So here it is. The most researched and measured stream in the world. A phenomenon in the hydrology world, Roel Dijksma assures me. A teacher of hydrogeology, he is my guide this Monday afternoon. He comes here often; this is where for 30 years he taught Wageningen and Delft students how to take and interpret hydrological measurements. On closer scrutiny it is no more than a tiny rivulet. The Hupselse Beek gets its name from the settlement of Hupsel between Groenlo and Eibergen, a stone’s throw from the German border. We are here to celebrate a special anniversary. Wageningen has been studying this stream for exactly half a century. Which is precisely the age of the Hydrology and Quantitative Water Management chair group where Dijksma works.
Little stream
The Hupselse Beek is part of the catchment of the Berkel, which flows into the Ijssel at Zutphen. Research focusses on the stream’s catchment, an area of 6.5 km2. It all started with an extreme drought year in 1959, says Dijksma. ‘It was so dry that there was no way the Pleistocene sandy soils could provide enough water for livestock and crops. Grass died off and maize stopped growing. Livestock was even transported to the west of the country because there was nothing for it to eat.’
The drought led to an increased interest in hydrology. The province of Gelderland wanted to know how much water agriculture really needed. Dijksma: ‘Drought was acknowledged as a cost for the fi rst time. The Leerinkbeek project was set up in collaboration with Rijkswaterstaat and the regional water authority; it was completed in 1965.’ Meanwhile Unesco launched the International Hydrological Decade in 1964, and a network of experimental stream catchments was designated to provide a boost for research. In the Netherlands the Hupselse Beek was chosen and Wageningen got involved through the then Laboratory for Hydraulics and Drainage at Duivendaal.
There is no question of drought today though. Just as Dijksma turns the white WUR bus into Professor Casimir road, it starts raining heavily. The dirt road fills up with puddles in no time. The source of the Hupselse Beek is somewhere off to the right in the maize. The water collects in a small drain. We have just visited the meteorological institute KNMI’s Hupsel weather station. With 22 mm of rain this is the wettest place in the country, as we can see later on the weather data map on the KNMI’s website.
Layer of clay
‘The Hupselse Beek is a typical example of a catchment in the higher-lying parts of the Netherlands,’ says Professor Remko Uijlenhoet (Hydrology and Quantitative Water Management) the next day in his office in Lumen. ‘Which means the sandy soil in the east and south of the country.’ The catchment is quite well drained: the altitude ranges goes from 35 to 22 metres above NAP [‘normal Amsterdam water level’].’ ‘Hupsel is an interesting choice because there is a poorly draining layer of clay underneath the catchment which pretty much closes off what’s below it,’ adds Uijlenhoet. ‘That make it possible to monitor water volumes, as very little water drains away.’ The stream and its catchment have been intensively monitored since 1965. ‘This was the first catchment in the world where all the components of the water balance were measured,’ claims Uijlenhoet confidently. ‘The whole hydrological process from rainfall to drainage. We now know which route the water takes and how substances dissolved in it are distributed.’
The stream can cope with today’s rainfall easily. The rain causes a marginal peak in runoff, as the website of the Rijn and Ijssel water authority shows. But this is nothing compared to what happened here fi ve years ago on 26 and 27 August 2010. Extreme quantities of rain fell in the eastern Netherlands on those days and fl ooded parts of the Hupselse Beek catchment. The KNMI’s weather station in Hupsel registered 16 mm of rain in 24 hours. According to statistics this happens less than once in a thousand years at any given spot. The runoff from the stream rose within one day from 4 to 5000 litres per second. A lucky day for hydrologists. For the fi rst time it was possible to study in detail how the catchment reacts to a flash flood if this kind.
Over the years several hydrologists have received doctorates for studies of the Hupselse Beek. The latest was Claudia Brauwer, who developed a runoff model for rainwater and got her PhD last year. The model, with which the chair group is taking the market by storm, is called Walrus: the Wageningen Lowland Runoff Simulator. The model maps the whole journey from rainfall to runoff and is already being used by five water authorities and a couple of big consultancy fi rms, says Brauer.
Bikes on the roof
Halfway through the Hupsel fi eld trip Dijksma parks the bus at ’t Eibernest campsite, which has for years been the base camp for fi eld work courses in Hydrology, Water Quality and Meteorology. A popular outing for 70-80 students every year. About 50 from the BSc in Soil, Water and Atmosphere, and the rest come from other programmes or from elsewhere. Delft, for example, or VHL university of applied sciences. Students really look forward to this course. Of course that is partly because of the social side of it.’ By that he means a week in the holiday houses at ’t Eibernest. The house rules have already had to expand to three sides of A4. You have to do something if you don’t want to be taking bicycles off the roofs all the time. Be that as it may, the fi eld work course won an Excellent Education Award last year.
But Hupsel research is not in full fl ood on its fi ftieth anniversary. In fact the stream of research is running a bit dry at the moment. ‘Hupsel needs a new boost,’ thinks Uijlenhoet. ‘In the 1970s and 80s a lot of measurements were taken of evaporation. In the 1990s the emphasis was on water quality. The measurements that are still taken now are limited to routine work by the water authority and the KNMI. Dutch hydrology organizations are keen to make it a well-monitored research area again. But that requires money and that is a problem.’