On 5/6/23 08:47, Little Maps wrote:
I don’t know if there’s a “correct” method as at least 3 different methods are
(or were) common in Vic, where I map. (1) continue named stream through dam,
(2) continue stream through dam but with no name tag, and (3) stop stream at
dam edge and start again the other side. Method 2 means dam name is rendered
but not stream/river as well inside the dam. If the stream/river is in a
relation this isn’t a problem as the whole named stream can be found using the
relation.
The river/stream 'needs' to be mapped continuous for those that care
about waterways. (That is not me.)
Ideally the thing would be mapped ;
(for the reservoir area) where ever the water flows if the dam is 'low' and
(dam area) where the water would overflow past the dam, if you don't
know then through the dam would be the next best thing.
I prefer continuing the waterway through the dam as it makes it a lot easier to
find gaps in waterways and to show connected watersheds, etc. If dams are often
dry or rarely full, it also shows where waterway is at low lake levels.
Logically, also the Murray River flows through Lake Hume. It doesn’t stop at
one side and start again on the other.
I’ve been editing heaps of streams in Vic over past few months, and it’s common
for waterways to cross dams but not actually connect with them. It’s important
that they share a node at each place they cross a dam. Lot’s don’t (or didn’t).
The same thing applies on the coast, where many streams cross the
natural=coastline polygon but don’t connect with it.
If all streams that connect with the coast connect properly you can easily do
an overpass query to find all watersheds that drain into a section of coast. If
all streams properly cross and connect with dams, it’s easy to find all streams
that enter the Murray - Darling Basin, for example.
A fine-detail issue on your query below is that, on the ground, streams don’t
normally pass over earthen dam walls. If they did the wall would erode.
Instead, there’ll be a side route where water will flow beside the dam when the
dam is full. Sometimes this can be seen on imagery, often not. IMO this is an
issue of mapping scale, and it’s fine to map a stream waterway as passing
through a dam. If someone wants to add the fine detail later they can, while
still maintaining the connectivity of the waterway.
So, broadly, yes, I think it’s much better if waterways pass through
constructed reservoirs.
Cheers Ian
On 4 Jun 2023, at 9:48 pm, Tom Brennan <[email protected]> wrote:
Quick question on streams and dams/reservoirs.
If a stream has been dammed, the centreline of the stream should still be
mapped as a waterway. Correct?
cheers
Tom
----
Canyoning? try http://ozultimate.com/canyoning
Bushwalking? try http://bushwalkingnsw.com
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