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| Titel |
The application of GEOtop for catchment scale hydrology in Ireland |
| VerfasserIn |
C. Lewis, X. Xu, J. Albertson, G. Kiely |
| Konferenz |
EGU General Assembly 2009
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 11 (2009) |
| Datensatznummer |
250027455
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| Zusammenfassung |
| GEOtop represents the new generation of distributed hydrological model driven by geospatial
data (e.g. topography, soils, vegetation, land cover). It estimates rainfall-runoff,
evapotranspiration and provides spatially distributed outputs as well as routing water and
sediment flows through stream and river networks. The original version of GEOtop designed
in Italy, includes a rigorous treatment of the core hydrological processes (e.g. unsaturated and
saturated flow and transport, surface energy balances, and streamflow generation/routing).
Recently GEOtop was extended to include treatment of shallow landslides. The GEOtop
model is built on an open-source programming framework, which makes it well suited
for adaptation and extension. GEOtop has been run very successfully in a number
of alpine catchments (such as Brenta) but has not been used on Irish catchments
before.
The cell size used for the spatially distributed inputs varies from catchment to catchment.
In smaller catchments (less than 2000ha) 50 by 50m cells have been used and 200 by 200 for
larger catchments. Smaller cell sizes have been found to significantly increase the
computational time so a larger cell size is used providing it does not significantly affect the
performance of the model. Digital elevation model, drainage direction, landuse and soil type
maps are the minimum spatial requirements with precipitation, radiation, temperature,
atmospheric pressure and wind speed been the minimum meteorological requirements for a
successful run. The soil type maps must also contain information regarding texture and
hydraulic conductivity.
The first trial of GEOtop in Ireland was on a small 1524 ha catchment in the south of
Ireland. The catchment ranges from 50 to just over 200m, the land use is predominately
agricultural grassland and it receives on average 1400mm of rain per year. Within this
catchment there is a meteorological tower which provides the meteorological inputs, soil
moisture is also recorded at this location. GEOtop was run from the end of April 2006 to
December 2007. A comparison of measured and simulated values of soil moisture
showed some good results and proved that the model could be successfully be used in
Ireland.
Following initial success in modelling soil moisture in a small catchment GEOtop was
then used in the much larger 115,000 ha Blackwater catchment. The variation of soil type
within the catchment was obtained from a national soils database while Landuse data was
obtained from the national Corrine Land use database. Hydraulic properties were estimated
by carrying out on site infiltration experiments. As GEOtop can accept multiple rainfall
inputs and it was known that the rainfall varies substantially within in the catchment it was
decided to make use of a rainfall study on the Blackwater catchment. A total of 21 rain
gauges were deployed around the catchment for year 2006. The data from these 21 rain
gauges were then added to the inputs which GEOtop interpolated the rainfall using the
kriging method.
Continuous flow is recorded at the outlet of the Blackwater catchment and as GEOtop
simulates stream flows we were able to see how well GEOtop modelled the hydrology of the
catchment. Comparisons of simulated versus real flow showed that GEOtop was providing us
with satisfactory results. Once we were satisfied that GEOtop was successfully modelling the
catchment we were able to see the effects of varying rain fall and land use on many different
hydraulic parameters such stream flow, soil suction potential, soil moisture content
etc.
When this process has been carried out for other parts of the country it is planned to use
GEOtop study potential threats to soil quality such as erosion, surface sealing, compaction,
landslides and loss of organic matter. New modules will be develop for GEOtop to
help understand and quantify these threats. The model will also be used to help
understand the interactions between soil hydrology, land use and climate change
(with climate projections from the IPCC fourth assessment). These outputs will be
combined with Irish geo-spatial data to develop a GIS-based risk assessment tool to
predict impacts on soil quality based on hydrology, land use and climate change. |
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