Drainage Checklist

 

Surface Water Drainage Proposal Checklist

Foreword

Before completing this checklist you are advised to read “Arun/Chichester District Council Supplementary Requirements for Surface Water Drainage Proposals”.


The Surface Water Drainage Proposals Checklist is designed to clearly outline Arun/Chichester District Council’s expectations and requirements for Surface Water Drainage Proposals and to expedite their review. This document should be used when completing Discharge of Conditions Applications or if the applicant wishes to avoid pre-commencement conditions relating to surface water drainage.


The Town and Country Planning Regulations now require pre-commencement conditions to have the prior agreement of the applicant regarding their wording and use. If an applicant wishes to avoid surface water drainage pre-commencement conditions they will need to submit detailed surface water drainage proposals in line with the Surface Water Drainage Proposal Checklist.


The below details are required to enable Arun/Chichester District Council to examine if proposals follow the hierarchy for sustainable drainage and if the design will adequately drain the site.


N.B. It will be difficult for Arun/Chichester District Council to undertake an appropriate and therefore timely assessment of your application if you answer “no” to any of the questions below, or if you fail to provide any of the information requested.

 

Checklist

Winter groundwater monitoring results included

Y/N

Winter infiltration test results included

Y/N

Period of winter groundwater monitoring

 

Maximum recorded groundwater level (AOD)

 

Date of infiltration testing

 

Minimum infiltration rate recorded
(at location of infiltrating structure)

 

Plan showing the location of winter groundwater
monitoring and infiltration testing included

Y/N

Method of surface water disposal proposed (Delete as appropriate)

Infiltration / Attenuation with discharge to watercourse
Attenuation with discharge to surface water sewer/
Attenuation with discharge to foul sewer

If infiltration is not to be used: Justification supplied

Y/N

If infiltration is proposed: half drain time for 10
year event + climate change allowance (hours)

 

If infiltration is proposed: half drain time for 100 year
event + climate change allowance (hours)
f infiltration is proposed: lowest base level of infiltrating structure

 

If attenuation is proposed: calculations of pre-development runoff
rates included *

Y/N       Rate     l/s

If attenuation is proposed: is proposed discharge rate less than
or equal to pre-development rate?*

Y/N Rate     l/s

Calculations included demonstrating that the 1 in 100 year
plus climate change event can be accommodated on site**

Y/N

If proposing an impermeable lined attenuation feature/s,
calculations included demonstrating that resistance to floatation
(due to groundwater levels) is achieved and catered for in the design

Y/N/Not applicable

If alterations or discharge to an ordinary watercourse is proposed:
has Ordinary Watercourse Land Drainage Consent been sought?

Y/N

Drainage layout plans included***

Y/N

Construction detail plans included****

Y/N

Exceedance flow route plans included (Not required for <5 properties)

Y/N/Not applicable

 

*If developing brownfield sites, please provide fully detailed plans of the existing surface water drainage arrangements on site, including impermeable areas, gullies, outfalls, pipes & diameters, manholes, etc.

**If infiltration is proposed the following factor of safety should be applied to calculations (in accordance with CIRIA R156/ CIRIA C609)

 
Size of area to be
drained
Consequences of failure
No damage or
inconvenience
Minor inconvenience, e.g.
surface water on car park
Damage to buildings
or structures or roads
Cv=1.0 Cv=0.75 Cv=1.0 Cv=0.75 Cv=1.0 Cv=0.75
<100 m sq 1.5 2 2 3 10 13
100m sq to 1000m sq 1.5 2 3 4 10 13
>1000m sq 1.5 2 5 6.5 10 13

***Please note that drainage layout plans should include:

  • All surface water drainage pipes labelled with; diameters, pipe materials, falls and invert levels.
  • All infiltrating and attenuating structures (including permeable paving) labelled with; dimensions, invert and cover levels.
  • All manholes labelled with; cover levels, invert levels, cover types detailed.
  • All silt traps clearly labelled with sump depths.
  • Control structures with outflow rates and invert levels.
  • Proposed/existing levels of any areas subject to ground raising, together with suitable measures/detailed drawings for the associated managing of surface water runoff. Please note that ground raising should be avoided unless there are exceptional circumstances.

****If your proposed drainage scheme includes any of the following elements site specific construction detail plans should be supplied: pipe bed and surround; infiltrating structures; attenuating structures; manholes; catchpits/silt traps; control devices; permeable paving; headwalls.