The Island of Dordrecht is part of the Rijnmond-Drechtsteden area that also comprises the city of Rotterdam, a number of smaller cities and the surrounding agricultural and nature areas (South-West in The Netherlands). This area is essential for the Dutch economy, mainly due to the harbour of Rotterdam. Besides that, due to its location in the estuaries of the Rhine and Meuse, it is also of great ecological importance (e.g. the Biesbosch, a Natura 2000 site).
The Island of Dordrecht (9,000 ha, 119,000 inhabitants) is part of the municipality Dordrecht. Dike ring 22 protects 7000 ha against flooding, with a safety standard of 1:2000. The historical port, parts of the historical centre and more recent housing and business areas (e.g. Stadswerven) lie outside the dike-protected area (Hegger et al 2014). The embanked area has an average height of 0 NAP. The unembanked area is situated higher (from 1.7m to 4m + NAP) and therefore less vulnerable to flooding, than the embanked area. Nevertheless, Dordrecht is generally highly vulnerable to flooding. It is enclosed by the rivers Oude Maas, Nieuwe Merwede, Beneden Merwede, Hollands Diep, Wantij and Dordtsche Kil (see figure 1). Furthermore, it is situated in a tidal area. The accessibility of Dordrecht is limited, only three bridges, two tunnels and shipping connect it to mainland. Accordingly, evacuation possibilities are limited. Only 15% of the residents could escape Dordrecht in case of flooding (Maaskant et al 2009). If a flood occurs, it will be deep and fast. Under present circumstances, the expected number of victims in case of flooding will be 300 and the material damage is expected to be 7 billion Euros. The probability of flooding is expected to increase due to sea level rise, an increase in extreme river discharges and land subsidence and an increase in economic value (Hegger et al 2014).
Table 1: overview of FRM measures in Dordrecht
|Flood prevention||Flood defence||Flood mitigation||Flood preparation|
Prohibition of construction in certain areas, e.g. in the South, or close to the dike
No urbanization byond the Zeedijk and Zuidendijk
|Primary flood defence (dike ring 22 and Maeslantkering), secondary flood defences||E.g. Stadswerven: floor levels (0 m – 5 m + NAP), most important living parts of houses on the first floor||Evacuation exercise (Voorstraat) and Flood Risk Management Plans|
Table 1 gives an overview of the FRM measures present in Dordrecht. The city of Dordrecht is protected flood defence structures: the Wieldrechtse Zeedijk and the Zuidendijk (both old, secondary dikes) (Waterplan Dordrecht 2009). Furthermore the construction of the Maeslantkering in the Nieuwe Waterweg has decreased the designated water level. Some houses function as flood defence themselves (e.g. the Voorstraat, see figure 2) (Hoss 2010, 26). To ensure safety, movable flood risk management barriers have been introduced to close off the entrance to the houses. The primary flood defence ‘Voorstraat’ meets the legal standards applicable to primary flood defences in 2014, but will probably not meet the legal standards for primary flood defences in 2020 (Kelder, E., Gersonius B. and Hulzebosch, M. 2013). This part of the flood defence has to be heightened by 75 cm to meet the standards for the next century (Pol 2012, Opvijzelen Voorstraat Dordrecht, Een innovatieve oplossing voor de hoogwaterveiligheid in Dordrecht (Kennis voor Klimaat), however, due to the historical location this is not feasible.
Movable flood risk management barriers in the Voorstraat during inspections (source: www.watericonen.nl)
Additionally, it was decided that urbanisation should not develop further than the Zeedijk and the Zuidendijk, which lies a little more north in the Eastern part of the dike ring. The preservation of the agricultural landscape is the main reason for this agreement (Hoss 2010, 119).
 Extended Third National Assessment Primary Flood Defences 2014