SuDs Dissertation Presentation Ryan Bruty

8/13/2019 SuDs Dissertation Presentation Ryan Bruty

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What effect will the National Standards for

Sustainable Drainage Systems (SuDS) haveupon the design and implementation of

surface water drainage on residential

developments?

by Ryan Bruty


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Aboutme

Engineer at Taylor Wimpey East Anglia, been with thecompany for eight years

During which time completed Taylor Wimpeys

Management Trainee Scheme

Whilst completing Foundation Degree in Construction atSuffolk College

Since completed Bachelor of Science with Honours in CivilEngineering at University Campus Suffolk in May 2012


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Contents

Introduction

Literature ReviewKey Changes in Legislation

InterviewsKey Findings

Case StudyKey Findings

Conclusions

Questions?


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Introduction

National Standards for Sustainable DrainageSystems from The Flood and Water

Management Act 2010

Research based on consultation version ofStandards dated December 2011

Research carried out in same four sections as

Part 2 of the National Standards:

Runoff Destination

Peak Flow Rate and Volume

Water Quality

Function


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Literature Review

i. Runoff Destination

Hierarchy previously identified in Building Regulations:

1. Infiltration

2. SW Body3. SW Sewer

4. Combined Sewer

Enforced through amendments to Water Industry Act

removing automatic right to connect

Now dependant upon SAB (SuDS Approval Body)

Approval


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Literature Review

ii. Peak Flow Rate and Volume Three key elements:

1. Runoff rates

2. Runoff volumes for small events (


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Literature Review

iii. Water Quality

First mandatory regulations on water quality treatment

stages (although previously referred to in The SuDS

Manual)

Specifies minimum treatment stages dependent upon

sensitivity of hazards and outfall

For residential developments typically Low (roof

drainage) and Medium (car parking and roads)

Can be beneficial to separate roof and car parking runoffinto separate systems


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Literature Review

iii. Water Quality


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Literature Review

iv. Function Three topics under Function:

1. Design

2. Flood Risk3. Operation and Maintenance

Designing for exceedance (Flood flow routes) already

Mandatory requirement of CfSH. Maintenance responsibility of SAB but approved

drainage plan must include the safe operation and

maintenance for SuDS.


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Interviews


Indicated hierarchy already in place through

PPS25 (Planning Policy Statement 25)

(now superseeded) and the planningprocess.

As is but delay in obtaining right to connect.


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Interviews

ii. Peak Flow Rate and Volume

Approach 2 provides alternative to that

required for CfSH compliancebut

increases storage required.

Area of concern was No discharge off site

for 5mm rainfall event Infiltration,

evaporation and rainwater harvesting onlyoptions for compliance.


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Interviews

iii. Water Quality

Main concern to all partiescurrently only

considered if overlying aquifer.

Innovative products emerging providing off

the shelf options for treatment stages.

Prevention of 5mm event discharging off site

as less dilutedFirst Flush.


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Interviews

iv. Function

Many aspects already in place through CfSH

and PPS25.


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Case Study

Selected Project: Greenfield site of 1.5Ha in Cambourne, Cambridgeshire

52 No. residential dwellings

Underlying ground conditions Glacial Till Drainage designed using three methods (based on current

site layout):

1. Traditional - unrestricted outfall

2. PPS25pre-development rates3. National Standards for SuDS


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Case Study


Infiltration not possible due to poor

permeability of soil.

No surface water bodies in vicinity.

Surface water sewer only method as

previous have been discounted.

Same for all three design methods.


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Case Study

ii. Peak Flow Rate and Volume Over 2400% increase in storage required from

unrestricted outfall to PPS25.

Over 3900% increase in storage required from

unrestricted outfall to National Standards. 60% more storage required for National Standards

compliance (in accordance with Approach 2) over

that of PPS25.

Also requirement for storage of 5mm event(additional 50m for case study).

Alternative - Approach 1 but approx. 380m of

rainwater harvesting but storage required as PPS25

design.


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Case Study

iii. Water Quality

No treatment stages required for roof runoff.

Two stages required for road and car park

runoff.

Separate drainage runs could be used for

eachbut due to treatment options

incorporated was not. Stages selected had limited effect on the

development proposals and could be

incorporated with existing layout.


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To Conclude

Two key changes affecting Residential

Developers

Peak flow rates and volume on areaswith

increased impermeable areas (where infiltration cannot beused).

Must be restricted to either 2l/s/ha or as CfSH.

No discharge off site for 5mm rainfall event.

Minimum treatment stages to improve waterquality.

Number of stages dependant on destination and risk of

contamination.


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Any Questions?

Or email

[email protected]

SuDs Dissertation Presentation Ryan Bruty

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