Last month, Cindy Quik received the Hissink Prize for her research into the old river course of the Overijsselse Vecht. She received a sum of money and a certificate for her well-executed master's thesis on this river, the largest of the small Dutch rivers. Quik studied old maps and dated the drifting sands near the banks of the old meanders. She discovered that, among other things, the drifting sand on the banks had led to the river course having changed so much.
Why do some meanders of the Overijsselse Vecht have such special shapes, Cindy Quik wanted to know. The old river bends are very long and winding. The most erratic, with a large 'pendulum' or amplitude are located between Ommen and Hardenberg.
The master's student of soil geography and surface dynamics selected two study areas in this region, with the atmospheric old Dutch names Junner Koeland and the Prathoek. Quik dug into the archives to find historical maps. By comparing the old plans, she saw how both meanders started to meander more over time.
Drifting sand monsters
To learn even more about the areas, she took core samples. Sand grains from the ancient sediments were analyzed in the lab using the technique of optically stimulated luminescence dating (OSL), which allows very accurate determination of the last exposure to light – and thus the last transport of the grain. In the case of Quik's excavated drifting sand samples, it came down to an accuracy of about twenty years. Very accurate when you consider that these are recent, medieval drifting sands. This is a special example of looking back in time in detail.
Dating the drifting sand samples and dating the expansion of the meanders was so important in order to be able to correlate the two processes (shifting sand activity and changes in the river course) chronologically. To correlate them, Quik formulated two hypotheses. The first hypothesis assumes that the drifting sand clogged the river so that the water had to flow in a different direction. This is how the shape of the river changed.
The second hypothesis assumes a more gradual effect of drifting sand activity. The drifting sand did not end up in the river itself, but on the banks. This caused the vegetation to disappear. The plant roots, which previously provided stability to the banks, also died. As a result, the banks collapsed. If such a process of bank erosion lasts long enough, the river's pendulum pattern changes.
Combination man and nature
Based on the collected OSL data, Quik concluded that the last five hundred years have been the most important for the meandering of the Overijsselse Vecht in her study area. By combining the data from the core samples and historical maps, it appeared that drifting and meandering had occurred simultaneously.
Drilling in the field provided necessary additional information. These showed that there is a sharp boundary between river sediments and shifting sands. This indicates that the river channel has eroded the banks covered with drifting sand. The second hypothesis was therefore more obvious.
Opinions are divided about the very beginning of drifting sand activity:was this caused by man or by nature? Quik thinks it was a combination of human activity (cutting sods down to the bare ground – the cover sand) and many storms during the Little Ice Age, a cold period from the sixteenth century.
River Landscape
It is no coincidence that Quik chose the old meanders of the Overijsselse Vecht for her master's thesis. She is a fan of the Dutch river landscape and was therefore looking for a master project related to rivers. The large bends, seen upstream from Ommen, have long been a mystery to landscape morphologists.
“What I particularly liked about this research was that I started with the idea of the relationship between shifting sands and meandering. But gradually I saw more and more the interaction between the physical landscape and the role of humans in it”, says Quik.
Restore Dutch rivers
She is very happy that she received the prize from the Association of Soil Experts during the symposium 'Soils and dune dynamics', on 11 November in the Amsterdamse Waterleidingduinen. The Hissink Prize – a sum of 500 euros – is awarded annually, alternately to university and higher professional education students. Her supervisors from Wageningen UR, Jakob Wallinga, specialist in OSL technology, and Bart Makaske, geomorphologist, sent her thesis to the assessment committee.
The knowledge from her research can be used in the recovery of Dutch rivers, including the Overijsselse Vecht. The Vechtdal near Junner Koeland is a so-called 'stream valley grassland', a type of river landscape that is characterized by the special plants and animals that live there.
Since 1990, the Vechtdal has been part of the National Ecological Network, a network of nature reserves in our country. The government wants the Overijsselse Vecht to regain the appearance of a so-called 'semi-natural lowland river'. What does that mean in concrete terms? Quik:“Then the landscape is arranged in such a way that the river can swing freely again. You then get completely different banks, where natural erosion has free rein.”
Cindy Quik. Historical morphodynamics of the Overijsselse Vecht:Extreme lateral migration of meander bends caused by drift-sand activity? Wageningen UR, June 2016.