Stormwater Attenuation Tanks

FLI Precast Solutions design and manufacture award-winning modular precast stormwater attenuation tanks.

We are the proud founders of the most recognisable precast attenuation tank on the market.

These attenuation tanks are the most widely used flood alleviation methods across the UK and Ireland. At FLI Precast Solutions, we have a proven and unrivaled track record of over 1,900 attenuation tank installations.

Our attenuation tanks are a robust answer to flood prevention and have been protecting communities for almost 20 years.

The FLI Precast Solutions stormwater attenuation tanks are recognised throughout the industry as the precast tank of choice by Designers, Engineers, and Local Authorities.

Southern water logog
Scottish Water
Northumbrian Water
National Grid

What is an Stormwater Attenuation Tank?

An Attenuation Tank is a large container that is designed to collect and store excess rainwater. The water is then held in the underground Attenuation Tank structure and is released in a slow and controlled manner using a mechanism called a hydro brake.

Often the water collected in the Attenuation Tank is released into a water source such as a river or reservoir.

This design provides the ability to reduce potential flooding in a specific area.

History of Stormwater Attenuation Tanks

Attenuation tanks or “Carlow Tank” as they are also known, are the industry standard for stormwater attenuation. FLI has played and continues to play a vital role in the stormwater attenuation sector.

From creating the design of the original “Carlow Tank” to being a leading provider of attenuation tanks almost 20 years later. With an emphasis on climate change and unpredictable weather patterns, there has never been a greater need to protect our homes, businesses, and environment.

Severe storms and flooding can have long-term effects on buildings and infrastructure. It can also have a huge financial impact. Therefore, it is important that flood alleviation methods are put in place.

Why Choose FLI Precast Attenuation Tanks?

FLI Precast Solutions have a long history of designing and installing attenuation tanks across Ireland, the UK and internationally.


FLI Precast Solutions have over 1,900 installations of bespoke precast attenuation tanks.


Over 20 years of experience providing attenuation tanks  across Ireland, the UK, and internationally


We are a trusted and chosen precast concrete provider for many companies and local authorities alike.

Our team of experienced designers and engineers prepare detailed designs before any work begins on our factory floor. Once the client is satisfied with their design, we make the bespoke precast elements in our factory in Ballon, Carlow, Ireland

These pieces are made to the highest standard and once ready, are sent to the site where our experienced on-site team installs them safely and efficiently.

FLI Precast’s attenuation tanks designs have the flexibility and can be used in a wide range of projects such as:

  • Residential Developments
  • Distribution Centres
  • Warehouses
  • Industrial & Medical facilities

The versatility of our designs offer the perfect solution for any ground conditions or loading. Whether it be green spaces, under roads, ports, or runways, FLI’s tanks can be adapted to suit any setting.

Our attenuation tanks also come with a long design life. They are easy to maintain with comprehensive access arrangements. Our tanks come with nationwide approval for adoption by all of the water authorities.

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Case Study

Bulkhaul Ltd

Bulkhaul is a business dedicated to the global transportation of bulk liquids, powders, and gases. FLI Precast’s engineers worked closely with Lynas on the hydraulic drainage design, but what set this project apart was the need for a loading capability, the like of which other manufacturer’s products just couldn’t provide. With containers potentially being stacked three high, the point loads above the tank were far in excess of anything you would typically find on other sites, but FLI Precast rose to the challenge.
This project was completed on time and on budget.
Project Highlight

This project shows the versatility of the FLI Precast Attenuation Tank offering. It highlights our tank in a non-residential setting and illustrates our design and engineering capabilities to cater for bespoke projects.

Main Contactor

Main contractor

FLI Precast Attenuation Tank Specifications

At FLI Precast Solutions, our designs are bespoke and made to order depending on the project requirements.

However, our attenuation tanks range in depths from 0.4m up to 5.0m deep. These can be configured to suit any size between these specifications. This offers unrivalled versatility to our clients.

Features of an FLI Precast Attenuation Tank

FLI Precast Solution Attenuation Tank includes several features such as:

Benefits of using a FLI Precast Attenuation Tank

Using an FLI Attenuation Tank provides benefits such as:

FLI Precast Solutions manufactures all our solutions to be compliant with the specified design codes and client requirements.


We have the ability to adjust our concrete mix to suit chemical classification and surface finish.

How do Attenuation Tanks work?

The purpose of an attenuation tank is to capture rainwater from surface runoff and to store it temporarily. It is then released slowly and in a controlled and managed manner to restore equilibrium with the environment prior to any development taking place.

Once the surface water is captured and retained, the risk of flooding is averted and assets are protected.

During spells of heavy rainfall, the Attenuation Tank will hold water within its system and will therefore minimise the risk of localised flooding.

At FLI Precast Solutions, we create bespoke and cost-effective Attenuation Tank solutions for our clients.

How do you size an Attenuation Tank?

Before installing an Attenuation Tank, there are various factors that must be considered. FLI Precast Solutions create bespoke solutions for clients building all products off-site to reduce time and increase efficiency.

When deciding on whether an attenuation tank should be installed and what size you may need, consider some of the following:

Geographical Location

Where your project is located will have a significant impact on rainfall levels throughout the year. As we supply Attenuation Tanks to clients across several countries, this is an aspect we must pay close attention to.

The below table highlights the average rainfall in different locations across Europe in both inches and millimeters per month in 2021.

City Average Annual Rainfall (Inches) Average Annual Rainfall (Millimeters) Days of Rainfall
Dublin 2.98 75.8 129
Birmingham 2.68 68.1 125
Glasgow 4.43 112.4 170
Amsterdam 33.0 83.8 132

The above table illustrates how much rainfall levels can vary by location. Geographically, these cities are not huge distances apart but have varying levels of rainfall.

This is important as the higher the average rainfall levels in a location, the larger the Attenuation Tank that will be required.

Storm Regularity

How regular, or irregularly an area is affected by storms is an important factor. If there are frequent storms with heavy rainfall, additional measures may need to be put in place.

In 2021 alone, Italy, Austria, and Germany were hit with significant storms and huge amounts of rainfall. This caused widespread flooding and damage.

Estimating the potential number of storms within a location will help determine what size Attenuation Tank may be required.

Climate Change

In recent times, rainfall levels have become more unpredictable. 

The Met Office has stated rainfall levels are increasing globally and are also becoming more intense. 

Therefore, products such as Attenuation Tanks are playing an increasingly important role.

Allowable release levels

If an Attenuation Tank is connected to a local water source, there will be restrictions on the level of allowable outflow.

The level of outflow must be calculated and released at a correct rate in order to avoid any potential flood risks.

Why use an Stormwater Attenuation Tank?

The introduction of stricter legislation means that local authorities and planning bodies place an important emphasis on flood prevention.

Using an attenuation Tank allows the site to deal with excess water in a controlled manner and redistribute it over time back towards a local water source.

Attenuation Tanks are preferred over alternative methods such as soakaway crates. Using an Attenuation Tank gives you the ability to store large quantities of water from a wide surface area and redistribute it over time. Flooding can cause significant financial losses and damage. Therefore, it is vital that flood prevention methods such as Attenuation Tanks are utilised where possible.

Interactive Attenuation Tank PDF

Feel free to use our interactive attenuation tank data sheet below

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Looking to discuss an Attenuation Tank?

At FLI Precast Solutions, we have the capability to create bespoke designs to meet our clients needs.
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