Chapter 1.pdf

Hydro-Metrological Network Design
HWRE-3122
Mengistu .Z (MSc in Hydraulic Engineering )
Lecturer @ Hydraulic and Water Resources Engineering department
Mizan Tepi university
Email: mengistu.zantet@gmail.com
mengistuzantet@mtu.edu.et
P.O.Box: 260
Tepi, Ethiopia
03-Dec-22 1

1.1 General aspects of Hydro-Metrological Network Design
1) General
2) Hydrologist data type
3) Sources of hydrological data:
4) Principles of Data Analysis
5)Design of meteorological data network
6)site selection survey, general site selection guideline, criteria for
water level gauging sites,
7)sediment discharge and sedimentation, and water quality stations
03-Dec-22
lecturer@ Hydraulic and water
resources Engineering Department 2

General
 Hydrology means the science of water and it deals
with the Occurrence, Circulation &Distribution of
water of the earth and earth’s atmosphere.
In general hydrology is a very broad subject of an
inter-disciplinary nature drawing support from allied
sciences such as: Meteorology, Geology, Statistics
Chemistry, Physics & Fluid mechanics
03-Dec-22

We need of Engineering Hydrology
03-Dec-22
For Estimation of water resources
For Study of processes such as: Precipitation,
Runoff, Evapotranspiration & their interaction
Study of problems such as: Floods & drought
Strategies to combat them
Design & operation of water resources engineering projects
such as: Irrigation, Water supply, Flood control, Water power

Hydrologist data type
03-Dec-22
1) Meteorological Data
Weather records (temperature, humidity & wind speed)
Precipitation data
Evaporation & transpiration data
Infiltration characteristics of an area / catchment

Cont.….
2) Hydrological Data
Stream-flow records
Sediment Data
Groundwater characteristics
Water quality data
3) spatial data
Soil of the area
Land use and Land cover and
Physical & geological
characteristics of the area
03-Dec-22

Sources of hydrological data:
03-Dec-22
In Ethiopia,
 Meteorological data are collected from Ethiopian Meteorological
service agency.
 Stream flow data of various rivers and streams can be found from Ministry of
water resources or any other concerned bureaus or departments.
 Data on Evaporation, transpiration, infiltration will be available in ministry of
agriculture, or water resources or any other concerned departments.
 The physical data of the area can be obtained from topographic map of the area
available with mapping agencies or specific studies conducted at the respective
areas.

Principles of Meteorological data analysis
03-Dec-22
a) Corrections to Point Measurements
b) Estimation of Missing Data
c) Estimating Mean Precipitation Over an Area
d) Checking the Consistency of Point Measurements

A) Corrections to Point Measurements
evaporation losses
Systematic errors
Instrument errors
wind eddies affecting the catch of the
smaller raindrops and snowflakes.
03-Dec-22

B) Estimation of Missing Data
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1)Simple arithmetic average Method
2) Normal ratio Method
3) Regression Method
4) Inverse Distance (Grid) Method

c) Estimating Mean Precipitation Over an Area
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1) Arithmetical-Mean Method
2) Thiessen- polygon Mean Method
3) Isohyet Mean Method
4) Quadrant Mean Method/ Grid point Mean
Method

d) Checking the Consistency of Point Measurements
03-Dec-22
 the most common method of checking for inconsistency
of a record is the Double-Mass Curve analysis (DMC).

