1.0
INTRODUCTION
1.1
General
Colombo is situated in the Western Province of Sri Lanka along the coast at
approximately North latitude 6° 6' 56" and East longitude 79° 19' 51". The city of
Colombo houses the main commercial hub of the country with a dense population of
approximately 642,000 (Sri Lanka Population and Housing Statistics, 2006). The
Greater Colombo region encompasses the Colombo city and its immediate suburbs to
the North. East and the South. the western boundary being the Indian Ocean. In the
context of its IO\\ lying terrain, the complex network of interconnected canals and
marshes crisscrossing the region, play a prominent role in ensuring a nood free
environment for the masses. The total length of canals is 29.2 km, while it is fed by a
catchment area of approximately 99 km 2 (Nippon Koei et al.-1992).
The canal system is generally divided into two as the Colombo North system and the
Colombo South system. The Colombo North System consists of all canals north of
Sri Jayawardenapura Mawatha while the Colombo South system consists of canals
south of Sri Jayawardcnapura Mawatha (Figure 1.1 ). The system has four outlets,
three of which, namely, Dchiwala and Wellawatte outfalls and Mutwal Tunnel
discharge directly into the sea. The North Lock outlet discharges into the Kclani
River. Earlier there used to be a fifth outlet in the form of the circular weir ncar the
old Parliament, facilitating spill from Beira Lake into the sea. However, the canal
system is no longer connected to the Beira lake in order to prevent polluted waters in
the northern canals from entering the lake (SLLR&DC, 2004). 'The Mutwal Tunnel
is also no longer in operation due to blockage and is almost closed" (SLLR&DC,
2004). Under dry weather conditions outnow occurs mainly through Dehiwala,
Wellawatte and North Lock outlets, while it is reduced to Dehiwala and Wellawarte
during a flood situation. Whenever there is a threat of nooding, the North Lock is
closed to prevent backwaters of Kelani from entering the canal system.
The Parliament Lake is the headwater boundary of the Colombo canal system (Figure
1.1 ). Other main canals arc Kolonnawa Eta , Kotte Eta , Mahawatte Ela, He en Ela,
Torrington canal, Kirillapone canal, Wellawatta canal, Dehiwala canal, Bolgoda
canal, Dematagoda Canal, St. Sebastian canal, Main Drain and Mutwal Tunnel
(Figure 1.1 ). The three main retention areas attached to the system are Heen Ela (88
ha), Kotte Lake(97 ha) and Kolonnawa (2 14 ha) totalling up to approximately 400 ha
of low lying marsh lands which play a sign ifican t role in detain ing excess nood water,
so that peak nows are reduced and lag times are increased.
As far as the Colombo canal system is concerned, not only the quantity, but also the
quality of the water is of utmost importance in deciding the health and well being of
the thousands who inhabit the immediate environs of the canals. Furthermore, it is
also a yardstick for measuring the aesthetics of the region, as well as the ecosystem
health of the canals themselves. However, at the moment the water quality of most of
the canals in the system are at a highly deteriorated level due to pollution from
domestic wastewater, industrial waste, solid waste and direct sewer outlets.
12
<>..._..-,jo..
~
$171•
<>
0~\.J,..
Moi!J•..1 ·
\
W-.r ~HaWn\cPo!*
l!gMd
M:At:f Bodes
I
I
l
3.
MaJOr Roads
I
6
4
j
8
•
Figure 1.1
-
'
~c.w.~.~~ ~IM~S<ha•
:T;
I
m~Ro.d~ Cl'osi\C
10 Scpacn 11'111
II Bn!o _.. ~.& bw:UJI\Cl\ St. S4WUII\ CIIIU
ll & a - Bq nt.. Ct"jja\ ~ CapcnbmCl\
I
13 c- ROid Bn!o a\ H.tl-.e c-1
14 ~ U.c~Bn!o m~ c-1
18 ~~Ka~,N~k
19. ~~B~Sotlh.Ptkw-..
lO . ~1M (MJrt On!lnJ~ I'IWMfht.
9
Rei! RCXK!s
S.lnt P.o.!~ a\ 0.~ c-1
lb1 Pott <I!. Stbti1lln c-1 (not to Btn IMa)
Bnlp m KolA N:d\ CIIIU
JldMylln!o m T~c-1
rule Ro.d Bn!o a\ Wt
c-1
rule :tto.d Bn!o a\~ c.w.
Wtru
0..~ c..!
MclrWOfl"9
Pons
General Layout of the Colombo Canal System and Location of
Water Quality Monitoring Points
Realizing the importance of the Colombo Canal System, the Sri Lanka Land
Reclamation and Development Corporation launched the Greater Colombo Flood
Control and Environment Improvement Project (GCFC&ETP) in 1993, embarking on
13
a massive exercise of canal clearing, widening, canal lining and a host of other
activities, including relocation of shanty communities living along canals. An integral
part of the project was a canal water level, discharge and water quality monitoring
program, where monthly measurements were taken at I 0 locations on the Colombo
Canal System, commencing in January 1997. By 2000, the number of locations had
been increased to 17, with 13 of them lying within the Greater Colombo Area. In
June 2004, another three locations ncar the Parliament were added to the list (Table
3.2). Under the water quality program, I 0 water qua lity parameters were monitored at
all of the above locations (Table 3.1 ). The present study was undertaken in order to
utilize this existing wealth of data to analyse the short term and long term variations
in water quality of the Colombo Canal System, and in the process, incorporate the
data and analysis in a simple decision support tool named the Water Quality Monitor
(\\'QM).
