PHYSICAL MODELING OF TIDAL CREEK MIGRATION DYNAMICS; IMPLICATIONS FOR DETACHED BAR DEVELOPMENT

Point bars are areas of high sediment deposition formed in fluvial and tidal meandering systems. In tidal environments, tidal point bars have a distinct evolution that is different from their fluvial counterparts. Barwis (1978) attempted to classify tidal point-bars using several geometry based metrics, including comparing the radius of curvature of the channel to the average width (r/w) along the channel meander. While compelling and intuitive, results from this classification do not explain fully detached tidal bars, found in many tidal creeks. We hypothesize that detached bars form as a function of lateral channel mobility, which is a function of bank migration, coupled with the creation of accommodation width along a meander to allow for the bar to detach. In addition to this, we hypothesize that these processes are scale invariant, and regardless of size the laboratory experiments should follow similar evolutionary laws. A small-scale physical model was used of a tidal creek with detached bars representing a real creek in the Plum Island Sound, MA. The analog was compared to four natural tidal creeks with detached bars. A pattern emerges when sinuosity is plotted against r/w and channels mature and channel mobility increases; an inflection point can be seen proximal to the detached bar. The width-radius of curvature relationship for both natural and experimental systems demonstrates that the processes governing tidal creek evolution are scale invariant, despite being orders of magnitude smaller than their natural counterparts.