Vertical integrals

[Simon Evans <simon@xxxxxxxxxxxxxxxxx>]

   Hello,

    I'm stuck trying to do a vertcial integral from the sea floor
 z=H(x,y) to the surface, z=0. It seems that when X and Y are single-
 valued, for example through

    set region/x=100/y=100

 then something like

   let Integral = Integrand[z=0:`H`@DIN]

 works fine. However, for a variable region like 

   set region/x=0:100/y=0:100

 the above falls over, since the expression contained in the grave marks
 is no longer scaler.

    I've played with various things based on WEQ, but without success.
 Also no help in the FAQ, nor (I think) in the mailing list archives.
 Can anyone help?