The PhD study presents research results from two re-established Danish riparian zones, Brynemade and Skallebanke, located along Odense River on the island Funen, Denmark. The overall objectives of the PhD study have been to improve the understanding of flow and transport in riparian zones. The methodology focuses on; construction of field sites along Odense River, understanding flow and transport, and performing numerical/analytical model assessments of flow and transport. An initial 2D simulation study was performed with a conceptual setup based on the Brynemade site. Through a series of 2D model scenarios with changing conditions for flow (steady state with no flooding or transient with flooding), hydrogeology, denitrification rate, and extent of flooding it is demonstrated how flow paths, residence times, and nitrate removal are affected. With this previous conceptual models on the hydrology of riparian zones are extended by accounting for the effect of flooding and a key result is that flooding enhances nitrate removal given the right hydrogeological characteristics. Moreover the re-established riparian zones were characterized to understand the effects of flooding on subsurface hydrological flow paths by combining a number of field investigation methods and 2D modeling for the Brynemade site. Field investigations included: (1) hydrogeological characterization using wells, slug and infiltration tests, (2) geophysical imaging of the subsurface using Multi-Electrode-Profiling, (3) and easurements of discharge to the river by seepage meter and river bed temperatures. The numerical model was used to simulate how observed dynamic seasonal flooding affects groundwater flow paths, residence times, and formation of zones with flow stagnation, all of which are key aspects in evaluating the capacity of a riparian zone for removing nitrate. In non-flooding periods groundwater flows horizontally and discharges directly to the river. During periods with flooding parts of the groundwater is forced upwards through the peat layer and causes flow in the area beneath the flood to be more stagnant. Discharge through the overlying peat ranged between 25% and 37% of the total incoming groundwater depending on the hydraulic conductivity of the peat. Finally we model the effect of flooding on the attenuation of nitrate for the Brynemade site. Model setup includes both the dynamic seasonal flooding and labdetermined
denitrification rates on a soil core collected within the Brynemade riparian zone.
In the end we test this scenario with no flooding simulating what effect and change the reestablishment of the riparian zone has resulted in. In all we find that groundwater-surface water interactions in these zones play a significant role in attenuation of nitrate and in the amount of nitrate the river receives.