>It's very common in Bolivia at least that river have very different
>water levels, is there a tag for this? Usually you have a large
>riverbed and then a very small river running in the middle for most
>part of the year, and then sometimes it will flood all the way up to
>the riverbanks.
I have take the approach that the 'river' is the part where vegetation doesn't
grow. A lot of the time much of this won't actually be underwater, but the
actual channel within the riverbed will change very rapidly, possibly with
every flooding, whereas the river bed itself will change less rapidly (but
still rapidly enough that, say, 10 years down the line it will be significantly
different). This is also relatively easy to tell from even low-res satellite
imagery - unless the river bed has green mud of course! Looked at another way,
the vegetation is there because that area hasn't had a flood severe enough to
wash it away, at least within the timespan it takes for the vegetation to grow.
Having said that, if anyone can think of a better way of doing this I'm open to
suggestions. I think in reality though the concept of 'edge of the river' is
fairly ill-defined in areas where it hasn't been interfered with by mankind, in
much the same way as the location of a coastline changes. The fact is that the
coastline oscillates nearly twice a day, and low-water and high-water are
merely approximations that allow us to put something on a map. You wouldn't
want to build a house between the two lines though.
Donald
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