A sediment budget employs conservation of mass to quantify sediment sources, sinks, and pathways in a littoral cell
environment. Moreover, a sediment budget can be used to quantify the effects of changing sediment supply on the coastal system and to
understand the large-scale morphological responses of the coastal system. Throughout the last several thousand years the Columbia
River has supplied sand to nearby bays, coastal dunes, the continental shelf, and the continental slope and submarine canyons
By quantifying the amount of sand that occupies each of these environments, the Study is attempting to better understand the
Columbia River dispersal system and better predict the response to changes in the system, whether they are natural or human-induced. To
help separate natural from human-induced changes in the littoral cell, the sediment budget is being calculated for pre-historic
periods as well as for historic and recent periods. By examining the sediment budget from various time periods, it is possible to compare
the natural evolution and variability in the system to changes forced by human intervention.
The Columbia River is the primary source of sand to the littoral cell. The figure below illustrates the dispersal of Columbia River sediment throughout the littoral cell.
Sediment-transport pathways and patterns of sediment accumulation in the littoral cell are not static, but change over geological,
historical, and seasonal time scales. Some changes in the sediment budget are the result of natural cycles such as long-term changes in
sea level, or of short-term fluctuations such as in wind and wave directions. Other changes in pathways and sinks in the sediment
budget are the result of human influences, such as the construction of jetties, or dredging practices.
Although research on the sediment budget is continuing, several observations can be drawn from the Study’s analyses: