Geological Society of America

2 Hydrogeology I: Water Resources and Water Balances

Sunday, 9 October 2011
8:00 AM - 12:00 PM
Room M100FG

GROUNDWATER-RIVER WATER INTERACTIONS IN THE CATCHMENT OF THE RIVER VANTAA AND ITS TRIBUTARIES, SOUTHERN FINLAND

Paper number: 2-1
Program: Technical Sessions
Time: 8:00 AM – 8:15 AM

Authors

Anne Brita Rautio Presenting Author
University of Helsinki, Helsinki, N/A
Kirsti Inkeri Korkka-Niemi
University of Helsinki, Helsinki, N/A
Anna-Liisa Kivimäki
) Water Protection Association of the River Vantaa and Helsinki Region, Helsinki, N/A
Juha Karhu
University of Helsinki, Helsinki, N/A
Maria Nygård
University of Helsinki, Helsinki, N/A
Kirsti Lahti
) Water Protection Association of the River Vantaa and Helsinki Region, Helsinki, N/A
Veli-Pekka Salonen
Univ of Helsinki, Helsinki, N/A
Heli Vahtera
) Water Protection Association of the River Vantaa and Helsinki Region, Helsinki, N/A

Abstract

Management of water resources in Finland has traditionally focused on either surface water or groundwater. However, surface and groundwater are normally interacting with each others. The research was focused on the River Vantaa and its tributaries ranging 360 km. The River Vantaa is one of the raw water reserves for Finland’s capital area (ca. 1 million people). In addition, within the River Vantaa drainage basin there are 25 important aquifers used by the local municipalities or water companies. The River Vantaa drainage basin is rather flat-lying or smoothly undulating glacial landscape. Aquifers are related to glaciofluvial sand and gravel deposits, i.e. eskers or ice-marginal end moraine complexes. The scope of this research was to identify the sections and branches of river systems where significant hydraulic connection between groundwater and river water exists and to evaluate the impacts of water exchange on water quality in the discharge/infiltration zones.

Field methods used in this study involved aerial infrared photography, thermal profiling of river sediments with multilevel sediment temperature probe and in situ water quality and water temperature measurements. Based on aerial infrared photography and site specific measurements, hundreds of groundwater-surface water interaction sites along the 360 km-long river system could be located. In narrow and shallow tributaries, stream flow rate and groundwater discharge were directly measured with a flow meter.

Water fluxes between groundwater and river systems were identified and quantified with water quality data (O₂, pH, EC, turbidity, COD_Mn, phosphorus and nitrogen compounds), main ionic concentrations, SiO₂, DOC and stable isotopes (δ¹⁸O, δ²H). A significant difference especially in SiO2, stable isotope ratios and NO3 between groundwater and surface water was observed. Therefore, the chemical and isotope data can be applied to confirm the water exchange.

At this stage we can conclude, that groundwater discharge zones have a larger effect on water quality and quantity in the River Vantaa and its tributaries than has thus far been acknowledged. In some groundwater-surface water interaction sites there is a risk of river water infiltration into an aquifer during peak flow and flood periods, resulting in deterioration of groundwater quality.