This paper describes the preliminary development of a network-index
approach to modify and to extend the classic TOPMODEL. Application of
the basic Beven and Kirkby form of TOPMODEL to high-resolution (2-0 m)
laser altimetric data (based upon the UK Environment Agency's light
detection and ranging (LIDAR) system) to a 13.8 km(2) catchment in an
upland environment identified many saturated areas that remained
unconnected from the drainage network even during an extreme flood
event. This is shown to be a particular problem with using
high-resolution topographic data, especially over large appreciable
areas. To deal with the hydrological consequences of disconnected
areas, we present a simple network index modification in which
saturated areas are only considered to contribute when the topographic
index indicates continuous saturation through the length of a flow path
to the point where the path becomes a stream. This is combined with an
enhanced method for dealing with the problem of pits and hollows, which
is shown to become more acute with higher resolution topographic data.
The paper concludes by noting the implications of the research as
presented for both methodological and substantive research that is
currently under way.