Water Reources Monitoring

1. CVS 445:
Lecture 3:
Field Monitoring of Water Quantity and Quality
Lawrence Omai

2. Quantity & Quality Monitoring
Why Monitor?
• A comprehensive assessment of our water resources is a key step in
properly managing water supplies for the long term
• Such an assessment requires a significant amount of information
• The information needs to be collected and compiled into a usable
database and format
• Once the information is collected, it is analyzed and applied using
methods that model and predict the response of water sources to water
withdrawals
• The information also needs to be accessible and useable by many public
and private sector users
• Combining the GEOLOGICAL, HYDROLOGICAL, & WATER QUALITY
information is a 1st and major step in assessing our water resource base

3. Hydrometric Networks
• Two of the greatest problems for water engineers
and engineering hydrologists are:
1. Quantifying the amount of water in the different
phases in the hydrological cycle
2. Evaluating the rate of transfer of water from one
phase to another within the cycle
• For efficient operations, there needs to be a
logical design in the pattern of hydrological
measurements (rainfall, streamflow or GW) hence
the need for NETWORKS

4. What is a NETWORK?
• “An organised system for collection of
information of a specific kind: that is, each
station, point or region of observation must
fill one or more definite niches in either
space or time”

5. What are the uses for the Network Data?
• 3 main uses have been proposed (WMO,
1976)
1. Data for Planning: Requires long-term
records
2. Data for Management: Requires real-
time measurements for daily operation
and forecasting
3. Data for Research: Requires high-quality
intensive data

6. Stages in Network Design
Stage 1
• Initial background research on the location and
known characteristics of the area
• Consider the following:
– Size of the area and whether it is a political entity or a
natural drainage basin (always choose the natural
catchment area)
– Physical features of the area (drainage pattern,
surface relief etc)
– General climatic features

7. Stages in Network Design…
Stage 2
• Practical planning
• Consider the following:
– Identify existing stations
– Plot existing stations on a topo map
– Examine the station distribution wrt physical features
and data requirements. Fill in any gaps or provide
more detailed info. for specific purposes. The number
of new stations depend on the considered optimum
for the area

8. Stages in Network Design…
Stage 3
• Detailed planning and design of required
installations on the new sites

9. Surface Water Networks
• The density of gauging stations depends on the
following:
1. Nature of the terrain, and
2. Water resources on the population creating a water
demand.
• Status of gauging stations
1. Primary/Principal stations
– Permanent stations to measure all ranges of discharges and
observations and records to be accurate and complete
2. Secondary/Subsidiary stations
– Provide a satisfactory correlation with primary stations
3. Special stations
– Serve particular needs such as reservoir levels and dry
weather flows
– May be permanent or temporary

10. Groundwater Networks
Main purposes of GW investigations:
1. Identify productive aquifers, to determine their
hydraulic properties
2. Make arrangements for monitoring the water levels
within the aquifers
Siting of observation wells must take into account the
following:
1. Differences in aquifer properties within an aquifer
2. Variations between aquifers

11. Water Quality Networks
• The first design criteria in any water quality
programme is to determine what are the
management issues for which water quality
data are required. The technical aspects of the
data collection follows from this decision
• In general, the convention is to utilise the “fixed
site” networks to provide water quality
information that are grouped into “Data
Objectives”

12. Water Quality Data Objectives
• 3 categories of data objectives can be identified as follows:
1. Descriptive data:
• Typically used for govt. policy and planning for public information.
Include the following:
– Status & trends of important water bodies
– Conformance of water bodies to use specific water quality
objectives
– Trans-boundary issues
2. Data specific to public health e.g.
– Pathogens
– Protection of waters of touristic value etc
3. Regulatory concerns e.g.
– Effluent permitting and enforcement
– Identification of contaminants requiring control measures
– Emergency response, including monitoring of spills etc

13. Water Quantity (Groundwater)
Most of the information comes from water supply
wells
• Wells provide answers to key questions such as:
1. What are the geologic materials the well
penetrated?
• The information gives insight of which strata
transmit water and which are barriers
2. What was the original water level in unpumped
wells?
• How have the static water levels changed with
time? Do they vary seasonally?
• The information characterizes the volume of
water stored in the source aquifer

14. Water Quantity (GW)…
3. How much water does the well produce, and how
much does the water level drop during pumping?
• What effects does the pumping have on other wells?
• This information tells about the aquifer’s ability to
transmit water
4. What amount of pumping has occurred for a given
well?
• This information is valuable in long-term use trends
and sustainability analysis
5. What is the quality of the water the well originally
produced? Has the quality changed through time?
Are there natural or societal impairments? Is the
quality good enough for various uses?

15. Confined Aquifer

16. Unconfined Aquifer

17. Water Quantity (Surface Water)
• The parameter quantifying SW is the
streamflow/discharge
• Discharge is the volume of water passing a single
point in a stream over time
• The basic objective in gathering flow information
is the development of flow hydrographs for
stations along the river
• The flow hydrographs should represent the entire
water year and cover as many years as possible
• Flow hydrographs are basic to an understanding
of how other resource values are affected by flow
• Typically, mean monthly or weekly flow is
measured, computed, or estimated at several
sites along the designated reach

18. River Flow determination
• Determination of river flow (river gauging) can be
done by taking river discharge measurements.
• Important gauging methods are
1. Velocity – area methods
2. Flow – measuring structures (River gauging
structures)
3. Dilution gauging
4. Use of empirical formulae

19. River Flow determination
• Velocity – area methods:
– Conventional for medium to large rivers
– Involves use of currentimeter (current meter)

