OR/16/009 Using the data
| Dearden, R. 2016. User guide for the infiltration SuDS map: detailed. British Geological Survey Internal Report, OR/16/009. |
Setting up the GIS
To ensure that the dataset is used as designed, follow the proceedings steps to set-up the map:
a) Make sure the required data layers, as shown below, are present.
- Infiltration_constraints_summary
- Soluble_rock_constraints
- Landslide_constraints
- Shallow_mining_constraints
- Shallow_groundwater_constraints
- Made_ground_constraints
- Drainage_summary
- Depth_to_water
- Superficial_thickness
- Superficial_permeability
- Bedrock_permeability
- Geological_indicators_of_flooding
- Ground_stability_summary
- Soluble_rocks
- Landslides
- Shallow_mining
- Collapsible_ground
- Compressible_ground
- Running_sand
- Swelling_clay
- Groundwater_protection_summary
- Groundwater_source_protection_zones
- Predominant_flow_mechanism
- Made_ground
If you have licensed data as a MapInfo .tab file and some of the infiltration constraint files are missing, this may be because the chosen area is not affected by those infiltration constraints (i.e. there is no data). MapInfo cannot create a file without data, conversely, ArcGIS shape files can be created regardless and so there should not be any .shp files missing.
To set-up the GIS to reflect Figure 3, the Infiltration Constraints Summary, Drainage Summary, Ground Stability Summary and the Groundwater Protection Summary layers need to be imported twice.
b) Import the data layers into the GIS software such that they appear in the order shown in Figure 3.
If you’re using ESRI ArcGIS, the GIS can be set-up simply by using the single group layer file called Infiltration_ SuDS_Map_Detailed.lyr. Either import this into an existing ArcGIS document, or double click on the file to open a new GIS document.
Alternatively, import the layer files (.lyr) from the Severe_Constraints, Drain, Stability, and Water_Quality folders provided. By using layer files, the polygons will be imported with the correct symbology. The map should be coloured via the short description attribute as shown in Table 8, such that it mirrors that shown in Figure 8 for the Drainage Summary layer.
If you import the individual layer files, please note the following:
- Where the data layer appears twice in the above list, e.g. soluble rocks appears in the first and third questions, the data layer was reclassified in two different ways to provide answers to both questions. Ensure that these layers are positioned in the correct position
- If possible, arrange the data layers in five sub-folders entitled ‘Infiltration SuDS Summary’, ‘Infiltration Constraints’, ‘Infiltration SuDS Drainage Potential’, Infiltration SuDS Ground Stability’ and Infiltration SuDS Groundwater Protection’, as shown in Figure 3
If additional data on internationally designated sites is required (special areas of conservation, special protection areas and Ramsar sites) this can be downloaded from the Joint Nature Conservation Committee’s website, http://jncc.defra.gov.uk/.
| Datasets | Score | |||
1 |
2 |
3 |
4 | |
| Infiltration_constraints_summary
Soluble_rock_constraints |
R: 156 G: 156 B: 156 | |||
| Drainage_summary
Depth_to_water Superficial_permeability Bedrock_permeability Geological_indicators_of_flooding |
R: 235 G: 240 B: 255 |
R: 199 G: 209 B: 255 |
R: 156 G: 156 B: 227 |
R:156 G: 156 B: 156 |
| Superficial_thickness | <3 m R: 205 G: 255 B: 115 |
>3 m R: 76 G: 115 B: 0 | ||
| Ground_stability_summary
Soluble_rocks
Landslides
Shallow_mining
Collapsible_ground
Compressible_ground
Running_sand |
R: 229 G: 245 B: 179 |
R: 198 G: 222 B: 133 |
R: 145 G: 163 B: 97 |
R: 156 G: 156 B: 156 |
| Groundwater_protection_summary Groundwater_source_protection_zones |
R: 245 G: 220 B: 229 |
R: 217 G: 169 B: 187 |
R: 179 G: 117 B: 143 |
R: 156 G: 156 B: 156 |
c) We recommend setting the polygon transparency to 30 per cent.
