Terrain Processing Steps.

[MuhammadIrfan1]

Hi all,
i am confuse in these steps (1-Dem Reconditioning, 2-Fill sinks, 3-flow direction).  Kindly guide me about the sequence is it correct sequence or not? if it is incorrect then which step should i perform first?

[MarkBoucher]

The sequence you listed (1,2,3), it is the necessary sequence.

The reconditioning and sink filling steps are necessary to get a good flow direction grid (fdr). The fdr is key for the rest of the steps in the Terrain Processing procedure. If the reconditioning and fill sink steps are done adequately, you will get a flow direction for each grid cell that is correct (in a gross sense). After this step, it can be helpful to use the flow path tracing tool. This tool uses the fdr to plot a graphical path from the point you click to the outlet.

[MuhammadIrfan1]

Thank you Mark :),
           Mark can u guide me regarding dem reconditioning inputs as following,
Stream buffer -------
Smooth drop/raise --------
Sharp drop/raise --------
  what would be the better inputs for Aster DEM 30m resolution?n if there any conceptual guide for above inputs (Stream buffer,Smooth drop/raise, Sharp drop/raise)then plz tell me.




M.Irfan Salahuddin
Research Student of MS (RS/GIS)
Dept.of Geography,University of Karachi.

[MarkBoucher]

M.Irfan,

It is really simple, actually.

This link provides a good overview of the process. It is for an earlier version of ArcHydro and the interface looks a little different, but the concepts are still applicable:
http://www.bae.uky.edu/tdowdy/BAE538/Readings/ArcHydroTools_Tutorial.pdf

This link has a good image on page 5-3 showing what the buffer is. Though it so for different software for GIS, it is the same concept:
http://www.hec.usace.army.mil/software/hec-geodozer/documentation/HEC-GeoDozer_10_Users_Manual.pdf

When you run the DEM Reconditioning function and click the "Help" button, it gives you on-screen explanations. Per the Archydro Help (my add comments in bold italics).

Stream buffer (cells) �?? this is the number of cells around the linear feature class for which the smoothing will occur. Stream buffer - Default is 5. With a 30m DEM you could change that to 2 or 3. The buffer is used to reduce the chance of getting a parallel stream in the hydrodem if the polyline you use for agreestream does not line up with the stream depression in the DEM (See second link above). So you may need to experiment with this to see how small you can make it.

Smooth drop/raise �?? this is the amount (in vertical units) that the river will be dropped (if the number is positive) or the fence extruded (if the number is negative). This value will be used to interpolate DEM into the buffered area (between the boundary of the buffer and the dropped/raised vector feature). Default is 10. This is what I think of as the "first drop". The stream is burned this much and then the area in the buffer is smoothed to come down to this elevation.

Sharp drop/raise �?? this is the additional amount (in vertical units) that the river will be dropped (if the number is positive) or the fence extruded (if the number is negative). This has the effect of additional burning/fencing on top of the smooth buffer interpolation. It needs to be performed to ensure preserving the linear features used for burning/fencing. Default is 1000. This is what I think of as the "second drop". After the "first drop" and smoothing within the buffer the stream is burned into the DEM really deep. It should be a big number, though  the default of 1000 could be overkill. The ultimate goal is to create a good flow direction grid (fdr). If the sharp drop is 100 feet deep or 1000 feet deep, that will not change the fdr. I'd just use the default and save time. If you will do any elevation measurements you will use the rawdem anyway.

Hope this helps.

[MuhammadIrfan1]

Thank you so much Mark, its really very helpful for me.. 🙂







M.Irfan Salahuddin
Research Student of MS (RS/GIS)
Dept.of Geography,University of Karachi.

[TatevikSimonyan]

Will you help me in finding the period between A and B in the case of water flow, the functions of finding their solution.
In ArMap 10

[DipikaBadal1]

@MarkBoucher  and everyone, wanted your opinion on something:

I am working on a hydrological modeling project in a relatively mixed agricultural area using a 10m resolution DEM captured via Radar. The study area is topographically diverse, covering both flat agricultural plains and the more rugged, incised valleys.

I am using the ArcHydro DEM Reconditioning tool to burn in a vector watercourse layer. I’m trying to find the right balance for the AGREE algorithm parameters to ensure flow consistency without over-distorting the terrain.

I am currently considering these parameters:

Number of cells for stream buffer: 3

Smooth drop: 5

Sharp drop: 30

Any suggestions on how to set these parameters would be really appreciated