red book volume_ii

VOLUME 2

HUMAN SETTLEMENT

PLANNING

AND DESIGN

G u i d e l i n e s f o r

Compiled under the patronage of the Department of Housingby CSIR Building and Construction Technology

Compiled under the patronage of the Department of Housingb y C S I R B u i l d i n g a n d C o n s t r u c t i o n T e c h n o l o g y

iGUIDELINES FOR HUMAN SETTLEMENT PLANNING AND DESIGN

Foreword

FOREWORD

The establishment of economically, physically, environmentally and socially integrated and sustainable builtenvironments is one of the most important factors which will contribute to harnessing the full developmentpotential of South Africa and addressing distortions of the past and the future needs of our growing population.This goal cannot be achieved without the active participation of especially local government, the private sector andcommunities in partnership with one another.

This manual, Guidelines for Human Settlement Planning and Design, provides a guiding vision for South Africansettlement formation, addressing the qualities that should be sought after in our human settlements, andproviding guidance on how these can be achieved. The publication has been developed over a period of more thantwo years through a participative process in which stakeholders and experts from various disciplines were involved.

This book is intended to be a living document and you, the reader, are one of its architects. I therefore encourageyou to use it, discuss it and debate the guidelines it contains. Still, this work is not the last word on the subject, andyour feedback and comments would be welcome. Your active involvement will be the key to the successfulattainment of sustainable, habitable living environments in South Africa.

MS S MTHEMBI-MAHANYELEMINISTER OF HOUSING

ii

GUIDELINES FOR HUMAN SETTLEMENT PLANNING AND DESIGN

Published by CSIR Building and Construction TechnologyP O Box 395, Pretoria, 0001

Copyright vests in the CSIR2000, CSIR, Pretoria

Boutek Report No. BOU/E2001

Reprint 2005Capture Press, Pretoria

ISBN 0-7988-5498-7

c

ACKNOWLEDGEMENTS

The following persons and organisations were involved in the preparation of this document:

Project manager:

Mr L M Austin CSIR Boutek

Project coordinators:

Ms H D Bekker CSIR BoutekDr S M Biermann CSIR BoutekMr J S Stiff CSIR TransportekMs L Vosloo CSIR BoutekMr K M Wolhuter CSIR Transportek

Authors:

Mr A Adam MCA Urban and Environmental Planners ccMr L M Austin CSIR BoutekDr D I Banks Energy & Development Research Centre, University of Cape TownMr R Behrens Urban Problems Research Unit, University of Cape TownMr W Blersch Ninham Shand (North) (Pty) Ltd, Consulting EngineersMs E Brink CSIR BoutekMs K Burger Burger & Waluk Town PlannersMr J W M Cameron TRC Africa (Pty) LtdMr W D Cowan Energy & Development Research Centre, University of Cape TownProf D Dewar School of Architecture & Planning, University of Cape TownMr L Druce VBGD Town & Regional PlannersMs L C Duncker CSIR BoutekMr O J Gerber GIBB Africa (Pty) Ltd, Consulting EngineersMr D J Jones CSIR TransportekMr G Jordaan Holm & Jordaan Architects and Urban DesignersMs T Katzschner Urban Problems Research Unit, University of Cape TownMs K Landman CSIR BoutekMs A Lebelo Ninham Shand (North) (Pty) Ltd, Consulting EngineersMs A Loots Holm & Jordaan Architects and Urban DesignersMs N Mammon Mammon Rendall Planners and Designers ccMr G J Morris Feather EnergyDr P Paige-Green CSIR TransportekMr E R Painting Mothopo Technologies cc, Management & Engineering ConsultantsMr C Sadler Bergman-Ingerop (Pty) Ltd, Consulting EngineersMr J S Stiff CSIR TransportekMr J S Strydom CSIR BoutekMr H L Theyse CSIR TransportekProf F Todeschini School of Architecture & Planning, University of Cape TownProf R Uytenbogaardt School of Architecture & Planning, University of Cape TownMr S van Huyssteen CSIR TransportekProf A T Visser Department of Civil Engineering, University of PretoriaDr K C Wall Ninham Shand (Pty) Ltd, Consulting EngineersProf V Watson Urban Problems Research Unit, University of Cape TownMr K M Wolhuter CSIR Transportek

The NRS Project, Eskom, provided material on electricity supply, based on documents approved by the ElectricitySuppliers Liaison Committee, on which Eskom, AMEU, the Chamber of Mines and the South African Bureau ofStandards are represented.

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Acknowledgements

iv


Acknowledgements

Steering Committees:

Ms G Abrahams Gemey AbrahamsDevelopment Planning andHousing Policy Consultant

Prof W J R Alexander Department of CivilEngineering, University ofPretoria

Mr W S D Clarke Southern Metropolitan LocalCouncil of GreaterJohannesburg

Mr P Dacomb Association of ConsultingTown and Regional Planners

Mr R Dauskardt Department of Development& Planning, Gauteng

Mr J de Meyer Wade RefuseMr F Druyts Department of Water Affairs

& ForestryMr S Hartley Department of Water Affairs

& ForestryProf E Horak Department of Civil

Engineering, University ofPretoria

Mr D Hunt Eskom / NRSMr B M Jackson Development Bank of

Southern AfricaMr A Lagardien School of Architecture,

Building and CivilEngineering, PeninsulaTechnikon

Mr N Letter Eastern MetropolitanSubstructure of GreaterJohannesburg

Mr N A Macleod Durban MetroMr G A Norris CSIR BoutekMr A Otto Department of Minerals &

EnergyMr I H Palmer Palmer Development GroupMr G Schermers CSIR TransportekMr C J Schlotfeldt CSIR BoutekMr C Theron Greater Pretoria Metropolitan

CouncilMr J van der Walt Department of TransportDr I van Wyk Africon, Consulting EngineersMr P S Van Zyl South African Planning

InstitutionMr P Vickers Department of Water Affairs

& ForestryProf A T Visser Department of Civil

Engineering, University ofPretoria

Mr H Vorster City Council of PretoriaMr J A Wates Wates, Meiring & Barnard,

Consulting Engineers

Coordinating Committee:

CSIR Boutek representatives:

Mr L M AustinMr C J Schlotfeldt

Departmental representatives:

Mr P F Jordaan Environmental Affairs &Tourism

Mr M Krynauw TransportMr Z Nofemela Constitutional DevelopmentMr G Oosthuizen Water Affairs & ForestryMr G Oricho Land AffairsMr A Otto Minerals & EnergyMr S J Smit Public WorksMr U Tembo TransportMs L van Zyl Trade & IndustryMr J Wallis HousingMs B Zinde Environmental Affairs &

Tourism

Provincial representatives:

Mr C W Browne GautengMr C Burger Eastern CapeMr J A Cattanach GautengMr D B Dunstan KwaZulu-NatalMr A T Fourie Western CapeMr S F Haasbroek Northern CapeMr H G Hadebe MpumalangaMr P Labuschagne Free StateMr M M Mokoena Free StateMr C H A Ratnam North WestMr R J Stubbs KwaZulu-NatalMr M van der Merwe Northern Province

Others:

Mr R G Bhmer CSIR BoutekMs C du Plessis CSIR BoutekMr D M Kruger CSIR BoutekMs S Liebermann CSIR BoutekMr M Mavuso CSIR BoutekMr K J Mkhabela CSIR BoutekMr M Napier CSIR BoutekMs I S Oberholzer CSIR BoutekMs I Ringel CSIR BoutekMs L Slump CSIR BoutekMs B J van Reenen

Photographs, Chapter 6:

Mr E R Painting Mothopo Technologies cc,Management & EngineeringConsultants

Cover design:

Truter & Truter Design & Advertising (Pty) Ltd

Design and layout:

African Watermark Graphic Design

RECORD OF REVISIONS AND AMENDMENTS

Revisions: Remove existing chapter(s) and substitute with the attached revised chapter(s).

Amendments: Remove existing page(s) and substitute the attached new page(s). A vertical line in the marginshows where a change has been made (there are no amendments to date).


