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Drainage 101

Introduction to Drainage Design

Presented by Dominic Cronin

Surface Water

Foul Water

Surface Water

Start

Discharge Rate and Attenuation

Session 1

Session 1

Discharge Rate and Attenuation

T&I Design - Flow Chart

What is Drainage

Definition: Artificial removal of water

Before Step 6, Produce Levels Model before undertaking Drainage Strategy

Surface Water

Foul Water

Rainwater runoff

Waste Water from toilets, sinks, bin store, showers

Gully

Channel Drains

Rainwater Pipes

Floor Gully (FG)

Soil Vented Pipes (SVP)

Soil Stack (SS)

Gravel Trench

Permeable Paving

Manholes

Petrol Interceptor

Attenuation Tank

Pipes

What is Drainage

Foul/Combined Sewer

Surface/Combined Sewer

Borehole

Standards

Building Regulations 2010 - Part H - Drainage and Waste Disposal

Sewers for Adoption 8th Edition

CIRIA SuDS Manual (C753) 2015

Guidance

Foul Guidance Document by Jean Benard

Two Day MicroDrainage Course Guidance

T&I Design flow Charts

Rainfall Background

Rainfall Distribution

Rainfall Profile

Difference in rainfall between NorthEast and SouthWest

15 minute, 1 year, Winter

High elevations on the West of the UK cause

the Westerly Atlantic Winds to form into frontal rainfall.

1 year

100 year

30 year

15

minute

Rainfall

Background

The intensity of rain decreases as the winds travel East across the UK.

71.271 mm/hr

174.612 mm/hr

226.002 mm/hr

1440 minute

3.092 mm/hr

8.237 mm/hr

6.457 mm/hr

Rainfall Terminology

Rainfall Theories

Rainfall Event:

Storm Duration

Return Period

Season

Climate Change

15 minute,

1 in 100 year,

Winter,

+40%

FEH99 - Flood Estimation Handbook

FSR - Flood Studies Report

Climate Change

Season Variability

Storm Duration

Published in 1999

Published in 1975

Summer

Winter (critical)

Available online, charged per dataset

Embedded, Free, within MicroDrainage

15 minutes

30 minutes

10080 minutes (1 week)

Climate change allowances are predictions of anticipated change for:

-Peak river flow

-Peak rainfall intensity

-Sea level ridse

Focused on hourly and above durations

Focused on sub-hourly events, aswell as above 1 hour

Return Period

Example: Warwickshire

20% - Minimum requirement

40% - Senstiivty Analyis

Definition - The probability of an event, such as a flood, to occur

Design Consideration

FEH shows a conservative value comapred to FSR. Therefore, FSR is an economical option.

BUT Council's request FEH data as part of planning conditions.

Return Periods

1 in 1 year

1 in 30 year

1 in 100 year

Probability

100%

33.3%

1%

Design

No Flooding, No Surcharged Pipes

No Flooding, Surcharged Pipes Allowed

Flood Allowed, if contained within site

Discharge Rates

Existing Rates

Drainage Hierarchy

Brownfield

Greenfield

Undeveloped Land

Previously Developed Land

Restrict to Greenfield Runoff Rate; varies between councils

Non-Statutory Technical Standards state:

Proposed Runoff must be "as close as reasonably practicable" to greenfield but not higher than the rate of discharge prior to redevelopment

Planning Practice Guidance and SuDS proposed the following hierarchy for surface water runoff

- 5l/s

- Restrict to each Rainfall event

- Restrict to QBAR

1. into the ground (infiltration)

Discharge Rates

2. to a surface water body

Restricting Discharge

3. to a surface water sewer, highway drain, or another drainage system

4. to a combined sewer

HydroBrake

Orifice

Small Pipe

Quick Storage Estimate (QSE)

MicroDrainage

Why is Attenuation Required?

