The document discusses above ground attenuation systems as a type of sustainable drainage system (SUDS). It describes different above ground attenuation options like basins, ponds, filter strips, and swales. It provides details on how these systems work for quantity control, quality treatment, and amenity values. The document also presents a case study of a school development that implemented a SUDS scheme using swales and detention basins, removing the need for a pumping station and providing an amenity resource.

1. Sustainable Drainage Systems: Above ground attenuation Thomas Geoghegan

2. 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

3. Background on SUDS

4. Background on SUDS 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

5. Selecting the best SUDS option

6. Selecting the best SUDS option When selecting Sustainable drainage systems it important to consider Quality, Quantity Amenity Equally

7. Selecting the best SUDS option 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

8. Above ground attenuation options Basins and ponds Filter strips & swales

9. Above ground attenuation options 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

10. Above ground attenuation options Basins and ponds Basins and ponds store water at the ground surface as: - Temporary flooding - Flood plains - Permanent ponds

11. Above ground attenuation options Basins and ponds Quantity 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

12. Above ground attenuation options Filters strips & swales Filter 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.

13. Above ground attenuation options Filter strips & swales They 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

14. Above ground attenuation options Filter strips & swales Amenity 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

15. Case Study Matchborough School

16. Case Study 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

17. Case Study 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

18. Case Study 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

19. Case Study Benefits The suds system has brought a valuable amenity and teaching resource for the school

20. Why choose above ground attenuation systems? 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

21. Any Questions?