Environmental Protection

Department

Technical Paper

Report No.: EPD/TP 1/05

Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning

Version 1.0

Author : Wallace Y. M. YIU, E(SI)7 Date : March 2005

Environmental Protection Department 4/F, East Wing, Island West Transfer Station 88 Victoria Road, Kennedy Road HONG KONG

Abstract

This paper outlines the methodology and provides guidance on good practice for estimating sewage flows for planning sewage infrastructure. The application of the GESF commences from the date of this Technical Paper. During this period, the parameters and methodology of flow estimation in Sewerage Manual - Part 1 would continue to be applied for planning sewage infrastructure for projects/developments by external parties and other government departments. EPD would carry out additional planning assessments based on the GESF and make reference to the assessment results in planning public sewage infrastructure.

(Information contained in this publication may be freely used. Reproduction of materials is permitted with notification to the Director of Environmental Protection. Acknowledgement must be made by indicating the title of this publication.)

Report No.: EPD/TP 1/05

Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning

Version 1.0

TABLE OF CONTENTS

TABLE OF CONTENTS

LIST OF FIGURES

LIST OF APPENDICES

Page No.

1. INTRODUCTION 1

2. FLOW COMPONENTS 1

3. FLOW DATA 2

4. POPULATION AND EMPLOYMENT DATA 2

5. METHODOLOGY OF FLOW ESTIMATION 4

6. SEWAGE FLOW PARAMETERS GENERAL 6

7. UNIT FLOW FACTORS DOMESTIC FLOWS 7

8. UNIT FLOW FACTORS COMMERCIAL AND INSTITUTIONAL 9 FLOWS

9. UNIT FLOW FACTORS INDUSTRIAL FLOWS 10

10. CATCHMENT INFLOW FACTORS 11

11. PEAKING FACTORS 12

12. CONTRIBUTING POPULATION 14

13. BROAD IMPLICATIONS OF THE GUIDELINES ON MAJOR 14 SEWERAGE FACILITIES

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LIST OF FIGURES

Figure F-1 Methodology for Flow Estimation Figure F-2 Peaking Factors for Sewers Contributing Populations Exceeding 50,000

Figure F-3 Peaking Factors for Sewage Treatment Works, Preliminary Treatment Works and Pumping Stations Contributing Populations Exceeding 50,000

LIST OF APPENDICES

Appendix I Comparison of Surveyed Unit Flow Factors (including flow due to employee) in Reviewed Sewerage Master Plans

Appendix II PVS Zones of 28 Major Sewage Catchments in 2002 and in 2016/Future Developed Scenario

Appendix III Unit Flow Factors of Typical Domestic Residents, Employees and Students

Appendix IV Unit flow Factor for Residential Permanent Housing Residents and Adjustment Factors for Private Permanent Residents

Appendix V Unit Flow Factors for Commercial Activities

Appendix VI Catchment-dependent Unit Flow Factors for Industrial Employees

Appendix VII Comparison of Total Average Flows of Major Sewage Catchments

Appendix VIII Analysis of Peaking Factors and Peak Flows

Appendix IX Preliminary Validation of Unit Flow Factors of GESF

Appendix X Implications of GESF

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1. INTRODUCTION

1.1 This set of Guidelines for Estimating Sewage Flows (GESF) is issued for EPDs initial internal sewage infrastructure planning use in accordance with the agreement between Environmental Protection Department (EPD) and Drainage Services Department (DSD) in the second and the third Steering Meetings on Review of Sewerage Manual. The recommendations in this GESF take into account EPDs past experience gained in sewerage infrastructure planning, findings in reviewed sewerage master plans and relevant DSDs technical reports.

1.2 This GESF provides guidance on good practice for estimating sewage flows for planning catchment level and sub-catchment level sewage infrastructure. The guidelines and recommendations are by no means exhaustive. The application of this GESF to planning sub-catchment local sewage infrastructure would involve deliberation of the worse case scenarios of usages and populations of the existing and proposed developments. During the initial internal implementation period of this GESF, the methodology in DSD Sewerage Manual Part 1 (SM1) is an acceptable alternative for planning sewage infrastructure by external parties although EPD would carry out additional planning assessments using this GESF. EPD welcomes feedback and comments on the guidelines and methodology for estimating sewage flows in this GESF to facilitate improvements for the future general use of these Guidelines.