Hydro-Metrological Network Design
03-Dec-22
is an organized system for collection of information of
specific kinds such as precipitation, runoff, water
quality, sedimentation and other climate parameters.
Data on temporal and spatial characteristics of water
resources of a region are obtained by a network of
observational stations

Objectives of Hydro-Metrological network design
03-Dec-22
Water resources assessment at basin or sub-basin scale
Water resources assessment for administrative geographical
unit
Water resources project planning like, irrigation, water
supply ,hydropower etc
Flood management
Assessing impacts of Climate Change on Water Resources

Why hydrometeorologic networks?
An appropriate hydrometeorologic network provide the
desired information
Principle: you can not manage thing that you are not
measure
03-Dec-22

Monitoring hydrometeorologic Networks
 is composed of a group of observational stations, set-
up and operated to observe underlying variables and
address a single or a set of interrelated objectives.
 Average area served by a hydrological station is known
as density of a hydrological network.
03-Dec-22

Minimum hydrometeorologic Network
Minimum number of stations necessary to initiate planning
for the economic development of the water resources
Minimum network will avoid serious deficiencies in
developing and managing water resources on a scale
commensurate with the overall level of economic
development of the country
03-Dec-22 17

Cont.…
03-Dec-22
 If the existing may not be adequate for the
formulation of detailed development plans,
Developed as rapidly as possible by
incorporating existing stations as appropriate.

Design of hydrometeorologic Monitoring Networks
Determine cost of establishing and running network:
costs for land acquisition,
station construction,
equipment, operation, maintenance, staff costs, etc.
An optimum network is obtained when amount and quality of
data collected is economically justifiable and meets users’ needs.
03-Dec-22 19

Types of Hydrometeorologic Networks
BASIC OR
PRIMARY
NETWORK:
Provide
basic/minimu
m data for
studies and
should run
continuously
and
indefinitely.
Low density
of stations.
SECONDARY
NETWORK
: are operational for a
short time to
establish a good
correlation with
principal stations.
Density
supplementary to
basic network, to
meet accuracy
demands.
DEDICATED
NETWORK
put in place for a
certain project:
project objectives
determine network
density and period of
operation.
NETWORKS
FOR
REPRESENTAT
IVE BASINS:
to study certain
phenomena in
detail, e.g., for
research
purpose.

Hydrometeorologic Network Design Process
03-Dec-22
1) Network design activity begins with collection of basin maps
and background information about the area/region.
2) Identify the objectives of the network by define the data users
and the purpose for which the data is needed. What is the
required data frequency?
3) Critically evaluate the existing network and find out how
well it meets the required objectives?
4) Review existing database to identify gaps, ascertain variability
in catchment behavior.

Cont..
03-Dec-22
5) Identify the weather the existing network is over-design (if
any) or under designed. New stations may be proposed and
existing stations may be deleted/shifted (if required so).
6) Prioritize stations by following appropriate classification
system.
7) Decide on approximate location of sites and carryout site

Cont..
03-Dec-22
8) Review revised network in relation to overall
objectives and available budget; adjust it as necessary.
9) Estimate average capital and recurrent costs of
installing and maintaining different categories of stations
and overall cost of operating and maintaining the network.
10) Prepare a realistic and achievable implementation
plan.

WMO Criteria for Minimum Network Density
03-Dec-22
The World Meteorological Organization (1976) has
recommended the minimum network densities for general
hydro-meteorological practices.
I. For plain regions of temperate Mediterranean and tropical
zones one station for 600- 900 sq. km.
II. For mountainous region of temperate Mediterranean and
tropical zones one station for 100-250 sq. km.
III. For arid and polar region one station for 1,500-10,000 sq.

Prioritisation system
– In the first instance, “ideal” network size is determined.
– All potential users of data should be consulted.
– Each station in “ideal” network should be prioritised.
Hydrometeorologic Network Density
Category Priority Relative Importance
A High Major, multi-purpose WRD project, State
boundary river, operation of major scheme,
major ungauged basin, heavily polluted
majorWS source
B Medium Medium scale WRD project, secondary basin,
industrial development area (i.e. potential
water quality problems)
C Low Minor irrigation project site, secondary
gauging station on tertiary tributary, major
water course but already extensively gauged

Financial Aspects of hydrometeorologic network design
 Monetary requirements should match with the
budget so that the proposed network is sustainable.
 In case of deficit in the budget, the network should
be realigned or additional budget should be
arranged.
 Stations in the network may be prioritized to best
attain the objectives, given the constraints.
03-Dec-22