Record of revisions and amendments

Date Chapter Title Rev Amdt PageNo. No. number(s)

August 2003 9 Water supply 1 - All

August 2003 10 Sanitation 1 - All

Volume 2

Index

Chapter 1 Introduction

Chapter 2 A framework for settlement-making

Chapter 3 Spatial and structural principles for settlement-making

Chapter 4 Planning method and participation

Chapter 5 Planning guidelines

5.1 Movement networks5.2 Public transport5.3 Hard open spaces5.4 Soft open spaces5.5 Public facilities5.6 Land subdivision5.7 Public utilities5.8 Cross-cutting issues

5.8.1 Environmental designfor safer communities

5.8.2 Ecologically sound urban development

5.8.3 Fire safety

Chapter 6 Stormwater management

Chapter 7 Roads: Geometric design and layoutplanning

Chapter 8 Roads: Materials and construction

Chapter 9 Water supply

Chapter 10 Sanitation

Chapter 11 Solid waste management

Chapter 12 Energy

12.1 Grid electricity12.2 Other forms of energy

Volume 1

Stormwater management

Chapter 6

6

TABLE OF CONTENTS

INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

The impact of development on the natural environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Drainage laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

The dual drainage system. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Development changes the environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

The requirement for integrated planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

THE PURPOSE OF STORMWATER MANAGEMENT. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

PLANNING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Master planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Detailed design. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

MANAGING THE IMPACT OF DEVELOPMENT ON THE ENVIRONMENT . . . . . . . . . . . . . . . . . . . . . . . . . 8

Rural development . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Layout planning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Preserving the natural environment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

TECHNOLOGIES AVAILABLE TO THE ENGINEER . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

The hydrologic cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Flood routing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Flood-line determination . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Detention and retention facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Outlets at stormwater-detention facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Bridge backwaters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Erosion protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Transitions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Kerb inlets. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Side weirs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Road drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Roof drainage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Upgrading issues. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

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Stormwater management Chapter 6

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POLLUTION ABATEMENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

Sources of pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

Soil erodibility. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Grass-lined channels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Detention ponds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Wetlands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Protection of the environment during the construction phase . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Street cleaning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Waste disposal sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Sanitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Water supply. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Selection of cemetery sites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

MAINTENANCE ISSUES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Detention facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

Design details . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

ENVIRONMENTAL HEALTH AND SAFETY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

The role of education and community involvement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Awareness of hazardous situations and flood warning systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

Recreational use of facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

General precautions for development on dolomites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

GLOSSARY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

APPENDIX A . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33

APPENDIX B . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

APPENDIX C . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

LEGISLATION CITED. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

CASE LAW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

LIST OF TABLES

Table 6.1 Design flood frequencies for major systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Table 6.2 Design flood frequencies for minor systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .7

Table 6.3 Suggested maximum encroachment of runoff on roads during minor storms . . . . . . . . . . . . . . .15

Table 6.4 Problems commonly experienced with storage facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26

Table 6.5 Suggested minimum grades for pipes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

Table 6.6 Suggested spacing of anchor blocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

LIST OF FIGURES

Figure 6.1 San Antonios famous main riverwalk loop. This tourist attraction can be isolated by itssophisticated flood attenuation and flood prevention facilities during major stormevents. The project will enable a 100-year flood to be accommodated through theSan Antonio River system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Figure 6.2 Damage from major floods can be catastrophic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Figure 6.3 Contour planning: An effective stormwater management tool . . . . . . . . . . . . . . . . . . . . . . . . . . . .8

Figure 6.4 Overgrazing exposes the land to rain damage and can result in extensive erosion . . . . . . . . . . . .9

Figure 6.5 Runoff from feedlots contains high levels of pollutants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9

Figure 6.6 Dump sites must be protected against extraneous runoff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10

Figure 6.7 Multiple-outlet structure of a detention pond . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11

Figure 6.8 Simple drop structures in a residential environment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Figure 6.9 Energy dissipator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Figure 6.10 Energy dissipator in a multiple land use setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12

Figure 6.11 A lined open roadside channel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Figure 6.12 Incorrect vertical alignment has caused stormwater to bypass this kerb inlet. Kerbinlets in the intersecting road on the left have also not captured runoff from that road so that stormwater flows across this bus route, creating a hazard . . . . . . . . . . . . . . . . . . . .14

Figure 6.13 This ponding is the result of encroachment of the grass verge onto the road.Grass-cutting maintenance operations should also include harvesting the grass, toprevent siltation and build-up of new grass growth . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Figure 6.14 Flow across this intersection has resulted in siltation, which is inconvenient andhazardous to road users . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Figure 6.15 Example of surface drainage in a residential setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14

Figure 6.16 Open channel alongside an arterial road . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15

Figure 6.17 The contour-planning concept, to impede the drainage of runoff from the development . . . . .16

Figure 6.18 (a) and (b): Concentration of stormwater drainage in a roadway resulting in major inconvenience to road users . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

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iv



Figure 6.19 Roadside drains of the major system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16

Figure 6.20 (a) and (b): Layout planning in steep terrain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17

Figure 6.21 This office complex incorporated the entrance to the building in a detention facility. Under normal conditions, this area functions as a pleasant park with water features . . . . . . . . .18

Figure 6.22 (a): Depressed area to store excess runoff . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

Figure 6.22 (b): Runoff from this parking area is stored in the drainage ways usingmultiple-outlet drains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18

Figure 6.23 Gully erosion by headwater upstream of a highway culvert inlet. Specific attentionneeds to be paid to structures founded in soils with high erosion potential . . . . . . . . . . . . . . . . .20

Figure 6.24 An example of a grassed waterway . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20

Figure 6.25 Part detention, part retention facility, including an artificial wetland . . . . . . . . . . . . . . . . . . . . .22

Figure 6.26 (a) and (b): Construction sites can be prevented from polluting the surrounding area bythe use of straw bales, mulching and geo-mats. Aggregates placed at exits from sites prevent the transport of pollution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22

Figure 6.27 Stone aggregate can be placed on the roadside while the shoulder grass establishes itself . . . . .22

Figure 6.28 The straw-bale barrier has allowed pioneer plants to establish themselves . . . . . . . . . . . . . . . . .23

Figure 6.29 Unmanaged domestic refuse is a serious health risk . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

Figure 6.30 Uncontrolled dumping at municipal waste sites can have a serious impact on surface and sub-surface water systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24

Figure 6.31 This water point has been placed in a low-lying area. Drainage of runoff and waterspilled from the point has not been allowed for, and a health hazard has resulted . . . . . . . . . . .24

Figure 6.32 These sports fields will act as a detention facility should the watercourse on the right of the picture not be able to convey the flood. Note that the playing surfaces are raised to aid drainage after such an event. The crest of the side weir between the watercourse and the sports fields is designed to accept the excess flow, but is made aesthetically pleasing with a meandering cycle path . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25

Figure 6.33 Inlet grids need attention . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

Figure 6.34 Kerb inlets require maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27

Figure 6.35 The use of underground drainage systems in unpaved roadways should be justified . . . . . . . . . .28

Figure 6.36 Stormwater drainage must occur off the roadway if kerbing is not installed . . . . . . . . . . . . . . . .28

Figure 6.37 Flood-warning systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28

Figure 6.38 This nature trail has a problem with pampas grass (Cortaderia jubata), an alien invader . . . . . . .29

Figure 6.39 Dolines are almost always the result of mans intervention in natural drainage systems. This sinkhole has been caused by a road culvert . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29

INTRODUCTION

The impact of development on the naturalenvironment

Development is a process of growth and change,which implies improvement. Any development willtherefore affect or impact on its environment in someway or other. We consider the building of roads, theerection of buildings and the general improvement offactors that cause inconvenience - like the drainage ofstormwater - as development. However, thisdevelopment may significantly change the hydraulicproperties of an area. Typically, pervious layers arerendered less permeable or even impermeable.Depressions are raised to prevent ponding. Surfacesand conduits are constructed to drain runoff moreefficiently. Natural vegetation is often removed,allowing reduced interception and transpiration.Limited vegetation cover exposes the soil to the impactof rain, which may lead to increased erosion. Naturalmeandering watercourses may be canalised to moreeffectively route flows through the development.Stormwater management is the science of limitingthese negative impacts on the environment andenhancing the positive impacts, or catering for thehydraulic needs of a development while minimisingthe associated negative environmental impacts.

