Infiltration opportunities in urban areas
One method to combat rainfall-related waterlogging is to have rainwater drain into the soil where it falls. This is referred to as infiltration. In addition, rainwater infiltration and retention in the soil may also help to reduce the impact of drought. However, not all soil types are equally suitable for rainwater infiltration. A location’s suitability for rainwater infiltration depends on various characteristics of the soil and the subsoil. The map below shows the opportunities for infiltration in urban areas. It gives you a basic impression of the infiltration options in each neighbourhood or city.
What types of situation feature many infiltration opportunities?
The following characteristics are conducive to infiltration:
- The infiltration capacity of the soil is large, as a result of which precipitation will quickly infiltrate into the soil. This is the case with, e.g., sand and gravel;
- The soil has a large storage capacity, i.e., a low groundwater level;
- The earth’s surface does not slope too much;
- The subsoil features sufficient room for infiltration.
What types of situation feature few infiltration opportunities?
Locations with limited infiltration capacity, limited storage capacity, and steep slopes feature few opportunities for infiltration.
Furthermore, the presence of objects in the subsoil may hamper the construction of infiltration provisions. Examples of such obstructions are cables and pipes; archaeologically valuable objects; soil pollution; non-detonated explosives; and tree roots.
What does the map show?
The map gives a basic impression of the infiltration opportunities in a neighbourhood or city. The infiltration options at a location are rated as very good, good, reasonable or poor. The map is based on a combination of the location’s scores in terms of infiltration capacity, storage capacity, and surface level slope.
You may also click the three underlying maps: “Infiltration capacity”, “Storage capacity” or “Surface level slope”. For example, when clicking “Storage capacity”, the map will only show the opportunities for water storage. Each of the three characteristics is rated in three categories: 1 = poor, 2 = reasonable, 3 = excellent.
For what purposes can this map be used?
Does your neighbourhood have good or very good infiltration opportunities according to the map? In that case, chances are that you will be able to construct infiltration provisions right away, without the need for additional measures. If the opportunities are reasonable, infiltration provisions may often be constructed but will require additional measures. For example, you may need to improve the permeability of the soil or to provide groundwater drains that prevent excessive groundwater levels.
This map helps you to determine whether and where further exploration of the infiltration opportunities in your city would make sense. For example, you may use the map when drawing up an adaptation strategy.
How can local infiltration opportunities be explored further?
This national map gives a first impression of the infiltration opportunities in a neighbourhood. It also provides insight into the role that the subsoil can play in climate adaptation. The map has been developed on the basis of national basic data sets. In urban areas, these data sets are quite inaccurate. Would you like to further explore the infiltration opportunities in your city or neighbourhood? At the local level, a more specific map can be developed using local data and expertise, such as a local soil map, drilling profiles, and knowledge of fill methods used.
In addition, subsoil interventions will limit the opportunities in urban areas. Examples include subsoil infrastructure such as cables and pipes; archaeologically valuable objects; soil pollution; non-detonated explosives; and tree root systems. Mapping out such obstructions and combining the results with the map of infiltration opportunities will generate a more detailed picture. This has been done in, e.g., Leiden and Rotterdam in the purview of the “DNA of the city and its environs” project ”.
How has this map been developed?
We have used the GeoTOP and NL3D subsoil models (data sets) to determine a location’s infiltration capacity. The slope was determined using the Netherlands Current Elevation Data (Actueel Hoogtebestand Nederland - AHN). The storage capacity is based on the Mean Highest Groundwater Level, which was calculated using the National Hydrological Model.
The table below reflects how the infiltration opportunities have been estimated on the basis of a location’s infiltration capacity, storage capacity, and slope:
In areas that have previously been raised to accommodate house construction, the infiltration opportunities will move up one category because sand as a fill material increases their infiltration capacity. The surface level slope is particularly restrictive in areas with poor permeability.
In the future, the reliability of the map may be enhanced by improving the quality of the basic subsoil data. Furthermore, the method may be refined by gearing it to the characteristics of a specific area and using local, more accurate information.
