Forward-Thinking on Flooding
When building in coastal or low lying areas, flooding is automatically an acute challenge for many new developments. Fortunately, the Jersey authorities must have given due consideration to rising sea levels and extreme weather events when they designed and carried out the ‘West of Albert’ reclamation as the JIFC site is at least 1m higher than properties on the north side of the Esplanade.
From the very early planning stages of the Jersey International Finance Centre (JIFC) we wanted to take every possible scenario into account. To do this, we commissioned independent consultants Arup to survey the land in detail, explain the potential flooding risks and suggest how best to mitigate them.
Given the JIFC development is located on the Esplanade, there are two key areas we need to take into account when making a comprehensive flood risk assessment: wave overtopping and the capacity of the local drainage network to transport the water away after this.
The sea wall at Victoria Avenue can be expected to overtop at least once a year on average. Generally, the storm drainage system or other losses will prevent this water reaching the Esplanade. However, in the more extreme cases, some of this water can be expected to drain down to the Esplanade and Gloucester Street junction and flow towards the development site.
The town marina and the La Route de la Liberation underpass are two obvious relief routes in the event of a flood. However, the floodwater would have to reach approximately +7.2 to 7.3m OD (Ordnance Datum, the measurement for altitude) to flow to these locations. Given all of the proposed buildings’ finished ground floor levels will be at or above +8.15m OD, they are high enough for the buildings to protect against flooding from either wave overtopping or sewer flooding in even the most pessimistic projections.
The threshold levels of the basement access off Castle Street is set at +8.34m OD which will also provide a good level of clearance from wave overtopping or sewer flooding.
The Flood Risk Assessment has confirmed that as a result of the JIFC site being at least 1 metre higher than the properties on the north side of the Esplanade, even in a major flood event, the site would remain unaffected. The Flood Risk Assessment concludes that even in a catastrophic event, which would see most properties on the north side of the Esplanade and Commercial Street flooded, the JIFC would have a clearance of 800mm from the highest flood water level to the basement entrances and the ground floor areas, which would provide more than enough clearance to protect the buildings.