Water4Coast. Modelling the effects of hydraulic barriers to control saltwater intrusion in a coastal chalk aquifer

Publikation: Bog/rapportRapport (offentligt tilgængelig)

Abstrakt

Coastal aquifers are at risk of saltwater intrusion. This is a well described problem from many coastal areas and from coastal areas with limited access to other freshwater resources. Hydraulic barriers are one technique to protect the coastal aquifers from saltwater intrusion, e.g. with injection wells creating an artificial groundwater divide between the seawater and the groundwater aquifer by injection of water into the subsurface.

Groundwater models including variable density flow can be used to evaluate the effects of different types and configurations of hydraulic barriers. Geophysical data like borehole logging and geophysical surveys can be used to improve the calibration of groundwater models.

The possible effects of using injection wells as hydraulic barrier against salt water intrusion have been tested with an existing groundwater model for the Marielyst area on Falster, and with generic models.

Geophysical data have been interpreted and implemented in the groundwater model in order to improve the model calibration. The pilot point calibration technique has also been tested for the study area in Marielyst, Falster.

The results of the pilot point test calibration suggest that it could be valuable to implement the more heterogenetic distribution of hydraulic conductivities found in the pilot point calibration.

Various configurations and pumping rates for injection wells have been tested. The model studies have shown that e.g. a horizontal well with a length of 150 m injecting 1/3 of the water injected by three vertical wells with horizontal spacing of 300 m have a larger effect on preventing seawater intrusion. With a large vertical spacing between vertical injection wells a lot of injected water may be wasted. The test of different injection well setups with generic models indicates that the injection rate is of most importance in heterogeneous aquifers.

Monitoring wells should be deep enough to be able to measure the changes in seawater intrusion below the freshwater lens. Monitoring wells should have monitoring points at different depth in the aquifer.

The modelling results show a large potential of hydraulic barriers and injection wells for controlling salt water intrusion and protection of coastal freshwater resources. However, further and more detailed investigations of the hydraulic parameters and geochemistry of the Chalk aquifer on Southern Falster is needed in order to further explore and define the possible and most efficient subsurface solutions for controlling salt water intrusion around the water supply wells of the Marielyst water works.

The upper part of the exploited Chalk aquifer has been strongly affected by several glaciations and glaciotectonics, and the hydraulic properties vary significantly. Hence, focused and detailed investigations at the water supply wells are needed in order to identify the best and most efficient options for controlling salt water intrusion and protecting the freshwater resources including the design and location of potential injection and abstraction wells.

The investigations on the use of managed aquifer recharge and other subsurface solutions on Falster, Denmark initiated in the Water4Coasts project is currently continued in the ‘SubSol’ project: ‘Bringing coastal SUBsurface water SOLutions to the market’ (European Commission, 2015a) in ‘Horizon 2020’ - the research and innovation program of the European Commission (European Commission, 2015b). A project flyer, results and updates on the progress of this project can be found on the project website: www.subsol.org
OriginalsprogEngelsk
UdgivelsesstedCopenhagen
ForlagGEUS
Antal sider66
Vol/bind2015
DOI
StatusUdgivet - 19 jan. 2018

Publikationsserier

NavnDanmarks og Grønlands Geologiske Undersøgelse Rapport
ForlagGEUS
Nr.92
Vol/bind2015

Emneord

  • Denmark

Programområde

  • Programområde 5: Natur og klima

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