Sevenoaks District Draft Local Plan Consultation July 2018

Document Section Draft Local Plan July 2018 Health and Wellbeing, Air Quality and Climate Change Flood Risk and Sustainable Drainage Policy 18 - Health and Wellbeing, Air Quality, Climate Change and Flooding [View all comments on this section]
Comment ID DLPP863
Respondent Kent County Council (Barbara C… [View all comments by this respondent]
Response Date 20 Sep 2018
Current Status Accepted

Public Rights of Way - KCC recommends that PRoW should be referred to within this policy, as the network provides substantial opportunities for active travel and outdoor recreation, which can help to address issues associated with air quality, health and wellbeing.

SUDS - KCC recommends that under the subtitle ‘Climate Change’, the following addition is made: “(g) resilient drainage design which includes a climate change
allowance”, recognising that this is not the same as seeking a reduction in surface water runoff.
KCC recommends that under the subtitle ‘Flood Risk’, KCC recommends that small sites should also be mentioned.
KCC recommends that under the subtitle ‘Sustainable Drainage’- the multi-functional aspects of SuDS should reference amenity or recreational
opportunities and integration within landscape strategy where feasible.
It is also requested that consideration is given to the following general topics, which could be incorporated into policy, as it sets direction for drainage
provision in new development.
1) Previously developed sites (brownfield development) Previously developed (i.e. brownfield) land usually has an existing connection to a sewer system and runoff rates from the site for any new development has
in the past been based upon the capacity of the existing connection. However, when KCC reviews planning applications, consideration is required of the
Non-statutory Technical Standards for Sustainable Drainage. The NSTS states that: “the peak runoff rate from the development to any drain, sewer or
surface water body for the 1 in 1 year rainfall event and the 1 in 100 year rainfall event must be as close as reasonably practicable to the greenfield runoff
rate from the development for the same rainfall event, but should never exceed the rate of discharge from the development prior to redevelopment for that
event.” KCC would recommend that policy reflects the intention to seek surface water control to greenfield runoff rates where possible and emphasizes that
this may be as important with previously developed land.
2) Delivery of multi-functional aspects of sustainable drainage measures
The new NPPF paragraph 163 references that where SuDS systems are used they should “where possible, provide multifunctional benefits.” Sustainable
drainage systems can comprise very many different measures and are determined by the googology, topography, layout and surrounding
catchment/networks. In the first instance, the drainage system must mimic natural surface water flows and drainage flow paths to ensure that flood risk is
not exacerbated on site or off site. However, for a drainage proposal to demonstrate a fully sustainable solution it must also provide additional benefits
through biodiversity and amenity benefits. There are additional benefits which accrue through certain drainage proposals e.g. ground water recharge,
recreation and air quality. It would be beneficial if Local Plan Policy could be clear in the expectation that all major development should provide for fully multifunctional sustainable drainage measures, which are integrated within the open space and landscape strategies of proposed development and maximise
where possible other benefits including biodiversity, amenity, groundwater recharge, and recreational opportunities.
3) Ensuring resilience in drainage infrastructure
Resilience of drainage design for new development is usually provided through the inclusion of a climate change allowance. This allowance ensures that the
infrastructure has capacity to accommodate surface water runoff from the proposed development over the life-time of the development. The EA published
new climate change allowances in April 2017. Any planning policy should reference that drainage should account for the “latest” policy direction with respect
to climate change.
KCC would recommend that the consideration of climate change also includes consideration on development on previously developed land. In these
instances, including an allowance for climate change within surface water runoff estimations can be critical given that there may be a reliance on existing
drainage connections. This ensures that going forward in time, the system will have improved resilience and capacity to accommodate surface water for the
life-time of the newly constructed development.
4) Minor development and development of small sites
Although the LLFA only has a duty to provide consultation on major sites, it should be noted that all development should clearly state how surface water is to
be managed from the new development proposals to ensure that adequate accommodation of surface water has been provided. The new NPPF specifically
states in paragraph 164 that some minor development may still be required to provide a site-specific FRA. We would recommend that the LPA considered
instances where this would be applicable e.g. geographical, situational (adjacent to areas of flood risk or known drainage problems) or development specific
(significant increases in impermeable area). Progressive development of small infill sites within existing urban areas may cumulatively place a significant
burden on drainage infrastructure, particularly in areas served by combined sewer systems or where sewers have constrained capacity. KCC would
recommend consideration of a maximum discharge rate from small sites of less than 1 ha, e.g. 2 l/s. This may therefore apply to minor development as well
as major development.