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I'm trying to calculate flow accumulation layer (with arcGIS) in a basin with 2 outlet points. I have used "dem reconditioning" tool to modify my dem according to a vector layer, which contains my digitized stream network. The problem is that a few km before the main river delta a diversion is constructed (for flood management) creating thus 2 riverbeds, the natural and the constructed one, resulting in two outlet points and two deltaic parts along the coastline. I'm trying to work with a specific flood event in the river and I need to calculate flow accumulation layer with these two outlet points . I've tried many things with no success.

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    welcome to GIS-SE. As a new user you will find that the tour provides valuable information on how questions should be asked. This specific question would be much clearer if you provide any information on what "many things" you have already tried. Please specify what you would like to achieve as well. Finally, images of the data, stream network and diversion would better demonstrate what you are trying to explain with words. – dof1985 Jul 24 '16 at 7:32
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    Vector solution is basic: set up a fractions at links going out of diversion node. With rasters I'd try setting sink no data at diversion point and apply ,"precipitation" =1 for catchment downstream and setting fractions of total at 2 cells slightly downstream of diversion – FelixIP Jul 24 '16 at 9:26

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