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stream/hydrojunction topology Stormwater Preprocessing Arc Hydro

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Yeaton
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Occasional Contributor

Is it ok for a stream to snap directly to a hydro-junction point feature when doing stormwater preprocessing?  And is it ok for that stream to emerge from a pipe outlet point feature by snapping onto it?  I am confused by the stormwater workflow manual.  To paraphrase it says that all streams must connect to another stream or pipe feature.  Then later on in the process it warns to look for streams that connect to sinks. 

The confusion for me arises from the fact that the hydro-junctions must be attached to pipes (stormdrains and culverts), therefore the stream must attach to the hydro junction; then those same hydro junctions are modeled as sinks sinks to attract water flow. Yet a stream cant end in a sink unless that is its true representation. 

I've tried omitting hydro junctions and pipe outlets form those pipe structures where i know the flow directions, but I still need the sink data modeled for stormwater delineation analysis.

Any help is much appreciated.

Best,

Aaron Y.

 

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ChristineDartiguenave
Esri Contributor

Things have slightly changed and we are in the process of documenting the changes...

Initially we were using Flow Direction/Fill Sinks. So if a stream was not connected to another stream, to a HydroJunction (i..e, Pipe Inlet or real Sink Point)  or exiting the DEM, then the Fill operation would fill the enforced stream back up and the flow direction would not honor the burned in streams.

With the new Derive Continuous Flow tool in Spatial Analyst (Flow  Direction and Accumulation Using CF in the Arc Hydro toolbox), the  Fill Sinks step is not needed anymore and the streams will never be filled. So you can now connect the streams to an outlet if you wish to do so. The process will create overland connector from the outlet using the flow direction. Note that it is possible to end up with a sink in the flow direction at the end of the isolated streams since we adjust the flow direction in the direction of the flow under the streams.  So it may be a good idea to trace from the end of the isolated stream to see whether the path is correct (sink or not). If the ends of the stream is a real sink, add a HydroJunction to indicate that.

If the trace ends at the stream but should continue, you can either:

- trace/digitize that path and add it to the input streaminit and reprocess. 

- do not burn those isolated streams so that the sink is not introduced

Christine

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Yeaton
by
Occasional Contributor

Hi Christine,

Thanks for the explanation.  Looking forward to seeing the documentation on this process when its available.

Best,

Aaron

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