Browsing by Author "Brander, Mikko"

Discharge measurements were conducted on four separate sites as part of a joint project between The Water Protection Association of the River Vantaa and Helsinki region and Helsinki University Department of Geosciences and Geography. Results from earlier studies from this project were used to identify potential groundwater-surface water interaction sites at the River Vantaa drainage area. Areas where groundwater was discharging into the river were identified mainly by means of aerial infrared photography over different river sections of the Vantaanjoki drainage area. Evidence of river water infiltrating into the aquifer at these same locations were obtained from water quality studies conducted at groundwater intake plants situated at close proximity to study sites. Discharge measurements were used to confirm and to study groundwater-surface water interaction at selected sites and to compare the used methods in different environments and at river channels with varying characteristics. Studies were conducted on four rivers located at Tuusula, Hyvinkää and Riihimäki municipalities across River Vantaa drainage basin. Study sites were located at sections of the river where the river cuts through locally important aquifers of Jäniksenlinna (River Palojoki), Hyrylä (River Tuusulanjoki), Herajoki (River Herajoki) and Hyvinkää (River Vantaan). Municipal groundwater intake plants were located at close proximity to every study site. Studies were conducted using two different methods. The FlowTracker is designed for wading discharge measurements on smaller river channels and was used on three sites (Jäniksenlinna, Hyrylä and Herajoki). The RiverSurveyor is better suited to larger river channels and was used on two sites (Hyvinkää and Herajoki). Studies were conducted during maximum spring discharge in April and during minimum summer discharge in July. FlowTracker could not be used at Hyvinkää study site due to River Vantaa being too deep even during the summer. Differences of the study sites and their river channels were used in comparing the practicality of the two methods at different circumstances. Locations of the measured river cross sections were chosen so that the first cross section was located before the groundwater discharge area as identified from results from previous studies. Following cross sections were the located in the middle and after this area. Changes in the measured river discharge at each cross section were used to estimate the amount of groundwater discharging into the river or river water infiltrating into the aquifer. Study results indicate that, especially during the low flow season, the accuracy of the used methods is sufficient to differentiate the changes in the river discharge that are caused by groundwater discharging into the river or river water infiltrating into the aquifer. Results also indicate that these processes can greatly influence river discharge on a relatively short distance. Studied rivers can also switch from a gaining stream to a losing stream and then again back to a gaining stream on a very short distance.