The development and migration of headcuts in rills and gullies can adversely impact soil resources in agricultural areas and accelerate landscape degradation worldwide. Analytical treatments of this erosion process have been based on a turbulent impinging jet analogue, though partially validated by field and laboratory data. Experiments were conducted using fixed headcut models to define the mean flow structure within these erosional features and to assess the applicability of similarity arguments for jets to characterize this flow domain. These data show that (1) flow within headcut scour holes is analogous to plane turbulent reattached wall jets and (2) similarity arguments used to define the limits, length scales, and velocity distributions in classical free jets and wall jets are applicable within discrete regions of the headcut scour hole domain but are affected by the ventilation characteristics of the overfall. This study contributes new knowledge on the hydrodynamics within headcut scour holes, and it confirms the applicability of jet theory for analyzing such soil erosion processes.