Sediment transport and dispersion in a cool-temperate estuary and embayment, Saco River estuary, Maine, USA

Abstract

The Saco River flows through a rock bound, mid-latitude estuary recognized as the primary source of sand to the Saco Bay barrier beach system. To better constrain the conditions under which the Saco River contributes sand to Saco Bay, three moorings equipped with current meters and a CTD were deployed inside and outside the Saco River jetty system, from April to June, 2005. These measurements characterized high-discharge events and their competence for transporting sand outside the jetty system. Discharge values from 125–175 m 3 s − 1 were identified as the threshold envelope at which the Saco River transports sand in its bedload to Saco Bay. Put in an 89-year historical context with USGS stream gauge data, the Saco River is expected to contribute sand annually to the embayment, but the amount of transport varies significantly from year to year. The moored hydrographic data were augmented by geophysical, Langrangian drifter data, and local wind observations to better ascertain nearshore dispersal patterns once sand exits the jettied river mouth. These data suggest that transported sand responds to seasonably variable shelf conditions, reacts to artifacts of the jetty system, or exits Saco Bay. The results and methods of this study suggest that relatively small, rock-bound estuaries are potentially significant sources of sand to adjacent beach systems and the inner shelf, although the pathway for sand from river to shoreface to beach or inner shelf is complex and mediated by local meteorological and oceanographic conditions.