nav[aria-label="Primary Navigation"] { padding: 0; & ul { list-style: none; width: 100%; display: flex; flex-direction: row; justify-content: start; align-items: start; gap: 30px; padding: 0; & li { margin: 0; } & ul li { list-style: none; } } }

identify the nearest gages downstream from dams

XianyingFan

Help please:

Task: identify the nearest gages downstream from dams

Data: Stream Flowline (line feature class), streamgage point feature class, dam point feature class (both point feature classes contain thousands of points)

What I did: Using geometric network analysis tools to first create a geometric network, then set flow direction and finally trace geometric network, I got the output of a group layer.

My questions: I am hoping to add a new field which contains the ID of the nearest gage point for each dam point in my dam point attribute table, is that possible to realize this using the output of tracing geometric network? How can I realize it?

Thank you so much!

Maggie

Find more posts tagged with

Arc Hydro

Accepted answers

All comments

XianyingFan

Thank you very much Bill! Here is the data.

For the two options that you mention:

Option1: I am able to trace downstream of one dam point using the Geometric Network Analysis Toolset and then join the selective line features with gage points to get the closest gage point info. My difficulty is to write the python code of the tracing process and automate to other points;

Option 2: I accept the logic of treating the flowline as one way street and use the Network Analysis Toolset (specifically: find closest facilities tool) to find the closest points for all dam point at one time, however I failed to get the result because I can't find a way to set the direction so that it will find the closest facilities downstream along the flowline.

HydroDATA.zip

BillDaigle

Use the "Advanced Editor" option, then you will see an "Attach" link in the lower right hand corner.

XianyingFan

Hi Bill,

Excited to see you're back! How can I share the zip file? I saw insert image, insert video, insert link, but no insert files. Can I send directly to your email? Many thanks!

BillDaigle

Hi Maggie,

Sorry for the lapse in response. I've been out for a few days. If you are still struggling, could you zip up a portion of you're network dataset and share it? It has been a while since I've worked with one and I don't seem to have any good examples for you.

BillDaigle

Hey Maggie

Now it’s coming back to me. It’s the network analyst toolset (instead of the geometric network tools…very confusing) that return an attribute table instead of a selection. The network analyst tools are designed for working with road networks, but also work for stream networks.

From here it seems like you have 2 options:

1. Use python or model builder to iteratively select each dam and run a the trace tool with one dam selected at a time.

2. Build a network dataset and use those tools.

From what I remember, setting up the other type of network dataset was significantly more complicated, but the tools are little more robust. Personally, I think I would lean towards option 1.

XianyingFan

Hi Bill, I use "trace geometric network" tool and set the dam points as flags, the gage points as barriers, I also disable gage point feature class so that it will stop trace when there is gage point. Then I limit the results to features stopping the trace. The output I get are the layers with selection features. Then I create layers from the selected features for both dam and gage point feature classes. But from the result I don't know which gage point are paired with dam point(nearest along the streamline) and what should I do next so that the nearest ID of gage point can appear in dam point attribution table.

Can you please recall which tools you used to realize the task? Is there any record available as my reference? May I write email to you or call you directly if possible? Thank you so much!

Maggie

BillDaigle

Yes, the info you’ll need should be in the attribution table. I will do what I can to help. I haven’t done it in a while.

XianyingFan

Yes, I am able to select all of the dams points and gauges points with tracing geometric network tool. Do you mean all the information are contained in the output lines attribution table, including the ID(OID or FID) of dams as well as gauges? The computer I am using now has no ArcMap, I will try later. Can I ask you if I have further questions later? Thank you so much Bill!!

BillDaigle

Yes, you should be able to do this without python. I think it is quite simple once you figure out how to add all of the flags and barriers at one time. I think if you select all of the dams there is an option to add then all as flags, then you can do the same with gauges as barriers.

The table for the output lines should have a should have a field with the OID (or FID) for the dam and the OID (or FID) for the associated gauge. You may need to fiddle with analysis setting so it only find the first (closest) barrier.

XianyingFan

Thank you so much for your reply Bill!

Do you mean to join the line output with the original dam feature class? How can I get the closest downstream gauge id and add it to dam's attribute table?

So you've done this to identify the nearest downstream points for many upstream points in one time and we don't need to use python to automate?

BillDaigle

Been a while since I have done this. It is certainly possible. Conceptually, you will want to add all of your dams as flags (starting points) and gauges as barriers (end points). When you run the analysis, you will get an output of lines for each set of start and end points. I believe you can join the line output back to the dam feature class if you want to populate the downstream gauge id.

Join the Conversation

Signed in members can post, follow updates, and more. New here? Register a free account.

Quick Links

Community Help
Find useful guides, FAQs, and documents to help you navigate and make the most of Esri Community.