Geoscience Reference
In-Depth Information
Figure 7.9
Rescaled likelihood weighted distributions for TOPMODEL parameters, conditioned on discharge
and borehole observations from the Saeternbekken MINIFELT catchment for the autumn 1987 period (after
Lamb et al., 1998b, with kind permission of Elsevier).
the individual parameters, each was sampled independently from uniform distributions across the range
shown. The uniform prior distributions would be represented by a straight diagonal line on each plot. The
strongest departures from the prior distributions are shown by the two parameters of the transmissivity
profile,
m
and
ln
(
T
o
). The other three parameters are much less well-conditioned by the observations.
This is to be expected since the shallow wet soil in the catchment would not be expected to strongly
limit evapotranspiration (controlled by the
S
Rmax
parameter), nor the time delay for vertical recharge
(controlled by the
t
d
parameter). The relatively poor constraint on an effective storage capacity of the soil
(
δθ
) was not surprising in the conditioning on discharges alone but was more surprising when the borehole
data were added as this parameter controls the calculation of a water table level from the storage deficits
calculated by the model. It may be a reflection of the interaction in the model between this and other
parameters in predicting the borehole levels. It must be remembered that, in the GLUE methodology, it
is the individual parameter
sets
that are assessed in terms of the chosen likelihood measure. Figure 7.9
represents only a summary or marginal distribution for each parameter over all the parameter sets being
considered. Prediction bounds for the 1987 period are not shown here but they showed that, in predicting
the catchment discharges, very little additional constraint was provided by adding the information from
the recording borehole information.
The resulting prediction bounds are shown in Figure 7.10 for discharges and Figure 7.11 for the
recording boreholes. In both cases, bounds are shown for the 1989 simulation period using parameter
