French Drain Design

The CivilWeb French Drain Design spreadsheet completes the design of french drain systems in accordance with the procedure outlined in the SUDS Manual. This standard design procedure ensures that the drain is able to accept the required rainfall runoff flow through the filter material and through the perforated pipe outfall. The spreadsheet is specially designed in order to be simple enough for homeowners and other non-professionals to use, but powerful enough for professionals to complete fully optimized compliant designs in seconds.

Note that french drain systems where infiltration of runoff into existing soils is expected to be significant, this is designed as an infiltration trench. This can be undertaken using a specialist design spreadsheet such as the CivilWeb Soakaway Size Calculator spreadsheet which can design infiltration trenches.

French Drain Design

French drains are very commonly used in the UK. They are well suited to drainage of linear infrastructure such as roads and railways and can be installed around the perimeter of small concentrated infrastructure such as small car parks. They are cost effective compared to gully and pipe drainage methods and can reduce runoff discharge, particularly where infiltration of runoff waters into surrounding soils is allowed for in the drain design.

French drains are also often used for small scale domestic purposes. French drains are well suited to small domestic projects such as a french drain around a patio, decorative french drains and foundation french drains for building and house foundations. Perimeter drain design and other types of domestic french drain design can be undertaken quickly and easily using the spreadsheet.

In order for a french drain system design to handle the runoff water anticipated from the design storm, there are three main design checks which need to be undertaken. These are;

  • That the runoff water is able to pass through the filter material quickly enough
  • That the runoff water is able to enter the perforated pipe quickly enough
  • That the runoff water is able to run through the pipe quickly enough

Any one of these parameters can become a bottle neck leading to the flooding of the whole drain if the runoff water is not able to pass quickly enough through any one part of the system.

In order to achieve these design aims, the french drain size, specification and design details must be suitable for the proposed catchment. All these parameters can be designed using the spreadsheet.

The CivilWeb French Drain Design Spreadsheet is able to complete all three of these design checks for any french drain design and any design storm event. It also produces unique optimization graphs showing the designer at a glance the sensitivities of the main design parameters and showing the designer where any bottle necks will take place. This makes the design very simple allowing the designer to complete a fully compliant design in seconds.

French Drain System Design Guide

The CivilWeb French Drain Design spreadsheet comes with a comprehensive 73 page user and design guide. This guide includes a detailed explanation of the full design procedure undertaken automatically by the spreadsheet in accordance with the SUDS Manual. The design guide also includes detailed guidance on all the design parameters with typical values for preliminary or non-critical design. The guide also includes detailed guidance on french drain design diagrams and details, water quality, construction and maintenance of the completed drain. This website also includes lots of detailed advice on all aspects of drain design. These posts are summarized on our French Drain System page.

CivilWeb French Drain Design Spreadsheet Suite

The CivilWeb French Drain Design spreadsheet package includes a number of useful design tools including the following;

  • French Drain Design Spreadsheet - Full license version of our market leading design spreadsheet which completes the design in accordance with the SUDS Manual.
  • Designer's Guide - A comprehensive 73 page user guide which includes detailed explanation of the calculations undertaken by the spreadsheet and thorough guidance and typical values for all design inputs. The design guide also includes typical construction details, and comprehensive french drain installation, maintenance and repair guidance.
  • Spatially Varied Flow Analysis Spreadsheet - A one of a kind spreadsheet which can complete a complex spatially varied flow analysis for french drains. This can be used as a more detailed solution for perforated pipe design where this is required.
  • Minimum Trench Width Checker - This spreadsheet calculates the minimum trench width in accordance with BS EN 1610.
  • Filter Material Permeability Calculator - This unique spreadsheet tool estimates the permeability of the filter material from the grading and porosity of the material. This can be used to check that particular filter materials will be suitable for the drain design where a certain permeability is required.

Get your copy of the CivilWeb French Drain Design spreadsheet now for only £20.

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Or why not bundle with the CivilWeb Soakaway Design spreadsheet for only £5 extra?

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Or save £50 by buying our full Drainage Design Suite including all our drainage design spreadsheets.

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