FIFTY YEARS OF CHANGE IN ONE SAN FRANCISCO BAY TIDAL CREEK

This research was motivated by the question: How did salt marsh creeks and creek networks change over fifty years? In order to address this question we conducted a topographic survey of a relatively undisturbed salt marsh intertidal creek network using RTK GPS. Moreover, the study site was one of the same sites documented in the seminal work of Pestrong [1965]. In this study the topographically-defined creek network was compared to Pestrong's original creek network delineation that was based on high resolution air photos and field verification. This comparison shows that the overall network structure remained relatively unchanged. In particular the first order creeks did not lengthen or widen, although the uppermost anabranching headward area developed better defined channels. On the other hand, the third order main creek segment narrowed by 27% and decreased in length by 16%. The cross-creek profiles show that infilling processes led to the development of in-channel “benches” along the banks – e.g. a salt marsh bench that is ~0.5 m lower than the main platform and extends from banks toward the thalweg. This process of infilling led to a net decrease in creek network volume of approximately 18%. Taken together these observations show that in this relatively undisturbed island system, lower order tidal creeks are more stable than the higher order creeks, and the net response to overall increased sediment supply in southern SF Bay is a narrowing and straightening of the main tidal creek.