If you need support setting up the GIS, please contact digitaldata@bgs.ac.uk.
How to use the data
This section provides advice on how to use the dataset. Turn on each dataset individually, so that only one dataset and the topography layer is visible at any one time.
Using the data for spatial planning
a) Load the Infiltration SuDS Map into the preferred GIS software as described in Setting up the GIS. View the datasets in the ‘Infiltration SuDS Summary’ section, using the instructions below.
b) Pan to, or locate by coordinates, the location of interest.
c) View the Infiltration Constraints Summary layer.
If an ‘infiltration constraints’ polygon is identified at the site it indicates that there is potential for a hazard if water is infiltrated to the ground. In such areas, infiltration SuDS should only be installed if the potential for, or the consequences of, the constraint are considered not to be significant.
d) View the Drainage Summary layer to obtain a spatial assessment of the drainage potential of the ground. At the location of interest, use the cursor in ‘Identify’ mode to determine the attributes of the polygon overlaying the site. The following attributes may be encountered:
- Highly compatible for infiltration SuDS
- Probably compatible for infiltration SuDS
- Opportunities for bespoke infiltration SuDS
- Very significant constraints are identified
e) View the Ground Stability Summary layer to obtain a spatial assessment of the expected stability of the subsurface should water be infiltrated. At the location of interest, use the cursor in ‘Identify’ mode to determine the attributes of the polygon overlaying the site. The following attributes may be encountered:
- Geohazard unlikely
- Potential for geohazard
- Significant potential for geohazard
- Very significant constraints are identified
f) View the Groundwater Protection Summary layer to obtain a spatial assessment of factors that may influence infiltration SuDS design with respect to protecting groundwater quality. At the location of interest, use the cursor in ‘Identify’ mode to determine the attributes of the polygon overlaying the site. The following attributes may be encountered:
- Low susceptibility
- Moderate susceptibility
- Considerable susceptibility
- Very significant constraints are indicated
Using the data for local assessment
a) Pan to, or locate by coordinates, the location of interest.
b) View the Infiltration Constraints Summary layer in the Infiltration SuDS Constraints section. This layer is identical to that in the section above and is repeated for convenience.
If an ‘infiltration constraints’ polygon is identified at the site, turn off the summary map and turn on the component layers one at a time (soluble rock constraints, landslide constraints, made ground constraints, shallow groundwater constraints and shallow mining hazards constraints) to determine from which dataset that polygon originates. Record the information obtained. If a constraint is identified, this factor will need specific investigation and verification during infiltration system planning and design.
TIP for ArcGIS users: to easily determine the attributes of all layers within severe constraints, turn on all layers and use the ‘Identify’ tool in ‘show all visible layers’ mode when selecting the site location.
c) View the Drainage Summary layer in the Infiltration SuDS Drainage Potential section to obtain a rapid assessment of the drainage potential of the subsurface. This layer is identical to that in the section above and is repeated for convenience. This layer will give you an overview of the drainage potential of the ground, the next set of data layers identify the properties of the ground and can provide an indication of the likely limitations.
d) View the drainage component layers (Depth to Water Table, Superficial Thickness, Superficial Deposit Permeability, Bedrock Permeability and Geological Indicators of Flooding) in turn. Record the information obtained.
TIP for ArcGIS users: to easily determine the attributes of all layers within severe constraints, turn on all layers and use the ‘Identify’ tool in ‘show all visible layers’ mode when selecting the site location.
e) View the Ground Stability Summary layer in the Infiltration SuDS Ground Stability section. This layer is identical to the Ground Stability Summary in the first section and is repeated for convenience. This layer will give you an overview of the potential for ground instability if water is infiltrated; the next set of data layers identifies which ground stability issues are possibly present.
f) View the seven ground stability component layers in turn and determine whether any stability issues are raised. Record the information obtained.
g) View the Groundwater Protection Summary layer in the Infiltration SuDS Groundwater Protection section. This layer is identical to the Groundwater Protection Summary in the first section and is repeated for convenience. This layer provides an overview of the susceptibility of the groundwater to contamination if water is infiltrated (within the limitations of the data); the next set of data layers identifies which factors.
h) View the three groundwater protection component layers in turn and determine whether any water quality aspects are raised. Record the information obtained.
