Updating of the Finnish drainage basin system and register –
Case VALUE
J. Oksanen1, M. Joukola2, R. Teiniranta2, J. Suikkanen2, T. Sarjakoski1
1
Department of Geoinformatics and Cartography,
Finnish Geodetic Institute, Masala, Finland
2
Geoinformatics Unit, Finnish Environment Institute, Helsinki, Finland
Abstract
The Finnish drainage basin register is one of the most utilized geospatial datasets
maintained by the environmental administration, but the current system does not fulfil
the needs of various user groups and the new requirements that are set by i.a. water
management. Therefore, the new Finnish drainage basin system and register need to be
planned and specified and production methods for updating the register need to be
defined. Beyond the INSPIRE Data Specification on Hydrography, added value to the
new register will be gained by also producing uncertainty-aware catchment delineations,
which take the DEM elevation uncertainty into account in the delineation process.
Background
The current Finnish drainage basin register was derived from topographical paper maps
at the scale of 1:50’000 for hydrological monitoring purposes. Register preparation was
finished and integrated as a part of the environmental data system in 1991 (Ekholm
1993). Since then, the register has served the needs of water management, conservation
and research, as well as national and international reporting and information system
work related to water resources. However, the current drainage basin register does not
fulfil the needs of various user groups and the new requirements that are set by i.a.
water management and water protection. Due to manual map-based delineation of
catchments, the catchment boundaries contain significant inaccuracy and even gross
errors in location, the boundaries are in contradiction with the current digital elevation
models (DEMs) and there are other obvious deficiencies reported by the key user
groups of the data. In addition, human influence on the topography and the directions of
flow is locally noteworthy and in the long term, crustal uplift also changes drainage
patterns significantly. The basis for the register, the drainage basin system, is also
problematic because it currently only accepts 9 sub-basins at each level of label
hierarchy, which cannot be justified on the basis of physical reality. This results in
catchments, which are very heterogeneous in size even at the same level of hierarchy
depending on the size of the main river basin. In addition, refinement of catchments
beyond the limit of 9 sub-basins is impossible. Finally, the current drainage basin
register does not contain the ‘hydroId’ attribute required by the INSPIRE. Therefore, the
two LYNET (Finnish Partnership for Research on Natural Resources and the
Environment) partners, Finnish Environment Institute and Finnish Geodetic Institute, in
co-operation started the VALUE I & II projects to update the Finnish drainage basin
system and register in order to fulfil the requirements of the register’s users, as well as
to fulfil the INSPIRE Data Specification on Hydrography.
Concept for the new drainage basin system
The core for the new drainage basin system will be the official pour point register, and
flow direction grid. It is based on the most accurate country-wide DEM and river
network register available. Thus, the concept makes it possible that the catchment
boundaries could change, when the accuracy of the country-wide data sets improve. The
system splits into two distinct sets of data: 1) the centrally administrated country-wide
drainage basin data set, and 2) the user-driven project oriented drainage basin data sets.
The delineations based on static or semi-static pour points, such as lakes having area
>50ha and streams having upslope catchment area >10km2, water bodies of the Water
Framework Directive (WFD), and hydrological monitoring stations belong to the first
category. All other delineations, which are not based on the static set of pour points, but
rather on occasional needs, belong to the second category.
While INSPIRE Data Specification on Hydrography set the need to report positional
uncertainty of the hydrographic features, no indication is given how positional
uncertainty of drainage divide should be derived. In VALUE-projects, we have decided
to offer to the end users of the Finnish drainage basin register the uncertainty-aware
catchment delineations, which communicate visually the influence of DEM quality on
the uncertainty of the watershed location (Oksanen 2006, Oksanen and Sarjakoski
2010). The INTUIT-project will focus on the methodological issues related to
characterisation of LIDAR DEM uncertainty. While the drainage network register acts
as the skeleton of the system, the DEM with inherent uncertainty will have a major
influence on the precise location of the catchment boundary between the skeleton
(Figure 1).
Figure 1. Experimental visualization of the uncertainty-aware catchment delineation.
(Background map © National Land Survey of Finland, licence 7/MML/12)
Acknowledgements
VALUE I & II were funded by the Ministry of Environment and the Ministry of
Agriculture and Forestry. INTUIT is funded by the Academy of Finland (grant 251987).
We also thank research assistant Friederike Schwarzbach for all the help during the
project and Sophia van der Made for improving English.
References
Ekholm, M. (1993). Suomen vesistöalueet (Drainage Basins in Finland), Publications of
the Water and Environment Administration, Series A 126, Finland.
Oksanen, J. (2006). Digital elevation model error in terrain analysis. Doctoral
dissertation, University of Helsinki. Publications of the Finnish Geodetic Institute 134.
Kirkkonummi.
Oksanen, J. and T. Sarjakoski (2010). Non-stationary modelling and simulation of
LIDAR DEM uncertainty. Proceedings of the 9th International Symposium on Spatial
Accuracy Assessment in Natural Resources and Environmental Sciences, July 20-23,
Leicester, UK, pp. 201-204.