Change reference_gauge paremeter to Long Change the reference_gauge paremeter of the GaugeDischargeCurveArtifact from Double to Long. It doesn't change the behaviour but the reference is a long value in the database too.

SYMBOLSET
SYMBOL
  NAME 'point'
  TYPE ELLIPSE
  POINTS
    1 1
  END
  FILLED TRUE
END
SYMBOL
  NAME "square"
  TYPE VECTOR
  POINTS
    0 0
    0 1
    1 1
    1 0
    0 0
  END
  FILLED TRUE
END
END