|Prasad, Shyam - UNIVERSITY OF MISSISIPPI|
Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 1, 2000
Publication Date: N/A
Interpretive Summary: Headcut development and migration plays a critical role in initiation of drainage systems, rill and gully formation, erosion of bedrock channels, and landscape evolution. In the agricultural areas of northern Mississippi, soil erosion due to headcut formation can be devastating because of the low cohesive strength of the soil. Such erosion processes lead to significant soil losses that may impact both ecology and water quality, reduce crop production, and cause ephemeral gully formation. Experiments were conducted to examine the effect of water discharge on the growth and development of headcuts in a laboratory channel. Soil indigenous to Mississippi was packed into a flume with a pre-formed step or headcut. This soil was subjected to rainfall, which produced a surface seal, followed by overland flow that caused erosion to occur at the step. The same bed slope was used in each experiment, but flow discharge varied from 23.9 to 82.4 l/min. After a short period of time (1 to 3 minutes), a steady-state condition was reached where the headcut migrated upstream at a constant velocity, the scour hole shape remained the same, and the sediment yield remained constant. The scour holes became much larger as flow discharge was increased, tbut their aspect ration remained the same. A sediment bed was deposited downstream of the migrating headcut, and its slope increased with flow discharge. This information will form the framework for predicting sediment load and enhancing the assessment of soil loss in upland areas impacted by headcut formation.
Technical Abstract: Experiments were conducted to examine soil erosion by headcut development and migration in concentrated flows typical of upland areas. In a laboratory channel, packed sandy loam to sandy clay loam soil beds with pre-formed headcuts were subjected to simulated rain followed by an overland flow. The rainfall produced a well-developed surface seal that minimized surface soil detachment. During overland flow, soil erosion occurred exclusively at the headcut, and after a short period of time a steady-state condition ensued where the headcut migrated at approximately a constant rate, the scour hole morphology remained unchanged, and sediment yield remained constant. A four-fold increase in flow discharge resulted in larger scour holes, yet aspect ratio was conserved. A sediment bed was deposited downstream of the migrating headcut, and its slope increased with flow discharge.