Setting the ET Extinction Depth to 90% of the cell thickness is not appropriate.

[DarkForceOne]

The following block inappropriately sets the ET Extinction Depth to 90% of the cell thickness. Instead of modifying user's input data, this block should be commented out and let the iterative solver to figure out the actual ET from various layers.

gsflow_v2/GSFLOW/src/modflow/gwf2uzf1_NWT.f

Lines 1407 to 1459 in af9eb1f

	C10-----CHECK FOR NEGATIVE ET EXTINCTION DEPTH.
	DO nrck = 1, NROW
	DO ncck = 1, NCOL
	IF ( IUZFBND(ncck, nrck).EQ.0 ) THEN
	etdpth = ROOTDPTH(ncck, nrck)
	IF ( etdpth.GT.0.0 ) ROOTDPTH(ncck, nrck) = 0.0
	ELSE IF ( ROOTDPTH(ncck, nrck).LT.CLOSEZERO ) THEN
	WRITE (IOUT, 9007) nrck, ncck
	9007 FORMAT (1X/, 'ROOTING DEPTH FOR CELL AT ROW ', I5,
	+ ', COLUMN ', I5, ' IS LESS THAN OR EQUAL TO ',
	+ 'ZERO-- SETTING DEPTH TO ZERO ')
	! ROOTDPTH(ncck, nrck) = 1.0
	ROOTDPTH(ncck, nrck) = 0.0
	END IF
	! RGN 6/22/09. Add coded to find upper-most active layer
	il = 0
	IF ( NUZTOP.EQ.1 .OR. NUZTOP.EQ.2 ) THEN
	il = IUZFBND(ncck, nrck)
	IF ( il.GT.0 ) THEN
	IF ( IBOUND(ncck, nrck, il).LT.1 ) il = 0
	END IF
	ELSE IF ( NUZTOP.EQ.3 ) THEN
	ill = 1
	il = 0
	DO WHILE ( ill.LT.nlayp1 )
	IF ( IBOUND(ncck, nrck, ill).GT.0 ) THEN
	il = ill
	EXIT
	ELSE IF ( IBOUND(ncck, nrck, ill).LT.0 ) THEN
	EXIT
	END IF
	CRGN made il = 0 when all layers for column are inactive 2/21/08
	ill = ill + 1
	END DO
	ELSE IF ( NUZTOP.EQ.4 ) THEN
	il = LAYNUM(ncck, nrck)
	END IF
	land = ABS(IUZFBND(ncck, nrck))
	!
	IF ( il.GT.0 .AND. land.GT.0 ) THEN
	thick = BOTM(ncck, nrck,LBOTM(land)-1)-
	+ BOTM(ncck, nrck,LBOTM(il))
	IF ( ROOTDPTH(ncck, nrck).GT.0.9*thick ) THEN
	ROOTDPTH(ncck, nrck) = 0.9*thick
	WRITE (IOUT, 222) nrck, ncck
	END IF
	END IF
	END DO
	END DO
	END IF
	222 FORMAT('***WARNING*** ET EXTINCTION DEPTH IS BELOW LAYER BOTTOM',/
	+ 'RESETTING DEPTH TO 90% OF CELL THICKNESS FOR ROW ',I7,
	+ ' COLUMN ',I7)

I recommend to replace that block of codes with the following:

C10-----CHECK FOR NEGATIVE ET EXTINCTION DEPTH.
          DO nrck = 1, NROW
            DO ncck = 1, NCOL
               IF (IUZFBND(ncck, nrck).EQ.0 .OR. 
     +             ROOTDPTH(ncck, nrck).LT.CLOSEZERO) THEN
                   ROOTDPTH(ncck, nrck) = 0.0
               END IF
            END DO
          END DO
        END IF 

@rniswon