Drainage laws

Increasing development densities have influenced theservitude required to safely discharge runoff into thenatural environment. This densification andmodification of undeveloped land has also resulted inincreased quantities and concentrations of flow with aconcomitant increase in pollution.

Upstream landowners responsibilities for dischargingrunoff onto downstream properties, and theconcomitant responsibilities of downstream ownershave a long history which is based largely on commonlaw. This has been modified somewhat by legislationgiving certain rights to central, regional and localauthorities.

Three rules are generally applicable throughout theworld today as far as the drainage of surface runoff isconcerned. These concern:

the common enemy concept; natural flow; and reasonable use.

Stormwater runoff is considered a common enemyand each property owner may fight it off or control itby retention, diversion, repulsion or alteredtransmission. The focus of the common enemy rulehas two focal points:

The need to make improvements to property, with

the acknowledgement that some damage resultsfrom even minor improvements; and

The principle of granting each landowner as muchfreedom as possible to deal with his land essentiallyas he sees fit.

The natural flow (or civil law) rule places a naturaleasement upon the lower land for the drainage ofsurface water along its natural course, and the naturalflow of the water may not be obstructed by the ownerof the lower property to the detriment of the interestsof the owner of the higher property.

This rule has been modified to some extent in allowing,for example, surface runoff to be accelerated orotherwise altered into the natural stream. Thelandowner may, however, neither overtax the capacityof the watercourse nor divert into it runoff that wouldnot naturally have drained into the watercourse (seeBarklie v Bridle 1956 (2) SA 103 (S.R.)).

In efforts to promote drainage, many of thesemodifications to the natural-flow rule increase theburden on the lower land.

The reasonable-use rule provides that each propertyowner is permitted to make reasonable use of his land,even though by doing so he may alter the flow of thesurface waters and cause harm to others. He incursliability when his interference is unreasonably harmful(see Redelinghuis v Bazzoni 1975 AD 110(T)).

One can see that, in developing property, it isextremely difficult not to concentrate, increase oraccelerate stormwater runoff onto downstreamproperties. Through the provincial ordinances, theauthorities have been invested with the right tochange the natural drainage of stormwater in theinterests of the public as a whole. However with thisright comes the responsibility to act with due care inkeeping the effects of such deviations withinacceptable limits. The general rule that statutoryauthority when constructing a work is excused fromliability for damage thereby caused to third persons issubject to the proviso that the work must not benegligently executed or maintained (see New HeriotGold Mining v Union Government (Minister ofRailways and Harbours) 1916 AD 415, 421;Johannesburg Municipality v Jolly 1915 TPD 432;Herbert Holbrow (Pty) Ltd v Cape Divisional Council1988 (1) SA 387(c)).

To ameliorate this development phenomenon, certainstrategies and technologies are available. The goals ofstormwater management should support thephilosophy of lessening the impact of stormwater flowthrough and off developed areas. Stormwater shouldbe considered a resource (see Figure 6.1).

1



2GUIDELINES FOR HUMAN SETTLEMENT PLANNING AND DESIGN


It is within the power of the local authority toconstruct works such as streets and drains which willhave an effect on the flow (quantity, quality andvelocity) of stormwater discharged on the downstreamland.

Public bodies have been entrusted with statutorypowers to enable them to carry out public duties. If itis impossible for them to carry out their duties withoutinfringing upon the rights of others, it may be inferredthat the legislators intended them to have the powerto do so, in spite of the prejudicial effect onindividuals. If, however, damage that could reasonablyhave been prevented is caused to individuals, thefailure to take reasonably practicable preventivemeasures is negligence.

Case law offers opinions and provides principles onwhich to base the extent of liability of a local authorityfor damage caused by an increase in stormwater flow.In some cases the issue may be whether interferencewith private rights is justified where the exercise ofstatutory powers is alleged to have resulted in aninjury to another.

Prohibition against pollution is addressed in Clause 19

of the National Water Act, Act 36 of 1998. This sectiondeals with pollution prevention, and in particular thesituation where pollution of a water resource occurs ormight occur as a result of activities on land. The personwho owns, controls, occupies or uses the land inquestion is responsible for taking measures to preventpollution of water resources.

The dual drainage system

Developed areas are defined as any man-induceddevelopments which have changed the environment.In this chapter, all developments in the continuumfrom rural to urban settings will be addressed.

Traditionally, runoff from frequent (minor) storms hasbeen carried in the urban formal drainage systems.Typically this was achieved by draining runoff fromproperties into the streets and then via conduits to thenatural watercourses. The system was intended toaccommodate frequent storms and associated runoff.Today, the value of property is of such significance thatengineers need to consider not only frequent stormsbut the more severe storms, which can cause majordamage with sometimes catastrophic consequences(see Figure 6.2). The dual system incorporates a minorsystem for the frequent storm events and a majorsystem for the less frequent but severe storm events.The major system may include conduits and natural orartificial channels, but would commonly also make useof the road system to convey runoff overland tosuitable points of discharge. This is not very differentfrom what has happened de facto except that formalcognisance is now given to the routing of runoff fromall storms via the secondary use of roads and otherfacilities in the urban environment.

The use of the road system and open spaces (such as

Figure 6.1: San Antonios famous main riverwalkloop. This tourist attraction can be isolated by its

sophisticated flood attenuation and flood preventionfacilities during major storm events. The project will

enable a 100-year flood to be accommodatedthrough the San Antonio River system

Figure 6.2: Damage from major floods can becatastrophic

parks and sports fields) as drainage components of themajor system, while imposing inconvenience to roadusers, is considered an acceptable land-use for thesesevere storm events.

Development changes the environment

High regard needs to be given to natural drainagepatterns and systems. This is because developmentinterferes with these systems. Stormwatermanagement must therefore consider howdevelopment has interfered or will interfere with thenatural systems. The design engineer, with theplanning team, must then plan on how to cope withthese changes, to lessen the impact of the alteredrunoff caused by this development.

It is recognised that development impacts negativelyon the natural drainage systems in several ways:

Permeability of the development area is decreasedthrough increased population densities and feweropen spaces such as parks and gardens, or by theintroduction of impervious areas such as surfacedstreets, houses and amenities associated with theurban environment. This increases the runoff fromthe area during storm events, because of thereduced infiltration properties of the developmentarea.

The introduction of efficient stormwater drainagesystems to deal with the common enemy impliesthat the runoff must be conveyed as efficiently aspossible to the natural watercourses. Theoperative word efficient is here related to cost-efficiency. This has the effect of decreasing thetime runoff takes to reach the naturalwatercourses. The result is a reduction of overlandflow, meandering watercourses and the like,through a system which drains runoff to thewatercourses as quickly as possible. The floodproblem is therefore transferred downstream.Quicker responses in larger catchments makethem more susceptible to the effects of high-intensity, shorter duration storm events.

In more efficient drainage systems, peak flowsoccur more quickly. This effect has madedevelopments more susceptible to shorter, moreintense storm events which in the smallercatchments may lead to greater peak flows.

The drainage systems are exposed to flows frommore frequent, higher intensity storms because ofthe decreased times of concentration. It isrecognised that short-duration storms have higherrain intensities than the longer rainfall events. Thisincreases the pressure put by the frequent, high-intensity storms on the man-made drainagesystems, which in turn put more pressure on thenatural drainage systems.

The quality of the runoff deteriorates. One only hasto consider runoff from man-made environmentswhich conveys pollutants such as fertilisers,discarded rubbish, spillages and discharges fromvehicles, septic tank effluent as well as eroded soil.

The requirement for integrated planning

Against this background, the responsibility for soundplanning to lessen these negative impacts rests withthe whole design team, and not just with the drainageengineer. A holistic approach to planning needs to betaken, whereby land use is identified and a commoncommitment to its optimisation forms the backgroundto the planning premises.

