Geology topics

M. D. Richardson

Publications and source records attributed to M. D. Richardson.

5 recordsLinked to original sources

USGS2007

Multibeam observations of mine burial near Clearwater, FL, including comparisons to predictions of wave-induced burial

A Kongsberg Simrad EM 3000 multibeam sonar (Kongsberg Simrad, Kongsberg, Norway) was used to conduct a set of six repeat high-resolution bathymetric surveys west of Indian Rocks Beach (IRB), just to the south of Clearwater, FL, between January and March 2003, to observe in situ scour and burial of instrumented inert mines and mine-like cylinders. Three closely located study sites were chosen: two fine-sand sites, a shallow one located in ??? 13 m of water depth and a deep site located in ???14 m of water depth; and a coarse-sand site in ???13 m. Results from these surveys indicate that mines deployed in fine sand are nearly buried within two months of deployment (i.e., they sunk 74.5% or more below the ambient seafloor depth). Mines deployed in coarse sand showed a lesser amount of scour, burying until they present roughly the same hydrodynamic roughness as the surrounding rippled bedforms. These data were also used to test the validity of the Virginia Institute of Marine Science (VIMS, Gloucester Point, VA) 2-D burial model. The model worked well in areas of fine sand, sufficiently predicting burial over the course of the experiment. In the area of coarse sand, the model greatly overpredicted the amount of burial. This is believed to be due to the presence of rippled bedforms around the mines, which affect local bottom morphodynamics and are not accounted for in the model, an issue currently being addressed by the modelers. This paper focuses specifically on two instrumented mines: an acoustic mine located in fine sand and an optical instrumented mine located in coarse sand. ?? 2007 IEEE.

IEEE Journal of Oceanic Engineering↗

USGS2007

Predicting seabed burial of cylinders by wave-induced scour: Application to the sandy inner shelf off Florida and Massachusetts

A simple parameterized model for wave-induced burial of mine-like cylinders as a function of grain-size, time-varying, wave orbital velocity and mine diameter was implemented and assessed against results from inert instrumented mines placed off the Indian Rocks Beach (IRB, FL), and off the Martha's Vineyard Coastal Observatory (MVCO, Edgartown, MA). The steady flow scour parameters provided by Whitehouse (1998) for self-settling cylinders worked well for predicting burial by depth below the ambient seabed for O (0.5 m) diameter mines in fine sand at both sites. By including or excluding scour pit infilling, a range of percent burial by surface area was predicted that was also consistent with observations. Rapid scour pit infilling was often seen at MVCO but never at IRB, suggesting that the environmental presence of fine sediment plays a key role in promoting infilling. Overprediction of mine scour in coarse sand was corrected by assuming a mine within a field of large ripples buries only until it generates no more turbulence than that produced by surrounding bedforms. The feasibility of using a regional wave model to predict mine burial in both hindcast and real-time forecast mode was tested using the National Oceanic and Atmospheric Administration (NOAA, Washington, DC) WaveWatch 3 (WW3) model. Hindcast waves were adequate for useful operational forcing of mine burial predictions, but five-day wave forecasts introduced large errors. This investigation was part of a larger effort to develop simple yet reliable predictions of mine burial suitable for addressing the operational needs of the U.S. Navy. ?? 2007 IEEE.

IEEE Journal of Oceanic Engineering↗

USGS2002

In situ acoustic and laboratory ultrasonic sound speed and attenuation measured in heterogeneous soft seabed sediments: Eel River shelf, California

We compared in situ and laboratory velocity and attenuation values measured in seafloor sediments from the shallow water delta of the Eel River, California. This region receives a substantial volume of fluvial sediment that is discharged annually onto the shelf. Additionally, a high input of fluvial sediments during storms generates flood deposits that are characterized by thin beds of variable grain-sizes between the 40- and 90-m isobaths. The main objectives of this study were (1) to investigate signatures of seafloor processes on geoacoustic and physical properties, and (2) to evaluate differences between geoacoustic parameters measured in situ at acoustic (7.5 kHz) and in the laboratory at ultrasonic (400 kHz) frequencies. The in situ acoustic measurements were conducted between 60 and 100 m of water depth. Wet-bulk density and porosity profiles were obtained to 1.15 m below seafloor (m bsf) using gravity cores of the mostly cohesive fine-grained sediments across- and along-shelf. Physical and geoacoustic properties from six selected sites obtained on the Eel margin revealed the following. (1) Sound speed and wet-bulk density strongly correlated in most cases. (2) Sediment compaction with depth generally led to increased sound speed and density, while porosity and in situ attenuation values decreased. (3) Sound speed was higher in coarser- than in finer-grained sediments, on a maximum average by 80 m s-1. (4) In coarse-grained sediments sound speed was higher in the laboratory (1560 m s-1) than in situ (1520 m s-1). In contrast, average ultrasonic and in situ sound speed in fine-grained sediments showed only little differences (both approximately 1480 m s-1). (5) Greater attenuation was commonly measured in the laboratory (0.4 and 0.8 dB m-1 kHz-1) than in situ (0.02 and 0.65 dB m-1 kHz-1), and remained almost constant below 0.4 m bsf. We attributed discrepancies between laboratory ultrasonic and in situ acoustic measurements to a frequency dependence of velocity and attenuation. In addition, laboratory attenuation was most likely enhanced due to scattering of sound waves at heterogeneities that were on the scale of ultrasonic wavelengths. In contrast, high in situ attenuation values were linked to stratigraphic scattering at thin-bed layers that form along with flood deposits. ?? 2002 Published by Elsevier Science B.V.

Marine Geology↗

USGS2001

Overview of SAX99: Environmental considerations

A 1-km2 area located 2 km off the Florida Pan-handle (30??22.6???N; 86??38.7???W) was selected as the site to conduct high-frequency acoustic seafloor penetration, sediment propagation, and bottom scattering experiments [1]. Side scan, multibeam, and normal incidence chirp acoustic surveys as well as subsequent video surveys, diver observations, and vibra coring, indicate a uniform distribution of surficial and subbottom seafloor characteristics within the area. The site, in 18-19 m of water, is characterized by 1-2-m thick fine-to-medium clean sand and meets the logistic and scientific requirements specified for the acoustic experiments. This paper provides a preliminary summary of the meteorological, oceanographic, and seafloor conditions found during the experiments and describes the important physical and biological process that control the spatial distribution and temporal changes in these characteristics.

IEEE Journal of Oceanic Engineering↗

USGS1997

Benthic boundary layer processes in the Lower Florida Keys

This special issue of Geo-Marine Letters, "Benthic Boundary Layer Processes in the Lower Florida Keys," includes 12 papers that present preliminary results from the Key West Campaign. The Dry Tortugas and Marquesas Keys test sites were selected by a group of 115 scientists and technicians to study benthic boundary layer processes in a carbonate environment controlled by bioturbation and biogeochemical processes. Major activities included remote sediment classification; high-frequency acoustic scattering experiments; sediment sampling for radiological, geotechnical, biological, biogeochemical, physical, and geoacoustic studies; and hydrodynamic studies using an instrumented tetrapod. All these data are being used to improve our understanding of the effects of environmental processes on sediment structure and behavior.

Florida↗