Improve/Create water storage

Improve/Create water storage

Category 01. Water flow quantity improvement

General description

Water flow and the flow regime can be altered by different factors such as changes in land cover, soil structure and compacting, loss of floodplains and wetlands, and stormwater runoff from urban areas. Loss of water retention combined with accelerated runoff typically increases the frequency and magnitude of flood peaks and reduces the availability of water to streams during low flow (base flow) periods (Saldi-Caromile et al., 2004).

Preferably, a more natural flow regime can be restored by increaseing water infiltration and retention at the catchment scale by e.g. changes in land cover and floodplain restoration (see measure water retention) since this addresses both, increaed peak flows and reduced base flows. An alternative local end-of-pipe solution to reduce peak flows caused by stormwater runoff are stormwater rention and detention basins, which are of special importance for small rivers where single effluents may already cause massive erosion and affect water quality (please note: polders are not covered here since they are mainly used for flood protection and not for river restoration).

Applicability

Detention basins are dry between floods, fill and store water during floods, slowly drain when water levels in the receiving channel recede, and hence attenuate the runoff and reduce peak flows but have very limited effects on water quality.

Retention basins have a permanent pool of water (like ponds) and, except for the runoff exceeding the capacity of the basin that drains to the channel, the water is stored permanently. Besides reducing peak flows, retention basin have a larger effect on water quality through sedimentation of pollutants and uptake of nutrients by plants. However, due to the water permanently stored, they have a lower capacity and hence, have to be larger. In contrast to infiltration basins, they are usually not explicitly build for groundwater recharge but may increase the risk of groundwater contamination.

It is important to only reduce the peak flows and to ensure that low flows and environmental flows are maintained in receiving channels.

Expected effect of measure on (including literature citations):

• HYMO (general and specified per HYMO element)
• physico � chemical parameters
• Biota (general and specified per Biological quality elements)

Pressures that can be addressed by this measure

• Hydrological regime modification
• Groundwater abstractions
• Surface water abstraction

Case studies where this measure has been applied

• Regge Velderberg
• Uilenkamp - Meander reconnection
• Sweden- Restoration of the Freshwater Pearl Mussel and its habitats (LIFE04/NAT/SE/000231)
• Polder Ingelheim – Restoring former floodplains (INTERREG Sustainable Development of Floodplains)
• Bemmelse Waard – Restoring former floodplains (INTERREG Sustainable Development of Floodplains)
• Hondsbroeksche Pleij – Restoring former floodplains (INTERREG Sustainable Development of Floodplains)
• Narew river restoration project
• Warta Middle River Valley