Where development projects are carried out withlimited funds, the question of minimum allowablestandards always comes to the fore. It is in thesecases, especially, that the development equationbecomes a question of balancing low capital cost atdevelopment stage against high maintenance costs forthe rest of the time.

THE PURPOSE OF STORMWATERMANAGEMENT

Stormwater management is based on

the need to protect the health, welfare and safetyof the public, and to protect property from floodhazards by safely routing and dischargingstormwater from developments;

the quest to improve the quality of life of affectedcommunities;

the opportunity to conserve water and make itavailable to the public for beneficial uses;

the responsibility to preserve the naturalenvironment;

the need to strive for a sustainable environmentwhile pursuing economic development; and

the desire to provide the optimum methods ofcontrolling runoff in such a way that the mainbeneficiaries pay in accordance with their potentialbenefits.

While these goals may be reflected in other disciplines- and indeed may even be in apparent conflict withone another - specific objectives supporting theseoverall goals need to be identified for each specificproject by the planning team.

3





PLANNING

Introduction

Planning is a fundamental function of the projectteam. It determines what the team wants to attain andhow it should go about doing so. Some strategic issuesneed to be considered before any detailed designwork can be entertained. This is strategic planning ormaster planning.

Master planning

The whole purpose of planning is to facilitate theaccomplishment of a projects objectives. Whichobjectives or goals drive the process really depends onthe state of mind of those formulating them, butgenerally should spell out the why, where, what, whenand how of the endeavour. Land use planning shouldbe a consideration of what land resources are availableand what they are suitable for, both in the short termand longer term.

Master planning should be concerned with thefollowing principles:

Sustainable development

A key concept of master planning should aim at anenduring or sustainable development.

An initiative called Caring for the earth, a strategyfor sustainable living, launched in partnership withthe World Conservation Union, the United NationsEnvironment Programme and the World WideFund for Nature, stressed two fundamentalrequirements for sustainable agriculture, namely:

securing a widespread and deeply heldcommitment to an ethic for sustainable living;and

integrating conservation and development.

The World Health Organisations Global Strategyfor Health and Environment was a direct result ofthe United Nations Agenda 21 which was drawnup during the Earth Summit in June 1992 at theUnited Nations Conference on Environment andDevelopment (UNCED) in Rio de Janeiro, Brazil.Agenda 21 was an action plan to guide nationaland international activities to ensure that thenatural resources of the world are managed in sucha manner that sustainable development isachieved. The term sustainable development canbe defined as development that meets the needs ofthe present without compromising the ability offuture generations to meet their own needs.

The idea that should guide all planning is thatthere is an interrelationship between the three

concepts of health, the environment anddevelopment. Any change taking place in the onehas a direct influence on the other two.

An essential element of rational land-use planningis land evaluation, which should be a systematicway of looking at the options available and ofconsidering the environment in which theseoptions are likely to operate, so that the results ofdifferent courses of action can be predicted.Physical planning therefore cannot be divorcedfrom social and economic circumstances or fromadministrative and constitutional processes. Moreimportantly, the protection of the environmentagainst pollution decay is essential, to optimise thebenefits of sustainable development.

Integration with other disciplines in theplanning team

Development produces waste products. Whenpeople choose to live closer both to one anotherand to economic opportunities, there is inevitablyan increase in the generation of waste products.The increased volume of wastes needs to bemanaged to lessen the impact on the environment.Solid waste technologies, the siting of cemeteries,water purification works, sewage works andindustries are typical issues facing the planningteam in the initial stage. All concern thestormwater specialist.

Layout planning and transport routes inevitablyaffect the natural drainage of stormwater. Theseconstraints must be explored. Natural habitatswill be affected and their importance must notbe ignored.

Drainage of both sewage and stormwater is anatural constraint to development that may haveto take priority over other services and amenities.

Policy impact assessment

All planning must start with certain premises. Manyof these are dictated by outside influences andtheir impact on the planning at hand must berecognised and considered.

Policy guidelines from external sources mayinfluence the objectives of any development. Apolicy impact assessment may be required toevaluate the importance of these policies and howthey can affect or impact on the planneddevelopment. External influences may includepolicies from

the World Health Organisation;

the United Nations (UNCED);

the South African Constitution;

the Governments Reconstruction andDevelopment Programme;

white papers involving water law, water supplyand sanitation - Department of Water Affairs &Forestry (DWAF); and

integrated environmental managementprocedures - Department of EnvironmentalAffairs & Tourism (DEAT).

While these issues may not all be obligatory, theydo serve as a platform or frame of reference froma global and national perspective. They mayinfluence the planning premises.

Strategic impact assessment

Certain constraints to planning and developmenthave to be considered. These are mainly connectedwith the legal environment. A strategic impactassessment must involve consideration of the aimsof the following legislation:

National Water Act Water Act (Act 36 of 1998):To provide for the fundamental reform of thelaw relating to water resources and to providefor matters connected therewith.

The legal responsibilities of the stormwaterspecialist influence the planning. The insertionof 20-year and 50-year flood lines on certaintownship plans is an example. Whatdevelopment takes place within these floodlines must be explored. The protection ofsewage treatment works, cemeteries and solidwaste sites from flooding must be considered.

Conservation of Agricultural Resources Act (Act43 of 1983):To provide for the control over the utilisation ofthe natural agricultural resources in theRepublic in order to promote the conservationof the soil, the water resources and thevegetation and the combating of weeds andinvader plants.

Government Notice No. R1048 of GovernmentGazette No. 9238 of this Act indicated that:No land user shall ... cultivate any land on hisfarm unit within the flood area of a watercourse or within 10 metres horizontally outsidethe flood area of a water course.

The flood area in relation to a water course isdefined as the area which, in the opinion of theexecutive officer, is flooded by the flood waterof that water course during a 1-in-10 year flood.

Environment Conservation Act (Act 73 of 1989):To provide for effective protection andcontrolled utilisation of the environment.

National Roads Act (Act 54 of 1971):To provide for the construction and control ofnational roads, including the disposal ofstormwater on a national road.

Minerals Act (Act 50 of 1991) and itsRegulations:Specific issues relating to the EnvironmentalManagement Programme (EMP) are relevant.

Minimum requirements for disposal of waste:Minimum requirements issued by theDepartment of Water Affairs & Forestryregarding the selection of sites, theirdevelopment and management and eventualclosure. Three specific references are:

- Minimum requirements for the disposal ofwaste by landfill.

- Minimum requirements for the handlingand disposal of hazardous waste.

- Minimum requirements for monitoring atwaste management facilities.

Health Act (Act 63 of 1977):To provide for measures for the promotion ofhealth of the inhabitants of the Republic.

Atmospheric Pollution Prevention Act (Act 45 of1965):To provide for the prevention of pollution ofthe atmosphere.

Specific measures are required for thepurification of effluents discharged fromappliances for preventing or reducing to aminimum the escape of any noxious oroffensive gases escaping into the atmosphere,and for preventing the release of noxious oroffensive constituents from such effluents intodrains and drainage canals.

Common law, case law and statutory law:Certain laws of parliament, provincialordinances and government notices can alterexisting rules and lay down the law, as it were.These statutory laws create legal duties uponspecific persons or bodies and thus determinewho is to be sued in delict when damage iscaused (Committee of State Road Authorities1994). Any person or body performing tasks inpursuance of statutory authority bestowedupon him or her to construct works such asstreets and drains should heed the principles ofthe delict, to avoid legal liability for damagesuffered by another party.

5





The basic starting point in South African law asregards the question of damage is the rule thatharm rests where it falls, i.e. everyone mustbear the damage he suffers, himself (Neethlinget al 1990). However, there are grounds whichcan cause this burden of damage to shift toanother, with the result that such other isobliged to bear the formers damage. Thisshifting (which forms the basis of the lawknown as law of obligations) of the burden canresult from the causing of damage to a personby means of a delict (law of delict). Delict can bedefined as the positive act or omission of aperson, which in a wrongful and culpable(intentional or negligent) way causes harm toanother. The main source of law upon whichthe South African law of delict has developed iscase law.

