6 Sep 2022

Short-range Near-surface Seismic Ensemble Predictions and Uncertainty Quantification for Layered Medium

Abstract: To make a prediction for seismic signal propagation, one needs to specify physical properties and subsurface ground structure of the site. This information is frequently unknown or estimated with significant uncertainty. This paper describes a methodology for probabilistic seismic ensemble prediction for vertically stratified soils and short ranges with no in situ site characterization. Instead of specifying viscoelastic site properties, the methodology operates with probability distribution functions of these properties taking into account analytical and empirical relationships among viscoelastic variables. This yields ensemble realizations of signal arrivals at specified locations where statistical properties of the signals can be estimated. Such ensemble predictions can be useful for preliminary site characterization, for military applications, and risk analysis for remote or inaccessible locations for which no data can be acquired. Comparison with experiments revealed that measured signals are not always within the predicted ranges of variability. Variance-based global sensitivity analysis has shown that the most significant parameters for signal amplitude predictions in the developed stochastic model are the uncertainty in the shear quality factor and the Poisson ratio above the water table depth.

6 Sep 2022

Brine, Englacial Structure, and Basal Properties near the Terminus of McMurdo Ice Shelf, Antarctica

Abstract: We collected ∼1300 km of ground-penetrating radar profiles over McMurdo Ice Shelf, Antarctica, using frequencies between 40 and 400 MHz to determine extent, continuity and depth to the brine. We also used profiles to determine meteoric ice thickness and locate englacial features, which may suggest ice shelf instability. The brine extends 9–13 km inland from the ice shelf terminus and covers the entire region between Ross, White and Black Islands. Jump unconformities and basal fractures exist in the brine and ice shelf, respectively, suggesting prior fracturing and re-suturing. One 100 MHz profile, the most distal from the ice shelf edge while still being situated over the brine, simultaneously imaged the brine and bottom of meteoric ice. This suggests a negative brine salinity gradient moving away from the terminus. The meteoric ice bottom was also imaged in a few select locations through blue ice in the ablation zone near Black Island. We suggest that brine, sediment-rich ice and poor antenna coupling on rough ice attenuates the signal in this area. When combined with other recent mass-balance and structural glaciology studies of MIS, our results could contribute to one of the most high-resolution physical models of an ice shelf in Antarctica.

6 Sep 2022

Coastal Resilience: Benefits of Wrack and Dune Systems and Current Management Practices

Purpose: The purpose of this US Army Engineer Research and Development Center (ERDC) technical note (TN) is to review both the ecological and geomorphological impacts of wrack on dune systems and provide an overview of current beach dune and wrack management practices. As part of the US Army Corps Regional Sediment Management (RSM) Program, this TN also introduces a case study investigating wrack management solutions for dune stabilization.

6 Sep 2022

Method to Evaluate Vessel Wake Forces on Wetland Scarps

Purpose: This Coastal and Hydraulics engineering technical note (CHETN) presents a methodology to compute normal forces on wetland perimeters with vertically scarped edges. The approach uses an empirical algorithm that predicts the normal force given the offshore vessel wake height, period, and water depth at a given point. Wave impact forces are measured using load cells, which have not been applied previously to marsh settings. Load cell and vessel wake measurements from two field sites are combined to generate an empirical transfer function relating forces to incoming vessel wake characteristics.

31 Aug 2022

Coastal Hazards System–Louisiana (CHS-LA)

Abstract: The US Army Engineer Research and Development Center (ERDC), Coastal and Hydraulics Laboratory (CHL) expanded the Coastal Hazards System (CHS) to quantify storm surge and wave hazards for coastal Louisiana. The CHS Louisiana (CHS-LA) coastal study was sponsored by the Louisiana Coastal Protection and Restoration Authority (CPRA) and the New Orleans District (MVN), US Army Corps of Engineers (USACE) to support Louisiana’s critical coastal infrastructure and to ensure the effectiveness of coastal storm risk management projects. The CHS-LA applied the CHS Probabilistic Coastal Hazard Analysis (PCHA) framework to quantify tropical cyclone (TC) responses, leveraging new atmospheric and hydrodynamic numerical model simulations of synthetic TCs developed explicitly for the Louisiana region. This report focuses on documenting the PCHA conducted for the CHS-LA, including details related to the characterization of storm climate, storm sampling, storm recurrence rate estimation, marginal distributions, correlation and dependence structure of TC atmospheric-forcing parameters, development of augmented storm suites, and assignment of discrete storm weights to the synthetic TCs. As part of CHS-LA, coastal hazards were estimated within the study area for annual exceedance frequencies (AEFs) over the range of 10 yr-1 to 1×10-4 yr-1.

