Spatial and temporal effects on urban rainfall/runoff modelling
- Publication Type:
- Thesis
- Issue Date:
- 2000
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Although extensive worldwide literature on urban stormwater runoff
exists, very few publications describe runoff development in terms of its basic building
blocks or processes and their individual and accumulative significance in response to
varying inputs and boundary conditions. Process algorithms should respond accurately
to varying input magnitudes and characteristics as well as to changes in antecedent
conditions.
The present state of estimation errors involved in many current numerical simulation
techniques has been reviewed in this thesis. A significant amount of errors that are
presently encountered for have been explained in terms of undefined process response
not explicitly included within many modelling methodologies.
Extensive field monitoring of intra-catchment rainfall and runoff within an urban
catchment at Giralang in Canberra, which is typical of Australian urban catchments,
was carried out over a 3-year period to define and measure individual runoff processes.
This monitoring work led to a greater understanding of the processes driving the
aggregation of local runoff from many sub-areas into the runoff observed at full
catchment scale.
The results from the monitoring process prompted a number of approaches to
potentially reduce standard errors of estimate from model-attributable errors based on
improvements to definable catchment response mechanisms. The research isolated a
number of basic building blocks associated with typical residential allotments, that can
be grouped into roof drainage, yard drainage and adjacent road drainage.
A proposed modelling approach was developed that allowed these building blocks at an
allotment scale to be simply computed using storage routing techniques. This then
aggregated via the total catchment’s public drainage system isochronal characteristics
utilising a “process tree” approach to provide full catchment scale runoff response.
The potential reduction in estimation errors utilising the developed procedure was
assessed using a large number of recorded events from the Giralang catchment
monitoring data.
The proposed numerical modelling approach was found to provide significant
improvements over current methods and offered a scale-independent and stormindependent
methodology to model catchments of any size without the need for
changes to any of the runoff routing parameters. Additionally the approach permits the
flexible sequencing and inclusion of a wide range of different urban drainage structures
within a catchment that are representative of the local characteristics.
The developed procedure also includes a spatially varied water balance approach to
infiltration estimation that is more suited to future continuous simulation models.
The developed “flexible process tree” approach provides an important step forward in
the numerical modelling of complex urban drainage systems. This can reduce errors of
estimate by improving intra-catchment process representation.
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