Arc Hydro (or other tools) for DEM-derived stream channels that respect MS4 infrastructure?
Hi all,
Relatively new to Arc Hydro and water resources as a subject area - apologies if the answer to this question should be obvious, but I have gone beyond scratching the surface at this point and have not found what I am looking for.
I am working on updating a layer of creek channels for a small city with relatively dramatic elevation gradients. The source layer they have currently was digitized in the 90s, and has some significant inaccuracies. Working from a current Lidar-derived DEM, I have used Arc Pro's Hydrology toolset to get Flow Direction, Flow Accumulation, and create stream channels. My goal is to develop an accurate stream channel layer suitable for watershed analysis across different stream order scales.
In undeveloped areas, the DEM-derived channels are clearly more accurate than the older layer - however, near infrastructure, developed areas, and urban areas, the DEM-derived channels start to behave strangely. Based on a visual inspection, many of the "strange" channel behaviors are in areas where MS4 infrastructure routes the water under the surface before releasing it back into surface channels on the other side of the obstruction (i.e. road, etc.).
I am wondering if it is possible to use the Arc Hydro toolset (or anything else that would work!) to "inform" the DEM-based stream derivation processing about the MS4 infrastructure - for example, to "link" the inlet and outlet nodes on either end of a storm drain pipe such that Flow Accumulation would add the total accumulated value in the cell under the inlet to the cell under the outlet, and Flow Direction would recognize the storm drain pipe as flow a channel thus preserving actual down-gradient flow without auto-filling, wandering over the road, and sometimes maybe finding its way back to the actual channel.
See attached image for old stream layer (bold, red), storm drain nodes and pipes (green dots/black lines respectively), and newly derived channels (blue) doing crazy auto-sink-fill stuff to maintain connectivity.
Based on my current (limited!) understanding of the Arc Hydro tools, they work in the opposite direction of what I'm asking - i.e., you need accurate channels to start with before you can integrate them with storm drain infrastructure. I'm also as yet unsure whether, even when fully integrated, flow is actually "piped" through the storm drain system with respect to inlets and outlets. I am considering trying to "burn" the storm drain pipes into the DEM to achieve a similar effect, but this strikes me as potentially bad practice so I am looking for more information on other methods (or, if this idea is as clever as I thought it was when it first occurred to me, please let me know and you'll make my day).
Any suggestions, resources, examples, etc. that can help me conceptualize a solution to this problem are welcome! Thanks in advance for any assistance.
PS - On a related note: I am planning to erase the new streams by a roads layer wherever streams pass under roads - when I erase the newly derived streams by the road area, does this disrupt my "downstream" (haha) ability to use the stream end nodes as pour points for watershed analysis? Haven't thought this far ahead, deeply grateful for any thoughts!
Ok @ChristineDartiguenave - thanks again for your attention to my questions!
Going to try to reframe pieces of my initial question with a better understanding.
Objective:
Use existing stormwater infrastructure features (nodes and pipes) to burn channels into a DEM, so that when stream channels (surface conveyance) are derived from that burned DEM their flow follows the path enabled by storm drain infrastructure (drains, culverts, etc.) rather than being diverted by e.g. the dams formed by an elevated roadway.
Key questions:
1) Is there a way to use Trace Network, or Trace Attribute(s), to get the elevation value(s) I should burn the pipe channels to? In the image below, for example, say the outlet node is at 400ft, the topmost node is at 415ft, the leftmost node at 425ft, and the central node is at 410ft. If I simply burned the entire network to the lowest value, i.e. the outlet at 400ft, would that be enough to get flow to follow those channels? If not, is there any way to get the incremental values I would need the rasterized channel lines to have at each cell so that flow would travel "downstream" the whole way?
2) Would I need to build "fences" along the edges of these burned in channels to prevent lateral flow from skewing e.g. Flow Acc values? Given that in "reality" there is no lateral surface flow into this burned channel, because the burned channel is really a pipe and the channel was only created to get a nice "drawing" of where stream channels actually go?
For both questions, is there a programmatic way to accomplish any necessary steps? I have experience with both ModelBuilder and writing/running custom scripts with arcpy and other modules, so those and similar approaches are options - I am still struggling to understand the connectivity and flow behavior that will govern how I accomplish what I'm aiming for.
Thanks in advance for any suggestions!
Currently we have a tool called Assign River Order in Arc Hydro that allows assigning Stream Order to features but it works on a single feature class. So you would need to merge the streams and pipes into one layer and make sure you only have one segment between confluences to be able to use it.
Here is an example of the stormwater process. Pipes are in green and in this example streaminit is the initial stream layer that was burnt in through reconditioning since the input DEM was not "perfect". The inlet to the pipe is a sink. When tracing from the surface, you can see that the flow in yellow ends in the sink point (HydroJunction). When we do a delineation we trace through the network of both pipes and streams to add upstream contribution. We do not burn in pipes since they do not impact the surface flow.
Christine
