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How To: 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)