A soakaway is a simple yet effective drainage system used to manage and disperse surface water runoff or effluent from septic tanks into the ground. It allows water to slowly infiltrate into the surrounding soil, preventing waterlogging and reducing the risk of flooding. Soakaways are commonly used for residential properties, gardens, driveways, and commercial sites as part of Sustainable Drainage Systems (SuDS).
How a Soakaway Works
- Collection and Dispersal of Water:
- A soakaway collects water from a variety of sources, such as roof gutters, driveways, or septic tanks. This water is funneled through a network of drainage pipes that lead to the soakaway chamber or pit.
- The soakaway is typically constructed underground and is filled with gravel, stones, or specially designed plastic crates that create void spaces for water storage.
- Temporary Storage of Water:
- As water flows into the soakaway, it is temporarily stored in the voids created by the gravel or plastic crates. This storage provides a buffer, preventing immediate runoff and allowing the water to gradually seep into the surrounding soil.
- The size of the soakaway is determined by the volume of water it needs to handle, which is calculated based on factors such as roof size, soil permeability, and rainfall intensity.
- Infiltration into the Soil:
- The key function of a soakaway is to allow water to infiltrate or percolate into the surrounding soil. The water slowly seeps through the porous materials of the soakaway and into the ground.
- This process mimics the natural water cycle, where rainwater soaks into the ground rather than flowing directly into stormwater drains or rivers, which can cause flooding and erosion.
- Natural Filtration and Treatment:
- As water passes through the soil, it undergoes natural filtration. The soil particles filter out debris, sediments, and some pollutants, helping to clean the water before it reaches the groundwater table.
- In cases where the soakaway is used to disperse treated effluent from a septic tank, the soil further removes harmful pathogens and nutrients through biological, chemical, and physical processes.
- Preventing Waterlogging and Flooding:
- By allowing water to disperse slowly into the ground, soakaways help to prevent waterlogging in gardens, driveways, or other areas around buildings. They are particularly useful in areas with heavy rainfall, as they reduce surface water runoff and the risk of localized flooding.
- Soakaways also play a crucial role in recharging groundwater levels, promoting sustainable water management.
Types of Soakaways
- Traditional Soakaway Pit:
- A basic soakaway is simply a pit filled with coarse gravel, rubble, or crushed stone. The voids between the stones allow water to collect and gradually infiltrate into the ground.
- Traditional soakaways are cost-effective and simple to construct but may require more maintenance as they can become clogged with silt and debris over time.
- Modern Soakaway Crates or Modular Units:
- Modern soakaways use specially designed plastic crates or modular units that create large, stable voids underground. These crates are lightweight, easy to install, and provide more efficient water storage and dispersion than traditional gravel-filled pits.
- They are covered with geotextile membranes to prevent soil and debris from entering and clogging the system, enhancing their durability and reducing maintenance needs.
- Perforated Pipe Systems:
- Another variation involves using perforated pipes laid in trenches filled with gravel. The pipes help distribute the water over a larger area, improving the efficiency of water dispersion.
- This type is often used for drainage fields in conjunction with septic tanks, especially when a larger soakaway area is needed.
Steps for Installing a Soakaway
- Site Assessment:
- Conduct a site assessment to determine the suitability of the soil for a soakaway. A percolation test is essential to measure the soil’s drainage capacity. Sandy or loamy soils are ideal, while clayey soils are less suitable due to poor drainage.
- Determine the Size and Location:
- The size of the soakaway depends on the volume of water to be managed and the soil’s permeability. It is generally recommended to place the soakaway at least 5 meters away from buildings and 2.5 meters from property boundaries.
- Excavation and Preparation:
- Excavate the area to the required depth and dimensions based on the soakaway design. For modern crates, this involves digging a trench or pit large enough to accommodate the units and providing sufficient depth for effective drainage.
- Install the Soakaway Components:
- For a traditional soakaway, fill the pit with clean gravel or stones, while for a modern soakaway, assemble and place the plastic crates in the pit.
- Cover the sides and top of the crates with a geotextile membrane to prevent soil from entering and clogging the system.
- Backfill and Cover:
- Backfill the area around the soakaway with soil, compact it properly, and cover it with turf, gravel, or paving as required.
- Connect Drainage Pipes:
- Connect the soakaway to the drainage pipes from the roof gutters, driveways, or septic tank to direct the water to the soakaway.
Conclusion
A soakaway is an efficient, eco-friendly solution for managing surface water runoff and effluent disposal. By allowing water to naturally infiltrate into the ground, soakaways help prevent flooding, recharge groundwater, and reduce the burden on stormwater drainage systems. Proper design, installation, and maintenance are key to ensuring a soakaway works effectively for years to come.