F o re w a rd
The hydrological data available for the
storage. However, much Hydrological and
This current WSC/IWT Hydrological
Maltese Islands dates back to 1841. At that
Hydrogeological data has been saved and
Report is the first issue of a hydrological
time only rainfall figures were measured.
is awaiting digitisation.
yearbook for Malta and Gozo. It presents,
Over the years, the then Government
mainly for academic and research
Water Works Department (WWD) began
Other data was inputted into ad hoc
purposes, considerable raw data, and
to measure more and more parameters.
databases during the 1990-1992 compilation
analysed data, related to Surface Hydrology
Unfortunately, due to various reasons,
of the Bureau de Recherches Geòlogiques
and Groundwater Hydrology, together
a m on g wh i ch w e r e e qu i p m e nt
et Miniéres (BRGM), Water Resources
with Hydrogeological and climate
breakdowns, the WWD did not keep
Report. The BRGM report acted as a
information for the hydrological years
certain readings on a continuous basis. In
catalyst to reconstruct, compile and
2001/2002 and 2002/2003 currently stored
addition to that, other data was lost
manage all the raw data related to
at the Water Services Corporation.
because of a variety of problems - lack of
groundwater and water supply in general.
backups and/or digitising and/or transfer
It ranged over such issues as quality,
to hard data from one location to another,
quantity, rainfall, evaporation and runoff.
insufficient security and inappropriate
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Hydrological Report 2001/02-2002/03
This report is the result of a joint effort of the personnel of the Hydrology Section within the Research and Development Unit of the
Institute of Water Technology. The Hydrology Section is responsible for collecting and processing hydrology and climate data as well
as the maintenance of all the measuring equipment used to gather record data. The Section's technical staff performed a major part
of the fieldwork necessary to prepare such a report.
Research & Development
July 2003
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Hydrological Report 2001/02-2002/03
I n t ro d u c t i o n
This Hydrological Report covers information on stream flows and meteorological information for the hydrological year under review.
The information on stream flows presented in this report (Appendix A) is based on observed discharges recorded at 3 gauging stations
in Malta and one station in Gozo. The recorded data for each station includes:
i.
Mean daily flows recorded at the station.
ii.
Monthly depth-area precipitation for the particular catchment
iii.
Annual flow given as a percentage for the corresponding annual depth-area precipitation
iv.
The peak discharge recorded at the station during the hydrological year under review
v.
Season hydrograph
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Hydrological Report 2001/02-2002/03
Inventory of Monitoring Network
For hydrological, hydrogeological, and geographic reasons, the Maltese Islands are divided into 3 separate regions namely, Malta, Gozo
and Comino. Additionally, Operational aspects of the islands of Gozo and Comino are distinct from those of Malta. Nevertheless the
hydrological set-up of the Islands is run and managed safely by the Hydrological Section.
Map 1 : Monitoring Network
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Hydrological Report 2001/02-2002/03
R u n o ff G a u g i n g S t a t i o n s
In Malta there are 74 catchment areas,
a continuous chart that illustrated the flow
The Marsa and Msida recorders measure
whilst in Gozo there are 33. Only the four
during each storm event that produced a
flow via water levels inside rectangular
major catchment areas in Malta and one
flow over the weir.
concrete-lined channels having a slope of
in Gozo are gauged. At one time
0.00275 and 0.004 respectively. Thus, using
mechanical water level recorders were
In 1996, however, the mechanical runoff
the Manning's formula, the flow passing
used at these stations. In the case of
recorders were replaced by electronic ones.
through the channel during a flood event
Mta˙leb and Marsalforn, these produced
These produce more continuous readings.
can be measured and recorded.
water levels above a rectangular broad-
Nevertheless, the WSC is still conducting
crested 3-stage weir. This was converted
maintenance on existing mechanical
into flow via an equation specific for that
recorders.
rectangular weir. Moreover, it produced
Figure 1: Mta˙leb rectangular broad-crested 3-stage weir
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Hydrological Report 2001/02-2002/03
R u n o ff G a u g i n g S t a t i o n s c o n t i n u e d
Figure 2: Runoff flowing through Burmarrad gauging weir
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Hydrological Report 2001/02-2002/03
Rainfall Gauging Network
The Water Sevices Corporation -
reservoirs, pumping stations and the WSC
(previously the Water Works Department)
offices in Malta, Comino and Gozo, as
- started collecting rainfall records as from
indicated in Map 1.
the beginning of the 20th century. In fact,
records show that in 1906, the WWD
Most of these places are situated in the
measured rainfall in the Rabat area.
outskirts of villages (except for the WSC
i.
offices). Hence, these gauges yield samples
Presently, the WSC owns and manages 20
of rainfall that represent conditions at the
rainfall monitoring stations. These gauges
periphery of the island. The rain gauges
are distributed in various localities such as
in this network comprise: -
3 daily rain recorders (Dines
Tilting Syphon),
ii.
11 weekly rain recorders (Dines
Tilting Syphon),
iii. 6 tipping buckets (electronic).
