Sand budgets at geological, historical and contemporary time scales for a developed beach system, Saco Bay, Maine, USA

Saco Bay hosts one of the largest sand beach and salt marsh systems in northern New England, USA. Unsuccessful remedies for chronic beach erosion have generated controversy and differing theories regarding (1) the source(s) of sand to the bay, (2) the sand transport paths and (3) the role of jetties in beach erosion. We constructed a sand budget for the bay by evaluating the past and present sand-transport pathways, fluxes and reservoir volumes. Side-scan sonar and bottom samples were employed to map the offshore areas; seismic reflection profiles and vibracores were used to measure the volume of offshore sand. On land, ground-penetrating radar and cores constrained the sand volume and stratigraphy. Time-series maps and aerial photographs provided data on historical sand movement, and current meters and recent harbor dredge data allowed contemporary sand movement to be estimated in the Saco River estuary. At the present time, 56 million m 3 of sand reside in the shoreface and 22 million m 3 of sand are beneath the barrier beach and dunes. The Saco River has been the major source of sand to the bay, providing an estimated 10,000–16,000 m 3 of sand per year. The net direction of sand movement is to the north, where river-derived sand has historically fed growth of barrier spits. Construction of the north jetty at the Saco River mouth profoundly altered the prehistoric patterns of sand movement and storage in the bay, causing the northward migration of almost 6 million m 3 of sand between 1867 and 1955. Contemporary dredging of tidal inlets involves sand volumes approximately equal to the influx of sand delivered by the Saco River.