SURFACE WATER TRANSPORT

SURFACE WATER TRANSPORT - is the flow of water on the surface. The water that is accumulated on the surface due to rainfall or fluxes from the gound is removed by gravitation, as it tends to find an adjacent location that has a lower elevation. The flow of surface water is therefore controlled by the head difference between the donor and acceptor locations. The rate is also a function of the surface roughness. That is why water will run faster over a concrete bed, a parking lot or a street, than over a wetland, a cropfield or a forest.

Surface water flow (F_i) is a function of H_i-H_i+1. H_i is total water head: H_i = E_i+D_i,
where E_i - is elevation, and D_i is water depth.

Strictly speaking surface water flow is not a process to consider within the framework of a unit model. It is driven by an elevation gradient, whereas elevation in this case, like other spatial characteristics, is assumed to be uniform over the whole modelled area. Therefore we will look at this process in more detail when describing the spatial implementation of the model. For the unit model it is enough to provide some sort of a function that will remove either all of the available surface water (works good for a highland, terrestrial area) or will take away a certain proportion of the available water (wetlands, waterbodies - areas where we want surface water to be constantly present).

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