Josip Rubini}
Nevenka O`ani}
Gordana Bu{eli}
Janja Milkovi}
WATER TEMPERATURE CHARACTERISTICS IN THE
KUPA RIVER CATCHMENT AREA
SUMMARY
Present paper analyses water temperature characteristics in the catchment area of Kupa river in
Croatia. Kupa is one of the most important water flows in the Danube river catchment area with its
spring in Croatia. Analyzed area is very heterogenic by its climate and hydrological characteristics.
Upstream part of the catchment area is located in mountain area rich in precipitation and it is partly
supplied by underground water from karst springs. Downstream part has characteristics of typical
lowland-areas.
Besides general characteristics of water temperature of Kupa and its affluents (characteristic values,
distribution during the year, frequencies, trends) the comparison of dynamic of average yearly
values with respective dynamics of temperatures of the air and average discharges was performed.
Keywords: Kupa river, water temperature, air temperature, discharges
1. INTRODUCTION
Besides the fact that water temperature directly influences general water conditions, especially
biological conditions in surface water flows, it is up to now one of least measured and analyzed
hydrological parameters. The water temperature conditions are rarely analyzed even when series of
measured data are available. Therefore this paper analyses water temperatures of Kupa and its
affluents from Croatian area.
Three hydrological stations (Kupari, Hrvatsko and Kamanje) on Kupa river were analyzed.
Parameters that were recorded on this three stations are water level, runoff and water temperature.
Fourth analyzed station on Kupa is station Karlovac where the water is slowed down and only water
temperature and water level were measured. Data from stations located on affluents ^abranka
(station Zamost), Gornja Dobra (station Luke), Donja Dobra (station Stative Donje) and Donja
Mre`nica (station Mrzlo polje) are also analyzed. Figure 1 represents the locations of analyzed
stations and in Table 1 are theirs general characteristics.
Table1. General data about hydrological stations located in the Kupa river catchment area
STATION
STREAM
KUPARI
KUPA
HRVATSKO
KUPA
KAMANJE
KUPA
KARLOVAC
KUPA
ZAMOST
^ABRANKA
LUKE
GORNJA DOBRA
STATIVE DONJE
DONJA DOBRA
MRZLO POLJE
MRE@NICA
Catchment
area surface
(sq. km)
208
370
2192
3461
103
175
1049
975
Altitude above sea Average yearly Average yearly Beginning of
level (ma.s.l.)
catchment
runoff (m3s-1) hydrological
precipitations
measurements
(mm)
304
285
124
103
298
354
116
114
2895
2512
1725
1674*
1892
1609
1678
1464
13.7
21.4
78.3
117.0*
3.88
7.42
37.3
29.4
1951.
1949.
1957.
1956.
1950.
1947.
1946.
1947.
Beginning of
water
temperature
measurements
1956.
1965.
1958.
1956.
1965.
1965.
1958.
1948.
* the data were measured on upstream located station Brodarci where water is not slowed down
It can be seen that on analyzed part of river Kupa catchment area is located relatively sufficient
number of hydrological stations with recorded data series for 40 or even 50 years, with measured
values of water temperatures also. But there exists a problem regarding preciseness of water
temperature measurement, that was, especially for the initial years, unsatisfactory limited to 0.5 to 1
o
C. That is the reason why station Hrvatsko was excluded from the major part of analyses
performed and why series of data for other included stations were shortened. Analysis included
period from 1967 till 1991. Water temperature measurement during that period were most regularly
performed.
The total Kupa river catchment area near Sisak city is 9202 km2. Because the fact that on the rest of
catchment area water temperature measurements were not performed this paper analyzes
approximatelly one half of this total surface - the part that is located upstream from the town of
Karlovac included also Kupa’s affluent Mre`nica that pours into Kupa immediatelly after Kupa
leaves Karlovac (Fig. 1).
For the comparison of water and air temperatures analysis included the data of average monthly and
yearly air temperatures recorded on meteorological stations Parg (for the upstream part of analyzed
catchment area), Ogulin (for the midstream part of analyzed catchment area) and Karlovac (for the
downstream part of analyzed catchment area). For the analyzed period from 1987 till 1991 average
yearly air temperature for the coldest Parg station varied from 6.1 to 7.7 oC (average 7.0 oC), for
Ogulin station varied from 8.7 to 10.6 oC (average 9.7 oC) and for Karlovac station varied from 9.8
to 11.7 oC (average 10.8 oC). For all analyzed stations the coldest month was January (average
temperature for Parg -1.6 oC, Ogulin 0.0 oC and Karlovac -0.1 oC) and the warmest was July
(average temperature for Parg 16.4 oC, Ogulin 19.3 oC and Karlovac 21.3 oC).
