In addition to several test sites in the Netherlands, a test site was installed in Werder, northeastern Germany by Hölscher Wasserbau GmbH. The test arrangement consists of 8 hw-dsi-infiltration units with total depth up to 25.0 m below ground level. On the test site, rain water is collected on a flat roof next to the test site and directly led to the infiltration field. In total 73.2 m3 were infiltrated into the groundwater during the observation period of 1 year. About 20% of the total precipitation fell in June 2023, 11.5 m³ during one rain event within 24 h hours.
In summary, water levels within the infiltration units do not rise more than 1,5 m above resting water level. All infiltration units show water levels that go back to resting water level right after the rain event stops. This is an indication that after one year of operation, all infiltration units still have a good hydraulic connection to the aquifer and divert the rain water instantly to the groundwater. This points out that the flow capacity of the treatment unit, consisting of a coarse sieve and a gravel filter, has not decreased within the past year.
In summary, the monitoring data showed that rain water infiltration can succeed even in location with not ideal conditions such as inhomogeneous extension of hydraulic conductivity and low ground water levels.