Geoscience Reference
In-Depth Information
Figure 4.6
(a) Time variable estimates of the gain coefficient in the bilinear model for the CI6 catchment
plotted against the discharge at the same time step; (b) optimisation of the power law coefficient in fitting the
observed discharges (after Young and Beven, 1994, with kind permission of Elsevier).
In fact, a simple link can be made with the prediction of saturated contributing areas in TOPMODEL
which depends on the distribution of an index derived from the topography in the catchment. The theory
underpinning this link can be found at the end of Box 6.1.
Although of some interest, this representation of the rainfall nonlinearity still requires further evaluation
since it takes no explicit account of seasonality of responses except in so far as seasonality is reflected in
the contributing area filtering based on discharge. In another application of the bilinear power law model
to the Canning River in Australia, Young
et al.
(1997) have shown that this approach can explain 95.8%
of the variance of daily discharges over a two-year period, including dry summer periods. A split record
test of the fitted model over two further years of data produced almost as good fits (88.9% and 92.4%).
The IHACRES model does take account of seasonal wetting and drying by including a temperature
