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Reconnaissance following Hurricane Ida. Wind damage to light structures, flooding, levee failures, coastal erosion. Field photos, Lidar, UAVs. 

The Rockefeller Wildlife Refuge, located along the Chenier Plain in Southwest Louisiana, was the location of the sequential landfall of two major hurricanes in the 2020 hurricane season. To protect the rapidly retreating coastline along the Refuge, a system of breakwaters was constructed, which was partially completed by the 2020 hurricane season. Multi-institutional, multi-disciplinary rapid response deployments of wave gauges, piezometers, geotechnical measurements, vegetation sampling, and drone surveys were conducted before and after Hurricanes Laura and Delta along two transects in the Refuge; one protected by a breakwater system and one which was the natural, unprotected shoreline. Geomorphological changes were similar on both transects after Hurricane Laura, while after Delta there was higher inland sediment deposition on the natural shoreline. Floodwaters drained from the transect with breakwater protection more slowly than the natural shoreline, though topography profiles are similar, indicating a potential dampening or complex hydrodynamic interactions between the sediment—wetland—breakwater system. In addition, observations of a fluidized mud deposit in Rollover Bayou in the Refuge are presented and discussed in context of the maintenance of wetland elevation and stability in the sediment starved Chenier Plain. 

Soil strength testing and collecting soil cores from wetlands is currently a slow, manual process that runs the risk of disturbing and contaminating soil samples. This paper describes a method using an instrumented dart deployed and retrieved by a drone for performing core sample tests in soft soils. The instrumented dart can simultaneously conduct free- fall penetrometer tests. A drone-mounted mechanism enables deploying and reeling in the dart for sample return or for multiple soil strength tests. Tests examine the effect of dart tip diameter and drop height on soil retrieval, and the requisite pull force to retrieve the samples. Further tests examine the dart’s ability to measure soil strength and penetration depth. Hardware trials demonstrate that the drone can repeatedly drop and retrieve a dart, and that the soil can be discretely sampled. 

This paper presents a method for performing free-fall penetrometer tests for soft soils using an instrumented dart deployed by a quadcopter. Tests were performed with three soil types and used to examine the effect of drop height on the penetration depth and the deceleration profile. Further tests analyzed the force required to remove a dart from the soil and the effect of pulling at different speeds and angles. The pull force of a consumer drone was measured, and tests were performed where a drone delivered and removed darts in soil representative of a wetland environment. 

Hurricane Harvey, a category 4 hurricane on the Saffir-Simpson hurricane wind scale that approached from the Gulf of Mexico, caused severe flooding in Texas and Louisiana. Recorded water levels along the Brazos River exceeded historic high-water levels, and erosion and slope failures of riverbanks were observed in many locations along the river. A near-surface site investigation was conducted in the Brazos River along a short section in Sugarland, Texas, post-Hurricane Harvey. In situ tests were conducted using a portable free fall penetrometer and a chirp sonar. Results showed that sediment properties varied between different locations. Weaker sediments underlying a loose top layer were observed at both riverbanks reaching a penetration depth of ~20 cm, whereas stiffer sediments were found at the center of the river with an estimate of maximum quasi-static bearing capacity ranging from 25 to 300 kPa at sediment depths less than 7 cm. Particle size distributions varied as well depending on the location. Results suggest a correlation between sediment strength and backscatter intensity of the chirp sonar. In summary, in situ geotechnical properties across and along short sections of the Brazos River exhibited a significant variability, likely governed by the local sediment remobilization processes that was reflected in portable free fall penetrometer and chirp sonar measurements of the riverbed surface.