Newsletter December 2023

December 1, 2023


Linear Drainage Systems

Linear drainage systems are designed to effectively channel surface water along a linear path, preventing water accumulation and minimizing the risk of flooding.  In highway and drainage engineering, these systems are indispensable for managing stormwater runoff, preventing erosion, and ensuring the overall stability and safety of the road network.

There is an enormous range available, from simple polymer concrete units for private driveways, to stainless steel units for medical or food preparation areas, to combined kerb and drainage systems.

Selecting the appropriate linear drainage solution involves careful consideration of various factors, ensuring optimal performance and longevity. Here we´ll briefly expose 4 factors that will help you to choose the right linear drainage system for your project:

Grating Types:

  1. Mesh Gratings: Ideal for pedestrian areas, these gratings provide efficient water drainage while preventing debris accumulation. The open structure allows for easy cleaning and maintenance.
  2. Heelguard Gratings: Specifically designed to prevent high-heeled shoes from getting caught, these gratings are suitable for areas with a mix of pedestrian and light vehicular traffic.
  3. Solid Top Gratings: Engineered for heavy loads and vehicular traffic, these gratings offer a robust surface, ensuring durability and load-bearing capability.

Loading Classes:

Linear drainage systems are categorized into loading classes based on their capacity to withstand different loads. These classes range from A15 (light duty, pedestrian areas) to F900 (extremely heavy duty, industrial applications):

Built-In Falls vs Regular Depth Configurations:

Linear drainage systems with built-in falls are designed to facilitate the natural flow of water towards designated drainage points. This design minimizes standing water and enhances the system’s efficiency. Ideal for sloped surfaces or areas prone to heavy rainfall.

In contrast, linear drainage systems with regular depth configurations maintain a consistent channel depth throughout. This design is suitable for areas where a constant depth is preferred, and the natural slope of the terrain or other drainage elements dictate water flow.

Anticipated Runoff Flows:

To ensure the optimal sizing and performance of linear drainage systems, the modified rational formula is commonly used by engineers for calculating anticipated flows:

Qp = 2.78 x Cv x CR x i x A


CV = Volumetric Runoff Coefficient

CR = 1.3 (Routing Coefficient)

i = Rainfall Intensity (mm/h);

A = Area (ha)

2.78 = Coefficient which accounts for the differences in units used for the inputs and the outputs of the equation.

An in-depth understanding of grating options, loading classes, the choice between built-in falls and regular depth configurations, and the anticipated runoff flow is essential. This allow us to make informed decisions, ensuring the resilience, efficiency, and longevity of linear drainage systems across diverse environments.

  • Private Drainage Detailed Design
  • External Hardstanding Detailed Design

Civilistix Civil Engineers were tasked to prepare Private Drainage & External Hardstanding Detailed Design packages and Adoptable Highway Design (S278) for a development comprising the creation of 293 student units within a 6-storey building along with courtyard and other associated external hardstanding areas.

Our Adoptable Highway Design (S278) consisted of upgrade of the surrounding footways and the creation of 2no. vehicular accesses from the proposed site. This included site clearance, surfacing and kerbing, dropped kerbs, footway levels, road markings and typical construction details.

Our surface water drainage design utilised a full gravity approach and included the use of a green roof and geo-cellular storage tank providing attenuation before releasing flows at 7.4 l/s to the Thames Water combined public sewer. Our drainage was designed to accommodate the critical 1 in 100 year plus 40% climate change event. Foul water was conveyed full by gravity to the Thames water sewer.

We worked in close collaboration with other design teams, to deliver a fully coordinated proposed external works and drainage design solution for the client.

In 1994 the American Society of Civil Engineers recognised the Eurotunnel, as a remarkable engineering achievement!

The Eurotunnel (also known as the Chunnel), is a 50.46 km tunnel that connects Folkestone in the United Kingdom with Coquilles near Calais in France and serves as a vital transportation link between the UK and mainland Europe.

Proposed as early as 1802 by French engineer Albert Mathieu-Favier, the Eurotunnel was only completed in 1994.

Noteworthy features include:
•  It has the longest underwater section of any tunnel in the world.
•  It is the world’s third longest railway tunnel.
•  It was a privately funded project with the final cost of £4.65 billion – 80% cost overrun.
•  It was a successful collaboration between French and British companies and banks

It is a true engineering marvel!

Civil Engineers changing the world, one project at a time!

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