Other requirements may include:

- Interim guidelines on safety in relation tofloods. Safety evaluation of dams. SouthAfrican Committee on Large Dams,September 1986. The new requirements arecontained in Government GazetteRegulation Gazette No 3979, Vol 253,No 10366. Government Notice No R.1559.

- A guideline for groundwater protection forthe community water supply and sanitationprogramme, 1995.

- South African Natural Heritage Programme.

- Conservation of wetlands (Department ofEnvironmental Affairs & Tourism) andreports to the Ramsar Convention.

Stormwater management master drainageplan (MDP):

Master drainage planning should be contemplatedon a catchment-wide basis, irrespective of urbanand other man-made boundaries. The fullenvironmental impact of the stormwater on thatcatchment must be investigated and is theresponsibility of the controlling regional or localauthority. The hydrological processes in the specificarea need to be investigated and statistical dataobtained. Hydraulic routing of the stormwatermust be considered. In analysing stormwaterdrainage, consideration may need to be given tothe use of open spaces like parks, sports fields, andtransport circulation routes.

It is assumed that with development there is anincrease in both the overall quantity and the peakflow rate of the runoff. Policies in the USA, forexample, desire to restrict post-development peakfactors to pre-development peak factors. This

involves the retarding of stormwater on its route tothe drainage streams. The important issue that thedrainage specialist must address is theconsideration of every storm event - from a severe,infrequent storm event (termed a major event) tothe frequent, common storm events (termed minorevents). Stormwater drainage technologies mustbe developed to deal with all these events. Atypical formal drainage system avoids the nuisancewhich might result from frequent storms. This istermed the minor system. The major system will besupported by the minor system but willaccommodate the unusually high runoff frominfrequent hydrologic events.

Master planning is predominantly concerned withthe major system. The minor system will beconsidered as a supporting one. Master planningmay involve

determination of the recurrence interval of themajor flood event;

determination of the recurrence interval for theminor flood events;

provision of overall guidelines on runoff-detention requirements, pollution-abatementstrategies, and the powers and responsibilitiesof developers and authorities within thecatchment area;

consideration of land use within flood plainsand multi-use of stormwater facilities;

guidelines on safety and maintenance;

guidelines on environmental conservation; and

reference to integrated environmentalmanagement (IEM) procedures and principlesunderpinning the Reconstruction andDevelopment Programme.

While the values in Tables 6.1 and 6.2 areguidelines, the onus is on the drainage engineer todetermine the risk associated with a certainrecurrence interval. For areas where the risk ofmonetary loss, loss of revenue or loss of utilities isunacceptably high, a more stringent (or higher)recurrence interval and a higher level of servicemay need to be considered. On large structuressuch as bridges and major culverts for example, theDepartment of Transport has its specific analysisrequirements (Committee of State RoadAuthorities 1994).

A 100-year recurrence interval flood line is requiredin terms of the National Water Act on residentialdevelopment plans. Municipal authorities may,however, stipulate other flood lines. The concepts

of best management practices (BMPs), goodpractice, or best available technology not entailingexcessive cost (BATNEEC) may convince theplanning team that more stringent recurrenceintervals need to be considered, including planningfor regional maximum floods (RMFs) or probablemaximum floods (PMFs).

Detailed design

Stormwater drainage plan

Detailed planning refers to the planning ofdevelopments within a catchment. The designphilosophies and critical concerns and issues willhave been addressed in the master drainage plan.Stormwater drainage planning is theimplementation of those policies and guidelines. Itshould strive to commit responsibilities to thedesign team and the authorities. Genericresponsibilities include

planning, feasibility studies and preliminarydesign;

records of decisions and the development of anauditing system;

detailed design;

implementation or construction;

the process of handing a scheme over to aresponsible authority;

operation and maintenance; and

monitoring and reporting (elements of theauditing system).

Typically the controlling authority should beresponsible for ensuring that detailed planning iscompatible with the master drainage plan and thatthe objectives of stormwater management areattained. The design team needs to considerresponsibilities throughout the design life of theproject or development - the cradle-to-graveapproach.

Responsibilities for runoff control

Stormwater management within an urban area isthe responsibility of the local authority for thatarea, since the control of stormwater is considereda purely local matter.

Certain central and provincial governmentlegislation, however, has encroached on the localauthoritys planning. Examples are

the requirement to insert the 1-in-100 yearflood lines on all township development plans(National Water Act 36 of 1998);

prevention of water pollution (consumers)regulated by the departments of Water Affairs& Forestry, Environmental Affairs & Tourism,and Health;

safety of dams (approved ProfessionalEngineer);

alteration of a public stream (Transvaal RoadOrdinance 22 of 1957; Agricultural Holdings(Transvaal) Registration Act No 22 of 1919;Orange Free State Roads Ordinance 4 of 1968);

auditing systems and records of decision (IEM);and

7



Residential 50 years

Institutional (e.g. schools) 50 years

General commercial and industrial 50 years

High value central business districts 50 - 100 years

Table 6.1: Design flood frequencies for major systems

LAND USE DESIGN FLOOD RECURRENCE INTERVAL

Residential 1 - 5 years

Institutional (e.g. schools) 2 - 5 years

General commercial and industrial 5 years

High value central business districts 5 - 10 years

Table 6.2: Design flood frequencies for minor systems

LAND USE DESIGN FLOOD RECURRENCE INTERVAL



Mines and Works Act.

Detaining and retaining stormwater

Runoff can be stored in constructed dams.However, to be effective, such dams usuallydemand much space. Successful detention ofrunoff may therefore have to rely on severaltechnologies involving

detention ponds (detention facilities) or roof-top detention;

a preference for overland flow as opposed tohydraulically efficient engineering conduits;

maintaining pervious surfaces and reducingimpervious structures; and

maintaining vegetation cover to increaseinterception and evapotranspiration.

MANAGING THE IMPACT OFDEVELOPMENT ON THEENVIRONMENT

Rural development

The issues and concerns in rural environments maydiffer from those in the urban setting. Typical issuesmay include erosion, and soil salinisation. Transportroutes may have gravel surfaces, and technologiesused to drain runoff need to be carefully considered.

Layout planning

Many of the grid-type layouts inevitably concentratestormwater in certain roadways. This is usually the casewhen planners design systems applicable to moderntechnological standards when they know thatupgrading to these standards may take place only inthe very distant future, if at all.

What is proposed is a move towards what agriculturalengineers and conservationists have always practised -contour planning (e.g. contour ploughing, which isploughing that follows the contours of land,perpendicular to its slope). This technology isparticularly applicable to the more rural type ofdevelopment (see the section on unsurfaced roadsbelow for more detail).

An example of a tea estate demonstrates this type oflayout well (see Figure 6.3). All access paths (whichcould be substituted by access roads in an urbanenvironment) follow the contours. Other tracks arerouted at right angles to the contours so that noextraneous runoff crosses or drains onto them. Allstormwater can then be routed along the access pathsto the natural channels or waterways.

The advantage of contour technology is that all flow isrouted overland in open channels. This minimises boththe flow volumes (drainage occurs regularly) andvelocities (open channel flow with flat gradients). Thisreduces erosion. Soakaways, permeable strata,vegetation interception, retention/detention facilitiesare some of the many tools at the drainage engineersdisposal. Overland flow in ditches or swales should bedesigned at the outset with the road layout planners,not afterwards. Where road crossings are required,causeways and drifts are easily constructed. This allowsfor the use of local labour and materials. Dropstructures may also be included with silt traps,allowing maintenance workers to reclaim soil lost fromthe upstream area.

Preserving the natural environment

Natural resources

Before any layout planning should begin, detailedinformation regarding topography, geology,hydrology, and fauna and flora, needs to beobtained. Areas containing building materials(sands, aggregates, road materials, clays and thelike) should not be sterilised by other land useswithout consideration being given to theirpotential utilisation. Sandy areas are useful forrecharging ground water. High-intensitydevelopment can be matched with soils of lowpermeability and vegetation of poor quality.

