Rivers exist in all land grid boxes and collect runoff from the soil and land ice models. Where there is a lake fraction, the water is considered a lake (as above). Where there is not, there is no intereaction with the atmosphere. Tranpsort of river water depends on the (fixed) downstream direction file and mean slope, and the depth of the upstream river/lake above a predefined sill depth. Some boxes do not contain an outlet, and so can accumulate water indefinitely. As the river water reaches an ocean box, the water is deposited uniformly within that box.