Geomorphic Analysis of Tidal Creek Networks

The purpose of this study is to determine if concepts in terrestrial channel network analysis provide insight on intertidal creek network development and to present new metrics for their analysis. We delineated creek network geometry using high-resolution digital images of intertidal marsh near Georgetown, South Carolina. Analyses reveal that intertidal creek networks may be topologically random. Length-area relationships suggest that salt marsh and terrestrial networks have similar scaling properties, although the marsh networks are more elongate than terrestrial networks. To account for recurrent water exchange between creek basins at high tide, we propose that the landscape unit of geomorphic analyses should be the salt marsh island as opposed to salt marsh creek drainage basin area. Using this approach, the relationship between maximum channel length per island and island area is well described by a power function. A similar power relationship exists for cumulative channel length versus island area, giving a nearly unit slope; this implies that marsh islands have a spatially uniform drainage density. Since the island boundaries are easily identified in remote sensing, taking the island as the unit of geomorphic analysis will eliminate discrepancies in delineating basin boundaries and preclude the need for defining basin area in intertidal landscapes. Analyses and results presented here may be used to quantify salt marsh reference condition and provide indicator variables to assess salt marsh disturbance

A method for estimating pore water drainage from marsh soils using rainfall and well records

Author Posting. © The Author(s), 2008. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Estuarine, Coastal and Shelf Science 79 (2008): 51-58, doi:10.1016/j.ecss.2008.03.014.Rainfall events during low tide exposure cause the water table in marshes to rise. If one has long time series of both rain events and water levels in wells along transects from creek bank to marsh interior, one can correlate well response with rain amount. In cases examined so far the well response is found to be a linear function of rain amount. As it is reasonable to assume that the amount of tidal infiltration required to restore the water table to the elevation of the marsh surface is equal to the amount of rain that would be required to do so, one can estimate the annual drainage of pore water from a well site by dividing the mean drawdown of the water table at low tide by the slope of the response-versus-rain regression and then multiplying the result by the number of tidal drawdowns in a year. Integration of such results along the transect then gives an estimate of the total annual drainage. An example of the use of this method is given for two well transects in a Typha and a Spartina marsh at the Plum Island Estuary Long Term Ecological Research (PIE-LTER) site in Massachusetts, USA. Both transects yielded pore water drainage rates of about 160 m3 yr-1 per meter of channel length. Although the annual volume of pore water drainage is small compared to the annual volume of the tidal prism its impact on nutrient budgets in the estuary could be large because of the high concentrations of nutrients in marsh pore waters. We also discuss the possible effects of the capillary fringe, air entrapment and tidal forcing during rain events on these results.Partial funding for this work was provided by National Science Foundation Grant Number OCE-0423565