"Removing" lakes from DEM

[AlexanderVentura]

Hello,

I need to recondition my DEM by burning in streams. Some of these don't "exit" the DEM but instead end up in lakes. As far as I understand it these lakes should by treated as sinks and essentially a sink structure should be created for them (for the streams to “exit” the DEM so they won’t get filled in during the “fill sinks” operation). However, I have read that an alternative approach is to “remove” the areas of the original DEM corresponding to "sink lakes". This way we ensure that all streams will be burnt in and not re-filled as they will “exit” the DEM. I found this procedure easier and was wondering if it can be considered a valid approach.

Thanks for the help.

Alex

[MarkBoucher]

We have detention basins that are normally dry. Some are large and we use them for flood control. We usually need to know the watershed area including the detention basin.

What I do is add an agreestream polyline that goes through the detention basin from the source stream to the outlet (through the dam). This keeps it from filling. I can create a batch point at the outlet or some location on the dam and get the watershed area that includes the detention basin.

If the DEM is null in your lake, to do it this way you'd have to calculate that null value to actual value (zero would work) so that it will have an elevation when filled, but it would not fill higher than the burned stream raster. The fil raster is the step toward the fdr raster which is what is really important in the rest of the processing.

Not sure if this applies to what you are doing, but thought I'd put it out there.

Mark

[AlexanderVentura]

Hi Mark,

Thanks so much for your reply, I really appreciate it.

So if I got this right essentially my approach is valid but it simply would not include the lake area (which is “no data” in my DEM) in the delineated watersheds, correct?

Actually my problem is that I would like all the streams I burn in using “DEM reconditioning” not to be re-filled when I run “fill sinks”. For most of them (the ones “exiting” my DEM) there is no problem, however some of the streams simply start and end somewhere in the middle of the DEM (they end in lakes and are not connected to the “main” stream network). These smaller “isolated” streams get filled when I run “fill sinks” after running “DEM reconditioning”.

I am following the manual you suggested: “Comprehensive Terrain Preprocessing Using Arc Hydro Tools”. According to this, as far as I understand it, in order to maintain the smaller isolated streams and prevent these from getting refilled, they must end into a “sink”. If this sink is a lake (like in my case) and a feature class for these lakes is available (I have this feature class too) one can create a “sink structure” using the lake feature class and the streams ending up in the lakes would then not be re-filled during the “fill sink” operation as they end up in a sink (which as far as I have understood it is equivalent to the streams “exiting” the DEM).

My problem is: how do I create a sink structure from the lake feature class and then use it during the fill operation so that none of the burnt in streams will be filled in?

Could this approach be the correct the one:

1. Use the “create sink structure” tool to create “lake sinks” using my lake feature class.

2. Use the “DEM reconditioning tool” to burn in my streams.

3. Use the “fill sinks” tool to fill sinks but specify that the “deranged polygon” should be the sink structure I created in the first step.

Does this make sense?

Sorry, I have been struggling with this for a while and despite it being a trivial issue (and probably specified in the manual I mention above) I can’t seem to find the solution.

Thanks again.

Alex.

[ChristineDartiguenave]

Check use case 5 in http://downloads.esri.com/archydro/ArcHydro/Doc/Overview%20of%20Arc%20Hydro%20terrain%20preprocessin... .

Use case 5: Combined dendritic/deranged terrain with known sink and stream locations (using synthetic streams)

1) Create Drainage Line Structures using your input streams

2) DEM Reconditioning (using strlnk previously created as input stream).

3) Create Sink Structures (using you lakes as sinks and pass the stream as draft input line: will create a sink point at end of line).

4) Level DEM (this will enforce and level down the sinkpoly coming from lakes: make sure you set an offset to realy enforce them).

5) Fill Sinks (pass your sinkpoly so that they do not get filled) .

6) Flow Direction.

7) Adjust Flow Direction in Sinks: will ensure that within the sinkpol/lake water flows toward the sink point located at the end of the stream).

😎 Adjust Flow Direction in Streams: will ensure that once the flows reach the stream, they go along the stream..

Christine Dartiguenave

Esri Water Resources Team

[AlexanderVentura]

Dear Christine,

Thanks so much for your suggestions. I have finally managed to get the process you describe above to work (I was using a basic license when I needed the standard license).

I was wondering if you could help me with a few simple things so that I can make sure to complete the process in the correct way:

- In step 3 (Create Sink Structures) should I input the AgreeDEM (from the reconditioning step) or the Raw DEM?

- In step 4 (Level DEM) can you confirm that it is the Raw DEM (not the AgreeDEM) that I should input?

- In step 5 (Fill sinks) can you confirm that it is the AgreeDEM (from the reconditioning step) that I should input?

Thanks a lot for the help, I really appreciate it.

Regards,

Alex.