Download Soakaway Design Summary

Soakaways are used to store the immediate surface water run-off from hard surfaced areas, such as roofs or car parks, and allow for efficient infiltration into the adjacent soil. They discharge their stored water sufficiently quickly to provide the necessary capacity to receive run-off from a subsequent storm. The time taken for discharge depends upon the soakaway shape and size, and the surrounding soil’s infiltration characteristics. Download soakaway design summary that will help you to study the concept of the soakaway design, types, construction and the challenges.

Soakaway Design

Media of Soakaway

They can be filled with rubble, Granular (gravel or brickwork), plastic cells, perforated pre-cast concrete ring units or any similar structure that collects rainwater and run-off. The structures are built to allow rainwater to infiltrate directly into the ground. Soakaways can also be deep bored.

Design and Construction Considerations

General

• Soakaways can provide a long-term, effective method of disposal of surface water from impermeable areas of several hundred square metres.
• Long-term maintenance and inspection must be considered during the design and construction process.
• Risk of pollution to the quality of groundwater must be considered.
  • Roof surface run-off should not cause damage to groundwater quality and may be discharged directly to soakaways. Those pollutants entering the soakaway from roofs tend to remain in the soakaway, or in its immediate environs, attached to soil particles.
  • Paved surface run-off for larger trafficked areas should be passed through a suitable form of oil interception device prior to discharge to the soakaway.
• Maintenance of silt traps, gully pots and interceptors will improve the long-term performance of soakaways.
• Soakaways should not normally be constructed closer than 5 m to building foundations.

Sustainable drainage

Sustainable drainage is a departure from the traditional piped approach to draining sites. Sustainable Drainage Systems (SUDS) mimic natural drainage through:

• Storing run-off rainwater and releasing it slowly (attenuation).
• Allowing water to soak into the ground (infiltration).
• Slowly transporting (conveying) water on the surface.
• Filtering out pollutants.
• Allowing sediments to settle out by controlling the flow of water.

Soakaways are one of the key technologies for SUDS. They enable stormwater to be dealt with at source rather than being diverted directly into the sewer system; they also satisfy the criteria listed in the bullet points above.

Design

The design of a soakaway depends on a number of factors including the following:

• Permeability of the ground.
• Groundwater level (preferably undertaken when water levels will be highest, during winter to spring)
• Type of ground
• Contamination
• Space restrictions
• Building foundations (It is not desirable to locate a soakaway close to a building. A minimum distance of 5 m is most often quoted)
• Risk of ground instability and other hazards.

Perforated pre-cast concrete ring unit soakaways should be installed within a square pit, with sides about twice the selected ring unit diameter.

• Granular fill can be separated from the surrounding soil by a suitable geotextile to prevent migration of fine particles into the soakaway.
• The top surface of the granular fill should also be covered with geotextile to prevent the ingress of fill material during and after surface reinstatement.
• Geotextile should not be wrapped around the outside of the ring units as it cannot be cleaned satisfactorily or removed when it has become blocked.

In order to limit any possible alteration to the quality of groundwater, attention should be paid to the source of the run-off water that is to be collected.

• If it is from a paved surface where there is a risk of oil or fuel spillage, a light liquid separator should be provided.
• Domestic drives and paths should not need a light liquid separator, but municipal roads and car parks will require them.
• For drained areas less than 100 m2, soakaways can be:
• square or circular pits, either filled with rubble or lined with dry-jointed brickwork, or perforated pre-cast concrete ring units surrounded by suitable granular fill.

For drained areas above 100 m2, soakaways can be:

• perforated pre-cast ring units or trench type and not substantially deeper than soakaways that serve small areas:
  • 3 to 4 m is adequate if ground conditions allow.

There is an increasing number of soakaways that are being built using plastic cells.

• These are typically lightweight modular water storage cells with a high void ratio.
• Plastic cells can be used for either attenuation or infiltration of surface water in residential, commercial, industrial and retail applications.
• Proprietary components such as silt traps, flow control units and adaptors will normally be used as part of these systems.

Download Soakaway Design Summary

Download soakaway design summary that will help you to study the concept of the soakaway design, types, construction and the challenges.

Conclusion

Soakaways are commonly used in residential, commercial, and agricultural settings as part of sustainable drainage systems (SuDS). They are especially useful for areas with limited access to main drainage systems, helping reduce the pressure on urban infrastructure while promoting groundwater recharge. In addition to their functional benefits, soakaways play a key role in mitigating environmental issues, such as reducing water pollution by filtering out debris and contaminants before water reenters the soil. Download soakaway design summary that will help you to study the concept of the soakaway design, types, construction and the challenges.