ESTIMATING THE MUD DEPOSITION BOUNDARY DEPTH IN LAKES FROM WAVE THEORY

The mud deposition boundary depth (mud DBD) is the depth in lakes at which the boundary occurs between high-energy erosive environments (coarse-grained noncohesive sediments) and low-energy depositional zones where fine-grained cohesive sediments accumulate. We have derived a model from the theory of waves and sediment thresholds that predicts the upper limit to the distribution of fine-grained sediments in lakes of any size. Our results suggest that the several biggest storms each year, rather than extremely rare events, are responsible for the upper limit to the distribution of mud. However, significant areas of coarse-grained sediments and many mud DBDs occur deeper than this upper limit, usually on slopes greater than 3%. For sediment at the mud DBD (23 mum), we have developed an empirical relationship between slope and maximum horizontal velocity that demonstrates the significant effect of slope on reducing either sediment threshold velocity or sediment stability.