[talk-au] Use of DEM data to generate streams

[Tom Brennan]

> Based on this I'm comfortable that we can use this data under the existing
> waiver we have.

Thanks Andrew

> What I'd suggest is to document your process for deriving the stream
> geometry from the ELVIS data and what you're proposing to import and how.
> eg. how do you determine how far upstream to map, how do you determine if
> what's in OSM is better already than ELVIS or if ELVIS is better.

The general process of deriving stream data from DEMs is documented at
https://maps.ozultimate.com/wiki/qgis_hydrology

In terms of detail, I have found that using the SAGA Channel Network tool, an Initiation Threshold of around 9.6-9.7 (based on D8 flow, log accumulation), along with a minimum length of around 60m, gives a similar level of detail to the existing DCS stream data. That's in my areas of interest, typically the Blue Mountains. A different threshold might apply in flatter country.

At this stage I'm not proposing an import. I think there are too many potential problems around connectivity. I did the "import" (manually!) of the missing named streams for the Sydney Basin, and it involved a massive amount of work manually connecting things up, fixing broken connections etc.

I have no idea how you would do an automated import of streams without a lot of manual work, though I'm happy to take suggestions/advice!

I was mainly proposing to improve the existing streams with the aid of an additional source of data.

cheers
Tom
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