New plans for the restoration of the Main dyke
09.08.2019 – The Main dyke between Carl-Ulrich-Brücke and Friedhofstraße needs to be renovated and raised - this has been known for a long time. Eight years ago, the Office for Urban Planning, Transport and Construction Management submitted the first plan for the renovation of the Main dyke to the Darmstadt Regional Council (RP). A year ago, the regional president rejected the planned lowering of the dyke at the castle for safety reasons.
"Good things come to those who wait. This wisdom applies to the renovation of the Main dyke," says Paul-Gerhard Weiß at the presentation of the new project planning for the upgrading of the Main winter dykes. It was not easy to reconcile the sometimes differing interests of the citizens and the objective requirements for safety and practicability, said the head of the construction department. At the same time, the refurbishment had to remain affordable. He considers the new planning, which takes into account both the desire to bring the city center and the Main River closer together visually and the safety requirements of flood protection, to be a success. The proposal had already been widely coordinated in advance. The city parliament is due to vote on the project resolution and the amended planning approval documents at the end of August, after which the documents will be submitted to the regional council.
Deputy Head of Office Sigrid Pietzsch recalls the intensive public participation that preceded the preparation of the planning approval documents in 2011. The planned lowering of the dyke at Schloßstraße was intended to take account of the citizens' wish to enable a view of the Renaissance castle from the Main and vice versa from Schloßstraße to the water. After the city planning office submitted the planning approval documents to the RP, a further five years passed for investigations and expert opinions on groundwater hydrology, which the RP objected to.
After the second hearing on the planning approval procedure was held in October 2017, the planners received a decision from the RP in April 2018 rejecting the planned lowering of the dyke in the Schloßstraße area. The reason: there were too many risks that would lead to a catastrophe if they all came together, which could not be completely ruled out. If heavy rainfall also occurred during the so-called 200-year flood, the Mainstrasse would be flooded, which would prevent the construction of the mobile protective wall. In this case, several thousand residents would have to be evacuated. "In principle, we could have carried out the renovation of the Main dyke except for the lowering of the dyke at Schloßstraße," Pietzsch recalls. However, the city wanted to tackle the renovation as a whole and applied to the RP in September 2018 for a postponement in order to revise the planning.
Barrier-free access and a clear view of the Main
The dyke gate on Schloßstraße is to be rebuilt and the passageway widened from the current 5.50 to 15 meters and raised from the current 2.20 to 2.50 meters. In addition, access to the dyke promenade, which is currently only possible via two staircases, will in future also be possible via a barrier-free ramp on one side. A public toilet facility is to be built under the stairs. In the event of flooding, a mobile dam wall is planned in front of the entrance to the dyke on the Mainstrasse side.
The new plans also include a new solution for access to the Main at Herrnstraße. Citizens and the Local Agenda had also called for better accessibility to the Main. Here, the steep stairs are to give way to a barrier-free combined solution consisting of stairs and a ramp. "The structure will be 65 centimetres high so that you can easily look over it," explains Pietzsch. At the same time, it is a threshold against flooding and a mobile dam protection can be easily installed. "The new planning not only takes safety into account, it also improves the connection for pedestrians and cyclists, increases the quality of stay and is barrier-free," summarizes the deputy head of department.
Costs and time schedule
Although the newly planned measures are cheaper, the office estimates that the renovation costs will be higher than seven years ago. Pietzsch explains this with the rise in construction prices and the increasing ancillary and landfill costs. Overall, the urban planning office is expecting costs of almost 19 million euros, around 6.7 million euros more than in the 2012 submission. "The good news, however, is that today not only 40 percent of the eligible costs are subsidized, but at least 80 percent," says the urban planner. For this reason, the city's share of the costs has increased only slightly from just under 8.6 to around 8.7 million euros. The amount also includes the demolition of the dilapidated sandstone retaining wall of the inner-city section of the dyke and the new concrete construction with sandstone cladding, which is estimated at 1.8 million euros.
At the end of August, the city council resolution on the planning approval procedure and project resolution should be passed and the planning approval documents submitted to the RP. In the fall, the city planning office would like to inform citizens about the current status of the dyke renovation at an information event. As the plans have already been agreed with the RP in advance, the office expects the RP to approve them quickly by the end of this year so that the tendering process can then begin. The urban planning office currently expects construction to begin in spring 2021 and take three years.