Policy FRD5 Artificial Modification of Watercourses
A proposal for the artificial modification of a watercourse, including culverting or canalisation operations, will only be permitted in either of the following exceptional circumstances:
Where the culverting of short length of a watercourse (usually less than 10m) is necessary to provide access to a development site (or part thereof).
Where the applicant can demonstrate to the satisfaction of the Council that a specific length of watercourse needs to be culverted for engineering reasons and that there are no reasonable or practicable alternative courses of action.
Applicants are also required to demonstrate that sustainable drainage systems (SuDS) have been considered as an alternative to culverting or canalisation (see Policy FRD4 Sustainable Drainage).
Justification and Amplification
The SPPS recognises the artificial modification of a watercourse, including culverting or canalisation of watercourses, as environmentally unsustainable, with potential to increase flood risk. Such operations can adversely impact upon visual amenity and can damage or impair the landscape quality, ecological integrity and biodiversity of watercourses. Some watercourses can themselves be heritage assets as they may have been utilised, diverted and reshaped in the past to become mill races.Culverting creates barriers to the passage of fish, while the higher flow velocities generated cause the unnatural movement of sediment, increased erosion downstream and hinder the future recovery of the watercourse. Whilst culverting may in some instances alleviate local flood risk, it can increase flood risk downstream by the accumulation of higher flows.
Applicants will have to demonstrate to the satisfaction of Council, through consultation with DfI Rivers, that there are no reasonable or practicable alternative courses of action. The policy, however, acknowledges that in exceptional circumstances, culverting of a section of a watercourse may be unavoidable. When culverting a short length of a watercourse for access reasons, the length and number of culverts should be kept to a minimum. If part of a watercourse is already culverted prior to the commencement of any development, this does not necessarily mean that it can automatically be lengthened or upgraded to meet the site discharge requirements.
Good layout and design should promote the retention of open watercourses as a central amenity feature, although re-alignment or diversion to enhance the quality of the site layout will normally be acceptable where there are no overriding environmental concerns. Incorporating watercourses into the open space requirements for new residential development will be preferred to locating them to the rear of properties where they are difficult to maintain or can become dumping grounds contributing to flood risk. Where possible the removal of culverts and the re-introduction of the natural watercourse should be encouraged.
The adoption of sustainable drainage solutions for the disposal of stormwater is a much more sustainable alternative than culverting or other options involving the artificial modification of watercourses. The use of SuDS source control solutions, particularly ‘soft SuDS’ elements such as ponds and swales and their integration into new development schemes as amenity features will therefore be promoted. Such solutions, by negating increased site discharges will reduce the need for flood alleviation/culverting works downstream and any associated maintenance. Applicants are therefore required to demonstrate that SuDS have been considered rather than culverting or canalisation of watercourses, where feasible/appropriate (see Policy FRD4 Sustainable Drainage).