Rain gauge Network Design
03-Dec-22
 To get a representative picture of a storm over a
catchment the number of rain gauges should be as large as
possible.
 On the other hand economic considerations to a large
extent and other considerations such as topography,
accessibility to some extent restrict the number of gauges
to be maintained

Objective of measuring rainfall network
03-Dec-22
1) Water resources assessment, projects planning and management
1) Drinking/ Industrial/ Municipal water supply, Navigation,
Recreation Activities
2) Hydrologic design of structures,
3) Agriculture Water Management
1) Irrigation, Rain-fed agriculture
4) Disaster warning systems, and protection:
1) Flooding, Drainage, hydrological forecasting
5) Ecologically sound water systems:
1) Ecology and Forestry, Erosion, Discharge of effluents
 Hydropower generation
 Research

Methods of Rainfall Network Design
03-Dec-22
1. Cv, Method
2. Key Station Network Method
3. Spatial correlation Method
4. Entropy Method
5. WMO Guidelines

Cv, Method
03-Dec-22
If there are already some rain gauges in the
catchment, the optimal number of stations that should
exist to have an assigned percentage of error in the
estimation of mean rainfall is obtained by statistical
analysis follow the following steps


Steps of Cv Method
03-Dec-22

Example#1
There are four rain gauges stations existing in the
catchments of a river .The average annual rainfall values
of theses station are 800,620,400 and 540 mm
respectively, if the it is desired to limit the error in the
mean values of rainfall in the catchment to be 10%
A) Determine the optimal number of rain gauges
B) How many more gauges will then be required to be
installed
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Solution
03-Dec-22

Example#2
A catchment has eight rain gauge stations. The annual
rainfall recorded by these gauges in a given year are as
listed in column 2 of the following Table
A) What should be the minimum number of the rain gauges in
the catchment for estimating the mean rainfall with an error
of less than 7% ?
03-Dec-22

Solution
03-Dec-22

Example#3
A catchment has six rain gauge stations. In a year, the
annual rainfall recorded by the gauges are shown below.
For a 10% error in the estimation of the mean rainfall
A) calculate the optimum number of stations in the
catchment
B) Additional rain gauges required
03-Dec-22

Exercise#1
03-Dec-22
For the basin shown in Figure below , the normal annual
rainfall depths recorded and the isohyets are given.

Elaborate and
03-Dec-22
1) Determine the optimum number of rain-gauge stations to be
established in the basin if it is desired to limit the error in the
mean value of rainfall to 10%.
2) Indicate how you are going to distribute the additional rain-
gauge stations required, if any.
3) What is the percentage accuracy of the existing network in the
estimation of the average depth of rainfall
over the basin ?

Site selected for Stream gauging
03-Dec-22
Places where major rivers cross State borders;
Locations of proposed dams/diversion/run-of-river
schemes including diversions or offtakes/joining
points for (proposed) inter-basin water transfers link
canals;

Cont..
Locations whose data may be needed for flood
forecasting;
Conservation areas and areas of ecological interest;
Areas of water supply shortages;
Areas expected to have significant land use change,
e.g., de-forestation or reforestation;

03-Dec-22

Evaluation and Adequacy of Networks
03-Dec-22
To evaluate the networks, the existing network and
proposed new stations should be marked on a 1:250,000
map.
The catchment area for each river gauging station could
be estimated from the basin maps (hard copy or in GIS).
Scanning the network systematically, the following
questions need to be considered for each station:

Questions of Evaluation of network
1) What purpose will the station fulfill?
2) Does a better location exist nearby?
3) Have any developments (e.g. dam construction) taken place or are
likely which could affect this station?
4) How close are the nearest upstream and downstream gauging stations?
5) Two stations should not be very close unless there are specific reasons.
6) Does any other organization operate a gauging station in the vicinity? If
yes, could the data from that station serve the purpose expected from
this station?
03-Dec-22

