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Channel cross-sectional changes since construction of Livingston Dam and Lake Livingston in 1968 were studied in the lower Trinity River, Texas, to test theoretical models of channel adjustment, and to determine controls on the spatial extent of channel response. High and average flows were not significantly modified by the dam, but sediment transport is greatly reduced. The study is treated as an opportunistic experiment to examine the effects of a reduction in sediment supply when discharge regime is unchanged. Channel scour is evident for about 60 km downstream, and the general phenomena of incision, widening, coarsening of channel sediment and a decrease in channel slope are successfully predicted, in a qualitative sense, by standard models of channel response. However, there is no consistent channel response within this reach, as various qualitatively different combinations of increases, decreases or no change in width, depth, slope and roughness occur. These multiple modes of adjustment are predicted by the unstable hydraulic geometry model. Between about 60 km and the Trinity delta 175 km downstream of the dam, no morphological response to the dam is observed. Rather than a diminution of the dam's effects on fluvial processes, this is due to a fundamental change in controls of the fluvial system. The downstream end of the scour zone corresponds to the upstream extent of channel response to Holocene sea level rise. Beyond 60 km downstream, the Trinity River is characterized by extensive sediment storage and reduced conveyance capacity, so that even after dam construction sediment supply still exceeds transport capacity. The channel bed of much of this reach is near or below sea level, so that sea level rise and backwater effects from the estuary are more important controls on the fluvial system than upstream inputs.

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Cambios en el lecho del canal y el tamaño de partícula de la cuenca baja que se producen en el sistema de Pascagoula River, un clima húmedo sub-tropical, arena del lecho de la corriente que fluye a través de la llanura costera del Golfo se resumen en este ensayo. Tomas de muestras recogidas en 59 sitios a lo largo de los dos principales sistemas de ríos se caracterizaron medi-ante análisis de laboratorio y estadísticos, e índices estándar de sedimentación (Φ5, Φ16, Φ50, Φ84, Φ95, y clasificando). Muestras del lecho del canal muestran una tendencia de refinación en la zona baja de la cuenca. Desviaciones estándar inclusivas gráficas se calcularon para estimar la clasificación; toda la cuenca reveló una clasificación moderada, sin una clara indicación de un aumento en la zona baja de la cuenca. La forma del grano Modal de todas las muestras de material muestra que el material del banco es ligeramente más angular que el material del lecho. Unos porcentajes bajos de recubrimientos se observan en la mayoría de las muestras, sugiriendo que la cuenca del río Pascagoula tiene un sistema de transporte de sedimentos activos. El bajo relieve y la litología similar dentro de la cuenca del río Pascagoula hacen estos datos empíricos únicos y los resultados relevantes dentro del estudio de la dinámica de los sistemas fluviales.