Rain gardens, infiltration trenches, permeable pavements contribute to mitigate flood risk in Santorso Municipality

One of the most interesting Natural Water Retention Measures carried out by the LIFE BEWARE project is the one located in the cemetery’s parking lot in Via Prati, in Santorso municipality. The main objective of the intervention is mitigating the impact of the flooding events that affect the southern part of the parking lot and the surrounding areas, due to the water run off coming both from the surface of the parking lot itself and from a close large agricultural area (about 5 hectares).

In order to efficiently manage high volumes of outflow from such a large area, multiple water retention measures have been applied jointly. Two rain gardens have been created in the southern area od the parking lot; whereas in the northern area, a draining trench and a portion of permeable pavement have been made (Recycle® di Favaro1, https://favaro1.com). The two rain gardens, connected in series by an overflow pipe, allow managing (accumulating and infiltrating underground) all the outflows produced by the parking lot’s waterproof portion. On the other hand, the infiltration trench allows to collect and inject part of the discharges coming from the upstream agricultural area, significantly delaying the arrival of the outflow to the parking lot. In addition to reducing the impermeable surface of the parking lot, the permeable pavement acts in conjunction with the infiltration trench, increasing its accumulation and infiltration capacity, mainly thanks to the large drainage foundation layer on which the paving blocks are laid.

For more detailed information about the intervention, download the complete project!

Permeable pavements

These are paved systems made with high porosity blocks or laid in such a way as to favor the infiltration of water, allowing it to percolate and reach the underlying layers and also performing a partial function of retaining pollutants.

Types and construction measures: Generally, these pavements are made of two different layers: the one on the surface is made by a permeable pavement whose function is to absorb and let drain rain water on the underneath layer; the lower one, placed between the pavement and the ground, is usually composed by a layer of washed gravel or gravel which has the function of facilitating the infiltration of water into the soil.

The surface layer can be realized using asphalt, porous materials or prefabricated alveolar elements in stone or synthetic material, porous concrete blocks, or blocks with increased spacers. The market offers many solutions depending on the needs and application type.

Functions: rainwater infiltration; groundwater recharging; reduction of the rainwater flow speed above ground; prevention of water stagnation, that can cause discomfort during thunderstorms; reduction of the heat island effect.

Costs: the installation costs may vary depending on the type of used pavement and on the surface to be paved; on average they are between 20-40 €/sqm for the cheapest solutions (grassed gratings in plastic or concrete), up to 100-150 €/sqm for the most performing solutions (including installation).

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