Hydrologic behaviour of stormwater infiltration systems

The hydrological behaviour of stormwater infiltration structures needs to be understood to ensure safe design and long lifetime. In co-operation with the Department of Inner City Renovation of Copenhagen Municipality two infiltration trenches constructed in a densely built-up area in central Copenhagen are equipped with on-line sensors measuring rain, runoff flow from the connected surfaces and water level in the trenches. Although the two trenches are placed close to each other they function rather differently, corresponding to effective soil permeability's of 2x10-6 m/s in one trench and a factor 10 smaller in the other. During 2¾ years of measuring 89 events were recorded, of which 7 caused overflows. Analyses of falling water tables after rain indicated slight clogging, but this effect is less important than the general lack of knowledge about soil permeability for normal design situations. The results indicate that the stormwater infiltration in central urban areas with compressed soils and backfill is more feasible than previously anticipated. Data from the first 2½ years of operation was published internationally in 1998-99.