Creating river or creek in AgreeDEM

[RoyDaniel]

Hi All.
I hope we're all having a nice day..:)..
Now I am making Agree DEM using Archydro 1.4 . What I want to do is, manipulating DEM by with creating river with its top width as 15 m and depth of 4 m. Additionally, DEM cell size is 2x2 m. I have tried to create it by inputting river buffer is 8 cells,soft drop 1m,and  hard drop is 3 unit of Z  but the results always show the river top width is only about 3-5 meter, meanwhile its depth is already correct which is created 2 m of depth. Is there anybody could help me to create river top width as width as 15 m in AgreeDEM?
Thanks in advance

Roy,
Golder Hydrologist
Best Regards

[MarkBoucher]

Roy,

When you burn streams in a DEM the width is a multiple of the cell size. Therefore, the buffer of 8 cells would give you a width of 16m (or 32 if it buffers both sides) if your river is parallel with the DEM grids. If the river is not parallel with the DEM grids, you will get a different value, possible less than 16m (or 32m). I would have to play around with the details to determine the varying results.

I have not used the Arc Hydro tools for creating a channel of specific width and depth. After looking at the soft and hard drops. To define a channel, I would set the soft drop to 0 and the hard drop to the depth I want. I believe the soft drop "rounds" the banks of the channel outside the buffer and the hard drop only lowers the cells w/in the buffer.

Mark

[RoyDaniel]

Hi Mark..
Thank you very much for trying to explain this issue. Yes you're right, for 8 cells of buffer should give 16 m of width of a creek. At the moment I'm still trying to use Archydro because of many of its tools in DEM Manipulation. actually I imposed one single river polyline, maybe It could be worked if I buffer the river to left and right as needed, then I superimposed into DEM again and try again to make DEM reconditioning.
Anyway Thank you again Mark.

Best Regards,
Roy
Hydrologist-Golder Associates

[MarkBoucher]

May I ask what kind of project you are burning the stream into the DEM for and why the width and depth are important?

[RoyDaniel]

Hi mark

This for nickel mining project, for river flood plain modeling adjacent to mining area. Since there is not available river cross section data, thus I tried to get cross sections data from DEM reconditioning, prior inputing to HEC RAS. Would you have any comments on this Mark?

Best Regards.
Roy

[MarkBoucher]

To me, a 2x2m grid seems course for creating cross sections for HEC-RAS (RAS). If you are assuming you can burn in the stream before taking cross secdtions, then it seems you could alternatively create the cross sections in RAS with depth and width you want.

Ideally your client or company would take the time and budget to survey the river and do a proper job of getting cross sections and elevations (for correct slope - Burning the creek into DEM will not necessarily give you an accurate slope.). If you have topo or LiDAR points, they can be used to create a TIN which is far superior for creating cross sections. Certainly a mining site would have topographic maps. If you have the contours in CAD or GIS, couldn't you convert those to the proper format to create a TIN?

You can do the flood analysis without going through ArcMap and GeoRAS. If it is not a really big project, it might be more time/budget efficient to do that assuming you have good topo. My 2-cents.

[RoyDaniel]

Hi Mark, acctually,that is a precious 2 cents from you...:).
Yes your explanation is correct. I have done in creating dtm for floodplain modelling which is almost like you said. And the result flood plain that I've made will be calibrated after site visit is undertaken.
Thank you Mr. Mark.

Best Regards,
Roy Daniel
Hydrologist-Golder Associates