Have been grappling mildly with the notion of the point of unity between lake infilling and dam-outlet lowering. Reading Caitlin's thesis got me thinking about it again, especially as it relates to the Qbw dam.
This simple diagram works for me. Here is the rationale:
There has to be erosion of the outlet channel well before the level of sediment reaches the outlet. The monolithologic overflow gravels demonstrate this.
The outlet is slowly lowering while the lake bottom (essentially) is slowly rising. As the prograding delta approaches the dam, the sedimentation rate increases. As the outlet channel matures, the availability of sediment from hillslopes, tributaries, and unraveling of the dam itself probably increases the incision rate. However, once the level of the lake bed (~delta) reaches the outlet elevation, all bets are off and the dam is over. Large increase in available bedload and an enlarging outlet channel result in accelerated incision and the dam is eventually removed.
