Core+ DynamicFlood – Soil infiltration parameters

In this section we list the soil infiltration parameters used by various parts of the SCALGO Live system. For instance, some, or all, of these are used in the Flash Flood Map with infiltration and drainage and in Core+ DynamicFlood. We refer to the documentation of those analyses for more information about how and why the soil parameters are used.  

There are different soil type maps in each of the countries in which we operate, therefore we apply a process to unify these into a set of generalized soil types, we then use our land cover map, and other information, to modify the soil map to better capture the top layer of soil. Finally, we assign Horton parameters to each of the generalized soil type.

Soil data in SCALGO Live

We use a set of generalized soil types to describe the soil types for use in our analyses. These soil types are:

  • Rocks and boulders
  • Gravel
  • Coarse sand
  • Fine sand
  • Coarse sand with clay
  • Fine sand with clay
  • Coarse clay with sand
  • Fine clay with sand
  • Clay
  • Fine clay
  • Very fine clay
  • Silt
  • Gyttja/peat
  • Bedrock
  • Glacier
  • Water

They match well to the soil types available from local authorities in a given country. We refer to the country specific information for information about how we map from the country-specific soil type to the generalized soil type for each country. 

Note that not all countries have this available at this time. Please contact us if you have questions about availability for your country.

The topsoil map

Following this mapping from local to generalized soil type, we perform an adjustment of the soil types to more closely reflect the type of soil in the top layer of the soil. We use the land cover map, and urban polygons for this mapping.  

The process of going from the generalized soil map to the topsoil map is the following:

  • If the land cover map says bare rock, the soil type map is set to bedrock, regardless of what it was before. 
  • Similary snow/ice become glacier, water becomes water and railroad become gravel.

We also apply rules based on some of the other soil type and land cover combinations, these rules are shown below. The soil types not listed below are not affected by the land cover map when producing the top soil mapping.

Soil type \ Land CoverUnpaved roadFarmlandShallow vegetationDense vegetation
Rocks and bouldersCoarse clay with sandCoarse sandCoarse sandCoarse sand
GravelCoarse clay with sandCoarse sandCoarse sandCoarse sand
Coarse sandCoarse clay with sand---
Fine sandCoarse clay with sand---
Coarse sand with clayCoarse clay with sand---
Fine sand with clayCoarse clay with sand---
SiltCoarse clay with sand---
Gyttja/peatCoarse clay with sand---
Bedrock-Coarse clay with sandClayClay

Following this mapping, we perform another adjustment meant to adjust urban areas, where the top soil may not match the value from the national mapping. We do the following inside urban areas:

  • Overwrite coarse sand, fine sand and coarse sand with clay with Find sand with clay.
  • Overwrite Clay, fine clay, veryfine clay with fine clay with sand.

Both the topsoil map, and the original soil type layer is available for you to see in SCALGO Live, but it is the topsoil layer that is used in our analyses.

To decide if something is an urban area, we use the datasets also used to determine sewer status.

Horton parameters

We use the Horton infiltration equation for modeling infiltration, and the table below lists the Horton parameters for the generalized soil types used in the SCALGO Live topsoil map.

We have split the Horton parameters into "High compaction" and "Low compaction" groups, these groups are based on the land cover map and are defined later in this section. This allows us to select a different set of infiltration parameters for a particular soil type depending on whether it's e.g. in a shallow or dense vegetation area.

Soil type

High compaction

Low compaction

fc

f0

k

fc

f0

k

Rocks and boulders

500

1000

5

2000

5000

5

Gravel

500

1000

5

2000

5000

5

Coarse sand

30

120

5

1000

4000

5

Fine sand

25

100

5

500

2000

5

Coarse sand with clay

21

85

5

85

150

5

Fine sand with clay

20

80

5

50

130

5

Coarse clay with sand

12

50

5

30

120

5

Fine clay with sand

9

47

6

25

100

4

Clay

5

20

5

20

50

5

Fine clay

0,5

2

5

2

20

5

Very fine clay

0,01

0,1

5

0

1

5

Silt

20

80

5

50

130

5

Gyttja/peat

21

85

5

85

150

5

Bedrock

0

0

5

0

0

5

Table: Horton parameters for the generalized soil types used in SCALGO Live

Grouping into high/low compaction

The land cover type of a given location decides whether we use the high or low compaction Horton parameters for that location, the table below details how we map each land cover type to a compaction degree.

Land cover type

Compaction degree

Note

Bare land

High

Shallow vegetation

High

Dense vegetation

Low

Fields

High

Unpaved roads

High

If the native soil type has higher infiltration rates than coarse clay with sand, the cell is applied parameters for coarse clay with sand (assuming this better represents the infiltration through the paving material)

Bare rock

N/A

All rainfall is turned to runoff, zero infiltration

Snow/ice

N/A

All rainfall is turned to runoff, zero infiltration

Table: Soil compaction degrees assigned to different land cover types.