Stormwater management in urban areas using dry gallery infiltration systems

The increase in the frequency of extreme precipitation events due to climate change, together with the continuous development
of cities and surface sealing that hinder water infiltration into the subsoil, is accelerating the search for new
facilities to manage stormwater. The Canary Islands (Spain) are taking advantage of the knowledge acquired in the
construction of water mines to exploit a novel stormwater management facility, which we have defined as a dry gallery.
Dry galleries are constituted by a vertical well connected to a horizontal gallery dug into highly permeable volcanic
layers of the vadose zone, from where infiltration takes place. However, the lack of scientific knowledge about these
facilities prevents them from being properly dimensioned and managed. In this work, we simulate for the first time
the infiltration process and the wetting front propagation from dry galleries based on a 3D unsaturated flow model
and provide some recommendations for the installation and sizing of these facilities. The fastest advance of the wetting
front takes place during the earliest times of infiltration (<2 h), with plausible propagation velocities and infiltration
rates higher than 1000m∙d−1 and 2m3∙s−1. As time progresses, the propagation velocity and infiltration rate decrease
as a consequence of the hydraulic gradient attenuation between the gallery and the aquifer. Therefore, stormwater infiltration
is a highly transient process in which a sizing underestimation of 100%may be committed if unsaturated conditions
or geological configuration are neglected.