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%                    (c) 2000 A.M. Thurnherr
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The simple model developed in this chapter indicates that basin/sill
combinations act as effective low-pass filters. The model was developed
with the intent to investigate some aspects of the low-frequency
along-segment flow in the \A segments. The time scales derived from the
appropriate parameters indicate that adjustment of the flow across \RS
to changes at the inflow takes months, while the inferred overflow from
\A into \FAM responds with a time scale of weeks to changes at the \RS
overflow.

The parameter space of the model has been explored in greater detail
than it is reported here but without any simultaneous inflow/outflow
measurements or laboratory experiments to validate the model solutions
our confidence in the details of the results is limited, especially
considering the simplicity of the model. The low-pass filtering
property of basin/sill combinations does not depend on the model
details, however. It is a direct consequence of the ``storage
capacity'' (determined by the horizontal area) of the basin. This is
easily observable, e.g.\ on rocky shores where breaking waves
periodically supply water to small pools which can drain continuously
without much apparent variability. Crudely representing the rift valley
as such a basin/sill combination therefore provides a plausible
explanation for the persistence of the \RS overflow and for the
apparent lack of transport variability observed during one year of
direct measurements \rchap{CM}.


