The outlet sections were assumed to collapse due to either: 1) gully headward erosion over a long period of time, or 2) the PMF flows in the ditches.
(The outlet sections; were assumed; ) (The outlet sections; to collapse; due to either: 1) gully headward erosion over a long period of time, or 2) the PMF flows in the ditches) (the PMF; flows; in the ditches)
The outlet sections The outlet sections the PMF
were assumed to collapse flows
due to either: 1) gully headward erosion over a long period of time, or 2) the PMF flows in the ditches
in the ditches