Mine

textureMatrix
  name water1
  shift -0.6 0.5
end

textureMatrix
  name water2
  shift 0.5 -0.6
end

material
  name water1
  addtexture water
  diffuse 1 1 1 0.5
  texmat water1
end

material
  name water2
  addtexture water
  diffuse 1 1 1 0.6
  texmat water2
end

meshbox
   pos -400 0 2.8
   size 200 600 0.1
   matref water1
   passable
   noradar
end

meshbox
   pos -400 0 0
   size 200 600 2.8
   matref water2
   noradar
end