Log-jams and avulsions in the San Antonio River Delta, Texas

摘要: The San Antonio River Delta (SARD), Texas, has experienced two major avulsions in the past 80 years, and a number of other historical Holocene channel shifts. causes consequences these – one which is ongoing were examined using combination fieldwork, geographic information system (GIS) analysis, to identify active, semi-active, paleochannels sequence shifting flow paths through delta. role deposition patterns antecedent morphology, large woody debris jams, tectonic influences given special attention. Sedimentation SARD exacerbated by effects. Channel aggradation ubiquitous, superelevation bed above level backswamp areas on floodplain common. This creates ideal setup conditions for avulsions, stable, cohesive fine-grained banks favor rather than lateral migration. Flood basins between alluvial ridges associated with aggraded channels exist, but occur re-occupation former found within or connected flood basins. Large channel-blocking log-jams are common, sometimes displace from channel, triggering crevasses. However, large, recurring log-jam at site avulsion into Elm Bayou not responsible shift. Rather, narrow, laterally stable resulting splits lead accumulation wood. Some aspects regime typical deltas, while others more novel. These includes involving tributaries subchannels delta as well dominant channel; backstepping changes delta; an indirect trigger formation (as vice-versa); maintenance multi-channel pattern distinct classic anastamosing distributary systems. Copyright © 2012 John Wiley & Sons, Ltd.