A conceptual model for groundwater discharge to a coastal brackish lagoon based on seepage measurements (Ringkøbing Fjord, Denmark)

• Published in: Hydrological processes Vol. 32; no. 22; pp. 3352 - 3364
• Main Authors: Duque, Carlos, Haider, Kinza, Sebok, Eva, Sonnenborg, Torben O., Engesgaard, Peter
• Format: Journal Article
• Language: English
• Published: Chichester Wiley Subscription Services, Inc 30.10.2018
• Subjects: Brackish water; Coastal lagoons; Coastal morphology; Coastal zone management; Coasts; Electrical conductivity; Electrical resistivity; Fjords; Fluxes; Fresh water; Freshwater; Freshwater environments; Groundwater; Groundwater discharge; groundwater discharge to lagoon; Inland water environment; Lakes; Landscape; Measuring instruments; Offshore; Profiles; Saline water intrusion; Saline-freshwater interfaces; Salt water intrusion; Salt water-freshwater interfaces; Saltwater intrusion; Seasonal variability; Seasonal variation; Seasonal variations; Seasons; Seepage; seepage meter; Shorelines; Spatial distribution; Spatial variability; Spatial variations; spatial–temporal variability; Variability; variable salinity; Water discharge
• ISSN: 0885-6087; 1099-1085
• DOI: 10.1002/hyp.13264

Groundwater discharge to a brackish lagoon (Ringkøbing Fjord) was quantified with seepage meters along four transects perpendicular to the shore during four seasons in 1 year. The objectives were to develop a conceptual model of the spatiotemporal variability of seepage and how landscape characteristics and saltwater intrusion affect seepage fluxes. The electrical conductivity of the groundwater was measured in vertical sediment profiles up to 3 m below the lagoon bed to assess the effects of the freshwater–saltwater interface location on flux distribution. The main differences compared with existing theoretical models are a lower discharge near the shore line (0–5 m) and two discharge peaks more offshore (15–20 and >25 m), which allowed the development of a conceptual model that is different from the classical concepts introduced for marine or lake environments and which can be representative of other similar areas. These differences are explained by the vegetation and organic material deposition in the near‐shore environment reducing discharge, the presence of the saline wedge leading to upward flow, and the increase of recirculation of brackish water due to wave pumping in areas offshore most exposed to the wind. The seasonal variability in discharge is smaller than the spatial variability between and within transects along the shoreline. Based on the conceptual model, fresh water discharge in a 20‐m‐wide fringe was calculated to be between 66 and 388 L·day−1·m−1 shore line, corresponding to a difference of a factor of six due to the variations in coast morphology and local characteristics of the area. The seasonal changes were responsible for changes of only 8% to 75% depending on the location.