Transcript Water quality indexing for predicting variation of water

Water quality indexing – surface water
Gopaul, Pravesh Roy
Nowbuth, Manta Devi
&
Baguant-Moonshiram, Yashwaree
AGENDA
Water Quality
Water quality indexing - methods
The study area
Data collected
Analysis
Discussion & Conclusion
Slide 2 /17
Introduction
Quality of water – governs the potential use
(domestic, agricultural, industrial)
Quantity of water – Q, VR (straight forward answer)
Quality of water – (pH, temperature, turbidity, nitrate
level, chloride level, conductivity, phosphate, cadmium,
zinc,…..) – several parameters
Interpretation of water quality data are complex
Slide 3 /17
Water quality index method
Water quality index method
an approach to combine the complex data into a single indicative
value.
Several key parameters are aggregated into a single dimensionless
number – indicator of quality
A single numeric expression - easily understood by non technical
people, for decision making.
Indicative of trends over time
Information for the public (not technical)
Slide 4 /17
Water quality index - methods
Concept of WQI – first introduced in Germany in 1848
Mainly qualitative in nature – later on numerical value associated:
Horton’s Index (1965)
National Science Foundation (US) – NSF WQI method (1970)
Modified arithmetic mean (1983), Solway modified weighted sum
(1985)
Many
countries
have
adapted
their
own
WQI
method:
Malaysia,Canada, Poland, New Zealand, India, UK, Taiwan
Minimum Operator - Smith (1990)
Slide 5 /17
NSF WQI method (1970)
A physico-chemical water quality index mostly, but also
bacteriological to a lesser extent
Four steps:
Indicator selection – (variable of concern – oxygen level,
eutrophication, health aspects, dissolved solids)
Indicator transformation – (Dimensionless scale & Rating
curve)
Indicator weighting – (Some indicators have a higher
importance than others)
Index Aggregation
Slide 6 /17
NSF WQI method (1970)
NSF carried out a detailed survey and identified the
following key parameters (9), for water quality:
Temperature,
pH,
Dissolved Oxygen,
Turbidity,
Feacal Coliform,
Biochemical Oxygen,
Total Phosphates,
Nitrates &
Total Suspended Solids
Slide 7 /17
NSF – Water Quality Index
For each parameter
identified by NSF, A
rating curve based upon
a 100 point scale (A)
has been derived.
A
B
The Q value (B) is read
off
from
the
corresponding curve for
a known value of the
parameter
–
here
Phosphate level
Slide 8 /17
NSF – Water Quality index
Water quality factors &
weights
Some parameters
more importance
others
have
than
A weightage factor is
associated with each one.
Parameter
Weights
DO
0.17
Feacal C.
0.16
pH
0.11
BOD
0.11
Temperature
0.10
Phosphate
0.10
Nitrate
0.10
Turbidity
0.08
TSS
0.07
Slide 9 /17
NSF – Water Quality index
Aggregated value =
Σ
Qphosphate*Weightphosphate
QDO*WeightDO….
+
QpH*WeightpH
+
Aggregated value compared to NSF WQI legend:
Range
Quality
90-100
Excellent
70-90
Good
50-70
Medium
25-50
Bad
0-25
Very Bad
Slide 10 /17
Minimum Operator - WQI
The minimum operator also called the Smith Index
(Minimum Operator) - developed by Smith in 1987.
This index gives information for the water quality according to its
specific use,
general water quality index,
bathing index,
water supply index and
Fishing - index
It also caters for the problem of ‘eclipsing’ which arises during
aggregation process.
Slide 11 /17
Minimum Operator - WQI
Almost similar steps as for NSF WQI
Different key parameters for different uses (General uses, bathing,
water supply, fishing)
Rating curve for each parameter – read off ISUB
For a given water sample, derive the ISUB for all the key parameters
Select the minimum ISUB from this set of value
Param
eter
DO
pH
TSS
Turbid
ity
Temp
BOD
NH3
ISUB
82
92
86
72
64
84
90
Slide 12 /17
MO – Calculating ISUB value
PARAMETERS
STN C1
ISUB
VALUE
Dissolved oxygen
6.61
76
PH
7.49
100
Suspended Solids
2.30
96
Turbidity (NTU)
2.40
90
Temperature
25.07
54
BOD (mg/l)
1.77
92
Ammonia (mg/l)
0.29
90
2.86
60
Log
Feacal
(/100ml)
Coliform
Slide 13 /17
Monitoring of water quality
Impact of landuse activities on the quality of water – surface &
ground
Samples taken at regular levels (weekly/monthly) – CWA & MoE
(Env. Lab.)
Physical, chemical and bacteriological tests – determine pollution
level
Typical tests –
pH, temperature, dissolved oxygen, total suspended solids, turbidity,
conductivity, nitrate, sulphate, phosphate, chloride, COD, BOD
Slide 14 /17
Study area – River Cere
Station
No.
Description
Landuse Activities
C1
St-Anne Bridge
Residential
C2
Near District council
Residential & Commercial
C3
Maurice Rousset Bridge
Commercial
C4
85km Downstream C3
Residential & Commercial
C5
Cite Hibiscus
Residential & Forested
C6
Near Floreal Knitwear
Forested & Sugarcane
C7
After
Plant
C8
La Porte Bridge
Sugarcane Plantation
C9
125km Downstream to C8
Sugarcane Plantation & Vegetation
C10
La Porte Village
Sugarcane Plantation & Vegetation
Wastewater
Treatment Sugarcane Plantation
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Results -NSF & MO WQI
Results for a specified
sample taken at a
given point in time.
Station
Ref.
NSF WQI
MO
C1
77.71
40
Note the results at C2
and C9 – different for
NSF & MO.
C2
77.29
36
C3
79.43
60
C4
80.57
46
C5
79.00
50
C6
75.14
54
C7
80.43
46
C8
80.86
72
C9
79.43
38
C10
81.00
64
Slide 16 /17
Results
Minimum Operator & NSF - Comparison Chart
90
80
70
Station along River Cere
60
50
40
30
20
10
0
C1
C2
C3
C4
C5
C6
Water Quality Index Value
C7
C8
C9
MO
C10
NSF
The locations of lowest quality is ‘eclipsed’ when the NSF WQI is
used, but very obvious using the Minimum operator method.
Slide 17 /17
Discussion & Conclusion
WQI – Simplified way of representing water quality information
WQI – used to indicate trends over time and in space
Create public awareness – an effective tool.
River classification – different reach for different uses
MO an improved approach over NSF WQI
Rating curves - to be derived (adapt method locally)
WQI however does not replace/enhance the raw data
Slide 18 /17
Thanking you for your attention