Horsens town is threatened by floods, because a major part of the town centre is lower than 1.5 meter above the normal sea level in Horsens Fjord. With rising sea levels and now with more water from watercourses in the hinterland due to increasing precipitation and more powerful downpours, there is a great need for securing the lowest lying parts of the town against flooding, cf. Figure 24 and 25.
Figure 24: Picture of flooding at the outlet of Bygholm Å and in Bygholm Park in December 2013
Figure 25: Map of Bygholm catchment area
The aim of C14 is to secure Horsens town centre against flooding when there is a storm surge and/or extreme flows in the three watercourses Dagnæs bæk, Bygholm and Hansted Å, which all run through the town. It requires overall considerations and scenarios of flooding for the fjord, watercourses and sewer systems, and holistic planning and coordination in relation to the port area Nordhaven, which is being converted into a residential, recreation and commercial area. An initial project was carried out by Horsens Municipality (ends April 2016) forms the basis of C14 with the purpose to carry out a detailed project design for flood proofing of Horsens town. The initial project, hereafter the 2016 project, included a simple watercourse model and involves an outline of proposed solutions to prevent flooding from precipitation, watercourses and sea levels under saturated and stationary conditions, respectively. The possible solutions are outlined for short-term flood proofing at a level off 1.8 meter above normal sea level, and a politically adopted long-term flood proofing at a level of 2.6 meter above normal sea level, se example in Figure 24. The results of the ‘2016 project’ proposes water retention in the catchment area and dike solutions using sluices and pumps in Horsens town. However, political reality are likely to change, and there has been discussions on establishing a small-scale barrier solution on the sea floor in Horsens’ outer fjord, inspired by the Mose Project in Venice. The ‘2016 project’ sets the basis of C14.
Action C15 supplements action C14 by its nuanced approach to the drainage of water, so that the production potential of farming is developed, and the towns do not end up functioning as delay reservoirs, when the watercourse has high flows. We expect that the two actions can greatly benefit from each other. The aim of C14 is furthermore to provide inspiration to the development of other solutions in other coastal towns that are threatened by rising sea levels and/or water from the hinterland catchment area.
Figure 26: Consequence map for flooding with preliminary outlined proposal that will protect Horsens town in the short term?, equivalent to flood-proofing at a level of 1,8 meter DVR90. The floof proofing will be established using a high tid wall earth dykes and mobile water tubes.
C14 will be contain the following activities: preparation of tender material and tender phase for external expert assistance for step 2 to 5; provision of knowledge in the form of status, data collection and model set-up; scenario calculations and initial stakeholder involvement; preparation of proposals and stakeholder involvement; preparation of project design and invitation to tender material for contractors; flooding related to watercourse Store Hansted Å and the northern part of Horsens town.
The project area covers Bygholm Å catchment area and extends to HEDKOM and Vejle Municipality, cf. Figure 27. Bygholm Å catchment area drains into the watercourses that flow through Horsens town centre and out to Horsens Fjord. The main focus is on Horsens town centre and covers the port, parts of the inner town and Bygholm Park, which will be flooded with a 5-year storm surge event in 2050 (2.4 m DVR90), cf. Figure 28.
Figure 27 All of the Bygholm Å catchment area with flow paths on terrain.
Figure 28 Flooding in Horsens town with a 5-year storm surge event in 2050, equivalent to 2.4 m above normal sea level (Horsens CCA plan p. 34).
Phase 1: Activity 14.1-14.3
Phase 2 and beyond: Activity 14.4-14.5