hilbert-Huang transform (HHT) is a method of spectral analysis that is suitable for application to nonstationary and non-linear signals that holds enormous potential for the analysis of turbulent flows in fluvial, aeolian, and coastal systems. HHT begins with decomposition of the signal into Intrinsic Mode Functions (IMFs) using the Empirical Mode Decomposition method. A Hilbert transform is then applied to each IMF, enabling the calculation of the local spectral characteristics of the signal. Four applications of the HHT are used to demonstrate the utility of this method for spectral analysis of turbulent flows. The method is applied to: (1) velocity measurements of unidirectional flow with high suspended sediment concentration (laboratory), (2) velocity measurements from a combined uni-i-direction and wave flow over a mobile, evolving bed (laboratory), and (3) temperature measurements from the mixing interface of a large river confluence (field). Comparisons among HHT, Fourier, and wavelet analysis are provided, and we identify a number of major benefits of HHT based on these four applications. The results presented show that the spectral method of HHT provides a very useful tool for analysis of turbulence in natural flows and can greatly enhance signal analysis in addition to traditional methods such as Fourier and wavelet analysis

A database solution for the quantitative characterisation and comparison of deep-marine siliciclastic depositional systems

In sedimentological investigations, the ability to conduct comparative analyses between deep-marine depositional systems is hindered by the wide variety in methods of data collection, scales of observation, resolution, classification approaches and terminology. A relational database, the Deep-Marine Architecture Knowledge Store (DMAKS), has been developed to facilitate such analyses, through the integration of deep-marine sedimentological data collated to a common standard. DMAKS hosts data on siliciclastic deep-marine system boundary conditions, and on architectural and facies properties, including spatial, temporal and hierarchical relationships between units at multiple scales. DMAKS has been devised to include original and literature-derived data from studies of the modern sea-floor, and from ancient successions studied in the sub-surface and in outcrop. The database can be used as a research tool in both pure and applied science, allowing the quantitative characterisation of deep-marine systems. The ability to synthesise data from several case studies and to filter outputs on multiple parameters that describe the depositional systems and their controlling factors enables evaluation of the degree to which certain controls affect sedimentary architectures, thereby testing the validity of existing models. In applied contexts, DMAKS aids the selection and application of geological analogues to hydrocarbon reservoirs, and permits the development of predictive models of reservoir characteristics that account for geological uncertainty. To demonstrate the breadth of research applications, example outputs are presented on: (i) the characterisation of channel geometries, (ii) the hierarchical organisation of channelised and terminal deposits, (iii) temporal trends in the deposition of terminal lobes, (iv) scaling relationships between adjacent channel and levee architectural elements, (v) quantification of the likely occurrence of elements of different types as a function of the lateral distance away from an element of known type, (vi) proportions and transition statistics of facies in elements and beds, (vii) variability in net-to-gross ratios among element types

Influence of riparian vegetation on near-bank flow structure and rates of erosion on a large meandering river

