Smart-SWS: Combining flood protection and drought prevention -- Concept and site selection criteria

Climate changes in the anthropocene lead to an increase of rainfall
intensity while the infiltration capacity of the soil is reduced
during extended dry periods. As a consequence surface runoff increases
and groundwater levels are reaching all-time lows: even close to the
alps water becomes scarce. Keeping precipitation water local is a must
and one option is to direct flood water into local aquifers
(Flood-MAR). This comes with a number of challenges, first of all, a
pronounced asymmetry of floods with very high volume flow in very
short times, and droughts requiring long-term storage. From a
hydrogeological perspective, infiltration of flood waves requires
extremely well-connected groundwater bodies with high hydraulic
conductivity contrasting with slow groundwater flow required for
long-term storage. Geotechnical measures like sheet-pile walls or sand
injections can be used to control the release of groundwater back to
the river. The infiltrated water has to be conditioned to meet
hydrochemical and sanitary criteria. In contrast to conventional
managed aquifer recharge (MAR) the time frame for treatment is
extremely limited. As floods are not occurring regularly, any treatment
system has to work autonomously and to be insensitive to long
downtimes between flooding events. The decision tree for the
selection of suitable sites starts with the occurrence and extent of
flooding events (regular flooding events with volumes less than
roughly 1 million m³), the morphology of the site (leveled with
groundwater levels below river water), and the hydrogeological
properties of the adjacent aquifers (ideally porous aquifers with high
specific yield and hydraulic conductivity). Further criteria are land
use (agriculture preferred), infrastructure (access to the site, no
subsurface installations), protection zones (groundwater, habitats,
...) and ecosystem services, and risk factors in the catchment
(hazardous substances, extended mobilization of soil during flooding,
...).  Three sites have been selected as pilot sites and will be
presented.