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Woodland habitat flood defence project in Hull now underway

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Graham Mann
I have been in the Water & Waste Water industry for 30 years and formed a Water Consultancy business called H2o Building Services both myself and my team have built a wealth of knowledge and expertise Saving companies money on their Water bi
  • Woodland habitat flood defence project in Hull now underway

A new woodland habitat project is now underway in Castlehill in East Hull to help improve local flood defences through a tree-planting programme that will see thousands of tree and hedgerow seedlings established across seven hectares.

The overall aim is to develop an aquagreen that will store floodwater to the east of the city, with tree species including English oak, downy birch, field maple and black alder all due to be planted alongside different species of will for hedges, as well as seedlings for scrubland such as guelder rose, dog rose, field rose, blackthorn and hawthorn.

It’s expected that the woodland will reach maturity over the next 15 to 20 years, with species also allowed to naturally recolonise areas to create more natural woodland as well, with grassland and scrub fringes to help support biodiversity.

These plans form part of the Holderness Drain Flood alleviation scheme (FAS), with the aim being to reduce flood risk to more than 800 properties. The FAS itself is a £28 million project designed to reduce local flood risks for homes and businesses alike from the Holderness Drain.

As well as this new aquagreen flood storage area, the existing pumping station in East Hull is also being replaced to help provide a long-term and sustainable approach to water management in the catchment area.

The scheme is necessary because the Holderness Drain catchment covers large swathes of agricultural land, which drain water from the Yorkshire Wolds to the Humber Estuary.

The land is flat and often below sea level at high tide, which makes water management particularly difficult, with water emptying into the Humber very slowly with the assistance of pumping stations.

When periods of heavy rainfall are seen, water levels in the Drain can remain high for quite some time, which represents a flood risk to homes and businesses alike. This was seen in 2007, for example, with large areas of Hull and the East Riding of Yorkshire badly flooded after intense rain, with thousands of properties finding themselves inundated as a result.

The Castlehill aquagreen will be situated on land south of the old Bransholme dairy farm, reducing flood risks for those in the SUtton and North Car wards in Hull. In normal weather conditions, the site will be completely dry and will only store water during flooding events.

Once the flood peak has passed, the site will then release water slowly back into the Drain to reduce flood risks in the local neighbourhood.

But it’s not just flood risk reductions that will be delivered by the aquagreen and the region will also enjoy a range of different environmental and social benefits as a result. For example, a new area of green space will be delivered along the western boundary to provide better public access, as well as creating new wildlife habitats.

Andrew Barron, flood risk adviser at the Environment Agency, said: “Woodland habitat holds high biological value and the new hedgerow planted across the site will promote a green corridor.

“We also plan on converting some of the arable land into open grassland which also has great biodiversity value and will be excellent habitat for many conservation priority species, such as skylarks, barn owls, and butterflies.

“We had a great response from volunteers locally and will be doing more planting this month as part of our ambitions to create new woodland habitat as part of our flood defence work to better protect homes from the risk of flooding.”

Why does Hull have such flooding issues?

Hull has the highest flood risk of any UK city, followed closely by Carlisle and Lancaster, with its proximity to the River Hull, the Humber Estuary and the North Sea.

The problem is also compounded by the very shape of the land itself, with the city sat in a flat-bottomed basin surrounded by the Yorkshire Wolds and the earth mounds of the Humber Bank. This means that there isn’t enough downward gradient for water to flow through the system with the help of gravity, so Hull’s drainage is heavily reliant on pumping stations.

Surface water and sewage flow through a network of combined sewers that lead to the Saltend treatment works. Typically, all wastewater is treated here and then returned to the Humber, with storm pumps working hard during periods of heavy rainfall to pump thousands of litres of water per second out of the system and into the estuary.

The sewerage system may not have enough extra capacity to handle water runoff that drains into the sewers during periods of heavy rain, which can then lead to surface water flooding.

Another issue that Hull has to take into account is tidal surges taking place along the Humber Estuary, but the tidal flood defences and the Hull Tidal Surge Barrier have been in place since the 80s to help alleviate the risks.

Flooding of the River Hull is closely linked to the tides, which can cause the waterway to back up and, because the city is built on clay earth above a chalk aquifer, groundwater flooding can also take place during intense rainfall.

This is why projects such as this new aquagreen are so important, helping to reduce the risks to homes, businesses and local communities.

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