14
1.2
Measurement of Water Q ua li ty and Quality Sta ndards
The quality of water is generally characterized in terms of its physical, chemical and
biological composition. Some important physical properties and chemical and
biological constituents of water are listed in Table 1.1. These parameters arc
measured and quantified through various techniques and such measurements
co llectively indicate the quality of any particular sample of water. However, many of
these physical properties and chemica l and biological characteristics are interrelated .
For example, temperature, a physical property, affects both the amounts of gases
dissolved in water and the biological activity in water (Inc. Metcalf and Eddy, 2002).
Table 1.1
Common Physical, Chemical and Biological Characteristics of
Water
..
Parameter
Physical
Measurement
Unit
.
mg/1
mg/1
mg/1
NTU
Pt mg/1
Total Solids
Total Suspended Solids (TSS)
Total Dissolved Solids (TDS)
Turbidity
Color
Odour
Temperature
Conductivit)
°C or °F
S/m
Chemical
mg/1
mg/1
mg/1
mg/1
hee Ammonia
Nitrates
Total :-.litrogen (TN)
( l'ho>phol<>
J
pH
-
Alkalini!)
Metals
Various gases
Five-Day Biochemical Oxygen Demand Amount of oxygen required
for 5 days by microorganisms to stabili/.C a waste biologically at 20 °C
temperature (BOD 520 )
Chemical Oxygen Dcmannd (COD)
Dissolved Oxygen (DO)
Total Organic Carbon (TOC)
mg/1
mg/1
mg/1
'
mg/1
mg/1
mg/1
mg/1
Biological
MPN (most probable
number)
MPN (most probable
number)
Total Coliform
Faecal Coliform
TU
Toxicit)
-·
15
'
Water quality standards are stipulated in order to specify a threshold value for each
measured parameter, considering the purpose for which a particular water is used.
Such threshold values are demarcated by relevant authorities so as to minimise the
health and associated risks to humans and nature by the use of that particular water.
The quality parameters monitored under GCFC&EIP are listed in Table 3.1.
Considering the recreational value of the Colombo Canal System, the proposed
ambient water quality standards for bathing waters in Sri Lanka (stipulated by the
Central Environmental Authority - CEA) has been adopted for this study (Appendix
D) as the applicable standards for canal water.
1.3
O bj ectives of the Study
The main objectives of this study arc to:
I. Develop a tool to integrate the available water quafity data of the Colombo
Canals in an easi ly accessible database with a user friendly interface
2. Provide decision support on setting criteria for water quality improvement,
spcci fically in the Colombo area, in a simple and understandable manner,
by studying the total water quality regime of canals.
3. Investigate the possibility of using the canal water level and average daily
rainfall as indicators of water quality and thereby provide decision support
on measures to be adopted for improving canal water quality in the Greater
Colombo area
4. Identification of areas needing immediate and priority attention m
implementing pollution prevention interventions.
5. Supplement other more comple>.. water qual it)' models
6. Disseminate Knowledge on surface \\atcr quality of the Colombo area, not
only to experts but also to anyone having a basic knowledge of water
quality concepts
7. Propose interventions for control of pollution in the Colombo Canal
System
Out of the total of 20 SLLR&DC monitoring locations only those falling within the
Greater Colombo area (16), and quality parameters BOD and COD have been
included in this study. It is intended to include the rest of the parameters as well in
the application in the future.
16
1.4
Scope of Work
In order to carry out the study the following tasks were identified:
I.
Literature survey
2.
Collection of canal water quality, water level, discharge, rainfall and GIS data
for Colombo
3.
Development of application structure of WQM
4.
Compilation oft\\ o databases containing numerical data (water quality, water
level, discharge and rainfall) and GIS data.
5.
Development of algorithms for each function of WQM
6.
Coding of algorithms
7.
Study of original data and initial graphical outputs of WQM and elimination of
data outliers
8.
Obtain results on applicable water quality criteria and water quality-water
level, water quality-rainfall, and water quality-discharge relationships
9.
Propose interventions for control of pollution in the Colombo Canal System
based on the above resu Its
1.5
Layout of the Report
The report consists of five chapters as follows:
Chapter I
presents the general description, objectives and scope of work of the
study
Chapter 2
describes a review of literature on existing water quality models, past
studies on water quality of the Colombo Canal System and other
mathematical models and tools used in the development of WQM. The
literature reviewed include research papers, consultant's reports,
textbooks and journals. The literature review is followed by a
justification of the present study.
Chapter 3
presents the rationale, framework, methodology, data and tools used in
the development of WQM.
17
Chapter 4
presents a detailed discussion of the results of application of WQM to
the Colombo Canal System including some of its shortcomings, as well
as applicable pollution reduction interventions based on the results.
Chapter 5
Presents conclusions reached at the end of the study.
Chapter 6
Winds up this report with recommendations for further studies.
Tables and figures are included within the main chapters, as well as in the appendices.
The) are numbered according to each chapter number. A copy of the software on CD
is provided in Appendix G.
18