Conceptual Design Investigations and Analysis

An investigation of the historical nature and use of tidal marsh drainage systems in the Delaware River Estuary was conducted as baseline information. Historical maps, aerial photographs, dike failure records, tidal range data, and present day tidal creek geomorphology provided the basis for analysis. These data, together with information on relative sea level rise, present an overview of the use and management of estuary tidal marshes. Select marsh systems are discussed to describe the restoration of tidal marshes following diked meadow land use. Restoration is depicted in terms of marsh system age. The prevalence of Phragmites australis in the Estuary has increased during this period of marsh restoration, now dominating many tidal watersheds by replacing or isolating more beneficial species, such as Spartina alterniflora. The pattern of P. australis spread is presented for two case study areas (Blackbird Creek in Delaware and Alloways Creek in New Jersey) based on aerial photography from 1930 to the present and is related through observations on site conditions and invasion pressure upon the survival of relic areas of S. alterniflora.