Abstract:
The probable pollution distribution and flushing times have been
calculated for the Columbia River Estuary, a coastal plain estuary.
The pollution distribution was determined by the fresh water fraction
and by the diffusion equation. The flushing times were calculated by
the modified tidal prism method and by the fraction of fresh water,
These methods are explained and discussed in the study.
The widely varying river flow and resulting salt water intrusion
were considered, as well as the varying semi-diurnal tidal range.
These changing factors cause a complex variation in estuarine classification
from well-mixed to stratified.
The data used was taken principally from the U. S. Corps of
Engineers current measurement program of 1959. The data show a
stronger flow on the north side of the estuary during flood tide and a
stronger flow on the south side during ebb tide. Due to this fact, the
estuary was also treated as two separate channels in calculating the
pollution distribution.
The results of the various calculations for combinations of conditions
are given in this study. A comparison of the different methods
is also summarized.
The estuary has been found to have a relatively short flushing
time, even under low river flow conditions. The variation in strength
of flow from the north side to the south side has been shown to produce
pollution distributions not normally expected in an estuary.
