ASK THE EXPERT: The Humber Estuary – A London Based Solution?

ASK THE EXPERT: The Humber Estuary – A London Based Solution?

Helena Du-Roe, Senior Environmental Hydrologist at Enzygo, discusses the importance of the Humber Estuary, with a short discussion on how to defend the Humber Estuary from future flood risk.

The North Sea flood of 1953 caused widespread flooding across the east of the United Kingdom (UK), the Netherlands and Belgium due to the rare combination of a high spring time and a severe windstorm. The event caused unprecedented flooding and significant damage, with the response of the UK being to construct storm surge barriers on the Thames Estuary and on the River Hull, with the Netherlands constructing the Delta Works to protect against future events. These extreme events are rare but are becoming more common, with their impacts becoming more severe.

The Humber Estuary drains a catchment area of over 24,000km2, which accounts for approximately 10% of the total land surface area of the UK into the North Sea. From the start of recent records, in 1862, six of the ten wettest years across the UK have occurred since 1998. The number of days where rainfall totals exceed 95% to 99% of the 1961-1990 average has increased in the last decade. This trend points to an increase in the frequency and intensity of rainfall across the UK, leading to an increase in flood events.

Coupled with sea levels that have risen by around 16.5cm since 1900. With levels now rising by up to 5.2mm a year, the chance of coastal flooding is an increasing threat. This is exposing more parts of the coast to powerful storm surges and winds, damaging the environment, thus defining a greater need to protect those locations identified at risk of flooding.

Compared to the Thames Estuary, the Humber Estuary is still undefended and a large-scale defence needs to be considered for the estuary to protect it from future flooding, due to its status as one of the most important estuaries in Europe for nature conservation. It is estimated that up to 1.26 million tonnes of sediment may be present in the water in the estuary, whose source emanates from the boulder clay cliffs along the Holderness coast. The deposited sediments maintain the estuary’s important habitats such as, mudflats, sandflats and saltmarsh. Any defence infrastructure would need to cause minimal disruption to the existing process already occurring.

With over 40,000 shipping movements each year, the Humber ports are the UK’s largest by tonnage for both import of raw materials and components and export of UK manufactured products. Its ports and wharves account for 14% of the UK’s international trade. Industries along the estuary include, chemical works, oil refinery complexes and power stations. The need to protect the estuary for the importance of trade near equals that of the environment.

There are currently three strategic approaches detailed by the Environment Agency to managing the Humber Estuary for the next 100 years to mitigate against flooding to the area, which consists of either managing the tide by using a combination of improvements to existing flood defences and acquiring additional storage areas. Inclusion of an improved level of personal and property resilience would be required to adapt to rising sea levels and spring high tides.

Alternatively, adapting to the tide by continuing to improve flood defences in areas of high importance (i.e. raising their height) combined with implementing resilience measures is a potential option. A retreat of defences inland may be required to generate additional capacity for flood storage and manage the future large-scale flooding of land adjacent to the estuary.

The construction of a tidal barrier on par with the Thames Barrier or the Maeslantkering (a storm surge barrier protecting the Port of Rotterdam) could be the future solution. Any project of this nature would come at a considerable cost and due to the width (14km at its widest point) of the estuary, the defence would need to be four times larger than the existing Thames Barrier. According to the Environment Agency as of 2022, the cost of this size of defence would be close to £13 billion.

Though there has been a historic investment of £150 million into the defences along the Humber Estuary, there is only a certain amount of time before a more robust long-term solution needs to be implemented. The uncertainty that the rate of the changing climate, along with social, economic and political factors pose greatly impact which strategic approach will be adopted. A holistic approach is one that is favoured to manage the increasing flood risk posed to the Humber Estuary by 2100.

Here at Enzygo we have the expertise available to assess flood risk at a site-specific scale to assess the most appropriate property level protection to mitigate against flooding.

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