Raingarden - Newmarket - All Saints School

Credits: Anglian Water/Atkins

Incorporating SuDS Solutions into Long-term Strategic Growth Planning

Titiksh Patel and Ben Mauck17 October 2018

Outline

› Background of the PR19 Growth Strategies

› Methodology – Process Development

› Technical Details

› Hydraulic Modelling

› Conclusions

Background

› The Anglian Water region is one of the fastest growing in the UK

› As part of PR19 planning for AMP7 Anglian Water needed to develop long term catchment strategies to manage growth risk

› The objective of the project is to understand increasing risk on the sewerage network and develop catchment strategies to meet two future design horizons:

• 2027;

• Long-term >2027 (up to and including 2040-45)

Long-termStrategic

Sustainable

Planning with

Confidence

Background – Catchment Prioritisation

› Confidence Assessment of the Growth Forecast was done based on local Plan status; Unknown, Emerging or Under Consultation

› Anglian Water Carried out Initial Catchment Screening and Seven out of the Finally Filtered Gold Catchments were Allocated to Atkins to carry out the Detailed Appraisal

Bronze >>>> Silver >>>> Gold

Source: Water Recycling Long-Term Plan (WRLTP), Anglian Water

Methodology

Project Phases

High Level Optioneering

• 25 % Area Removal & Offline Storages

Strategic Optioneering

• Targeted Area Removal from SuDS Opportunity

Mapping Tool & Flow Conveyance

Delivery Strategy • Year-on-Year Scenario Analysis• First Point of Detriment – Flow Monitoring• GIS Mapping Query to identify Flooding & Growth

Overlaps

Phase 1

Phase 2

Phase 3

Methodology - SuDS Opportunity Mapping

Opportunity mapping generated for each

catchment across the Anglian Water region

Engineering

and

geospatial

constraints

Type of

SuDS

Technical Details – Growth Modelling & Scenarios

› Growth - GIS Tool

› Development details (Nr. of Dwellings & PCC)

› Represented Development Storage

› Compliant with Anglian Water Specifications

› Modelling Scenarios

› Scenario 1 – until 2027 (No CC)

› Scenario 2 – Long-term >2027 (No CC)

› Climate Change Scenarios

› Scenario 1 – until 2027 (10 % uplift)

› Scenario 2 – Long-term>2027 (20 % uplift)

Hydraulic Modelling – Detriment Analysis

› Flooding: Develop SuDS Hybrid Solutions for Detriment of >10 % or 25 m3 and new flooding

for a 1 in 30 year return period

› Overflows: Develop SuDS Hybrid Solutions for Detriment of >1 m3 for a 1 in 5 year return

period.

Hydraulic Modelling – Solution Hierarchy

SuDS

› Blanket removal of 25 % of impervious surfaces (Phase 1 – High level)

› SuDS Opportunity mapping (Phase 2)

Sewer upsize

› Utilise downstream network capacity

Offline Storage

› Provide additional localised storage at feasible locations

Catchment A

Type of SuDSConventional

Options

Tree Pit 10 units

• 2257 m of

Sewers upsized

• 1432 m3

of off-

line storage

• 613 m3

of on-line

storage

• 2 Sealed

Manholes

Bioretention 47 m2

Swales 1127 m3

Attenuating Rain

Gardens66 m2

Disconnect Downpipes 47 m3

Filter Drains 69 m3

Permeable Block

Paving23 m2

Attenuation Pond 16 m3

Rain Gardens (Surface) 1692 m2

Soakaway 28 m3

Worst Case: Scenario 2 (>2027 + 20 % CC):

SuDS + Conventional SolutionsSuDS Hybrid Solution Summary

Catchment B

Worst Case: Scenario 2 (>2027 + 20 % CC):

SuDS + Conventional Solutions

Type of SuDSConventional

Options

Tree Pit 1 units

• 10 527 m of

Sewers upsized

• 6 071 m3 of off-line

storage

• 1 328 m3 of on-line

storage

• 14 Sealed

Manholes

Wetlands 1 m3

Bioretention 40 m2

Swales 355 m3

Attenuating Rain

Gardens20 m2

Disconnect Downpipes 11 m3

Filter Drains 23 m3

Permeable Block

Paving23 m2

Attenuation Pond 1 m3

Green Roof 41 m2

Rain Gardens

(Surface)1352 m2

Soakaway 21 m3

SuDS Hybrid Solution Summary

Delivery Strategy and Growth Profiling

› Trigger Points

› Baseline SuDS Removal

› Peak flow and volume analysis

› Overlap Analysis

› Flooding locations Vs Growth detriments

0 0765

15152353

36144477

51995754

66097604

84879325

1017010822

Y2013_14 Y2014_15 Y2015_16 Y2016_17 Y2017_18 Y2018_19 Y2019_20 Y2020_21 Y2021_22 Y2022_23 Y2023_24 Y2024_25 Y2025_26 Y2026_27 Y2027_28

Bu

ild

Ou

t R

ate

Year

Ensure solution of greatest cost benefit is promoted for Long-term investment.

Challenges and Limitations

› Growth Sites Data:

› Limited Growth Details – Polygons, Size and Connection Points

› Modelling Challenge:

› Model Quality/Confidence – Need for future surveys and verification

› Model Complexity – Stability Issues & non-linear response

› Solution Feasibility:

› SuDS – Greater Stakeholder Engagement required

› Constructability of the Capital Schemes at an early stage is not possible

Conclusions

› Value of Strategic Assessments

› More confidence in the early stages of the planning process for Anglian Water

› Collaborative approach with the Anglian Water stakeholders

› Sustainable and hybrid solutions can be incorporated as part of the growth scheme

› Developed robust modelling process for future large scale strategic growth studies

Cheaper >>> Faster >>> Smarter >>> Better

Thank You!

Acknowledgements:

› Kerry Rhodes, Supply Demand Planning Manager (Anglian Water)

› Vanessa Greaves, Lead Infrastructure Modeller (Anglian Water)

› Neil Breton, Principal Hydraulic Engineer (Atkins, Member of the SNC Lavalin Group)