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Water quality indexing – surface 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. Introduction .

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Water quality indexing – surface water

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  1. Water quality indexing – surface water Gopaul, Pravesh Roy Nowbuth, Manta Devi & Baguant-Moonshiram, Yashwaree

  2. AGENDA • Water Quality • Water quality indexing - methods • The study area • Data collected • Analysis • Discussion & Conclusion

  3. 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

  4. 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 trendsover time • Information for the public (not technical)

  5. 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)

  6. 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

  7. 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

  8. A B NSF – Water Quality Index • For each parameter identified by NSF, A rating curve based upon a 100 point scale (A)has been derived. • The Q value (B) is read off from the corresponding curve for a known value of the parameter – here Phosphate level

  9. NSF – Water Quality index • Water quality factors & weights • Some parameters have more importance than others • A weightage factor is associated with each one.

  10. NSF – Water Quality index • Aggregated value = Σ Qphosphate*Weightphosphate + QpH*WeightpH + QDO*WeightDO…. • Aggregated value compared to NSF WQI legend:

  11. Minimum Operator - WQI • Theminimum 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.

  12. 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

  13. MO – Calculating ISUB value

  14. 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

  15. Study area – River Cere

  16. Results -NSF & MO WQI • Results for a specified sample taken at a given point in time. • Note the results at C2 and C9 – different for NSF & MO.

  17. Results The locations of lowest quality is ‘eclipsed’ when the NSF WQI is used, but very obvious using the Minimum operator method.

  18. 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

  19. Thanking you for your attention

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