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The US Gulf of Mexico coastal region has repeatedly been subjected to major flood events. Local geotechnical site characteristics and geomorphology can change due to sediment transport processes during such events. However, field measurements during extreme conditions are challenging. This paper discusses initial attempts at a combined geotechnical and geophysical site investigation of the uppermost layers of riverbeds following severe flooding events at three different rivers in Texas: the Guadalupe, Brazos, and Colorado Rivers in terms of sediment strength derived from a portable free fall penetrometer, backscatter intensity recorded by a chirp sonar, and soil sample characterization. Results show low strength sediments (<40 kPa) along the investigated sections of the Guadalupe and Brazos riverbanks. Although sediments in the center of the Brazos River were characterized with higher strength (>50 kPa) and larger grain sizes (d 50 ∼ 0.3 mm), sediment strength of the Guadalupe and Colorado Rivers displayed more variations around bridge piers. The spatial variations likely resulted from sediment remobilization processes and local scour under severe hydrodynamic conditions. Both, geotechnical and geophysical results, reflected the observed variations in the riverbed sediments; nonetheless, a quantitative correlation among the rivers was impeded by challenges primarily related to limitations of spatial accuracy and the significant riverbed heterogeneity, as well as shallow water limitations of the chirp sonar. • Combined geotechnical and geophysical site characterization at three Texas river sections • Measurements from small vessels and in areas of unknown riverbed conditions • Sediment dynamics were reflected in geotechnical and geophysical data • Qualitative relationship between portable free fall penetrometer and chirp sonar • Three river sections differed significantly in local sediment properties [ABSTRACT FROM AUTHOR]

Abstract: The largest rivers draining to the Gulf of Mexico in Texas are at more advanced stages of valley filling than rivers with smaller drainage areas, with corresponding differences in alluvial morphology and architecture, and avulsion style. This seems to imply that the larger fluvial systems either produce more sediment relative to the accommodation space in the alluvial valleys, or that they have undergone longer periods of valley aggradation. However, it is not clear that either of these is the case. This paper presents a theoretical analysis showing that fluvial systems with larger drainage areas can produce more advanced stages of infilling than those with smaller drainage areas (but with identical histories and sediment production per unit area) due to the nature of the scaling relationships between drainage basin area and incised valley size, and between basin area and sediment yield. Data for rivers in the region shows a strong linear relationship between valley width and drainage area. The nonlinear relationship between drainage area and proportion of the incised valley filled is somewhat weaker, but still significant, and major deviations are readily explained in terms of local inherited morphology or tectonic features. Results show that major differences in the degree or stage of valley filling could occur due to differences in drainage basin size alone. This indicates caution in interpreting incised valley fills of drainage basins of different sizes in terms of sediment supply. [Copyright &y& Elsevier]

Abstract: Surface deformation in the Houston area has been quantified by using a variety of methods including LIDAR, InSAR, extensometers, drilling (to approximately 100m), and Ground Penetrating Radar. In this paper we report on GPS data acquired during the period between 1995 and 2005 that found evidence of ongoing subsidence (up to −56mm/year) in northwestern Houston and of possible horizontal surface movement towards the Gulf of Mexico (up to 6mm/year). We describe the methods of data-processing used in the study and speculate on the possibility that the active elevation of salt domes, mainly at the south and east of the city, may indirectly influence other surface movements including fault movements and subsidence over areas >1km2. Making use of our observations and analysis could help in natural hazard mitigation in the Houston area and possibly also indicate approaches to surface subsidence study that might be used in other urban areas. [Copyright &y& Elsevier]

This paper provides an evidence-based contribution to understanding coastal governance in response to hurricane hazards. It uses the five-part conceptual framework for coastal governance, which includes 1) complexity, 2) vulnerability, 3) adaptive management, 4) stakeholder participation, and 5) the integration of technical knowledge in decision-making. A case study of the Harvey-impacted Texas communities in the Gulf of Mexico is presented within this framework. This particular case is important because of current high level discussions that suggest subnational, state-centric policy response to hazards may be the new model for disaster response moving forward. This study presents insights on the current trends toward devolved, subnational policy response to disasters, as well as a revised framework for coastal governance, where resilience is linked to all concepts in the governance framework as an outcome. Several major findings are discussed. First, higher scales of government take much longer than is necessary to respond to hazards because of their complex administrative policies and procedures. This is worsened in places that have not experienced hazards in recent decades. Innovative adaptation by subnational policy-makers may be one pathway to quicken policy response, as are the commendable but fragmented efforts of charities and voluntary groups. However, devolved policy responses may face their own challenges in implementation, increasing adaptive capacity but decreasing resilience. This study found that participatory, multi-stakeholder processes enhance resilience through disaster simulation exercises and participatory planning processes. These participatory processes enhance learning and the capacity to implement recovery-focused public policy within the constraints of the disaster. [ABSTRACT FROM AUTHOR]

Beach and dune morphology are spatially and temporally variable, changing over a broad range of scales simultaneously. Strong wind, waves, and storm surge from Hurricane Harvey substantially eroded the beach and dunes along the Texas coast, causing significant scarps and berms. This paper presents information about how anthropogenic activity, such as driving on the beach, affected the response and recover of a barrier island with regard to the post-storm resiliency along the Texas-Gulf of Mexico coast by comparing two adjacent 7 km stretches of coast: a driving section and a limited-access section. A collection of field photos, aerial imagery, and a September 2016 LiDAR-derived digital elevation model (DEM) dataset provide information on pre-storm morphology, while field photos, taken only 3 days after Hurricane Harvey made landfall, and a structure-from-motion (SfM)-derived DEM and imagery provide qualitative and quantitative information about the post-storm morphology. While beach and dune erosion in the non-driving section was restricted entirely to the beach and incipient dune system, the driving section exhibited complex patterns of erosion and deposition along the beach and the entire foredune profile was altered. Despite the hurricane making landfall north of the study site and closer to the non-driving section, beach-dune erosion and scarping was greatest in the southern section which is accessible to public vehicles. Results demonstrate that human activity affects the response and recovery of the beach-dune system along the Gulf side of the island by decreasing alongshore variability in erosion-deposition and limiting vegetative and geomorphic recovery. Unlabelled Image • Driving on the beach affects beach-dune response to and recovery following a storm. • Non-driving areas show substantial evidence of recovery within 6 months post-storm. • Driving on the beach limits incipient foredune development and recovery. • Limiting low dune recovery can reinforce the effects of framework geology. [ABSTRACT FROM AUTHOR]