| This paper introduces
TOPKAPI (TOPographic Kinematic APproximation and Integration), a
new physically-based distributed rainfall-runoff model deriving from the
integration in space of the kinematic wave model. The TOPKAPI approach
transforms the rainfall-runoff and runoff routing processes into three ‘structurally-similar’
non-linear reservoir differential equations describing different hydrological
and hydraulic processes. The geometry of the catchment is described by a lattice
of cells over which the equations are integrated to lead to a cascade of
non-linear reservoirs. The parameter values of the TOPKAPI model are shown to be
scale independent and obtainable from digital elevation maps, soil maps and
vegetation or land use maps in terms of slope, soil permeability, roughness and
topology. It can be shown, under simplifying assumptions, that the non-linear
reservoirs aggregate into three reservoir cascades at the basin scale
representing the soil, the surface and the drainage network, following the
topographic and geomorphologic elements of the catchment, with parameter values
which can be estimated directly from the small scale ones. The main advantage of
this approach lies in its capability of being applied at increasing spatial
scales without losing model and parameter physical interpretation. The model is
foreseen to be suitable for land-use and climate change impact assessment; for
extreme flood analysis, given the possibility of its extension to ungauged
catchments; and last but not least as a promising tool for use with General
Circulation Models (GCMs). To demonstrate the quality of the comprehensive
distributed/lumped TOPKAPI approach, this paper presents a case study
application to the Upper Reno river basin with an area of 1051 km2
based on a DEM grid scale of 200 m. In addition, a real-world case of applying
the TOPKAPI model to the Arno river basin, with an area of 8135 km2
and using a DEM grid scale of 1000 m, for the development of the real-time flood
forecasting system of the Arno river will be described. The TOPKAPI model
results demonstrate good agreement between observed and simulated responses in
the two catchments, which encourages further developments of the model.
Keywords: rainfall-runoff modelling, topographic, kinematic wave approximation,
spatial integration, physical meaning, non-linear reservoir model,
distributed and lumped |