20. Current-meter

22. Currentimetering…
 The mean velocity at a given depth is approximated by
observations made at 0.2 and 0.8 of the full depth (two point
method) or approximated by the velocity measured at 0.6 of the
full depth (one point method)
 The width of the river is divided into about 20 sub – sections so
that no sub – section has more than 10% of the flow

23. Calculating the discharge
 At the gauging station or selected river cross – section, the mean
velocities for small sub – areas of the cross – section )
( i
v
obtained from point velocity measurements at selected sampling
verticals across the river are multiplied by the corresponding
sub – areas (ai) and the product summed up to give the total
discharge:
i
n
i
i a
v
Q 


1
where n = the number of sub – areas
 The calculation of the discharge from the velocity and depth
measurements can be made in several ways. Two common
methods are
1. Mean section method
2. Mid – section method

24. Mean section method
 Averages of the mean velocities in the verticals and averages
of the depths at the boundaries of a section sub – division are
taken and multiplied by the width of the sub – division /
segment
)
(
2
)
(
2
)
(
. 1
1
1
1









 

 i
i
i
i
n
i
i
i
i b
b
d
d
v
v
a
v
q
Q
where bi is the distance of the measuring point (i) from a bank
datum & n is the number of sub – areas

25. Mid – section method
 The mean velocity and depth measured at a subdivision point are
multiplied by the segment width measured between the mid –
points of neighboring segments
2
)
(
.
.
. 1
1
1






 

 i
i
i
n
i
i
i
b
b
d
v
a
v
q
Q where n is the
number of measured verticals and sub - areas

26. Disadvantage of Mid section method
• Some flow is omitted at the edges of the cross
– section, and therefore the first and last
verticals should be sited as near to the banks as
possible

28. River Flow determination…
Flow – measuring structures
 Designed so that stream discharge is made to behave
according to certain well known hydraulic laws (e.g.
discharge as a function of the head over a weir).
 Used in streams and fairly small rivers (expensive to
build)
Types of structures
1. Weirs (i) V – notch
(ii) Crump
(iii) Compound
2. Flumes: Geometrically shaped regular channel sections
e.g. Trapezoidal

29. Flumes
 The upstream sub – critical flow is constricted by
narrowing the channel, thereby causing increased
velocity and a decrease in the depth. With a sufficient
contraction of the channel width, the flow becomes
critical in the throat of the flume and a standing wave is
formed further downstream. The water level upstream of
the flume can then be related directly to the discharge
(see attached figure 6.18 for an example. Ref pg 122
Hydrology in practice by E M Shaw)
 Relating the discharge for a rectangular x – section to the
measured head, H, the general form of the equation is:
2
3
KbH
Q 
where b is the throat width and K is a coefficient
determined experimentally

32. Weirs
 constitute a more versatile group of structures providing
restrictions to the depth rather than the width of the flow
in a river or stream channel
 a distinct sharp break in the bed profile is constructed
and this creates a raised upstream sub – critical flow, a
critical flow over the weir and a super – critical flow
downstream
 The upstream head is uniquely related to the discharge
over the crest of the structure where the flow passes
through critical conditions

33. V-notch sharp crested weir

34. Flow rating curve determination…
Dilution gauging
 Suited to small turbulent streams where depths and flows
are inappropriate for currentimetering and flow
structures would be unnecessarily expensive and /
permanent
 Involves injection of a chemical into the stream and the
sampling of the water some distance downstream after
complete mixing of the chemical in the water has
occurred
 The concentration of chemical in the samples is used to
compute the dilution from which the discharge of the
stream can be obtained
Types
1. Constant – rate injection: Chemical is added at a
constant rate until the sampling downstream reveals a
constant concentration level
2. Gulp injection: Chemical is added in a single dose as
quickly as possible. Sampling over period of time is used
to develop concentration – time correlation

35. Dilution Gauging

36. Dilution Gauging…
• The desired chemical characteristics:
– High solubility
– Stability in water
– Capable of accurate quantitative analysis in dilute
concentrations
– Non-toxic to aquatic life
– Unaffected by sediment and other natural chemicals
in water
• Most favourable is Sodium Dichromate

37. Water Quality Monitoring
Objective
• Characterisation of the condition and variability of the water
at the time of designation or in its normal state
• Measurements should focus on physical and biological
factors that describe the conditions at the time of
designation, thereby establishing the baseline for protection
& enhancement
• A monitoring strategy should be developed with
consideration to any anticipated threats to water quality
• Monitoring efforts to:
1. Conform with the appropriate Catchment Management
Authority (CMA) standards
2. Monitor the most significant threats to water quality from
existing land uses within the catchment e.g. Mining is likely
to affect TDS, SS, Turbidity, pH and Heavy metals
concentrations
• Note: Water Quality baseline data is critical for describing suspected
impacts from changes in management practices within the catchment

38. Typical Water Quality Parameters
• pH
• Dissolved Oxygen (DO)
• Biochemical Oxygen Demand (BOD)
• Temperature
• Conductivity
• Turbidity
• Suspended solids (SS)
• Fecal Coliform
• NB: Methods for sampling and measuring water
quality are well documented and can be
referenced

39. General Process for Determining the Water
Quantity and Quality Values for River
Protection
• Steps include:
1. Preliminary assessment and study design
2. Description of water quantity and quality dependent
values
3. Description & quantification of hydrology &
geomorphology
4. Description of the effects of water quantity & quality on
resource values
5. Identification of water quantity & quality required to
protect values
6. Development of a strategy to meet water quantity &
quality requirements as a joint effort by agency staff,
legal counsel, and other stakeholders

40. Assignment # 04
• Seek to explain in detail the above six steps