Figure 3 - Dines Tilting Syphon Rain Recorder and a Tipping Bucket.
Rainfall in both the daily and weekly rain recorders is measured on a chart, while
rainfall is stored in data loggers when it is measured by electronic tipping buckets.
Apart from these rain recorders, the network also consists of 8 storage gauges, Met
Office Mk. II. These are installed near rain recorders, and serve as a back up. These
gauges are also used to confirm rainfall measurements.
Figure 4 - Met. Office Mk II Storage Gauge.
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Hydrological Report 2001/02-2002/03
Evaporation Networks
The WSC is in possession of 2 evaporation pans. Both form part of the meteorological stations. One of the pans is at Ta' Qali Reservoir,
and the other at the Ta' Çenç Reservoir in Gozo.
Both evaporation pans are of a US Class
A Pan type and are installed according to
standard specifications.
The WSC monitors the pans for water
level weekly, and ensures that they are
cleaned regularly. Water level is monitored
by means of a pressure transducer that is
connected to a data logger. Data is
collected and processed hourly.
Figure 5 - Ta' Qali and Ta' Çenç Evaporation Pans
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Hydrological Report 2001/02-2002/03
G ro u n d w a t e r G a u g i n g B o re h o l e s
Groundwater levels in Malta and Gozo are
gauged using level recorders in vertical
boreholes. Not so long ago, the WSC
measured water levels with a dip tape.
However, the dip tape did not provide
continuous information, only a snap shot
of the water level. Readings using the dip
tape were measured on a monthly basis
and it was not possible to have sufficient
information about changes in water level
over time.
The Corporation has now installed level
sensors, together with data loggers. As a
result, level fluctuations are easily
recorded.
In Malta, the WSC manages 38 gauging
boreholes that are equipped with data
logging facilities. In Gozo, to-date, there
are only 5. The Corporation intends to
expand this network to include other
boreholes.
These collected readings give a clear
indication of water levels in the aquifers,
or water table. The WSC converts this data
using the Rockware Contouring software.
This produces a piezometric contour map,
giving clear indications of the level of water
in the aquifer, or water table, over time.
Maps 2 and 3 show contour maps that
represent the aquifer status in 1944 and in
May 2003. The map shows that in 1944 the
highest groundwater level of the Mean Sea
Level Aquifer was + 4.6 m (above mean
sea level). In the 2003 map, the level was
+ 2.9m. This value was obtained from the
Buskett Road gauging Borehole. These
images clearly indicate that there was a
consistent decline in the water level of the
water table.
The Reduction of water stored in the water
table was also calculated using the
Rockware Software. The piezometric
storage volume in 1944 was found to be
37.7 x 106 m3, and that of 2003 was 27.76 x
106 m3. Using the above figures, the loss of
water stored was calculated to be
9.94 x106 m3.
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Taking into consideration the Gyhben
Herzberg Principle whereby the density
difference between salt and fresh water
effects the water level of the aquifer below
the mean sea level and assuming that the
difference is 1:37, therefore the storage lost
since approximately 520x10 6 m 3 . The
effective porosity assumed in these
calculations was 0.1.
It is important to note that the above is a
theoretical calculation that gives a uniform
decrease in water storage over the years.
However, in practice, we know that this is
not the case. The loss in water storage was
not gradual or evenly distributed over
time. Groundwater extraction started in
the late 70's and increased considerable in
the 80's. It then increased to an
uncontrolled level in the 90's, as a result
of private illegal extraction. The situation
today is unsustainable.
Hydrological Report 2001/02-2002/03
G ro u n d w a t e r G a u g i n g B o re h o l e s c o n t i n u e d
Typical Data gathered from some of the stations and relative graphical representation are given in Appendix A and Appendix B.
Table in Appendix C illustrates various extreme events based on data gathered since 1994. It also gives the mean total rainfall (mm)
and the number of days with rainfall over the same period, and global averages of all parameters gathered in all stations.
Typical graphical representation of data gathered from weather and wind stations is shown in Appendix D.
