THE INFLUENCE OF LARGE WOODY DEBRIS ON THE GEOMETRY OF THE SUBAERIAL BRAZOS RIVER DELTA, AS DEMONSTRATED THROUGH FIELD OBSERVATIONS AND A FIRST ORDER COASTAL MODEL
Our data reveal the prevalence of densely packed, large woody debris (LWD) at the ocean-delta interface, and we hypothesize that the LWD supplied by the river collects along the delta shoreface. The largest wood (up to 5-m length, 0.5 m radius) traps smaller wood (e.g., decimeter to meter length, centimeter-scale radius), and this framework attenuates wave energy, allowing for the accumulation of fine sand at the shoreface. Our modeling efforts reveal that the LWD stabilizes the delta from wave attack, promotes a growing shoreline, and aids in the creation of a relatively steep shoreline profile. Over the time period of delta development, each major flood event brings sand that accretes along the delta shoreline and wood then collects, thus attenuating wave energy.
While the woody shoreface creates an important local effect to aid delta preservation, the long term role of wood in terms of influencing the delta planform morphology (e.g., the welded delta ridges) is associated with the construction of topographic relief that aids in additional trapping of sand via aeolian processes. We use ground penetrating radar data to demonstrate that each of the growing ridges of the Brazos delta are rooted by a woody matrix. Our study reveals the critical role that LWD plays in terms of the development of a wave dominated delta.