Delineate a watershed based on an elevation grid

Summary

This article contains a basic procedure for delineating a watershed from a grid of elevation values.

Procedure

1. Remove localized sinks using FILL:
   
   

   Code:
   Grid: FILL demraw demfill SINK 4.5

   
   
2. Create FLOWDIRECTION grid:
   
   

   Code:
   Grid: demfdir = FLOWDIRECTION(demfill)

   
   
3. Create FLOWACCUMULATION grid:
   
   

   Code:
   Grid: demfacc = FLOWACCUMULATION(demfdir)

   
   
4. Find cells of highest accumulation:
   
   

   Code:
   Grid: strm = CON(demfacc gt 300,demfacc)
   

   
   
5. Find the outlets with SNAPPOUR. A prompt appears requesting a graphical selection of the outlet point at the bottom of the watershed.
   
   

   Code:
   Grid: outlet = SNAPPOUR(*,demfacc,5000)

   
   
6. Use WATERSHED to find watershed of stream networks:
   
   

   Code:
   wshed = WATERSHED(demfdir,outlet)