- Copyright © 2017, Environmental & Engineering Geoscience
Post-dam removal geomorphologic adjustment of a stream channel has been documented in the scientific literature at watershed, hillslope and laboratory scales. Hillslope scale studies in channel-cross-sections are most common, and add significant value in the dam-removal literature. This study examines geomorphic stream channel adjustment following dam removal at the hillslope scale under natural climatic conditions. A sediment-filled silt fence dam (1 m tall, 12.65 m wide) was removed in three stages and the width and depth of the upstream developing channel was monitored at six transects for fifteen months. Headcut retreat and changes in channel sinuosity were also recorded. After the silt fence dam was removed, channel development was initiated by headcut formation which migrated upstream at a rate of 4 cm/day for about ten months and then gradually reached attenuation. The channel progressed through four distinct stages: Stage 1 [Initial conditions]; Stage 2 [Downcutting] -wide, shallow, meandering channel incised to a maximum depth of 0.52 m, and sinuosity decreased; Stage 3 [Floodplain development] -upon reaching base level, surface runoff began to meander within the channel, widening it through bank slumps and erosion; Stage 4 [Quasi-equilibrium] -channel development reached dynamic (quasi) equilibrium with only minor widening at downstream transects [maximum width of the incised channel reached 0.46 m] accompanied by sediment aggradation. The stages of upstream channel development and headcut retreat pattern in this study are consistent with other studies at the laboratory and watershed scales indicating that channel development after dam removal is scale independent.