I want to calculate the total flow in an administrative area which is independent of the basin boundaries.

I used the DEM file from HydroSHEDS and so far I have followed these steps:

  1. Spatial Analyst -> Hydrology -> Fill
  2. Spatial Analyst -> Hydrology -> Flow Direction
  3. Spatial Analyst -> Hydrology -> Flow Accumulation
  4. Spatial Analyst -> Math -> Logical -> Greater Than
  5. Spatial Analyst -> Hydrology -> Flow Length
  6. Spatial Analyst -> Hydrology -> Stream Link
  7. Spatial Analyst -> Hydrology -> Stream Order (Strahler)
  8. Spatial Analyst -> Hydrology -> Stream to Feature

The figure below shows the results of my work. Red lines are watershed boundaries and yellow lines are administrative zone boundaries. There are more than 80 zones. I have highlighted one of them for better visuals.

enter image description here

Now since I know the total amount of water available in a watershed (flow measurements), I want to estimate the relative amount of water accumulating in each of these administrative zones.

Flow accumulation already calculates a value at point O. If I can calculate the relative share of A, B, C and D, I can calculate the amount of water stream A accumulates. However, I still need to calculate the accumulation at points E, F, G, H and I, which are from another watershed, in order to calculate the total amount of water in the yellow zone.

Is there any automated way to calculate these values?

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