Figure 6.3: Contour planning: An effectivestormwater management tool

Alternative fuel sources may need to be developed.Otherwise uncontrolled denudation of the naturallandscape may seriously damage the environment,leading to rapid degradation and soil erosion.

All life forms depend on water and, indirectly, onthe soil. These two elements must therefore receivepriority in any development planning.

All consequences of mans use of natural resourceshave to be analysed. In many informal settlements,for example, residents grow crops and keepanimals, both for subsistence and informal selling.These agricultural practices must be recognised aspart of the urban fabric. However, if agriculturalpractices are to be accepted, potential problemsneed to be addressed.

Assessing past failures

Poor farming practices have impacted negativelyon the environment (Department of Agriculture1995). Some of the consequences have been thefollowing:

Decreasing biodiversity. Natural habitats havebeen destroyed, leading to a decrease in theabundance and diversity of fauna and flora.

Overgrazing. Overstocking and limited grazingrotation have resulted in denuded land and athreat of desertification. Selective grazing byanimals on certain preferred plant species oftenleads to encroachment by unpalatable andundesirable plant species. Overgrazing is aparticularly endemic problem (see Figure 6.4).

Pollution by fertilisers, pesticides, herbicidesand fungicides. Cattle dips and feedlots arepotential sources of pollution. Their proper

design and management cannot beoveremphasised (see Figure 6.5).

Inorganic fertilisers are often environmentallycostly. They can leach out of the soil andcontaminate groundwater and streams. Otherconsequences of injudicious use of fertilisers canreflect in the build-up of toxicity, acidificationand salinisation.

Pesticides often kill non-targeted and usuallybeneficial organisms in the immediateapplication area. Non-biodegradable pesticidescan accumulate in the soil and water, withhazardous consequences to animal and humanlife.

Soil crusting. Incorrect tillage changes thestructure of the soil compaction, resulting inpoorer water infiltration: runoff increases andthere is a greater risk of erosion.

Dump sites also need protection (see Figure 6.6).

9



Figure 6.4: Overgrazing exposes the land to raindamage and can result in extensive erosion

Figure 6.5: Runoff from feedlots contains high levelsof pollutants

10



TECHNOLOGIES AVAILABLE TO THEENGINEER

The hydrologic cycle

There are four basic aspects in the hydrologic cycle ofinterest to the hydrologist, namely:

precipitation; evaporation and transpiration; surface runoff; and ground water.

Hydrology is used in stormwater management for thedesign and operation of hydraulic structures. Thesecould include spillways, highway bridges and culverts,or urban drainage systems (Alexander 1990; Linsley etal 1975; Midgley 1972; Adamson 1981).

Flood routing

Many methods and techniques are available to aid thedesign engineer in calculating runoff hydrographs andassociated flood peaks. The scope of this documentdoes not allow for any detailed dealing with thesetechniques; reference only is made to them. There aremany competent references for adequate coverage(Alexander 1990; Midgley 1972; Rooseboom et al 1981;Pansegrouw 1990).

There are also hydraulic simulations, methods andcomputer programs available that route stormwaterrunoff and predict hydrographs at nominated reachesin watercourses and drainage ways, e.g. Hydrosim(routing model using the kinematic flood-routingequation), and the SCS method.

Routing of storm water through drainage ways andrivers requires the computation of varied flow.

Gradually varying flow is normally assumed. Thecomputation to determine the variation in depth offlow with distance is available from many sources andis discussed later.

Flood-line determination

The determination of flood lines is usually based onthe routing of stormwater through the water course(drainage way). The capacity of a natural channel (orany channel for that matter) is affected by theinteraction of local features and the graduallyvarying flow profile. The routing problem has beenaddressed by Bakhmeteff (1932), Chow (1959),Henderson (1966) and French (1994). Theirclassifications of the flow profiles are welldocumented. Several computer programs areavailable to aid in the determination of water surfaceprofiles.

Detention and retention facilities

A detention facility is designed to attenuate runoff,specifically the peak flows experienced in the reachesof a water course. These facilities may be planned on amulti-purpose basis as required by the controllingauthority, and can achieve a number of stormwaterobjectives.

Many municipalities now require in their subdivisionregulations that runoff from a development may notexceed pre-development runoff for a particularfrequency design flood. This is normally accomplishedby the construction of a detention basin or facility. Thefacility acts as a small flood-control reservoir, whichcan attenuate the peak of the runoff before it flowsdownstream.

The sizing and positioning of detention facilities needsto be done on a catchment basis, and should form partof the master drainage plan. The combined effect ofdischarges from various sub-catchments should beanalysed to minimise possible adverse effects on thewatercourse under consideration.

All dams need to be registered, classified andevaluated as dams with a safety risk, specifically anystructure with a wall height greater than 5 meters. Theevaluation process must involve an ApprovedProfessional Engineer (APE).

To effectively determine the parameters of such afacility, flood routing the design inflow hydrographsthrough the storage in the basin with a predictableoutflow needs to be done, so that downstream effectscan be determined. Typical design data may include

the relevant hydrographs for each of a range ofdesign flood recurrence intervals or frequencies,taking cognisance of the ultimate possible post-development characteristics of the catchment;

Figure 6.6: Dump sites must be protected againstextraneous runoff

details of the storage and stage characteristics ofthe detention basin;

details of the outlet structures with reference tothe discharges from the structures at the variousstages;

structural and geotechnical details of the dam wallwith regard to type of wall, materials, filters,founding details, spillway structure, erosionprotection and freeboard;

safety precautions related to floods and otherhazards;

possible recreational use of the facility; and

maintenance issues, including sedimentation andmaintenance of vegetation.

See also: American Society of Civil Engineers 1982;Brink 1979; Gerber et al 1980; Jennings et al 1978;Knight et al 1977; SA Institution of Civil Engineers,1985.

Programs are available to do the flood routing of aninflow hydrograph through a detention facility toproduce the downstream outflow hydrograph (HEC-1,Pond Pack). Many of these use the storage-indicationworking-curve method or Modified Puls method whichis discussed in more detail in Appendix A to thischapter (Golding 1981).

Storage facilities may be purpose-built, designedprimarily to attenuate runoff, and are usually in theform of wet (part retention, part detention) or dry(detention) facilities. Certain cities in America useunderground tunnels and disused quarries, into whichpeak flows are routed. The effluent is then pumpedfrom these facilities through purification systemsbefore being discharged into the receiving rivers.

Supplementary facilities, whose primary function isnot stormwater attenuation but which have beendesigned to function in an emergency as astormwater-detention facility, can be designed inparking areas, sports fields and areas upstream of roadembankments.

Outlets at stormwater-detention facilities

Culverts

Flow through culverts is dealt with in many textbooks. Nomographs are available, for example inUS Department of Transportation (1985). Flowthrough culverts is also dealt with in Chow (1959)and French (1994). Most local authorities,provincial and national roads departments havetheir own design guidelines, to which the drainagedesigner should refer.

Flow types are categorised according to inletcontrol, barrel control or culvert, or outlet control.However, all culverts act to some extent asdetention structures, because some stormwaterupstream of the culvert accumulates beforeflowing through the culvert. An accurateassessment of the behaviour of a specific culvertconfiguration for detention facilities needs to beobtained over a range of flows and headwaters(see Figure 6.7).

Proportional weirs

The proportional weir has one uniquecharacteristic in that it has a linear head-dischargerelationship. Details are provided in Appendix B ofthis chapter.

Improved inverted V-notch or chimney weir

The inverted V-notch (IVN) weir is a more practical,linear sharp-crested weir. Details are given inAppendix B of this chapter.

Spillway crests

Overflow spillway crests are widely used as outletsfrom detention facilities. Their design is outside thescope of this publication. Reese and Maynord(1987) provide an adequate reference.

Other control structures

Weirs are structures widely used in hydraulicengineering to control or measure flow. Typicalweirs include the following:

Broad-crested weirsRectangularTriangular

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Figure 6.7: Multiple-outlet structure of a detentionpond

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Sharp crested weirsRectangularV-NotchCipoletti weirProportional or Sutro weir

Parshall flume.

