Case Study: Blue Drempel

In the last 20 years, the ten worst international flood events alone claimed over 50,000 lives, affected one billion people and resulted in damages in excess of $165 billion. Storm events both worldwide and in the UK are occurring with greater intensity and frequency over the past decade and many local boroughs are declaring a state of climate emergency. The failing of recently constructed flood defenses such as those in Cumbria have exposed a growing uncertainty in weather patterns and a weakness in relying on traditional flood defenses alone.

In 2009 the Author co-published The LifE  ‘Long-term Initiatives for Flood-risk Environments’ Project for Defra marking a fundamental shift from traditional flood prevention towards a non-defensive approach; based on ‘Making Space for Water’ – working with natural processes to provide space for the extent of water to expand during times of flood. Where housing could not be located within areas of least vulnerability then the authors defined appropriate building typologies and mitigation measures.  The LifE approach encourages developments that are more adaptable to future flood risk changes. The general principles of LifE can be used on all sites.

In 2013, Baca Architects’ built the UK’s first Building Regulations compliant amphibious house. The amphibious dwelling located in Marlow, Buckinghamshire has undertaken several float tests with a vertical travel distance of 300-500mm; and awaits its first full flood event. Baca have since built a second amphibious home in Salcombe, UK.

The practice envisages large communities that are holistically planned to be better prepared for flooding and climate change. Dwellings will be carbon neutral and organized around multifunctional landscapes that will help control surface water flooding or act as a large flood storage area. New communities will be made up of streets of flood resilient dwellings located on the highest ground with amphibious homes adjacent to waterbodies subject to flooding.  The long-term goal is to design communities that function as normal, preserving continuity of daily life during both droughts and floods. Our intention, through our research and built work is that we can demonstrate that the future is already here.

So how will they look? And what are the basic urban planning principles that set out these settlements?

The site strategy is firstly to reduce the vulnerabilities within the site and then to designate zones of risks to which appropriate house typologies can be assigned.

Residential development is identified by the Environment Agency as more vulnerable use. However, this classification is attributed to static residential buildings with fixed floor levels and assumed low levels of protection. Principle floors including kitchen, living, bathrooms and importantly no bedrooms are typically permitted below 1 in 100 flood event level, plus an allowance for Climate Change and freeboard. In the UK it is also a planning presumption that the occupants can maintain safe access and egress to Flood Zones 1 and 2 during a flood event.

An Amphibious house, dynamic in its nature, does not have these constraints. They can rise to maintain the principle floor level at a safe distance from floodwaters. Consequently, one might suggest that as long as the condition of safe access and egress can be met, then amphibious homes could be permissible in Flood Zone 3a; unlocking many brownfield sites. Additionally, it should be noted that in Holland there is a planning acceptance that owners can stay within their homes for up to a week, if the home is designed to provide sanitation, fresh water, and power during flood events.

If the Dutch approach was adopted in the UK, then floating homes could be located within the river course (FZ3b), amphibious homes in Flood Zones 3a and FZ 2, flood resilient homes in FZ 2 and traditional homes (that can be designed to be retrofitted) in flood zones 1. Housing layouts assume that they follow basic urban principles of active street frontages, appropriate densities as set out in local plans, provision of public and private amenity, and overlooking considerations.

Once the housing typologies are established, then space for Green infrastructure is identified and incorporated in the heart of the development and the amount of hard infrastructure is reduced to a minimum.

Swales are planned tangentially to the water’s edge to gather water from higher ground (as well as the river / waterbody) into potential flood storage areas. By setting aside flood storage areas (which are landscape elements), a larger proportion of the site is available to be at less flood risk than before and is zoned for development.  The swales complement the grading of the site into different levels and act as wayfinding markers from the site perimeter to the water’s edge. Additionally, they provide a green space, which can incorporate leisure and play spaces when flood risk is low.

“Our books have become primary reading sources at a number of universities around the globe. This will be our ultimate legacy as these ideas are adopted’.​

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Authors: Richard Coutts and Matthew Sharman-Hayles

An amphibious house rests on the ground on fixed foundations but whenever a flood occurs, it rises in its dock and floats there buoyed by the floodwater.

“Blue Drempel” or Blue Threshold –is a non-defensive planning strategy that locates architectural housing types according to flood risk: floating within the river; amphibious; elevated; resilient (dry proof and wet proof) to traditional to correspond with diminishing flood risk; and to connect these with the least amount of road and servicing infrastructure to allow as much space for natural landscaping. This landscaping is multi-functional, it accommodates places for play and sustainable urban drainage that is designed to anticipate flooding; it keeps water away from housing for as long as possible during a flood event. In the event of the landscaping being breached during an extreme flood event then the resilient and adaptable measures of each architectural housing type help keep occupants dry and safe.

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Summary

The soft (green) infrastructure is complemented by hard elements that combine road access with flood defence. The ‘drempel’ is a multi-functional element, which provides a threshold between areas, which can flood, and areas, which are protected. In a light floodwater is absorbed within the swales and held back by the ‘blue drempel’.

Road layouts, which are slightly elevated, provide safe access and egress for pedestrians and emergency vehicles in worst-case scenarios to higher ground. In the absence of being able to escape to less vulnerable areas and it is important to provide areas of ‘safe haven’. These can be community buildings.  The roads also contain all the servicing and utilities, ensuring robustness and a heightened level of protection.

Gardens

The site development integrates infrastructure (soft and hard) with the original site contours and defines the geometry of the housing layout within which amphibious, elevated and traditional house types can be laid out.

This approach provides a cohesive, legible and resilient neighbourhood.

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