RAPID - Tree Blowdown Impacts of Hurricane Harvey on Hydrologic Surface Connectivity in a Coastal River and Its Floodplain
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Flood inundation typically enables the largest and most abrupt material and energy exchanges between a river and its floodplain and the size of the area affected is highly dependent on river-channel and floodplain geomorphology. Given the vulnerability of coastal plains to the wind and rain impacts of tropical cyclones with increasing strength and frequency, it is critical to advance our understanding of these impacts on river-floodplain interactions in these environments. This knowledge is also crucial to successful preservation and management of the coastal plain river systems, their ecosystems, and ecosystem services. The Mission River on the Coastal Bend of Texas, which is also a part of the Mission-Aransas National Estuarine Research Reserve (MANERR), was on the path of the destructive core of Hurricane Harvey, which made its first landfall on Aug. 25, 2017. Hurricane driven heavy rainfall resulted only in moderate flooding of the river; however, the extreme winds induced a substantial amount of tree blowdowns and large woody debris (LWD) on the river and its floodplain. LWD creates logjams and barriers that can alter the flow of the river and redirect flood and river flow into floodplain environments, resulting in erosion and reconfiguration of the river system. This rapid-response research project will be the first assessment of the tree blowdown impacts of Hurricane Harvey ? and one of the first of any hurricane? on a coastal river system. The outcomes are expected to contribute to the very limited literature in fluvial geomorphology on the subject by advancing the knowledge-base on extreme wind impacts of tropical cyclones on river systems. The findings will provide insights for developing successful landscape and ecosystem management of the riverine habitats at the MANERR, with applicability to similar systems which might include human habitation and infrastructure. This research will establish partnerships with staff/researchers at the MANERR and Coastal Resilience Collaborative (CRC) within Texas Sea Grant. The findings will be disseminated via the MANERR environmental stewardship program and CRC education and outreach communities with the aim of increasing awareness of coastal communities, resource managers, and land-use planners on the impacts of tropical cyclones on river and floodplain systems and associated ecosystem services. The proposed study will provide training and mentoring of graduate and undergraduate students from underrepresented groups. This study aims to answer the question: What are the tree blowdown and LWD impacts of Hurricane Harvey on hydrologic surface connectivity between the Mission River channel and floodplain? The study is driven by two objectives: 1) determine quantitatively the spatial extent and patterns of tree blowdowns on the floodplain and LWD inputs into the river channel; 2) evaluate the impact of tree blowdowns and LWD after an extreme event (i.e., hurricane-force wind) on flood inundation and hydrologic surface connectivity between the river channel and the floodplain in a spatial and temporal context. To address these objectives, the study will integrate field investigations, high spatial- and spectral-resolution geospatial data, and hydrodynamic modeling. Findings of the study will advance our process understanding of how an abrupt change in floodplain configuration due to hurricane-force wind influence the surface water induced interactions within river-floodplain systems and how this influence varies across a range of river-stage conditions.
