Technical tasks relating to the implementation of Slovenian regulations in the field of flood risk

Revision and amendment of the Flood Warning Map

The Flood Warning Map (OPKp) and its role are defined in the Rules on the Methodology for Determining Areas at risk of flooding and associated erosion of inland waters and the sea, and on the method of classifying land into risk categories, Official Gazette of the Republic of Slovenia, No. 60/2007.

One of the main purposes of the OPKp is to consolidate available data on the extent of flooding. The content is updated and supplemented in line with available data and financial resources, and the presentation is suitable for maps at a scale of 1:50,000 and less precise.

The aim of publishing this layer is to alert spatial planners and the general public to the risk of flooding.

The following guidelines and principles were applied:

from a source providing multiple flood lines with different return periods, the one with the greatest extent was selected;
there is a single flood area. The categories of frequent, rare and very rare floods are combined into a single flood layer (client’s guidance);
each polygon has an ‘frequency category’ attribute and a ‘reliability rating’;
flood areas for which a watercourse was excluded in the source data have been combined into a single polygon.

The contents of OPKp2012 November are:

flood warning map (flood-prone areas)
flood warning map (direction of flooding)
flood warning map (flooding watercourse section)
flood events
functional floodplains

Sources

The data used to update the OPKp are drawn from various sources, with varying levels of production accuracy and (cartographic, digital) representation, as well as differing time periods. The graphics are based on:

OPKp2007;
OPKp2012 February;
flood events recorded in the recent and distant past (flood lines determined on the basis of actual flood events);
models (flood lines determined on the basis of hydrology and hydraulics);
other sources (e.g. the magazine Ujma, Geografski zbornik, etc.)

The flood areas shown do not cover all flood-prone areas, but only those for which data were available and which could be integrated into the OPKp layers within the time available.

Therefore, PLEASE NOTE: Where a flood area is NOT marked, this does NOT mean that there is NO risk of flooding in that area.

Occasional changes to the layer are possible insofar as obvious errors or additional information are identified and taken into account, leading to the definition of additional (revised) flood areas or to a change in the accuracy of the extent of already shown flooded areas and water levels.

The accuracy of the display varies considerably from one data source to another, but adheres to the accuracy standard for maps at a scale of at least 1:50,000. The sources vary in terms of production accuracy and (cartographic, digital) recording, as well as in terms of temporal distance, and cover flood events recorded in the recent and distant past, the results of hydraulic models, publications, etc.

RELIABILITY RATING: 1…lowest, 10…highest reliability of the representation, covering both the reliability of the content and the accuracy of data capture.

The reliability rating is an expert assessment:

1–4 based on knowledge of the area, individual flood data of varying quality, and data from a long time ago;

5–6 better knowledge of the area, individual flood data of better quality, more recent data, hydrological data, simplified hydraulic calculations;

7–8 better knowledge of the area, higher-quality flood data – recorded events, more recent data, better hydrological data, hydraulic calculations based on older data;

9–10 good knowledge of the area, good flood data – recorded and analysed events, more recent data, good hydrological data, recent hydraulic calculations using modern tools.

Content currently available on the Environmental Atlas (OPKp 2007):

flood warning map (frequent)
flood warning map (rare)
flood warning map (very rare)
flood warning map (direction)
flood line (note: these are sections of watercourses that flood)
flood events

were replaced in the OPKp 2012 November by the following content (layers):

flood warning map (flood-prone areas)
flood warning map (direction of flooding)
flood warning map (sections of watercourses that flood)
flood events (defined by date)
functional floodplains

The data layer has been updated and submitted to the Ministry of the Environment and Spatial Planning (MKO), which is expected to forward it to the Agency for the Environment and Spatial Planning (ARSO) for publication on the Environmental Atlas following approval.