There are also other weirs. However, there arelimitations to the applications of these types ofweirs and contractions. French (1994) and Chow(1959) provide ample discussion on the subject. Seealso Keller (1989) and Francis (1969).

Bridge backwaters

Backwaters produced by bridge restrictions need to beanalysed when flood lines are considered. For furtherreference see US Dept. of Transportation (1978),Hydraulics of bridge waterways, Hydraulic designseries No 1.

Erosion protection

Energy dissipators

The dissipation of energy of water in canals or ofwater discharging from pipes must be consideredwhen downstream erosion and scouring arepossible. The drainage engineer is always facedwith the problem of achieving this in anaesthetically pleasing way. Several technologies areavailable:

Widening the drainage way and decreasing thedepth of flow. This will have the effect ofreducing the velocity of flow. Overland flow is atypical example.

Increasing the roughness of the canal ordrainage way. Although this will increase thetotal cross-sectional area of flow, it willdecrease the velocity.

Structures which include the following:Roughness elementsUSBR type II basinUSBR type III basinUSBR type IV basinSAF stilling basinContra Costa energy dissipatorHook type energy dissipatorTrapezoidal stilling basinImpact-type energy dissipatorUSFS metal impact energy dissipatorDrop structuresCorps of Engineers stilling wellRiprap basins.

Reference to their selection and hydraulic design isgiven in US Department of Transportation (1983).

Examples of some energy dissipators are shown inFigures 6.8, 6.9 and 6.10.

Figure 6.8: Simple drop structures in a residentialenvironment

Figure 6.9: Energy dissipator

Figure 6.10: Energy dissipator in a multiple land usesetting

Structural elements

Structural elements that are typically used include:

Geocells (e.g. Hyson-cells); Geotextiles (e.g. Bidim, MacMat, Sealmac); Geomembranes (HDPE linings and others); Riprap; Gabions (refer to SABS 1200); Reno mattresses (refer to SABS 1200); Linings (e.g. Armorflex); and Stone pitching (adequately covered in SABS

1200).

The reader is urged to approach the suppliers ofthese products for technical information.

Transitions

Kerb inlet transitions

Kerb inlets (lateral stormwater inlets) are widelyused with kerbs and surfaced roads. Theirperformance has been discussed adequately byothers. Forbes (1976), for example, proposed thaton moderate to steep road gradients, the capacitycould be substantially improved by incorporatingan extended length of depressed gutter upstreamof the inlet.

Culvert transitions

Culvert transitions are structures that attempt toconverge wide, shallow subcritical flows into high-velocity critical flows which can be passed throughdeep, narrow throats that are more cheaplyconstructed as culverts or bridges. Sometimestermed minimum energy or maximum dischargedesigns, this concept allows large flows to berouted through smaller, more efficient andeconomical culverts or bridges without the usualbackwater or headwater required to provide theenergy necessary to pass the flow through a typicalopening (Cottman and McKay 1990). Considerationmust be given to the immediate downstreameffects and energy dissipation.

Modification of the headwall and culvert openingdetails to conventional culverts and bridges canalso reduce the energy loss at the entrance. Thislends itself to a more efficient hydraulic design (USDept. of Transportation 1985, Hydraulic design ofhighway culverts). However, a more efficienthydraulic design through the culvert structuregenerally leads to higher-energy waters at theoutlet. Energy dissipators may have to beincorporated into the design.

Kerb inlets

The standards used by municipalities vary considerably.Generally, cognisance should be taken of thefollowing:

hydraulic performance;

accessibility for cleaning purposes;

ability of the top section of the culvert to bearheavy traffic;

safety for all road users; and

cost.

For further information, refer to Forbes (1976).

Side weirs

Side weirs are structures often used in irrigationtechniques, sewer networks and flood protection. Aspecial case of this is the kerb inlet (Hagner 1987;Burchard and Hromadka 1986).

Road drainage

Surfaced roads

The main function of urban roads is the carrying ofvehicular, cycle and pedestrian traffic. However,they also have a stormwater managementfunction. During minor storm events, the twofunctions should not be in conflict. During majorstorm events, the traffic function will beinterrupted, the flood control function becomesmore important and the roads will act as channels.Good road layout can substantially reducestormwater-system and road-maintenance costs.

A well-planned road layout can significantly reducethe total stormwater-system costs. Whenintegrated with a major system this may obviatethe need for underground stormwater conduits. Akey element is that the road layout should bedesigned to follow the natural contour of the land(Miles 1984). Coordinated planning with the roadand drainage engineers is crucial at the pre-feasibility stage.

Stormwater runoff may affect the traffic-carryingcapacity through:

sheet flow across the road surface; channel flow along the road; ponding of runoff on road surfaces; and flow across traffic lanes.

Refer to Figures 6.11, 6.12, 6.13 and 6.14.

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14



Sheet flow

This flow is generated on a road surface and isusually least at the road crown, increasing towardsthe road edge. This can lead to hydroplaning whena vehicle travelling at speed has its tyres separatedfrom the road surface by a thin film of water.

Sheet flow can also interfere with traffic whensplashing impairs the vision of drivers.

Channel flow

Channel flow is generated from sheet flow andfrom overland flow from adjacent areas. As theflow proceeds it increases in volume, encroachingon the road surface until it reaches a kerb inlet ordrain inlet. The result is reduced effective roadwidth. Again, splashing produced by the tyres canlead to dangerous driving conditions.

It is important that emergency vehicles should stillbe able to use the road during major storms.

Figures 6.15 and 6.16 illustrate examples of channelflow.

Figure 6.14: Flow across this intersection has resultedin siltation, which is inconvenient and hazardous to

road users

Figure 6.13: This ponding is the result ofencroachment of the grass verge onto the road.

Grass-cutting maintenance operations should alsoinclude harvesting the grass, to prevent siltation and

build-up of new grass growth

Figure 6.11: A lined open roadside channel

Figure 6.12: Incorrect vertical alignment has causedstormwater to bypass this kerb inlet. Kerb inlets in

the intersecting road on the left have also notcaptured runoff from that road so that stormwater

flows across this bus route, creating a hazard

Figure 6.15: Example of surface drainage in aresidential setting

Ponding

Ponding on roads may occur at low points, atchanges in gradient, at sump inlets and roadintersections. This can have a serious effect ontraffic flow, particularly as it may reach depthsgreater than the kerb height or remain on theroadway for long periods. A particular hazard ofponding is that it is localised and traffic may entera pond at high speed.

Flow across traffic lanes

Flow across traffic lanes may occur at intersections,when the capacity of the minor system is exceeded.As with ponding, localised cross-flows can createtraffic hazards. Therefore, at road intersections, forexample, traffic devices should be used to reducetraffic speed during downpours. In such casesallowing cross-flow may be preferable tomaintaining the road gradient, which would havethe effect of creating irregularities in the cross

slope of the road.

Encroachment on roads by runoff

Major storm events

The encroachment by runoff from a major stormevent onto primary roads should not exceed adepth of 150 mm at the crown of the road. Thiswill allow access by emergency vehicles.

Minor storm events

The suggested maximum encroachment on roadsby runoff from minor storms is given in Table 6.3.

Road gradients

Maximum road gradients

The maximum road gradient should be such thatthe velocity of runoff flowing in the road edgechannels does not exceed 3 m/s at the limitsindicated in Table 6.3. Where the velocity of flowexceeds this value, design measures should beincorporated to dissipate the energy.

Minimum road gradients

The minimum gradient for road edge channelsshould be not less than 0,4% (to reduce depositionof sediment).

Maximum road crown slope

The maximum slope from the crown of the road tothe road edge channel is not governed bystormwater requirements.

15



Figure 6.16: Open channel alongside an arterial road

Residential and lower-order roads No kerb overtopping.*

Flow may spread to crown of road.

Residential access collector No kerb overtopping.*

Flow spread must leave at least one traffic lane

free of water.

Local distributor No kerb overtopping.*

Flow spread must leave at least one lane free in

each direction.

Higher-order roads No encroachment is allowed on any traffic lane.

