Identifying controls on shallow groundwater levels in a lowland urban catchment: a scenario-based approach

Shallow groundwater levels in lowland catchments are highly sensitive to geological heterogeneity, climate variability and human activities. The town of Bylderup-Bov (southern Jutland, Denmark) is characterized by persistently high groundwater tables, especially in winter months, resulting in recurrent basement inundation and excessive inflow of groundwater into the wastewater system. After a major renovation of the sewer system in 2014-2016, groundwater intrusion into the sewer system remains substantial, leading to wastewater volumes up to five times higher than expected. 

This study investigates the controls on shallow groundwater dynamics in and around Bylderup-Bov using a catchment scale hydrological modelling approach evaluating the effects of different hydrogeological and anthropogenic factors. To do this, a suite of scenario simulations was used to quantify the effects of (i) local stream geometry, levels and resistance, (ii) drainage efficiency and depth, (iii) changes in groundwater recharge related to urban development, (iv) groundwater abstraction, (v) restoration of surrounding lowland peat areas, and (vi) projected climate change.

Model results show that drainage depth and drainage efficiency are the most influential parameters controlling groundwater levels within the urban area of Bylderup-Bov, lowering the groundwater table by up to 50 to 75 cm during critical winter periods. Stream depths affect groundwater levels by lowering levels up to 10 to -30 cm over large parts of the town, indicating strong lateral groundwater surface–water connectivity controlled by geological layering. In contrast, climate change scenarios based on three regional climate models indicate only modest increase in mean groundwater levels (+0 to +10 cm by 2071–2100), suggesting that recent groundwater rise is unlikely to be primarily climate-driven. Scenarios introducing enhanced groundwater recharge through local infiltration measures further exacerbate high groundwater conditions during already critical wet winter periods.

The findings demonstrate that shallow groundwater dynamics in the study area, are governed primarily by anthropogenic drainage and subsurface connectivity rather than climate change alone. Detailed urban hydrological modelling provides valuable insights for identifying effective mitigation strategies, avoid maladaptation, and supporting groundwater management under future climatic and land-use change.