Geoscience Reference
In-Depth Information
6
Hydrological Similarity,
Distribution Functions and
Semi-Distributed Rainfall-Runoff
Models
Faced with this situation, it has been usual to incorporate what knowledge we have about
the operation of the processes into some conceptual model of the system It is common
that some parts of a complex conceptual model may be more rigorously based in physical
theory than others. Even the most physically-based models, however, cannot reflect the true
complexity and heterogeneity of the processes occurring in the field. Catchment hydrology
is still very much an empirical science.
George Hornberger
et al.
, 1985
6.1 Hydrological Similarity and Hydrological Response Units
In any catchment the hydrologist is faced with a wide variety of geology, soils, vegetation and land
use, and topographic characteristics that affect the relationship between rainfall and runoff. One way
of taking these characteristics of any individual catchment into account is the type of fully distributed
model that was discussed in Chapter 5 but, as was shown there, such models are difficult to apply because
of their demands of both input data, much of which is not directly measureable, and computational
resources. However, in any catchment, there may be many points that act in a hydrologically similar
way with a similar water balance and similar runoff generation characteristics whether by surface or
subsurface processes. If it were possible to classify points in the catchment in terms of their hydrological
similarity, then a simpler form of model could be used based on a distribution of functional hydrological
responses in the catchment without the need to consider every individual point separately. We should
note at this point that it is also possible to consider defining hydrological similarity at the catchment
