Policy information sourced from the Welwyn Hatfield Local Plan
SADM 14 Flood Risk and Surface Water Management
- Development proposals in areas at risk of flooding from any source should be informed by and be consistent with relevant national planning policy and guidance, local and regional strategies and plans, and the latest flood risk information available.
- Flood Risk Assessments will be required in line with national policy and guidance and should be prepared in accordance with the requirements and advice set out in the Council’s Strategic Flood Risk Assessment. In addition, proposals that require a site-specific Flood Risk Assessment will be required to:
- Protect and enhance the flood risk management function of existing overland flow routes, watercourses and flood plains/storage areas to ensure there is no net loss of flood storage, flows are not impeded, and opportunities to make space for water are taken.
- Maintain an appropriate development free corridor along watercourses and take opportunities to naturalise watercourses to improve their ecological status, biodiversity and habitat connectivity.
- All major development proposals, and all proposals in areas identified as being at risk of surface water flooding, will be required to manage surface water runoff and surface water flood risk via the use of Sustainable Drainage Systems that:
- Have been incorporated into the layout and design of proposals at the earliest stage of scheme design;
- Are designed in accordance with the national non-statutory technical standards (or their successor) as well as guidance and advice provided by the relevant flood risk management bodies;
- Wherever feasible improve upon peak greenfield runoff rates, particularly in locations identified as experiencing surface water flooding problems, in order to help reduce overall flood risk in the wider area;
- Use management and control measures that aid multi-functionality of space, enhance visual amenity, support biodiversity and allow for safe interaction with the water environment, as opposed to hard engineered and/or sub-surface features which will be resisted;
- Protect water quality by using an appropriate number of treatment stages before discharging to the ground or a surface water body;
- Avoid discharging to a combined sewer particularly in locations where the existing sewer network is identified as having constrained capacity; and
- Enable maintenance of individual measures and the system as a whole to be undertaken in a financially sustainable way and without significant disruption to occupiers and users of development.
- Sustainable Drainage Systems that include measures for managing surface water runoff beyond the individual building or plot-level will be required to demonstrate how the long term maintenance of the system will be secured.
- All development proposals should seek to incorporate suitable source control measures at the building and plot-level. The loss of permeable surfaces and other features which help reduce and manage surface water flood risk without suitable compensatory provision will be resisted.
For more information please see the Welwyn Hatfield Local Plan