Our ability to numerically model natural systems has progressed enormously over the last 10–20 years. During the last decade computational power has increased to the stage where we can now have a super-computer on our desk, and the detail and fine scale processes that can be included in models are fantastic. The computational tools available for analysis and display have opened doors beyond the dreams of our forebears. However, as modelling power has increased there has been a concurrent reduction in “data power”, particularly in the collection of hydrological data. While we undoubtedly have access to large datasets of extraordinary technological finesse such as the remotely sensed data from satellites, our collection of more basic and traditional datasets suffers. We can read car number plates from outer space, but we still, in the main, measure rainfall by putting a bucket out in a paddock. This paper discusses the growth in sophistication of hydrological modelling through the last hundred years. The concept of validation or verification of models is questioned, and the role of data in modelling discussed. It is argued that modelling in the absence of adequate data is not science, unless it is to develop hypotheses that are to be tested by observation. Several modelling case studies with and without adequate testing data are discussed. It is also argued that improvement in the management of our environment and water resources will not come with improved models in the absence of improved data collection because we cannot manage what we do not measure.

Hydrological models are so good, do we still need data?

Development-perched watertables and subsurface lateral flows in texture-contrast soils (duplex) are commonly believed to occur as a consequence of the hydraulic discontinuity between the A and B soil horizons However, in catchments containing shallow bedrock, subsurface lateral flows result from a combination of preferential flow from the soil surface to the soil—bedrock interface, undulations in the bedrock topography, lateral flow through macropore networks at the soil—bedrock interface, and the influence of antecedent soil moisture on macropore connectivity Review of literature indicates that some of these processes may also be involved in the development of subsurface lateral flow in texture contrast soils However, the extent to which these mechanisms can be applied to texture contrast soils requires further field studies Improved process understanding is required for modelling subsurface lateral flows in order to improve the management of waterlogging, drainage, salinity, and offsite agrochemicals movement

https://downloads.hindawi.com/journals/aess/2012/861358.pdf

Subsurface Lateral Flow in Texture-Contrast (Duplex) Soils and Catchments with Shallow Bedrock

Antecedent soil moisture significantly influenced the hydraulic conductivity of the A1, A2e and B21 horizons in a series of
strong texture-contrast soils. Tension infiltration at six supply potentials demonstrated that in the A1 horizon, hydraulic
conductivity was significantly lower in the ‘wet’ treatment than in the ‘dry’ treatment. However in the A2e horizon, micropore
and mesopore hydraulic conductivity was lower in the ‘dry’ treatment than the ‘wet’ treatment, which was attributed to the
precipitation of soluble amorphous silica. In the B21 horizon, desiccation of vertic clays resulted in the formation of shrinkage
cracks which significantly increased near-saturated hydraulic conductivity and prevented the development of subsurface lateral
flow in the ‘dry’ treatment. In the ‘wet’ treatment, the difference between the hydraulic conductivity of the A1 and B21 horizons
was reduced; however, lateral flow still occurred in the A1 horizon due to difficulty displacing existing soil water further down
the soil profile. Results demonstrate the need to account for temporal variation in soil porosity and hydraulic conductivity in soilwater
model conceptualisation and parameterisation.

Influence of antecedent soil moisture on hydraulic conductivity in a series of texture-contrast soils

Measuring and monitoring the effects of agroforestry and drainage in the ‘Ucarro’ sub-catchment

Mechanisms and control of water logging and groundwater flow in the ‘Ucarro’ sub-catchment

A bio-physical modelling study is presented which simulates the drainage under an annual clover and a perennial lucerne pasture. The simulations are compared with measurements taken at a trial near Katanning, Western Australia, subject to a Mediterranean climate. The results show the water balance of the site to be dominated by the vertical dimension, with no apparent lateral flow in the B soil horizon. Drainage under lucerne was found to be less than that under the clover during the growing season of the annual pasture. However, our results suggest the dominant drainage control may be site and soil characteristics rather than pasture type. We found that using measured values of hydraulic conductivity led to much higher drainage than could be supported by observations of perched watertables within the A and B horizons. The observations suggest that the subsoils change their structure when they moisten in winter and become much less conductive. In order to model the site, a soil profile had to be invoked which reflected field water table hydrograph observations rather than soil water characteristics determined in the laboratory or from field profile texture observations.

Modelling Drainage and Transient Waterlogging in an Agricultural Catchment

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Modelling Drainage and Transient Waterlogging in an Agricultural Catchment