water quality monitoring

1. Water Quality Monitoring
Dr Ing. Kinfe Kassa
1

2. Water Quality Monitoring:
= the collection of the relevant information on water
quality
Water Quality Assessment:
= the overall process of evaluation of the physical,
chemical and biological nature of the water
Definitions
2

3. • Setting up a monitoring programme requires a clear
definition of the objectives, in order to avoid waste of time,
efforts and money.
• “Need to know” and not “would be nice to know”
• Necessary information will depend on various “users” of
water.
Objectives of monitoring
3

4. MONITORING
Long-term, standardised measurement and observation
of the aquatic environment in order to define status and
trends
SURVEY
A finite duration, intensive programme to measure and
observe the quality of the aquatic environment for a
specific purpose
SURVEILLANCE
Continuous, specific measurement and observation for
the purpose of water quality management and
operational activities
Types of monitoring (1)
4

5. Types of monitoring (2)
Ambient monitoring
• Status and trend detection
• Testing of water quality standards
• Calculation of loads
Effluent monitoring
• Calculation and control of discharge standards
• Monitoring of plant performance
Early warning
• Warning for calamities
• Protection of downstream functions
Operational monitoring
Monitoring for operational uses such as irrigation,
industrial use, inlets for water treatment works.
5

6. Single-objective monitoring which may be set up to address
one problem area only.
This involves a simple set of variables, such as:
• pH, alkalinity and some cations for acid rain
• nutrients and chlorophyll pigments for eutrophication
• Na, Ca, Cl and a few other elements for irrigation.
Multi-objective monitoring which may cover various water
uses and provide data for more than one assessment
programme, such as drinking water supply, industrial
manufacturing, fisheries or aquatic life, thereby involving a
large set of variables.
Types of monitoring (3)
6

7. Simple monitoring
based on a limited number of samples, simple analysis or
observations, and data treatment which can be
performed by simple software
Intermediate-level monitoring
requiring more variables, stations, and specific laboratory
equipment and PCs/software for data handling
Advanced level monitoring
involving sophisticated techniques and highly trained
technicians and engineers for sample analysis (e.g.
micropollutants) and data handling, often using
mainframe computer systems.
Levels of water quality assessment
7

8. The monitoring cycle
8
1:“what do you want to know?”
2: “how to find out”
3: “the real field and labwork”
4:“evaluation”
5:“feed-back; changes”

9. 9

10. Water quality monitoring & assessment
Monitoring contributes to rational decision by:
– Describing water resources and identifying actual
and emerging problems of water pollution.
– Formulating plans and setting priorities for water
quality management.
– Developing and implementing water quality
management programs.
– Evaluating the effectiveness of management actions.

12. What to measure?
1. Quantity: Discharge, Water level, Volume
2. Quality variables of aggregated effects (e.g. turbidity,
temperature, pH, conductivity, BOD, COD, anions and
cations)
3. Quality variables producing aggregated effects (e.g.
turbidity producing variables: suspended solids,
colloids, biota groups, dissolved minerals)
4. Detailed quality variables (e.g. minerals affecting
turbidity: manganese compounds, alumina, iron
oxides)

13. Where to sample
Rivers
• Macro-location —selection of river reaches that
will be Sampled
• Micro-location —selection of a station location
within a selected river reach
• Representative location —selection of points in
the river cross-section that provide the best lateral
water quality profile of the stream

14. River sampling location
• Sampling reach:
– as a function of land use type (industrial,
agricultural, urban)
– Sampling station location:
– Completely mixed zone (lateral & vertical)

15. Distance to completely mixing zone
• Ly is the mixing distance between the point source and complete lateral
mixing.
• Lz is the mixing distance between the point source and complete
vertical mixing.
• σy is the distance between the point of injection and the farthest
lateral boundary of river.
• σz is the distance between the point of injection and the farthest
vertical boundary of river.
• d is the depth of flow; u is the mean stream velocity; u* is the shear
velocity; g is the gravity acceleration; R is the hydraulic radius; Se is the
slope of the energy gradient.

16. Example- minimum distance to completely mixed zone
Compute the minimum distance between a pollutant discharge
point in a river and the complete mixing zone. The outfall point is
located in mid-depth and mid-width in the river cross section.
Assume that the average stream velocity is 0.9 m/sec, the average
width is 100 m, and the average depth is 4 m. The slopes of the
stream bed and the energy gradient are assumed to be the same
and equal to 0.002.
Answer:
• Ly = 4367.23 m
• Lz = 241 m
• Therefore, the mixing distance from the waste discharge point
is 4367.23 m

17. Sampling frequency
• Single station and single variable
• Single station and multiple variables
• Multiple stations and single variable
• Multiple stations and multiple variables

19. Example- determination of sampling frequency for a single
variable
parameter at a single site
• Select the sampling frequency for a station that monitors
BOD concentration in an important control point on a river.
The annual mean and variance of the BOD concentration
based on historical data are 6.01 mg/l and 8.1 (mg/l) 2,
respectively. The desired confidence interval width is
assumed to be 3 mg/l with a 95% confidence level.
Ans.
n = 14 samples/year

20. Single station and multiple variables
• Compute a weighted average of confidence interval widths for
several water quality variables
• Relative weights of water quality variables can be selected by
Engineering judgment
Example: Select the sampling frequency for a station that has four
water quality variables. Assume that the 95% confidence interval
width about the mean of the water quality variables will be equal to
one fourth of the average of these variables. The historical population
statistics of the variables are as follows:
Ans. 20 samples/year

21. Sampling frequency for multiple stations and single variable
• The total number of samples (N) is allocated to stations based on
their relative weights using the following equation:
ni = wiN
Where,
ni is the number of samples at station i,
wi is the relative weight of station i,
N is the total number of samples.
The relative weights show the relative importance (priority) of
stations and can be estimated based on historical data. For
example, relative weights based on historical means or historical
variances can be computed using:

22. • Separate sampling frequency should be selected
for each water quality variable at each station and
a weighted average of them can be considered as
each station’s sampling frequency.
• A weighted average variance for the water
quality variables can be computed for each
station as shown in the previous slide
Multiple stations and multiple variables

23. Example
The historical means and variances for three water
quality variables in four stations have been calculated
and are shown below. Select the sampling frequency for
each station using the weighting factors based on
historical variances. The total number of samples per
year is considered to be equal to 40.

25. Thank you