RE: Flow Direction Problem

[Max Shaw]

Hi Tom, hope you are well. 

I'm having an issue with the flow direction from my input discharge location. I'm investigating Milton Brook's river body at Great Barrow (Cheshire west and Chester), which is a complex fluvial system that has multiple riparian drainage networks surrounding it which I believe is causing a problem. It is an area that has multiple flood events which you can see at (https://www.cheshirewestandchester.gov.uk/asset-library/flooding/s19-great-barrow-report.pdf)

The banks of the river are very low and I think this is the reason why the dem is struggling to pick up a definitive stream. I have followed the steps for processing my dem in arc hydro by filling in the sinks etc. 

I'm using a resolution of 1m because of the complexity. There are multiple bridges which I have removed in RasterEdit already, but the presence of a weir at Barrow Mill splits the river into two which is proving quite challenging to edit (any suggestions?). I have tried to alter my dem in both point edit and reach edit mode but this seems to create further problems?

Furthermore, highlighted in the image filed as 'pathway_error', you can see how the direction of the water starts by flowing down Milton Brook, but then deviates pretty quickly from its usual main river course, across the floodplain, following the descent route that is a drainage system. (The red arrows highlight the route it should take which is Milton Brook).

Have you got any suggestions on how I can amend this flow direction and get it to predominately flow down Milton Brook? Attached is the raw image output from c-l, the edited output image and my asc raster image. 

Any help will be much appreciated. 

[tom.co...@gmail.com]

Hi Max,

Sorry for delay – been on holiday

It might be the pit filling the DEM in arc hydro has filled in the channels too much? Also assuming its lidar data consider the DTM or DSM – there are two different products, one with the bridges/structures removed and one with them included. Either way, the lidar gives a return on the water surface not the bed – so sometimes you have to excavate where the channel is in your DEM…

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