Using LECA® LWA to Prevent Flooding

flood water storm management

Using LECA® LWA to Prevent Flooding

Why do we need to manage rain fall? - flood water storm management

Climatic changes followed by increased rainfalls are transforming our traditional ways to prepare for extreme weather. Focus has shifted from simply coping with regular weather events to how we can reduce societal risks associated with climate change. Preparing for consequences caused by extreme weather and flood water storm management are on the political agenda, and most governments have started ambitious programs to deal with the challenges. As an increased amount of precipitation and flood water within the built environment must be handled, new innovations and solutions can be seen worldwide.

Due to urban densification, stormwater runoff in larger cities can cause major problems for the existing infrastructure. Runoff water accumulates rapidly when natural areas are replaced by impermeable surfaces, such as asphalt and roofscapes. Additionally, excess runoff results in proliferation of pollutants and pathogens that may pose a public health risk. In order to increase city resilience against stormwater, local councils usually encourage local water management efforts and have initiated water management strategies or introduced incentives or regulations for the reduction of overflows of drainage- and sewer systems.

A governing parameter for circular economy is the capability to manage water by using sustainable and ecological methods with small environmental footprints.

A healthy water cycle can be maintained by implementing measures that simulates mechanisms found in natural environments, such as water detention, water retention and infiltration, in forests and grasslands.

water management with LECA LWA
Applying water detention to water run-off

Managing stormwater by simply draining the water through pipes or combined sewer systems is an outdated method. Nowadays, limitations in geography, infrastructure and wastewater treatment have dramatically increased the cost of building new reservoirs and drainage pipes. Although many alternative solutions have become available, identifying the best and most sustainable water management practice is a challenging for both city and community planners.

Leca LWA can be used to manage the rainwater from a catchment. Water interacts with Leca LWA in a way that allows the material to provide water detention. In addition, Leca LWA can facilitate infiltration processes of water into the ground. By using Leca LWA, suitable areas can become functionalized reservoirs and temporary storage places for catchment areas.

Storm Water Management Flood Prevention
Applying Leca LWA to a real water management project

Leca LWA can help cities fulfil their climate adaptation strategies – and by using water management areas as recreational spaces, a community can build healthy and aesthetically pleasing surroundings that promote wellbeing and biological diversity.

Assessments of stormwater runoff reduction, flood risk and pollution control should all be included in the cost-benefit analyses, as well as the added benefits of having appealing outdoor areas.


Leca Storm Water Management
Leca Lightweight Expanded Clay Aggregate

Flood water storm management is usually defined by local requirements. Developers and land owners are obliged to follow regulations, but physical limitations, such as topography, ground conditions and meteorological trends are equally important when choosing a water management design.

water run off storm water management for flooding
In order to adapt to the changing climate, new and innovative methods must be employed to manage water runoff.


Leca LWA has the ability to delay water runoff by a principle known as water detention. Proper detention provides a steady and manageable flow of water and reduces the risk of flooding. Leca LWA has a highly porous internal structure and an abundance of voids between the grains. This property allows Leca LWA to detain a flow and thereby reduce the peak intensity of runoff from an area. Thus, Leca LWA will diminish the intensity of water from severe storms and moderate loads through slow release of water during and after a serious down pour.

Without a detaining sublayer the value added from a vegetated or permeable surface can be limited, but with Leca LWA, the flood prevention properties of these surfaces can be maximised. Leca LWA can provide a dependable and robust sublayer, and its intrinsic water detention works regardless of ground infiltration.


Ideal ground conditions allow for infiltration of surface water to the groundwater level. Leca LWA has many air-filled voids and pores that act as temporary storage space for water. After adsorption, water can seep into the ground by infiltration or be discharged to a nearby deposit. By facilitating infiltration, a more manageable quantity of water is achieved through steady volume reduction of the total runoff.


Leca LWA is great for drainage applications. There are ample voids for water to flow between the grains and fillings. Leca LWA can divert water to more suitable locations, for example if used in construction of swales or closed drainage ditches. If the preservation of natural drainage lines of an area is important, i.e. the preferred pathways of water, Leca LWA can be installed as a load bearing backfill material without disrupting existing drainage plans.


The following examples illustrate how Leca LWA can be used in constructions as a subsurface detention medium. A solution can be constructed as an open-ended system by using the inherent detention capability of Leca LWA. Alternatively, a detention solution can be constructed with a restricted outlet for water. Assessments of components should be done independently and a suitable runoff coefficient for the complete solution should be estimated.

flood water storm management Example 1

water storm water managment

This illustration shows how rainbeds, swales, green roofs and other vegetated areas could be constructed with Leca LWA as a sub-surface. A minimum of 100 mm of Leca LWA is recommended, and a thicker layer will contribute accordingly. After complete submersion, Leca LWA will rapidly regenerate as it releases water. When the topsoil is saturated, the Leca LWA continues to detain and drain as long as water reach the layer. For all constructions, Leca LWA will prevent waterlogging, provide temporary storage and detain of water.

flood water storm management Example 2

storm water management

A permeable surface area with paving stones for pedestrian traffic is good use of available space. The finest fractions of Leca LWA are suited for setting of pavers and tiles, and in some cases a sand support layer can be omitted. Instead a plastic grid or a net can be used as stabilization for the top pavers. Such constructions are often referred to as blue-grey solutions. They are ideal for creating a variety of open areas, such as on flat rooftops, above underground parking facilities and as patios in gardens with shallow bedrock. The sublayer is shown in the example, and if needed, an extra layer of thermal insulation could be added.

flood water storm management Example 3

storm flood water management


And finally.......because of the highly porous structure and large surface areas of the crushed grains, Leca LWA is perfectly suited for treatment of rainwater. Leca LWA can physically, biologically or chemically bind both dissolved and solid particles. Expanded clay has long been used for water treatment purposes - offering long term resistance to clogging. The local environment can be protected by immobilization and removal of pollution that would otherwise end up somewhere else. Leca LWA as a filter solution has low estimated operating costs and a long life span.

Try our Leca® Water Management Online Calculator

leca water management calculator
Assess how LECA LWA can provide effective water management and flood prevention


We have a team of representatives in the UK with extensive experience and knowledge on utilising Leca® Lightweight Expanded Clay Aggregate on a variety of Geotechnical Civil Engineering projects.


For a free quote and consultation on Leca® Lightweight Expanded Clay Aggregate contact Leca® UK:

TEL: 0844 3351770 


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