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Sustainable Drainage Systems:

Above ground

attenuation

Thomas Geoghegan

Agenda

Background on Sustainable Drainage Systems (SUDS)

Selecting the best SUDS option

Above ground attenuation options

Case Study

Why choose above ground attenuation systems?

Questions

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Background on SUDS

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Background on SUDS

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• Drainage Design in the past has been simply using a rational method size pipes to ensure water is removed as quickly as possible

• Sustainable Drainage Systems:   is a concept that includes long term environmental and social factors in

decisions about drainage.

• In rural areas 80% of rivers are below ground status

• Most pollution comes from:

- Underperforming small treatment plants

- Overloaded communal septic tanks

- Clusters of single unit septic tanks

- Farmyard runoff

• Over the past decade Ireland & the UK have been developing a more sustainable approach

Selecting the best SUDS option

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Selecting the best SUDS option

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When selecting Sustainable drainage systems it important to consider Quality, Quantity Amenity Equally

Selecting the best SUDS option

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• There is no correct way in choosing the best SUDS option but these factors must be adhered to:

- Design techniques to meet design criteria

- There is no single correct solution: selection could result from

external factors

- The sustainable drainage system should be in accordance with

the original drainage system

- Decision must be on a wider context and not purely technical

Above ground attenuation options

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Basins and ponds Filter strips & swales

Above ground attenuation options

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Basins and ponds Basins are areas for storage of surface runoff & are free from water under dry

weather flow conditions. These include:

- Flood plains

- Detention basins

- Extended detention basins

Ponds contain water in dry weather and are designed to hold more when it

rains. They include:

- Attenuation ponds

- Flood storage reservoirs

- Lagoons

- Retention Ponds

- Wetlands

Above ground attenuation options

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Basins and pondsBasins and ponds store water at the ground surface as:

- Temporary flooding

- Flood plains

- Permanent ponds

Above ground attenuation options

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Basins and pondsQuantity

They store floodwater and release it slowly once the risk of flooding is over

Quality

Treat:

- Settlement of solids in still water

- Conditions and promotes settlement

- Adsorption by vegetation of soil

Amenity

Offer:

- Sports and recreation

- Wet ponds are great to store water for reuse

Above ground attenuation options

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Filters strips & swalesFilter strips and swales are vegetated surface features that drain water evenly

off impermeable areas. Swales are long shallow channels whilst filter strips

are gently sloping areas of ground.

Above ground attenuation options

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Filter strips & swalesThey work by imitating natural drainage patterns by allowing rainwater through

vegetation, slowing and filtering the flow.

Quantity

Swales & filter drains are designed for:

- Conveyance systems

- Infiltrations

- Reduce drained impermeable areas

Quality

Swales and filters remove polluting in the solids through filtration and

sedimentation

Above ground attenuation options

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Filter strips & swalesAmenity

Swales and filters trips are often interpreted into surrounding land use

Examples are:

- Public open space

- Road verges

- Grass and flowers can be planted for wildlife

Case Study

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Matchborough School

Case Study

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Location:

Redditch, Worcestershire, England

Description:

A school development was designed with conventional drainage that flowed to

a pump station from where it was pumped to a sewer

During construction one playground area could not be drained by gravity to the

pumping station.

Main suds used:

Swales

Detention basins

Case Study

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• The suds scheme was implemented & removed the need for the station

• Now follows the contour of the site and drains downhill to a ipsley stream

Initial proposal Sustainable drainage outline proposal

Case Study

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Swales collect overland flows from: - Adjacent site - Runoff from car park

- Playgrounds - Hence providing source of control

The retention basins drain the main driveway that is connected to a

constructed wetland (pond) which also takes runoff from the roof.

Car park Inlet

Case Study

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Benefits

The suds system has brought a valuable amenity and teaching resource for the

school

Why choose above ground attenuation systems?

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- Installed and maintained at a lower cost compared to more traditional

systems of drainage

- Problems can be observed and dealt with as they arise(swales)

- Can be incorporated into any terrain

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Any Questions?