The dynamic process of meandering in alluvial rivers occurs through complex interactions among autogenic processes such as three-dimensional flow structure, channel planform geometry, and sediment transport. These internal processes can be strongly influenced by the geotechnical properties of the channel banks and floodplains, as well as riparian and in-channel vegetation, modifying rates of erosion and mechanism of bank retreat, often leading to complex planform geometries. While extensive research has been conducted on each of these processes independently, few studies have examined through detailed field measurements the combined effects and interactions between the internal processes and external forcings driving channel migration. Furthermore, most of the studies investigating the influence of bank material properties and vegetation have been conducted on small and moderately sized rivers with relatively simple planform geometry, or using simplified experimental flumes and numerical models. Thus, the influence of these external forcings on the meander dynamics of large rivers remain poorly understood. This dissertation research is organized into three separate investigations from two elongate meander loops with different riparian vegetation on a large river. The first study focuses on the spatial patterns of three-dimensional flow structure throughout these meander loops and examined the effects of near-bank large woody debris (LWD) on near-bank flow structure and boundary shear stress, and how the hydrodynamics varied during different hydrologic conditions. Data consist of time-averaged three-dimensional velocity measurements, which were obtained using a boat-mounted acoustic Doppler current profiler (ADCP) during varying hydrologic conditions. Patterns of depth-averaged velocity through the meander loop without near-bank LWD are fairly consistent with previous investigations of flow through elongate meander loops, however, LWD near the outer bank of the forested loop has a strong influence on the near-bank flow field. Specifically, the LWD produces a zone of low velocity against the outer bank that extends up to 40 m into the channel and over the entire flow depth, and creates several streamwise-oriented secondary cells. These effects from the LWD on the near-bank flow field prevent advection of high momentum fluid against the outer bank. In contrast, the roughness elements along the outer bank of the unforested bend are primarily large-scale topographic irregularities that are not effective at reducing flow velocities near the bank toe. The second study explores the various scales of outer bank form roughness produced from large-scale bankline irregularities and small-scale surface roughness, the influence of bank material properties and vegetation on scales of roughness, and how scales of roughness differ during variable discharge conditions and through time. Detailed morphology of the outer banks was obtained using terrestrial LiDAR during low flow conditions and multi-beam echo sounding (MBES) during near-bankfull conditions, and scales of roughness were evaluated using Hilbert-Huang Transform spectral analysis and root-mean-square analysis. Results show that scales of roughness along banks composed primarily of non-cohesive sediment vary as bank elevation increases and show a tendency for a dominant length scale of roughness, whereas banks composed of fine-grained silt and clay increase the resistance properties of the banks and promote uniform roughness vertically over the bank face and do not appear to have a dominant scale of roughness through the bend. Additionally, comparison between small-scale surface roughness obtained during subaerial and subaqueous conditions shows that bank roughness is considerably reduced during high flow conditions when the banks are inundated, most likely related to the removal of small woody and leafy vegetation during subaqueous and eradication of small-scale erosional features in non-cohesive bank materials. The third study examined the lateral and vertical heterogeneities in bank material properties and riparian vegetation between these two bends using various geotechnical tests, and a numerical model of bank retreat and repeat terrestrial LiDAR surveys to evaluate the capacity of bank material properties to modify the rates and mechanisms of bank retreat. Results show substantial differences in the characteristic grain size of the bank materials, soil cohesion, and critical shear stress necessary for sediment entrainment between the forested and unforested bends, and are highly variable within each bend, both laterally and vertically. Results also reveal that riparian trees are capable of enhancing bank stability through increased cohesion due to root-reinforcement, and that bedrock outcrops within the downstream limbs of both of these bends that are highly resistant to erosion. The findings from the model simulations of bank retreat show that the variations in bank material properties and riparian vegetation greatly contribute to rates of erosion and the style of bank failure, and suggest that hydrologic variability is an important factor influencing the erodibility of cohesive banks. For the unforested bend, the non-cohesive bank materials, lack of riparian and in-channel vegetation, and limited influence of the bank roughness elements produce high rates channel migration near the bend apex. However, on the downstream limb of this bend, the platform of bedrock exposed within the channel is strongly influencing patterns of near-bank flow and shear stress, leading to a small zone of deposition along the outer bank downstream of the bedrock. In contrast, at the forested bend, the high resistance of bank materials, stabilizing effects of riparian trees, and reduction of near-bank shear stress from increased flow resistance by LWD, limit extension of this bend near the apex. On the downstream limb where the highest shear stresses occur, the channel is confined by bedrock from the upland valley, restricting the downstream translation of the bend. In conclusion, the results from this research advance knowledge and understanding of how the interactions and feedbacks among three-dimensional flow structure, material properties of the banks and floodplains (sediment and bedrock), and vegetation characteristics near the outer bank influence the morphodynamics of meandering rivers. The findings also provide an empirical foundation for the refinement and calibration of numerical models aimed at predicting these morphodynamics in complex natural settings

LiDAR, GIS, and multivariate statistical analysis to assess landslide risk, Horseshoe Run watershed, West Virginia

Current stream restoration practices focus on stabilizing banks, transporting sediment, and creating aquatic habitats. However, only channel morphology data are collected prior to typical restoration project designs. A more thorough approach to assessing restoration projects incorporates the geomorphology of the contributing hillslopes within the watershed. For this project, a landslide risk assessment was conducted for Horseshoe Run watershed in West Virginia using LiDAR data, GIS, and multivariate statistical analysis to provide the restoration projects with information concerning the geomorphology of the hillslopes and identify areas of greater risk for slope failure. A landslide inventory map was created using field observations and remote mapping on a LiDAR-derived shaded relief map within ArcGIS 9.2. Landslides were classified as planar slides, rotational slumps, debris flows, debris fans, debris slides, or active slopes. Seven variables were determined for all landslides: elevation, slope angle, slope aspect, distance from roads, distance from streams, plan curvature, and profile curvature. Similar data on the same seven variables also were collected for a random sample of unfailed slopes, and both data sets were used for discriminant analyses using Minitab 13.30. A first discriminant analysis of all failed and unfailed slopes was 71.8% accurate in predicting failures and non-failed slopes, suggesting a significant difference between the two populations. A second discriminant analysis was 76.3% accurate in determining differences between classifications of slope movements. The discriminant analyses results were used to create a landslide susceptibility map for Horseshoe Run watershed, classifying the hillslopes as low, medium, or high risk for failure. Areas classified as high risk areas were further analyzed to determine whether they were contributing to the channel instability of Horseshoe Run. The landslide susceptibility map also provided a means to evaluate locations of concern for slope stability and also identify potential areas of disturbance for Horseshoe Run