Drainage

By definition drainage means the draw off of liquid, flow or trickle through purpose built channels, conduits or pipes carrying the liquid away from an area. This can be achieved by gravity based drainage disposal systems and capture and pump out types. This water must be either graded or pumped away from buildings. It is advisable to try to maintain the existing topography and drainage pattern.

Drainage can be constructed for a variety of reason, that being for exterior patios, swimming pool areas, walk ways, driveways, storm water and dispersion of surface or underground water, ultimately any place water collects.

All sites should be able to maximise permeable surfaces such as garden beds, lawns, porous paving and paths.

The specific problem area must be properly assessed and an appropriate plan of action compiled according to the findings.

• Things to consider

  • Soil type – check the soil type. Sandy soils are excellent for infiltration but clay soils tend to become waterlogged. This will affect the efficiency of some of the water sensitive design solutions. For example, water sensitive design in heavy clay soils may need to be supplemented with traditional conveyancing methods.
  • Soil depth – ensure that you have sufficient soil depth. Areas with shallow soil underlain by impervious rock such as granite, shale or limestone may impede infiltration and may require some storm water pipes to remove water for discharge off site.
  • Groundwater – determine the depth to groundwater. A high groundwater table may reduce the effectiveness of infiltration methods during storms.
  • Slope – ensure that the storm water design accounts for the terrain as severe slopes increase run-off velocities.

Soakaways

The soakaway or percolation trench is an underground soil treatment system, which receives partially treated sewage from the septic tank. The trench which is filled with rocks, stone or similar medium and is usually covered with geo-textile or corrugated iron. The effluent from the septic tank filters through this bed of rocks where the bacteria have established themselves. If there are any solid particles in this effluent this will settle on the rocks where it will be broken down further by the bacteria before percolating into the soil to the ground water table. Therefore providing a final biodegradation process and polishing of the effluent.

It is noted here that the effluent from a septic tank is by no means fit (in terms of health) for discharge into a water course (e.g. a river, vlei or an aquifer) or onto the ground where it could possibly be accessible to animals, humans included.

You cannot simply construct a soakaway to the specification that you wish. There are other considerations including where the soakaway is built particularly from a practical and legal standpoint. It cannot be built near any open water such as a river or vlei because of the possibility of seepage from the soil into the water. This would result in contamination of the water source which could lead to many problems including health concerns.

Of primary concern is the soil type and porosity of the soil at the site. Soils that are too coarse or too fine can limit the effectiveness of the treatment system. One must carry out percolation tests on the ground soil to ascertain its suitability.

The size of a soakaway is determined by the size of not only your septic tank but the size of your dwelling the nature of waste being generated the slope of the ground and the distance from buildings and property boundaries.

• Things to consider

  • Soil type – check the soil type. Sandy soils are excellent for infiltration but clay soils tend to become waterlogged. This will affect the efficiency of some of the water sensitive design solutions. For example, water sensitive design in heavy clay soils may need to be supplemented with traditional conveyancing methods.
  • Soil depth – ensure that you have sufficient soil depth. Areas with shallow soil underlain by impervious rock such as granite, shale or limestone may impede infiltration and may require some storm water pipes to remove water for discharge off site.
  • Groundwater – determine the depth to groundwater. A high groundwater table may reduce the effectiveness of infiltration methods during storms.
  • Slope – ensure that the storm water design accounts for the terrain as severe slopes increase run-off velocities.