Working in co-operation with the Environment Agency, Severn Trent Water Ltd., the Highway Authority and developers, the planning system can play a vital role in preventing the drainage of urban developments from damaging our environment.
Conventional drainage systems have led to many problems including:
Traditional systems have aimed to remove rainfall from impervious surfaces as quickly as possible resulting in higher rates of flow for shorter periods and flooding down stream.
Surface water outfalls contain certain contaminants including oil, organic matter and toxic chemicals. Cross connection of surface and foul sewers can cause serious degrading of water quality.
An increase in impermeable areas caused by development results in less water available for infiltration into the ground, which reduces the volume of water stored in the ground, thereby decreasing ground water levels and the base flow of streams.
The above factors, combined with erosion/deposition, caused by higher flows, and reduction in oxygen levels due to silt blanketing stream life can destroy natural habitats, flora and fauna.
The alternate approach which aims to safeguard the environment for existing and future generations is referred to as Sustainable Drainage Systems (SUDS).
These are physical structures built to receive surface water run off from urban developments. e.g. ponds, wetland swamps, pervious surfaces and soakaways. These may provide treatment for water prior to discharge using natural processes of sedimentation, filtration, absorption and biological degradation.
By reducing the quantity of run off, slowing down flow rates to rivers and streams and treating water in a natural way, it will:
The two main rivers in the District (Severn and Stour) flow through at least one of the three towns. It is therefore particularly important that sustainable drainage measures are adopted here. The Development Plan provides the framework for drainage relating to urban developments. The Wyre Forest District Local Plan (Policy D.7) requires that "Wherever practicable and subject to other layout, design and conservation considerations, all development proposals should include infrastructure that directs surface water to sustainable drainage systems rather than to sewer and watercourses. Proposals for schemes in settlements adjoining the Rivers Severn and Stour will be subject to particular scrutiny".
Legal agreements may also be sought in riverside locations to reduce the impact of storm water run-off on flooding. Planning permission will not be granted for development contrary to this policy and the council will wherever practicable promote sustainable drainage measures. Permission will not be granted for urban development in flood plains (without the support of the Environment Agency) or where there is a risk of flooding and the development may accelerate the problem.
A system that collects rain water from where it falls rather than allowing it to drain away. It includes water that is collected within the boundaries of a property, from roofs and surrounding surfaces.
A surface that infiltrates water to the sub-base across the entire surface of the material forming the surface, e.g. grass, gravel, porous concrete and porous asphalt.
Surfaces that allow inflow of rainwater into the underlying construction or soil.
Contained flooding - it may be acceptable to allow shallow flooding of a car park once or twice a year rather than building a larger drainage system to cater for such events.
A trench, usually filled with permeable granular material, designed to promote infiltration of surface water to ground.
A dry basin designed to promote infiltration of surface water to the ground.
A linear drain consisting of a trench filled with permeable material, often with a perforated pipe in the base of the trench to assist drainage, to store and conduct water, but may also be designed to permit infiltration.
A shallow vegetated channel designed to conduct and retain water, but may also permit infiltration; the vegetation filters particulate matter.
A vegetated area of gently sloping ground designed to drain water evenly off impermeable areas and to filter out silt and other particulates.
A vegetated depression, normally dry except after storm events, constructed to store water temporarily to attenuate flows. May allow infiltration of water into the ground.
Vegetated areas designed to collect and treat water before discharge via a piped system or infiltration to the ground.
These are features where run-off is detained for a sufficient time to allow settlement and possibly biological treatment of some pollutants.
A pond that has a high proportion of emergent vegetation in relation to open water.
Where appropriate a flood risk assessment should be carried out and submitted with a planning application (see www.pipernetworking.com for guidance on flood risk assessments or contact the Environment Agency for advice).
Consideration should be given to the employment of sustainable drainage systems and they should be clearly described in the application. Soakaway systems should be employed where ever practicable.
Wyre Forest House