INTER COMPARISON OF EXPERIMENTAL CATCHMENT DATA AND
HYDROLOGICAL MODELLING
Shailesh Kumar Singh,1 Hilary McMillan,1
1
National Institute of Water and Atmospheric Research, Christchurch, New Zealand
Hydrological model account for the storage, flow of water and water balance in a watershed,
which includes exchanges of water and energy within earth, atmosphere and oceans. Generally
the parameter of lumped, semi or distributed hydrological model has depended on the parameter
estimated at gauged location which is generally at outlet of a basin. In this approach it is hard to
judge real performance of model to represent each process of hydrological cycle. This limit the
utility and confidence in use of the model.
Aims
The objective of this study is, to identifying model weaknesses in reproducing actual internal
catchment processes and to improve in understanding hydrological processes, through field
observation. The other objective of this study is to validate physically-based semi-distributed
hydrological model (TopNet) with spatially observed data from small experimental catchments to
ensure that the internal dynamics and processes of the catchments are properly represented in
the model.
Method
This study was carry out at Waipara experimental catchment, which is located in South Island of
New Zeeland. In filed campaign, in Waterscape project of NIWA, we made distributed
measurement of streamflow, soil moisture and groundwater levels across range of hillslope,
aspects and distances from stream and different depths. TopNet rainfall-runoff model was setup
waipara catchment. To achieve the objective of this study following steps were carried:
 The data collected were analysis for understanding the flow generation process in the
catchment.
 A semi-distributed physically based (TopNet) hydrological model was set up for the
catchment.
 The model was run for given time period and all the different fluxes were saved for further
inter comparison with observed data.
 Detail analysis for each hydrological process was conducted to look the patter observed
in the filed with flux obtained by model.
Results
Analysis of rainfall runoff ratio and average soil moisture measured at 30 cm and 60cm shows
that approximately 32 % of soil moisture at 30cm trigger the runoff from the soil or around 40% of
soil moisture at 60cm depth of soil. The total amount of simulated runoff from TopNet model
showed reasonable agreement with observations. But regarding the specific runoff components,
the model overestimated base flow and underestimated surface flow. Comparison of dynamic of
soil moisture obtained from TopNet model is compared with average observed soil moisture and
given in Figure 2. The results shows that soil moisture dynamic observed is well represented by
the model.
Conclusion
In this study, experimental catchment Waipara data was used to validate the hydrological model
TopNet. Preliminary results shows that soil moisture dynamic observed is well represented by the
model. This current study is ongoing, hence, further investigation is required to prove the other
internal dynamics and processes of the catchments are properly represented in the model.
Figure 1 Rainfall Runoff Ratio VS Average Soil moisture North face
Figure 2 Average Soil moisture (red and black) at 30cm and 60cm (North face) along with soil moisture
(green) dynamic from model.