HOBE - the Danish hydrological observatory - Denmark

The HOBE experimental catchment is located in the western part of Denmark. The topography of the catchment is relatively flat. The surface elevations in the eastern part of the catchment are about 125 m above sea level at the Jutland ridge and gently decreasing to sea level elevations towards the coast. Alluvial outwash deposits in the form of sand and gravel dominate the central part of the catchment. Towards east, glacial deposits of moraine till are present with a higher content of clay. Also the remnants from the Saale glaciation have higher clay content and the dominant sediment type at these locations is clayey sand. Overall the top sediments are highly permeable with little water retention capability and the stream flow is therefore dominated by groundwater inflow. Based on a classification of the topsoil four soil classes can be identified in the catchment. The by far most dominating soil type is fine/coarse sandy soil. The Quaternary deposits have a thickness less than 50 m in the eastern and central part of the area increasing up to 250 m towards west. The Quaternary deposits are underlain by Miocene sediments in the form of alternating layers of marine, lacustrine and fluvial deposits forming layers of clay, silt, sand and gravel. Further below thick layers of Paleogene clay are found with little permeability and thus acting as a lower impermeable boundary for the aquifer systems. The sand and gravel layers from the Quaternary and Miocene periods form interconnected aquifer systems. The land surface of the catchment is predominantly agriculture and due to the sandy soil characteristics extensive irrigation of the agricultural crops takes place. Based on satellite data the land-use distribution is estimated as follows: grain and corn (55%), grass (30%), forest (7%), heath (5%), urban (2%) and other (1%). The climate of the observatory is of maritime origin and influenced by weather systems coming from the Atlantic Ocean. The weather conditions are variable with frequent precipitation. The prevailing winds from west lead to relatively mild winters and cool summers. The mean annual precipitation is about 1050 mm/year. It varies over the season with highest amounts in the months of October-December and lowest in the months of April-May. The mean annual temperature is 8.20C. The highest mean monthly temperature is in August (16.50C) and the lowest in January (1.40C). Precipitation in the form of snow is highly variable from year to year; in some years, no snowfall occurs and in others, it may stay on the ground for months.