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| AI image generated by Grok Imagine. |
The geometry of a conduit through which any fluid passes affects the velocity profile of that fluid. In the case of a river, on
the inside of a bend, water flows slower. On the outside of the bend,
water flows faster. Erosion due to faster flow causing a scouring effect is probably responsible for the so-called
"Sally Hole" in the riverbed near St Brigid's Well. Eventually there may
be landslides as the riverbank is undercut. However, tree roots and
other vegetation act as reinforcement, holding the bank together. So it's
not necessarily imminent. Meanwhile, on the meander opposite
Castlemartin, debris such as bottles and other rubbish accumulate on the
inside bend, where water flows slower. Water also flows faster where
there's a bottleneck in a watercourse. (You can observe this from the
farm trail near the island that's north of the bridge. However, this may
be partially due to a gradient in the river bed).
Bernoulli's
principle is a law in fluid dynamics which states that an increase in
speed occurs simultaneously with a decrease in pressure. It's a
principle that's used in engine carburettors. A venturi (a narrowing of
the passage in a carburettor through which the fuel/air mixture flows)
causes a drop in pressure. That drop in pressure causes fuel to be
sucked into the venturi. Small engines such as those used on lawn mowers
still use this arrangement for supplying the engine with a fuel/air
mixture. However, modern petrol engines on vehicles use fuel injection.
(Since the late 1980s, early 1990s I believe).