The Waiwhero wetland (16 ha) is one of the largest wetlands in the Rosedale Hills, 35 km north-west of Nelson, New Zealand. It has an extensive cover of Salix fragilis L. (crack willow) and has been hypothesised to be a source of groundwater recharge for the Moutere aquifers, an important local groundwater system. However the wetland could also be a groundwater discharge zone, because of the geological boundary that it straddles. The overall aim of this study was to determine the direction of groundwater flux of the wetland by measuring the water balance, with particular emphasis on the transpiration rates from the crack willow trees. The average daily transpiration (measurement was for 230 days) of crack willows in the wetland (6.4 mm/day) was close to twice the potential evapotranspiration (PET) for grassland (3.9 mm/day). The highest measured willow transpiration rate was 12.4 mm/day and the lowest was 0.8 mm/day. High transpiration from crack willows was due to the horizontal energy fluxes (advective energy), tree physiological characters and high soil water content. The study established that the wetland is a groundwater discharge zone with, on average for the two summer periods (2008 and 2009), the net groundwater discharge being 4.8 mm/day. The daily water balance results between two major rainfall events showed that the initial discharge source was from the surrounding hills and later stabilized at around 6 to 14 mm/day. It was believed to be a contribution from the shallow and deep aquifers or a combination of local region inflow and aquifers. The water balance showed that the main loss of water through the hydrological system of the wetland during summer was from the high transpiration of willows (7.7 mm/day). The extent of water savings estimated for the 16 ha wetland through a hypothetical situation of willow removal, and the assumption that it is filled with open water without any canopy cover, was 688 m3/day. However this water savings rate if applied to a large area of crack willow stands would be quite high. On similar lines it is important to understand the transpiration rates of other wetland tree species in New Zealand. This information would help in preparing regional council plans for the introduction of tree species in the wetland for better management of the water resources and sustainable ecosystem management.

Groundwater interactions at a regional scale are of great importance to characterize subsurface flow processes. Extensive researches have been conducted previously to determine the main factors controlling the regional implications on groundwater flux circulation. Groundwater circulation occurs due to variation in the groundwater table (hydraulic gradient) across the spatial scale. Previous research highlighted the correlation between groundwater table with both topography variation and the recharge from precipitation. This study aims to highlight the impact of these boundary conditions. Five catchments located across different regions of Sweden with different topographical, hydrological, and meteorological properties considered for this study: Bodalsån, Forsmarksån, Tullstorpsån, Sävaån, and Krycklan. Relevant data were collected and numerical models were set up in steady- state conditions for each of these catchments, using 3D Multiphysics COMSOL. Models were set up for both of the boundary conditions, using 10 m grid resolution.Groundwater flux profiles along the depth of the catchments were obtained as a result, in which significant differences were observed. This was associated predominantly with the difference in the nature of the topography, the slope and soil permeability in these regions. The data thus collected and the models so established have increased the understanding in these regions from a research perspective. / En ökad förståelse för hur grundvatten interagerar med ytvatten är av stor betydelse för att karakterisera underjordiska flödesprocesser. Omfattande undersökningar har tidigare genomförts för att bestämma de viktigaste faktorerna som styr de regionala konsekvenserna för cirkulationen av grundvattenflöde. Grundvattencirkulation uppstår på grund av variationer i grundvattentabellen (hydraulisk gradient) över den rumsliga skalan. Tidigare forskning belyste korrelationen mellan grundvattentabellen med både topografivariation och laddning från nederbörd. Denna studie syftar till att belysa effekterna av dessa gränsförhållanden. Fem avrinningsområden placerade över olika regioner i Sverige med olika topografiska, hydrologiska och meteorologiska egenskaper som beaktas för denna studie: Bodalsån, Forsmarksån, Tullstorpsån, Sävaån och Krycklan. Relevanta data samlades in och numeriska modeller sattes upp under steady-state-förhållanden för vart och ett av dessa avrinningsområden med användning av 3D Multiphysics COMSOL. Modeller konfigurerades för båda gränsförhållandena med 10 m nätupplösning. Grundvattenflödesprofiler längs avrinningsdjupet erhölls som resultat, där signifikanta skillnader observerades. Detta var främst förknippat med skillnaden i topografins natur och lutningen i dessa regioner. De data som samlats in och de så etablerade modellerna har ökat skapat en värdefull grund för vidare hydrologisk forskning i dessa regioner.