CHARACTERISTICS OF ACTIVELY ERODING EPHEMERAL GULLIES IN AN EXPERIMENTAL CHANNEL

Abstract

The formation of ephemeral gullies can significantly increase soil losses from agricultural lands and severelyimpact farm productivity, yet few data exist on the physical characteristics of actively eroding gullies. The objectives ofthe current study were to examine the time variation of gully morphology and sediment load in response to a range ofoverland flow discharges and the impact of soil moisture content and soil density on erosion rates. Preformed ephemeralgullies were constructed at field scale in a large experimental channel using the same cohesive soil but at two differentmoisture contents and bulk densities. For the bed with relatively high soil moisture content and bulk density, clear-waterflows caused low rates of erosion, detachment-limited flows prevailed, and bed degradation was uniform along the flume.For the bed with relatively low soil moisture content and bulk density, comparable clear-water flows caused high rates oferosion, both detachment-limited and transport-limited flows prevailed, and bed degradation was greater in the upstreamreaches. In both experiments, erosion caused the gullies to incise, to significantly increase gully bottom width, and tosteepen gully sidewalls. These results compare favorably with field studies of ephemeral gullies, and the hydraulics andsediment transport processes observed are similar to those reported for actively eroding rills.