MICROCHANNEL AND CREEK DEVELOPMENT IN A NEW ENGLAND SALTMARSH, ROWLEY, MA

Many marsh platforms in New England exhibit poor drainage, creating standing water pannes (where short form S. alterniflora dominates) and stagnant ponds that experience tidal exchange only during high spring tides and storm-induced flooding events. The processes related to tidal creek incision and headward erosion that may eventually drain these features are poorly understood. However, it is hypothesized that panne and pond formation are cyclic in nature: once creeks incise into ponds and improve drainage, S. patens re-colonizes the area, which increases sedimentation and vertical marsh accretion.

The heads of tidal creeks extending onto the marsh platform and into saltmarsh pannes in Rowley, Massachusetts are being studied to investigate processes that lead to creek incision and drainage morphology in high marsh settings. The topography of shallow surface microchannels is analyzed using a modified surface elevation table (SET). The channels, which have a relief of less than 15 cm and are partially obscured by vegetation, are present at the heads of both natural and anthropogenic (drainage ditches) tidal creeks. Preliminary results indicate that these features change slowly over time; however, their morphologic changes may be episodic and related to freeze-thaw processes and high velocity flows during storm conditions. For example, rapid drainage has been observed during high precipitation events when tide levels are low and hydraulic gradients high. It is speculated that these same conditions are likely to occur during the waning stages of large extratropical cyclones when tidal surge waters have flooded the marsh. Historical evidence of creek incision into marsh platforms provides clues to understanding the drainage history of a particular marsh, the formation of saltmarsh pannes and ponds, and the relationship between drainage density and pond density.