1.3 Unless specific information in SM1 are stated to be valid and adopted for use in this GESF, the approach of estimating sewage flows essentially in Chapter 4 of the SM1 will be replaced by that of GESF for sewage infrastructure planning purposes.

1.4 Findings in DSDs Research and Development Report No. RD 1011 and DSDs previous comments on the initial draft of these Guidelines have been taken into account in this GESF.

2. FLOW COMPONENTS

2.1 The average flow (AF) comprises domestic, commercial, institutional, industrial and inflow/infiltration components. The domestic component consists of flows from residential and institutional premises. The commercial component is made up of flows from offices, shops and restaurants. The institutional component includes flows mainly from schools and universities. The industrial component includes those flows from various manufacturing processes.

2.2 Inflow/infiltration is the flow due to ingress of ground/storm water and due to seepage and connections to the stormwater drainage system. In practice, it is difficult to determine accurately the amount of local inflow and infiltration. Despite every effort has been employed to reduce the amount of inflow and infiltration, the dry weather flow components have included infiltration and a certain amount of inflow. The inflow quantities in some catchments are considerable and cannot be wholly taken into account in the dry weather flow components. The contribution of this excessive inflow to the total sewage flow of a catchment is further addressed by the catchment inflow factor (PCIF). This factor accounts for the average quantity of the excessive inflow of a catchment as a factor on the total component flows. The equation for average flow, QAVERAGE, is as follows:

EPD/TP 1/05 Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning Page 1 of 14

QAVERAGE = (QDOMESTIC+ QCOMMERCIAL + QINSTITUTIONAL + QINDUSTRIAL) x PCIF ,

where QDOMESTIC is the average dry weather domestic flow, QCOMMERCIAL is the average dry weather commercial flow, QINSTITUTIONAL is the average dry weather institutional flow, QINDUSTRIAL is the average dry weather industrial flow, and PCIF is the catchment inflow factor.

3. FLOW DATA

3.1 Flow data for existing sewage treatment works are available from Sewage Treatment Division of Drainage Services Department. Flow survey data are also available from the following sources:

(a) Sewerage Master Plan Review Studies

-Yuen Long and Kam Tin

-Outlying Islands

-Hong Kong Island

-Central and East Kowloon

-Tuen Mun and Tsing Yi -North District and Tolo Harbour

(b) Sewerage Master Plan Studies

-Port Shelter -Tseung Kwan O

-Tsuen Wan, Kwai Chung and Tsing Yi -North West Kowloon

(c) Other studies:

-Pilot Study for Inflow and Infiltration Reduction Strategy -Sewage Flow Measurement for the North and South West Hong Kong Island

(final results to be available by year 2007)

3.2 Flow surveys are recommended for obtaining the latest flow data for analysing flow components. Flow survey data should be carefully logged and the results should be interpreted by experienced professionals.

4. POPULA TION AND EMPLOYMENT DATA 4.1 Population projections based on Working Group on Population Distribution (WGPD)

papers, Outline Zoning Plans and Development Permission Area Plans issued by the Planning Department are good sources of reference of existing and projected population figures for sewerage planning. Census data are also useful in providing the baseline information. Employment projections and Quarterly Survey on Employment and Vacancies of Census and Statistics Department are sources of employment data.

EPD/TP 1/05 Guidelines for Estimating Sewage Flows for Sewage Infrastructure Planning Page 2 of 14

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4.2 Each Sewerage Master Plan or reviewed Sewerage Master Plan (both known as SMP) has taken into account the latest planning data available during the study period. As planning projections will be updated over time, users of SMP data should take account of all updated planning and development projections of the concerned catchment in planning sewage infrastructure.

4.3 New development plans are available from Government planning and engineering feasibility studies which are carried out from time to time for the continued development of Hong Kong. The results and recommendations of these studies play an important role in projecting the most likely development scenarios in terms of population and employment distribution. In formulating population and employment forecasts, latest findings of these studies should also be taken into account.

4.4 Available population data of the following categories for various planning horizons should be obtained for estimating sewage flows. Mobile residents are required to be considered while transient residents or vi