31 Aug 2022

Photographic Aerial Transects of Fort Wainwright, Alaska

Abstract: This report presents the results of low-altitude photographic transects conducted over the training areas of US Army Garrison Fort Wainwright, in the boreal biome of central Alaska, to document baseline land-cover conditions. Flights were conducted via a Cessna™ 180 on two flight paths over portions of the Tanana Flats, Yukon, and Donnelly Training Areas and covered 486 mi (782 km) while documenting GPS waypoints. Nadir photographs were made with two GoPro™ cameras operating at 5 sec time-lapse intervals and with a handheld digital camera for oblique imagery. This yielded 6,063 GoPro photos and 706 oblique photos. Each image was intersected with a land-cover-classification map, collectively representing 38 of the 44 cover categories.

31 Aug 2022

Sediment Supply from Bank Caving on the Lower Mississippi River, 1765 to Present

Abstract: Bank caving rates and associated total sediment supply were calculated along the Lower Mississippi River from Cairo, IL, to Baton Rouge, LA, using historical maps between 1765 and 1992. Comparison of these maps reveals that the added sediment loads from bank erosion have greatly declined through time. In the pre-1960s period, erosion rates generally ranged from approximately 300 million cubic yards (MCY) to 400 MCY, with the 1880–1930s period having the highest erosion rates of approximately 600 MCY. By the 1990s, the sediment supply from bank erosion was essentially eliminated, with significant erosion being observed at only a few locations, totaling approximately 40 MCY/year. This equates to approximately a 90% reduction in the amount of total sediment being supplied to the channel system from bank erosion.

31 Aug 2022

Current State of Practice of Nearshore Nourishment by the United States Army Corps of Engineers

Abstract: This US Army Corps of Engineers (USACE) special report prepared by the US Army Engineer Research and Development Center, Coastal and Hydraulics Laboratory, provides an overview of the current state of practice for nearshore nourishment with dredged sediment. This special report was completed with responses and input from professionals across the dredging and placement teams from each of the USACE Coastal and Great Lakes districts, providing comprehensive overviews of the decision trees these districts utilize in the placement of their dredged sediment. This report describes the general practice of nearshore nourishment, the impediments and concerns faced by nearshore nourishment projects, and the practical methods utilized by the Coastal and Great Lakes districts for their nearshore nourishment projects. Understanding the current state of practice, along with the general and specific impediments the districts face, enables further research in and development of best practices for use across the USACE and better communication of the practice to other stakeholders.

30 Aug 2022

Automated Detection of Austere Entry Landing Zones: A “GRAIL Tools” Validation Assessment

Abstract: The Geospatial Remote Assessment for Ingress Locations (GRAIL) Tools software is a geospatial product developed to locate austere entry landing zones (LZs) for military aircraft. Using spatial datasets like land classification and slope, along with predefined LZ geometry specifications, GRAIL Tools generates binary suitability filters that distinguish between suitable and unsuitable terrain. GRAIL Tools combines input suitability filters, searches for LZs at user‐defined orientations, and plots results. To refine GRAIL Tools, we: (a) verified software output; (b) conducted validation assessments using five unpaved LZ sites; and (c) assessed input dataset resolution on outcomes using 30 and 1‐m datasets. The software was verified and validated in California and the Baltics, and all five LZs were correctly identified in either the 30 or the 1‐m data. The 30‐m data provided numerous LZs for consideration, while the 1‐m data highlighted hazardous conditions undetected in the 30‐m data. Digital elevation model grid size affected results, as 1‐m data produced overestimated slope values. Resampling the data to 5 m resulted in more realistic slopes. Results indicate GRAIL Tools is an asset the military can use to rapidly assess terrain conditions.

30 Aug 2022

Screening Dredged Material to Meet Placement Requirements

Abstract: Certain types of dredging projects require screening of the dredged material (DM) to achieve the project’s DM placement requirement(s). Screening in the context of this report will be defined as the separation of an oversized fraction of the DM from the remaining fraction to meet project-specific placement compliance criteria (or criterion). Examples of DM placement requirements include aspects such as removing Munitions and Explosives of Concern (MEC) to address safety concerns and extracting over-sized material for beneficial use of DM (e.g., gravel and debris from sand to meet beach nourishment placement standards). Welp et al. (2008) provide detailed guidance for personnel involved in dredging projects with sediment containing MEC. The purpose of this document is to not only update the previous MEC-centric guidance with newly developed or identified technology but to also expand upon screening aspects to provide guidance for personnel involved in dredging projects that require removal of an oversized fraction for screening purposes other than just MEC removal.