SCALGO Live Documentation


Country Specific - Denmark

Our Danish elevation model is based on the official Danish elevation model (also known as DHM) produced by the Agency for Data Supply and Efficiency. The model has a horizontal resolution of 0.4 m, much higher than the previous model from 2007, where the resolution was 1.6 m. Since 2018, SDFE has been updating the elevation model from 2015 in partial increments of about a fifth of the country every year. This model is available in SCALGO Live under the name Terrain (Terræn). There are a couple of different variants of the model available.

Terrain/Buildings (Terræn/Bygninger): This is the raw model enriched with building footprints from the national GeoDanmark data set. For each GeoDanmark building footprint, we've raised the elevation of the cells there are inside the buildings with 10 m, relative to the highest elevation value of the original terrain model.

The Danish elevation model with GeoDanmark building footprints.

Terrain/Buildings/Rain (Terræn/Bygninger/Regn) and Terrain/Buildings/Sea (Terræn/Bygninger/Hav): Both models are derived from the Terrain/Buildings model and include the set of hydrological corrections from GeoDanmark.

Terrain/Rain includes the corrections made for modeling water flowing downstream on the terrain, e.g., water from rain events. Terrain/Sea is targeted for modeling flooding from sea. The main difference between the two models is infrastructure like sluices, and whether they are open or closed.

A hydrological correction cutting through a bridge in the Terrain/Buildings (2015) model.

Surface (Overflade): This is the Digital Surface Model (DSM) version of the DHM. In this model houses, vegetation etc. is preserved in the elevation model.

The DSM for a section of downtown Aarhus.

Sources: A source layer, showing the acquisition year of the data, is available by clicking the gear icon next to an elevation layer and selecting the "Source" ("Kilde") tab, and then "Show source information" ("Vis kildedata"). Use it to figure out how old the data is for your project area. You can use the point query tool to get the acquisition year for a particular area.

Each color represents a different acquisition year.

Terrain (2015) (Terræn (2015)):

This is a historical version of DHM, released in 2015 based on scans from 2014-2015. It is the first model released by SDFE with a resolution of 0.4 m.

Surface (2015) (Overflade (2015)):

This is the Digital Surface Model (DSM) version of DHM from 2015.

Terrain/2007 (Terræn/2007):

This is an older model of Denmark released in 2007 based on scans from 2005-2007. It has a horizontal resolution of 1.6 m.

Imperviousness (Befæstelseskort)

The impervious surfaces map in SCALGO Live is produced by SCALGO based on machine learning techniques at a resolution of 20 cm. It is available as a standalone layer in the Imperviousness category in the library.

A section of the impervious surface mapping.

The mapping of impervious surfaces segments the country into 3 different classes: pervious, impervious and lake. The pervious class is further subdivided into a forest category and a general other pervious category (based on the GeoDanmark forest polygon layer), and the impervious class is subdivided into a building category and a general other impervious category. When downloaded as a raster, the categories have the following numerical encoding: 1 for pervious, 2 for forest, 3 for impervious, 4 for lake, and 5 for building.

The map is indirectly available through other layers in SCALGO Live as well:

Watershed queries

When you perform a watershed query you get the total area of impervious surfaces in the watershed.

A watershed query showing watershed imperviousness statistics.

Annotated administrative regions

We have annotated a number of datasets, including the cadastral parcels, sewer catchments, planning zones as well as municipal regions with information about imperviousness. You can find those layers in the Imperviousness category alongside the impervious surfaces map itself. For each region in those data sets we have added a field that provides the total impervious area in the region, as well as the ratio of imperviousness to perviousness in the region.

A point query on the cadastral map showing the impervious surface area and the ratio of a cadastral polygon.

Soil type (Jordtypekortet)

SCALGO Live uses Jordtypekortet (30 m resolution) from the Department of Agroecology at Aarhus University, both for watershed queries and in the Flash Flood Map. In watershed queries it is available as aggregate information about the composition of soil types in a given watershed, and in the Flash Flood Map it forms the basis for determining rates of infiltration from pervious cells when enabling infiltration and drainage. Jordtypekortet classifies the topmost soil layer of Denmark into types based on soil samples taken mainly from farmland, interpolated to cover the entire country in a 30.4 m resolution grid. We refer to a memo (in Danish) published by the Danish Centre for Food and Agriculture for more information on the soil type map.

Infiltration and drainage to sewers

The Flash Flood Map supports the use of runoff functions to specify the runoff generated from each cell as a function of the rain depth. In Denmark we have produced a national Flash Flood Map where we use runoff functions to include infiltration and drainage to sewers in the model. When you enable infiltration and drainage in the Flash Flood Map, the infiltration at a cell is determined by the cell’s imperviousness class as well as its soil type (in pervious areas) and sewer map status (in impervious areas).

Runoff functions can be accessed by clicking on the rain drops next to Flash Flood Mapping in the dock.

In impervious areas, if a cell is in an area that has a combined sewer system (treating both surface water and wastewater), then an amount of rain corresponding to a 10-year event is subtracted as initial loss; if the cell is in an area with a dedicated surface water system, a 5-year event is subtracted as initial loss. Other impervious areas use the glass model with no initial loss.

In pervious areas, forested areas are assumed to have loose soil, while other pervious areas are assumed to have compacted soil. Each soil type in the soil type map has a CN curve for both compact and loose conditions. For the full picture, consult the decision diagram below:

Decision diagram using the previously-mentioned input layers. This diagram shows what runoff function we use for each pixel of the computation.

For more information about the Flash Flood Map with infiltration and drainage, including information about parameter settings and CN-curve numbers, we refer to our in-depth white-paper.

To view the runoff functions used for individual soil types, click “View Runoff Functions” in the infiltration and drainage popup.

Individual runoff functions can be highlighted by clicking on them.

If you want to investigate the forest polygons, the sewer type mapping and the soil type data used in the computation you can find them all in the library.

Inputs used to determine the runoff function for a cell in SCALGO Live: Jordtypekortet (soil type map), GeoDanmark Skov (forest polygons), Impervious Surfaces, and Kloakoplande (sewer plan)