Swale and infiltration basins calculator
Its primary function is to determine the required area and parameters of swales and infiltration surfaces that enable effective infiltration of stormwater into the ground, while in the case of swales also providing temporary retention. These solutions support the natural water cycle, reduce stormwater discharge into drainage systems, and help minimize the risk of overloading stormwater infrastructure.
Infiltration basins serve an infiltration function only and represent the solution closest to natural conditions. They are typically permeable, vegetated areas located adjacent to impervious surfaces such as roads, sidewalks, squares, parking lots, terraces, or courtyards.
Swales are shallow, properly shaped depressions designed to allow stormwater infiltration into the ground while simultaneously providing temporary surface retention. Their filling depth does not exceed 30 cm.
The calculator enables the selection and sizing of solutions based on key design parameters such as: reduced area Fz [m²], risk factor, rainfall model (e.g. PANDa), rainfall duration [min], rainfall probability [%], available infiltration area [m²], and soil infiltration coefficient kf [m/s].
The application is available in Poland and Germany.
Proper Sizing of Swales and Infiltration Basins
How can swales and infiltration surfaces be correctly sized?
To perform the calculations, the following data is required:
- risk factor,
- design rainfall frequency,
- reduced area,
- assumed flow time through the channel [5–30 min],
- available infiltration area,
- soil infiltration coefficient.
Built-in Verification Checklist
The tool supports the design process through a checklist of key site and soil-water conditions (including groundwater level, soil permeability, distances from buildings, landslide risk, and presence of contaminants). This allows for a quick assessment of whether infiltration solutions can be applied and helps identify potential design constraints.
Results of the Swale and Infiltration Basins Sizing
Based on the provided information, the calculator determines:
- the minimum required storage volume based on the PANDa rainfall model,
- total inflow to the swale,
- total outflow from the swale.
The calculator also proposes a list of recommended solutions and allows users to review example implementations.
Note: The calculator, similarly to the guidelines on which it is based, assumes complete management of the calculated stormwater flow within the swale through infiltration into the ground supported by temporary retention. In engineering practice, when sufficient space for a facility meeting these assumptions is not available, designers should not abandon such solutions entirely.
Using this calculator, it is also possible to design a retention–infiltration basin, which differs from a swale mainly by allowing a filling depth greater than 0.3 m. In such cases, depending on the basin location and maximum water depth, additional safety considerations for the surrounding area should be taken into account.
Another practical way to use the calculator is to assess how much stormwater can be managed by a swale occupying all available space and equipped with an emergency overflow to a storm sewer system (if available nearby) or with overflow directed to another discharge location.
