GULLY HEADCUT ADVANCE

Gully headcut advance rates were examined in a cohesive soil with mult iple overfall heights and discharges. Eleven rests were conducted in a 1.8-m-wide and 29-m-long flume at nearfield scale. Preformed overfall s with average heights of 0.96, 1.25, and 1.55 m were tested to failur e at average discharges of 0.75, 1.59, and 2.42 m(3)/s. Soil from the same source was used for all tests. The observed headcut advance rates ranged from 0 to 1.6 m/h. All but one test displayed uniform headcut advance rates. The rests were performed while attempting to hold soil moisture and soil density constant and examining the influence of over fall height and discharge on headcut advance. The observed variation i n placed soil conditions appeared to have as much influence on headcut advance as did the overfall height and discharge variations. Examinat ion of a subset of the data suggests that the advance rare increases a s the overfall height increases. The aeration status of the headcut an d the dominant mode of failure are discussed.