Appendix A
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Hydrological Report 2001/02-2002/03
G ro u n d w a t e r G a u g i n g B o re h o l e s c o n t i n u e d
RAINFALL MONITORED AT LUQA STATION 2001-2
160
120
rainfall (mm)
140
rainfall (mm)
100
120
80
Rainfall (mm)
Rainfall (mm)
RAINFALL MONITORED AT LUQA STATION 2002-3
60
40
100
80
60
40
20
20
0
Sep-01
Oct-01
Nov-01 Dec-01
Jan-02
Feb-02
Mar-02 Apr-02
May-02
Jun-02
Jul-02
0
Aug-02
MONTH
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Sep-02
Oct-02
Nov-02
Dec-02
Jan-03
Feb-03
Mar-03
Apr-03
MONTH
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Hydrological Report 2001/02-2002/03
May-03
Jun-03
Jul-03
Aug-03
G ro u n d w a t e r G a u g i n g B o re h o l e s c o n t i n u e d
RAINFALL MONITORED AT TA’ QALI STATION 2001-2
160
120
rainfall (mm)
140
rainfall (mm)
100
120
Rainfall (mm)
Rainfall (mm)
RAINFALL MONITORED AT TA’ QALI STATION 2002-3
80
60
40
100
80
60
40
20
20
0
Sep-01
Oct-01
Nov-01 Dec-01
Jan-02
Feb-02
Mar-02 Apr-02
May-02
Jun-02
Jul-02
0
Aug-02
MONTH
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Sep-02
Oct-02
Nov-02
Dec-02
Jan-03
Feb-03
Mar-03
Apr-03
MONTH
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May-03
Jun-03
Jul-03
Aug-03
G ro u n d w a t e r G a u g i n g B o re h o l e s c o n t i n u e d
Appendix B
RAINFALL-RUN-OFF RELATION CHART FOR MTAÓLEB 2001-02
1
120.0
Monthly Volume Tot. (m3)
Precipitation Tot. (mm)
0.8
100.0
80.0
RAINFALL-RUN-OFF RELATION CHART FOR MTAÓLEB 2002-03
140.0
1
Monthly Volume Tot. (m3)
Precipitation Tot. (mm)
0.8
120.0
100.0
0.6
60.0
0.6
80.0
0.4
40.0
0.4
60.0
20.0
0.2
0
0.0
Sep
Oct
Nov
3
Dec
Monthly Flow (m /Month)
Jan
Feb
Mar
MONTH
Apr
May
Jun
Jul
Aug
-20.0
40.0
0.2
20.0
0
Sep
RF (mm)
Oct
Nov
Dec
Monthly Flow (m3/Month)
Jan
Feb
Mar
Apr
MONTH
May
Jun
Jul
Aug
0.0
RF (mm)
RF: Rainfall
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Hydrological Report 2001/02-2002/03
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RAINFALL-RUN-OFF RELATION CHART FOR M’FORN 2001-02
1
Monthly Volume Tot. (m3)
Precipitation Tot. (mm)
0.8
0.6
0.4
0.2
0
Sep
Oct
Nov
3
Dec
Monthly Flow (m /Month)
Jan
Feb
Mar
Apr
MONTH
May
Jun
Jul
RAINFALL-RUN-OFF RELATION CHART FOR M’FORN 2002-03
350,000
70.0
60.0
50.0
40.0
30.0
20.0
10.0
0.0
-10.0
Monthly Volume Tot. (m3)
Precipitation Tot. (mm)
300,000
250,000
200,000
150,000
100,000
50,000
0
Aug
Sep
RF (mm)
Oct
Nov
Dec
Monthly Flow (m3/Month)
Jan
Feb
Mar
Apr
May
MONTH
Jun
Jul
160.0
140.0
120.0
100.0
80.0
60.0
40.0
20.0
0.0
Aug
RF (mm)
RF: Rainfall
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Hydrological Report 2001/02-2002/03
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RAINFALL-RUN-OFF RELATION CHART FOR MSIDA 2001-02
RAINFALL-RUN-OFF RELATION CHART FOR MSIDA 2002-03
120.0
140,000
100.0
120,000
80.0
100,000
30,000
60.0
80,000
80.0
20,000
40.0
60,000
60.0
20.0
40.000
40.0
0.0
20,000
20.0
50,000
Monthly Volume Tot. (m3)
Precipitation Tot. (mm)
40,000
10,000
-20.0
0
Sep
Oct
Nov
Dec
Monthly Flow (m3/Month)
Jan
Feb
Mar
MONTH
Apr
May
Jun
Jul
Aug
RF (mm)
0
140.0
Monthly Volume Tot. (m3)
Precipitation Tot. (mm)
Sep
Oct
Nov
Dec
Monthly Flow (m3/Month)
Jan
Feb
Mar
Apr
MONTH
May
Jun
Jul
Aug
120.0
100.0
0.0
RF (mm)
RF: Rainfall
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RAINFALL-RUN-OFF RELATION CHART FOR B’MARRAD 2001-02
8, 000.00
7, 000.00
6, 000.00
5, 000.00
4, 000.00
3, 000.00
2, 000.00
1, 000.00
0.00
RAINFALL-RUN-OFF RELATION CHART FOR B’MARRAD 2002-03
40,000
35,000
30,000
25,000
20,000
15,000
10,000
5,000
0
120.0
Monthly Volume Tot. (m3)
Precipitation Tot. (mm)
100.0
80.0
60.0
40.0
20.0
0.0
Sep
Oct
Nov
Dec
Monthly Flow (m 3/Month)
Jan
Feb
Mar
MONTH
Apr
May
Jun
Jul
Aug
-20.0
RF (mm)
140
Monthly Volume Tot. (m3)
Precipitation Tot. (mm)
120
100
80
60
40
20
Sep
Oct
Nov
Dec
Monthly Flow (m 3/Month)
Jan
Feb
Mar
Apr
MONTH
May
Jun
Jul
Aug
0.0
RF (mm)
RF: Rainfall
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Appendix C
Appendix D
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Hydrological Report 2001/02-2002/03