Worked examples
Table 9 summarises data outputs obtained from the Infiltration SuDS Map: Detailed for three locations; A, B and C, each of which represents a location where an infiltration system has been installed. The data does not state which type of infiltration system is appropriate, or, in any way, offer advice on appropriate infiltration systems, but does allow you to develop a conceptual model of the subsurface geology as shown in Figure 9.
The data outputs for Location A suggests that the site is suitable for a free-draining infiltration system, on condition that the minor stability concerns (landslides and running sand) are satisfactorily addressed. The water table is >5 m deep and the superficial deposits (which are over 3 m thick) are freely draining. The impacts of infiltration on groundwater quality should be considered via a risk-based approach; however the Infiltration SuDS Map doesn’t highlight any specific issues.
The data output for Location B suggests that the site is suitable for infiltration; however drainage is likely to be spatially variable, the water table is likely to be shallow (<3 m) and the location is within a geologically-indicated floodplain. There is also potential for, or significant potential for, a number of ground stability hazards, in particular, running sand, compressible ground, landslides, and swelling clays. Because the drainage potential of the ground underlying this site is spatially variable, the infiltration rate is difficult to predict and hence the type of infiltration SuDS appropriate at this site is highly dependent on the specific site conditions. An infiltration basin or permeable pavement may be more appropriate than a soakaway, depending on the measured infiltration rate. The shallow water table at this site should be investigated to ensure that a 1 m thickness of unsaturated zone is present beneath the base of the infiltration system. In addition, it should be noted that the site is located on floodplain deposits. In such areas, the water table may rise in response to river levels, potentially resulting in inundation of the soakaway. The impacts of infiltration on groundwater quality should be considered via a risk-based approach; however the SuDS Map doesn’t highlight any specific issues.
The data outputs for Location C suggests that the site is suitable for infiltration; however the ground is likely to be poorly draining and there are a few minor ground instability hazards that need to be addressed. At this site, the superficial deposits are anticipated to be less than 3 m thick and therefore the permeability of the bedrock should also be taken into account. At this location, both the superficial deposits and bedrock are relatively poorly draining and hence a system with an extensive surface area for infiltration, or capacity for water storage, may be appropriate depending on the measured infiltration rate. The impacts of infiltration on groundwater quality should be considered via a risk-based approach. At this site, water migrates through the unsaturated zone via fractures and intergranular flow; hence pollutant removal might be reduced compared to a case where intergranular flow predominates.
| Data layer | Location A | Location B | Location C |
| System installed | Soakaways | Permeable pavements | Infiltration basin |
| Infiltration constraints | |||
| Soluble rock constraints | Null | Null | Null |
| Landslide constraints | Null | Null | Null |
| Shallow groundwater constraints | Null | Null | Null |
| Made ground constraints | Null | Null | Null |
| Shallow mining constraints | Null | Null | Null |
| Will it drain? | |||
| Depth to water table | >5 m | <3 m | >5 m |
| Superficial thickness | >3 m | >3 m | <3 m |
| Superficial permeability | High to very high | Low to high | Low to very low |
| Bedrock permeability | High | Moderate to low | Moderate to low |
| Geological indicators of flooding | Null | Floodplain (sea) | Null |
| Will it be stable? | |||
| Soluble rocks | Null | Null | Null |
| Landslides | 2 | 2 | 2 |
| Compressible ground | 1 | 3 | 1 |
| Swelling clay | 1 | 2 | 1 |
| Running sand | 2 | 3 | 2 |
| Shallow mining | Null | Null | Null |
| Collapsible ground | 1 | 1 | 1 |
| Water quality precautions | |||
| Source protection zones | Null | Null | Null |
| Predominant flow mechanism | Intergranular | Intergranular | Superficial: Mixed |
| Made ground | Null | Null | Null |
All red text derived from Infiltration SuDS Map.
