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I have created flow direction and flow accumulation files for my DEM. Using the feature to point function, Ive got all the points in point form and then I converted them to arrows.

But most of the arrows are colliding and some are making a loop. I need them all in a nice form like they are accumulating and making a stream.

I have posted a photo of what kind of problem I have. enter image description here

My area is large and I dont want to do it manually. Do we have an automatic process for this??

  • Does it not make sense though? See the bottom right of the image, there are lots of arrows pointing at each other but that's because at that point they are flowing towards the river inbetween them. If you had an arrow directly on top of the river it would show the direction the river is flowing but at those exact point water is merging into the river perpendicularly. It may just be a case of your DEM being coarse. – TeddyTedTed Dec 14 '18 at 12:03
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    Welcome to GIS SE. As a new user, please take the Tour, which explains how our "Focused question/Best answer" model operates. Please remember to always include the exact software in use in the body of the question. I removed the tag for long-retired ArcGIS 10.0 because you had a10.5 tag as well, but placing the exact release ("10.5.1", hopefully) in the question helps to resolve some release-specific issues. – Vince Dec 14 '18 at 12:17
  • @TeddyTedTed, actually I am working on VIC model and it works on grid data, so all grids should accumulate at one outlet point and no grid should point directly at another. – lsr729 Dec 14 '18 at 12:36
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There are a number of possible reasons for this.

Preparing the DEM for hydrological processing first is the key, rather than editting the results afterwards. ESRI provide a lot of information on the Hydro Tools. For instance, make sure you run the sink process to fill sinks before you do your analysis. Optionally, you can then use the fill tool to further normalise the DEM for hyrdoligical analysis. This latter tool also removes peaks which could cause other anomolies. Sinks and peaks are often glitches in the DEM data and will be your chief cause of poor flow accumulation.

Secondly, some of the areas you have highlighted could well be correct in that the flow is accumulating in the 'crease' between cells. Also, are you certain that there are no pools, ponds or lakes in your area?

I recomend that you follow the ESRI tutorials and undertake preparation of the DEM first.

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My hypothesis is that you have some local minima that attract the flows (called sink). This is frequent when you start with a raw DEM. I therefore suggest that you run the fill sink function first. This should solve your problem.

A sink is a cell with an undefined drainage direction; no cells surrounding it are lower. The pour point is the boundary cell with the lowest elevation for the contributing area of a sink. If the sink were filled with water, this is the point where water would pour out.

  • Ive already filled the DEM, I dont think filling again would help – lsr729 Dec 14 '18 at 12:32
  • did you look at the z profile of your DEM across one of your collision area ? Maybe your area is relatively flat which makes hydrological modelling very sensitive to DEM "noise" – radouxju Dec 14 '18 at 13:47

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