[GRASS-user] r.watershed

[Mark Seibel]

Hi Shane.


How did you add culverts or other artificial flow control features to
achieve water flowing through roads?

Culverts can be added by digitizing the connection points (line) across the
road from high accumulation to high accumulation on the other side of the
road. It can be a long iterative process, that can be encapsulated in a
script. I've wondered if machine learning could be used to automate what
seems to be such repetitive and easy culvert connections.

>
> Also, why is sink filling needed for terraflow and not watershed?
>
> I am not into the code, but I know r.watershed use different code to
produce different model results. r.watersheed seeks the lowest points in
the terrain, thus internal sinks get modeled with exit points rather than
internally drained. On the other hand, r.terraflow hydrologically fills the
terrain, then models flow accumulation. The results are similar, but the
differences can be used to add another check on reality from another model;
especially in really flat, depressional terrains.

Mark



> Thanks for your help :-)
>
> On Máirt 5 Noll 2017 at 23:43, Mark Seibel <mseibel at gmail.com> wrote:
>
>> Hi Shane.
>>
>> I'm happy to report that I've modeled overland water flow with
>> r.watershed for over a quarter million acres, consisting of several large
>> project sites, at 1 meter DEM resolution. The data source was LiDAR
>> points to make the DEMs.
>>
>> At this resolution, it becomes necessary to add culverts, or other
>> artificial flow control features, to achieve water flowing through a road.
>> Otherwise, water is routed along roads until a lowest point is reached for
>> crossing.
>>
>> I also use r.terraflow outputs as ancillary data to help drop in culvert
>> locations and help provide guidance in problem areas.
>>
>> My geographic area is central Florida, which is very flat and full of
>> topographic depressions known as wetlands. These depressions interrupt the
>> stream network continuity in reality, but r.watershed does a fantastic job
>> making a continuous drainage network model, especially in these difficult
>> areas.
>>
>> Happy Modeling!
>>
>> Mark
>>
>> On Tue, Dec 5, 2017, 3:49 PM Shane Carey <careyshan at gmail.com> wrote:
>>
>>> Hi,
>>>
>>> I am trying to extract river network from a 5m DEM with some success
>>> using r.watershed. Has anyone tested this algorithm on high resolution
>>> LiDAR data for example - 1meter DTM and what kind of results have they
>>> obtained?
>>>
>>> Thanks
>>>
>>> --
>>> Le gach dea ghui,
>>> *Shane Carey*
>>> *GIS and Data Solutions Consultant*
>>>
>> _______________________________________________
>>> grass-user mailing list
>>> grass-user at lists.osgeo.org
>>> https://lists.osgeo.org/mailman/listinfo/grass-user
>>
>> --
> Le gach dea ghui,
> *Shane Carey*
> *GIS and Data Solutions Consultant*
>
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