Site Selection Surveys
03-Dec-22
To select the most appropriate site for a station, site
selection surveys are carried out.
These surveys can be divided into four distinct phases:
a) Desk study,
b) Reconnaissance surveys,
c) Topographic surveys, and
d) other surveys

General site selection guidelines
03-Dec-22
1) The approach channel should be of uniform cross-section
and free from irregularities
2) Sites where high sediment deposition or scouring occurs or
those which are subject to weed growth should be avoided.
3) Locations which are subject to high turbulence or wind
effects should be avoided.
4) The channel bed should be solid, relatively smooth and free
from obstructions

Cont..
03-Dec-22
5) The station should be located where the flood plain is at its
narrowest and the out of bank flood flow is the minimum.
6) The banks of the river should be high and steep and free from
larger vegetation
7) River banks at the site should be well-defined, stable, and free
from vegetation and other obstructions.
8) Downstream conditions should preferably be stable

Cont.…
03-Dec-22
9) Factors such as unhindered access to the site in all seasons,
availability of office accommodation in to account
10) Enough land should be available near the site to install various
instruments
11) Sites with a tendency for formation of vortices, reverse flow
or dead water shall be avoided
12) The measuring section should be away from obstructions
(artificial and natural) and control structures

Water Level / River stage
03-Dec-22
Water level or river stage is the primary variable
that is measured at stream gauging sites and most
frequent measurements pertain to river stage.
Stage (height of water surface) is observed at all
stream-gauging stations to determine discharge.

Criteria for Water Level Gauging Sites
1) Steep banks or sides are preferred
2) The stage measurement device should be installed as close to the
edge of the stream as possible
3) To minimize the effects of turbulence and high velocities, water
level measuring devices can be installed in a suitable stilling bay at
the bank
4) It is desirable to have access to the site and gauge posts at all
times.
5) The site should not a tendency to collect floating debris
03-Dec-22

Lake and reservoir stages
Stage, temperature, surge, salinity, ice formation,
etc., should be observed at lake and reservoir stations.
Stations should be established on lakes and reservoirs
with surface areas greater than 100 km2
03-Dec-22

Lake and reservoir station
03-Dec-22

Criteria for Streamflow Measurement Sites
1) The measurement section should be clearly visible across
its width and unobstructed by trees
2) There should be sufficient depth of flow across the whole
cross-section:
3) Sites with mobile beds and bank shall be avoided.
4) In some rivers, this is not possible and the site may be
chosen so that the bed and bank changes are minimized.
03-Dec-22

Cont.…
4) Ideally, flow should be confined to a single channel. When this is
not possible, each channel should be gauged separately to obtain the
total flow.
5) The site shall be sufficiently far away from the disturbance caused
by rapids and falls.
6) If the site is upstream of confluence of two rivers, it should be
located sufficiently far upstream so that it is beyond backwater and
any disturbance due to joining of two rivers.
7) Velocities should be well in excess of the minimum required speed
03-Dec-22

Sediment discharge and sedimentation
Sediment stations may be designed either to measure
total sediment discharge to the ocean or to measure the
erosion, transport and deposition of sediment within a
country, basin, etc.
An optimum network would contain a sediment station
at the mouth of each important river discharging into
the sea

03-Dec-22

Sediment discharge and sedimentation
03-Dec-22

Water quality stations
The usefulness of a water supply depends, to a large degree, on
its chemical quality.
The greater the water quality fluctuation, the greater the
frequency of measurement required.
In humid regions, where concentrations of dissolved matter are
low, fewer observations are needed than in dry climates, where
concentrations, particularly of critical ions such as sodium, may
be high.

03-Dec-22

Water quality stations
03-Dec-22

03-Dec-22

THE END
03-Dec-22

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