Rapid sediment mapping and in situ geotechnical characterization in challenging aquatic areas

Abstract

Yakutat Bay, Southeast Alaska, is characterized by significant spatial variations in sediment type and dynamics. The northwestern side is supplied by sediments from the nearby glaciers, and is affected by longshore sediment transport processes, while the southeastern side has no direct sediment input, and is affected by human activities. In situ seabed investigations can be difficult, and expensive, due to logistical challenges in such remote locations. A portable free fall penetrometer (PFFP) was deployed 149 times along 16 transects in water depths of 2–48 m. The deceleration and pore pressure records during the probe's penetration into the seabed were used to characterize the surficial sediments. Equivalents of quasi‐static bearing capacity were determined using the deceleration‐depth signatures, and yielded strong variabilities ranging from 5 to 107 kPa at sediment depths of 10.3–41.9 cm. Correlating the PFFP results to visual field observations and literature, a regional classification scheme, and an updated sediment distribution map were derived. The pore pressure response was correlated to the different sediment types, and was used to assess the sediment's consolidation state. At the northwestern side, an increasing pore pressure trend indicated underconsolidated cohesive sediments. At the southeastern side, clayey sediments appeared to be more consolidated except of sediments of high organic content near the populated areas. The use of the pore pressure measurements represents a novel way for rapid sediment characterization using PFFP. The presented approach to create rapidly a regional sediment classification scheme offers a time‐ and cost‐effective method to derive seabed sediment maps in areas of difficult access and logistics.

Geotechnical Measurements for the Investigation and Assessment of Arctic Coastal Erosion—A Review and Outlook

“…Significant efforts are ongoing to include in situ and even remotely assessed geotechnical parameters in nearshore morphological models. Similarly to above mentioned studies, significant variations in geotechnical properties have been documented in Arctic and sub-Arctic environments [17,117]. Those data have improved the understanding of local sediment dynamics processes, and it can be hypothesized that, similarly as for non-Arctic environments, the consideration of in situ geotechnical properties in Arctic nearshore geomorphologic models would serve the improvement of accuracy and decrease in uncertainty of those models.…”

Performance of a novel sediment sampler as an add‐on unit for portable free‐fall penetrometers: Combining in situ geotechnical testing with sediment sampling

“…The goal of this study was to evaluate the performance of novel sediment sampler designs that can be used as an add‐on unit to PFFP, enabling simultaneous sediment sampling and geotechnical profiling of the uppermost seabed surface with a special attention to potentially mobile seabed layers. PFFP is suitable for deployment in subaqueous areas of difficult access, including areas where more sophisticated and larger traditional samplers can hardly be deployed due to requirements of vessel stability, size, or infrastructure (Stark et al ; Albatal and Stark ). In comparison with a simple, easy‐deployable grab sampler, the novel sampling add‐on unit allowed sampling in some spots where the grab sampler remained unsuccessful and always delivered a complementary geotechnical strength profile that also offered suggestions why sampling remained unsuccessful in some locations.…”

“…However, those areas are typical target areas to study sediment stratification in response to sediment dynamics. Conversely, PFFP measurements suffer from a lack of high‐quality samples at key locations for calibration and verification of the readings (Stark et al ; Albatal and Stark ). Therefore, a sampling mechanism added on to a PFFP could potentially enable novel insights into surficial seabed stratification by (i) improving PFFP data interpretation, (ii) providing quality samples from coastal areas of difficult access, and (iii) solving the current issue of potential bias from spatial inhomogeneity when applying a two‐step PFFP and sampler deployment strategy.…”

“…Mulukutla et al () introduced a more detailed classification scheme based on the firmness factor, which is a function of the maximum deceleration, impact velocity, and the penetration time. Albatal and Stark () utilized the PFFP deceleration and pore‐water pressure measurements in addition to sediment traces on the probe and available local knowledge to develop a regional soil classification scheme for PFFP. All of the proposed classification schemes depend on or benefit from a calibration using physical samples from the PFFP deployment locations.…”

To What Extent Can a Sediment Yield Model Be Trusted? A Case Study from the Passaúna Catchment, Brazil

“…In order to acquire fast and accurate sediment information in areas where no previous data are available, a socalled portable free-fall penetrometer (PFFP) was used to assess the sediment distribution in the reservoir. PFFPs are not new in marine research (mostly sediment management in harbors), while their application in freshwater is still limited [54][55][56][57][58][59][60][61][62][63].…”