Table 6.3: Suggested maximum encroachment of runoff on roads during minor storms

ROAD CLASSIFICATION MAXIMUM ENCROACHMENT

* Where no kerb exists, encroachment should not extend over property boundaries.

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Minimum road crown slope

The minimum slope from the road crown to thechannel should be not less than 2% for a plain,surface or an average of 2% where the surface hasa variable cross slope.

Unsurfaced roads

The drainage function of unsurfaced roads isdependent - and has a significant impact - on theplanning of the road and access layout. If theroadway is to be used to channel and drainstormwater runoff, then the velocity of this runoffmust be such that minimal erosion potential exists.This means that gravel roads, together with theirside drains, need to have low gradients. Roads withsteep gradients should, as far as possible, not beused as drainage ways, nor should any adjacentside drains without proper erosion protection. Thisprotection can include drop structures, linedchannels at critical sections, or regular drainagefrom the roadway into intersecting roads ordrainage ways. Refer to Figures 6.17 and 6.18.

Runoff from earth or gravel roads will contain gritand its conveyance in pipes can eventually block oreven damage the pipe network. Blockages aredifficult to clear. In many instances maintenance isnot done, rendering the network ineffectual. Useof pipelines in environments of high erosionpotential is not recommended because of the highexpense of maintenance and high risk of failure ornon-performance.

An alternative to a network of pipes is an open-channel system on the roadsides for conveyingminor storm runoff. This system may also conveydry weather flow in areas where there are high orperched water tables, and there is sullage fromindividual households or from communal waterpoints. The positioning of communal water pointsmust be carefully considered and soakaways ordrainage from these points included in their design(see Chapter 9). Suitable erosion protection of thecanal invert, including drop structures and silttraps, is important. See Figure 6.19

Figure 6.17: The contour-planning concept, toimpede the drainage of runoff from the

development

Figure 6.18 (a): Concentration of stormwaterdrainage in a roadway resulting in major

inconvenience to road users

Figure 6.18 (b): Concentration of stormwaterdrainage in a roadway resulting in major

inconvenience to road users

Figure 6.19: Roadside drains of the major system

The use of open roadside channels may necessitatea wider road reserve than that required toaccommodate subsurface drains. This is particularlypertinent where open channels intersect withroadways or property access ways. The width of anopen channel may increase progressively as thedrain accepts more runoff. The road reserve mayhave to be widened or the channel deepened. Theadvantages of these alternative technologies mustbe compared. Open drains, like all systems, willrequire maintenance. However, this technology isnot out-of-sight, out-of-mind. Siltation and otherproblems will immediately become apparent.

Where the whole roadway is used as a drainageway for the major system, erosion protection onthe downstream road edge may need to beconsidered. The crossfall of the road shouldgenerally be against the natural ground slope sothat the whole road width can act as a drainageway in the major system. To maximise the storagefunction of the roads as part of the drainagesystem in major storm events, the settlement layoutshould be planned so that the greatest length ofroad closely follows the ground contour (thecontour-planning concept). Figure 6.20 shows anexample of this planning concept of a rural villagein highly erodible granitic soils. The erosion fromthis area was effectively eliminated.

Roof drainage

High-intensity short-duration storms are experiencedin many parts of southern Africa. These violent stormsare often accompanied by strong winds and hail,which may lead to damage and the flooding ofbuildings containing valuable assets.

It is considered prudent that designers of roofstructures for large buildings take cognisance of theroof drainage system. The research done by Schwartzand Culligan (1976) suggested that the five-minutestorm is likely to cause overtopping of gutters inbuildings of conventional size. The approach to thedesign of roof lengths, gutter size, box receivers anddownpipes is discussed in this reference.

In the United States of America certain authoritiesrequire that all runoff generated on certain propertiesbe stored for slow discharge into the municipaldrainage system. Ponding of rain on roofs is oneretention technology. Others include using depressedareas on the property to store excess runoff. SeeFigures 6.21 and 6.22.

17



Figure 6.20 (a): Layout planning in steep terrain

Figure 6.20 (b): Layout planning in steep terrain

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Upgrading issues

While greenfield development may encompass a morerigid planning procedure, upgrading projects shouldalso be subjected to assessment of their possibleenvironmental impact. In development, wheregreenfield development may be at the one end of thecontinuum and projects associated with maturedeveloped areas at the other, the issues to beaddressed in planning should be similar. A rigorousassessment of impacts - which may include operationand maintenance issues - should be considered. Theclassification of project proposals and their possibleeffects on certain areas and features are consideredfully in the Guideline Document 1 of the IEMprocedure (Department of Environment Affairs1992b).

POLLUTION ABATEMENT

While the issue of quantity of stormwater runoff hasbeen addressed in South Africa for some time,emphasis on the quality of runoff has lagged behind.While economic and social attention to developmenthas been largely beneficial, the total cost oftechnology (that is, the opportunity costs of notconsidering the total waste stream produced by atechnology) has not been considered in great depth inSouth Africa. This typically refers to issues, like healthcare, which concentrate on treating the symptomsinstead of striving for a balance between prevention(reducing or eliminating the cause) and cure. The user,the man in the street, pays sooner or later, carryingboth financial cost and forfeiting quality of life.

Figure 6.21: This office complex incorporated theentrance to the building in a detention facility.

Under normal conditions, this area functions as apleasant park with water features

Figure 6.22 (a): Depressed area to storeexcess runoff

Figure 6.22 (b): Runoff from this parking area isstored in the drainage ways using multiple-outlet

drains

Sources of pollution

Air pollution

With the exception of pollution generated bymotor transport, stationary fossil-fuel processesproduce the bulk of air pollution in South Africa(Petrie et al 1992). Five activities in this categorywhich generate air pollution are recognised:

fuel combustion and gasification fromstationary sources (particularly electrical powergeneration);

fossil fuel burning in dense unservicedsettlements;

industrial and chemical processes (ferro-alloyindustries, fertiliser production);

solid waste disposal (incineration of industrial,residential and hospital wastes); and

land surface disturbances (mining andconstruction activities, agricultural practicesand veld fires).

Of particular concern is the acidic deposition byrain (acid rain) which may result in acidification offreshwater ecosystems, denudation of forested andagricultural areas, corrosion of metal surfaces anddestruction of masonry structures.

While the Atmospheric Pollution Prevention Actprovides for both administrative and judicialcontrol measures, air pollution control isadministered in practice by the chief officer of alocal authority and the government miningengineer.

Point sources of water pollution

Industrial

Apart from the air pollution produced by industry,most industrial processes use water and produceeffluent. Some of these processes include

abattoirs; breweries; pharmaceuticals; fishing; tanning; and the fruit and vegetable industry.

The strategies for pollution abatement are focusedon the reduction of water use at source andimproved effluent purification technologies.

Runoff from industrial plant sites may contain toxicor hazardous pollutants. The installation of

detention facilities can be one technology to storethe effluent during periods of runoff and release itat a slower rate to a treatment process such as awetland.

Mining

There are many pollutants emanating from miningoperations, depending on the operationsthemselves. Probably the main concern to thedrainage engineer is the so-called acid minedrainage and heavy metals.

The standard practice on South African minesvaries considerably. The fundamental principles ofkeeping clean water and polluted water separateand preventing clean water from becomingcontaminated are largely ignored by many mines(Pulles et al 1996).

Non-point sources of water pollution

Non-point sources of water pollution are difficultto locate. Some success has been obtained usinginfra-red aerial photography (Perchalski et al 1988).This technology can prove helpful in identifyingnon-point source problems that include

oxygen depletion in dams; and

runoff from city streets, farms, forests, mines,construction sites and atmospheric deposition.

Agricultural pollution

Poor farming practices have often impactednegatively on the environment. Some of theobserved consequences have been

decreasing bio-diversity; overgrazing through overstocking; pollution by fertilisers; pollution by pesticides, herbicides and

fungicides; soil crusting; and irrigation with polluted water.

The scarcity of water has been identified as thesingle most limiting factor for economic gr

red book volume_ii

Documents

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i n e s f o rcompiled

human settlement planning

o g yiguidelines

university of cape townms