Quick Storage Estimate (QSE)

Due to discharge rates being restricted, attenuation will be required

Attenuation (Storage)

Attenuation Pond

Attenuation Tank

Permeable Paving

Objectives

Topics

To understand the basic principles of Drainage

To understand the BWB process for Drainage Design

To understand Discharge Rates

To calculate and apply attenuation to a Drainage system

Session 2

Drainage principles

Surface Water

Start

Drainage

the artificial removal of water

Introduction

Flooding

Standards

Building Regulations 2010 - Part H - Drainage and Waste Disposal

Sewers for Adoption 7th Edition

Standards

CIRIA SuDS Manual (C753) 2015

Supporting Guidance

Foul Guidance Document by Jean Benard

Two Day MicroDrainage Course Guidance

Objectives

Designing for Flooding

Probability

Sewers for Adoption

Return Periods

1 in 1 year

1 in 30 year

1 in 100 year

100%

3.33%

1%

No Surcharge

No Flooding

Contain Flooding within site

101

Climate Change Allowances

Developed site

Undeveloped site

Development Types

Greenfield

Phase 2

Topic

Rainwater Pipes

Channel Drains

Gully

Start

Permeable Paving

Gravel Trench

Middle

Surface Water

Petrol Interceptor

Pipes

Attenuation Tank

Manholes

Outfall

Outfall Manholes

Boreholes

Topic

Foul Water

Brownfield

PCC Manhole

PCC - Pre-Cast Concrete Chamber

Type 1 (3-6m deep) and Type 2 (<3m deep) Manholes

Sizes: 900mm, 1200mm, 1500mm, 2100mm dia.

Typically serves Surface Water

Principles

PPIC Manhole

PPIC - Polypropelyne inspection chambers

Type 3 (<3m deep) and Type 4 (<2m deep) Non-entry Manholes

Sizes: 450mm dia and 600mm dia

Typically serves Foul Water

CL - Cover Level

Finished ground level

SL - Soffitt Level

Topic

Top of pipe

IL - Invert Level

Bottom of pipe

Topic

Cover Depths

What

Depth between the CL and the SL

Why

- Ensure pipe isn't crushed by surface loading

- Ensure pipe doesnt clash with services

Cover Depths

Minimum Cover Depths

Part H

Landscaping/Footway- 0.6m

Road - 1.2m

Sewers for Adoption

Landscping - 0.35m

Domestic driveway - 0.5m - 0.9m

Highawys - 1.2m

Pipe Gradient

Lower IL = Upper IL +/- Length/Gradient

Gradient = (Lower IL +/- Upper IL) / Length

Pipe Gradient

Minimum velocity that ensures non-settlement of suspended mater in sewers

Self-Cleansing Velocity

1 m/s - Surface

0.7 m/s - Foul

100mm - 1 in 60

150mm - 1 in 100

225mm - 1 in 170

300mm - 1 in 240

375mm - 1 in 320

450mm - 1 in 400

600mm - 1 in 580

Pipe Diameter

Q (l/s) = 2.78 x C x I (mm/hr) x A (ha)

Discharge

Pipe Diameter

Colebrook-White

Pipe Diameters

150mm

225mm

300mm

375mm

450mm

525mm

600mm

Diameter

Q (l/s) = 2.78 x C x I (mm/hr) x A (ha)

Q = Discharge (l/s)

"proportion of water that falls on the site entering the drainage system"

Cv = Volume Runoff Coefficient = 0.75

C = Cv x Cr

Cr = Routing Factor = 1.3

"Cr is used to factor the shape of the time-area diagram, and the peakedness of the rainfall profile"

Topic

C = 0.75 x 1.3 = 0.975 = 1

50 (mm/hr)

I = Rainfall Intensity (mm/hr)

BS8005

A = Impermeable area (ha)

Q (l/s) = 0.014 x A (m^2)

Q (m3/s) = C x I (m/s) x A (m2)

Q 0.001 (l/s) = C x I 0.001/3600(mm/hr) x 10000 A (ha)

Unit

conversion

Q (l/s) = 2.78 x C x I (mm/hr) x A (ha)

Topic

Topic

Storm Durations

15

60

10080

Foul - 1.5

Surface Water - 0.6

Example

Area of Car Park = 1000m2

Q = 0.014 x 1,000m2

Q= 14 l/s

Topic

100mm

150mm

225mm

300mm

375mm

Topic

Q = 0.014 x A (m2)

Topic

100mm - 1 in 60 (Q = 7.809)

150mm - 1 in 100 (Q = 17.723)

225mm - 1 in 170 (Q = 39.680)

300mm - 1 in 240 (Q = 71.294)

375mm - 1 in 320 (Q = 111.056)

450mm - 1 in 400 (Q = 160.387)

600mm - 1 in 580 (Q = 283.326)

Pipe Length

Pipe Length

Reference

Type 1

Type 2

Manhole Type

Type 4

Type 3

Manhole Diameter

Manhole Diameter

Exmaple

Standard/Details

Calculations

Sustainability

Session 3

Drainage Principles

Foul Water

Session 4

Introduction to Microdrainage/SuDS

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