Make sure your proposal is designed to cater for the existing drainage patterns on the site as well as the new ones you will create with your development.
Surface water should not be discharged into foul drains or storm water system because this can:
- reduce the effectiveness of the sewage treatment plant;
- lead to overloading of sewers and pollution at times of peak flows;
- result in water being returned to the river system too quickly.
Only use soakaways where:
- ground conditions are suitable;
- water tables are low enough that they will work properly;
- they will not receive effluent from septic tank outfalls.
Try to slow down the rate at which water runs away from your site using:
- ponds, lakes, grass swales or wetland habitats;
- permeable surfaces for car parking and other paved areas where ground conditions are suitable, and the risk of pollution is low;
- French drains (gravel filled trenches) rather than pipes;
- hydro-brakes at pond or reservoir outfalls where the downstream drain capacity is limited.
Avoid pollution - If there is a risk of pollution from oil or chemicals from roads and industrial and parking areas, consider the following remedies:
- silt and oil traps;
- biological filters in layered French drains or hard surface construction.
Reduce maintenance requirements by:
- making sure pipes are laid at gradients which promote self-cleansing;
- placing traps, rodding points, inspection chambers and manholes where access for cleaning or emptying is easy.