New longitudinal dams in the Waal River are expected to improve water management, navigation and ecology. TU Delft participates in the three-year-long evaluation study.
The longitudinal dam in the Waal River near the city of Tiel divide the river into two parts: a main channel (230 metres) for ship navigation and a 90-metre wide side streams along the bank. The new dam replaces the traditional row of short dams or groynes, laid out in a straight angle to the stream.
Because the longitudinal dam is in line with the current, water flows more easily past the structures, especially so in the case of high water. Their orientation thus reduces the risk of flooding.
Groynes originate from the 1880’s as a solution for the ice masses coming down the river and causing huge damages in the early nineteenth century. Rijkwaterstaat devised the transversal dams as an affordable means to sculpt the rivers into a uniform flow that would transport the masses of ice into the sea as quickly as possible.
Now that ice sheets are less common than large runoffs and better technology is available, hydraulic engineer Henk Eerden at Rijkwaterstaat designed the longitudinal dams as a solution for the 21-ste century river management.
He also designed two or three 200 metre gaps in the dams in places where gullies in the floodplains end. “I don’t design behind my desk”, Eerden said. “I just look how nature solved it and adapted to that.”
Rijkswaterstaat, who handles water management in the Netherlands, expects beneficial side effects of the longitudinal dams including banks remaining wet at low water, an improved ecology of plants and animals along the edges and less dredging of the main channel.
Waves from shipping will no longer reach the banks, meaning the water behind the dams will become much quieter than it was, providing a peaceful ecological zone for plants and animals. At least, that is what designer Eerden expects.
A research programme called RiverCare with TU Delft, Wageningen University and Radboud University Nijmegen has been set up to evaluate the effect of the first 10 kilometres of dams over the next three years.
Professor Wim Uijttewaal, who coordinates the TU Delft part of the research, said one PhD candidate will monitor water movement and water quality behind the dams. Tweaking with the gaps in the dam, the width and the depth of the inlet is expected to influence the flow and the amount of sediment of the water near the banks.
Another PhD candidate will study the influence of the longitudinal dam on the transport of sediments with a 1:50 model in the TU Delft Waterlab.
Henk Eerden (Rijkwaterstaat) is excited that his design has at least been built as a prototype and challenges master students to join his hydraulic innovation.
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