During analyzed period according to the average monthly runoff values the driest month for all
analyzed stations was July and the wetest was April. Average monthly discharge values varied for
Kupari-Kupa station from 4.85 to 21.76 m3s-1, for Kamanje-Kupa station from 27.57 to 107.13 m3s1
, for Zamost-^abranka station from 1.42 to 5.82 m3s-1, for Luke-Gornja Dobra station from 2.96 to
12.60 m3s-1, for Stative-Donja Dobra station 13.74 to 56.42 m3s-1 and for Mrzlo Polje-Mre`nica
station from 11.04 to 41.26 m3s-1.
2. ANALYSIS OF WATER TEMPERATURE CHARACTERISTICS FOR THE KUPA
RIVER CATCHMENT AREA
For the analyzed 25 years period from 1967 till 1991 basic water temperature characteristic values
for all stations included were determined and presented in Table 2.
Table 2. Basic water temperature characteristics of the Kupa river catchment area
STATION
STREAM
KUPARI
KUPA
HRVATSKO
KUPA
KAMANJE
KUPA
KARLOVAC
KUPA
ZAMOST
^ABRANKA
LUKE
GORNJA DOBRA
STATIVE DONJE
DONJA DOBRA
MRZLO POLJE
MRE@NICA
Average
temperature
(oC)
Standard
deviation
(oC)
Cv
MIN
(oC)
MAX
(oC)
7.2
7.2
11.2
12.3
7.7
7.8
11.5
12.4
0.10
0.66
1.72
0.98
0.53
0.25
0.58
0.69
0.01
0.09
0.15
0.08
0.07
0.03
0.05
0.06
7.0
5.6
7.9
10.8
6.9
7.3
10.4
11.1
7.4
8.2
13.4
14.2
9.6
8.3
12.8
13.8
It can be noticed that according to average yearly water temperature values, results have logical
distribution - the value range is narrower and the values are lower for upstream located stations
(Kupari, Hrvatsko, Zamost, Luke), while for downstream located stations (Kamanje, Karlovac)
values are more variable. Analysis of mutual correlation was also performed and the results are
presented in Table 3. It can be seen that average yearly water temperature values recorded on the
Kupari station are best correlated with the data recorded on nearly located station Zamost on
^abranka river. The data recorded on the Kamanje station, that is distant from all the other stations,
are not correlatively connected with the data from other stations. Average yearly water temperature
values recorded on the Karlovac station are slightly correlatively connected with the data from
closely located stations Stative Donje in Donja Dobra and Mrzlo Polje on the Mre`nica river, while
the strongest correlative connection (k=0.89) exists between the data recorded on Stative Donje and
Mrzlo Polje stations that are near and located on simillar streams by hydrological regime.
Table 3. Correlation coefficients of average yearly water temperature values between different
stations (1967 - 1991)
STATION
KUPARI
KAMANJE
KARLOVAC
ZAMOST
LUKE
STATIVE DONJE
MRZLO POLJE
KUPARI
1
0.24
0.21
0.73
-0.21
0.44
0.42
KAMANJE
KARLOVAC
ZAMOST
LUKE
STATIVE
MRZLO POLJE
1
0.15
0.15
0.12
0.36
0.31
1
0.16
0.36
0.52
0.75
1
0.003
0.45
0.38
1
0.40
0.40
1
0.89
1
Analysis of frequency and duration of certain water temperature value was also performed within
temperature range of 1 oC for each station. It was determined that the majority of stations analyzed
(Kupari, Kamanje, Zamost, Luke) have had most frequent temperature appearance between 7 and 8
o
C, stations Karlovac and Mrzlo Polje between 8 and 9 oC and station Mrzlo Polje between 6 and 7
o
C. Figure 2 represents average curves of frequencies and durations for three characteristic stations Kupari located on upstream part of the Kupa river influenced by cold spring waters, Karlovac
located on downstream part of the Kupa river and Luke located on upstream part of the affluent
Gornja Dobra river. The differences between their characteristic curves of temperature frequencies
and durations can be noticed.
Figure 2. Curves of frequencies and durations of water temperatures for analyzed Kupa river
catchment area from 1967 till 1991
3. INTERRELATION BETWEEN WATER TEMPERATURE, RUNOFF AND AIR
TEMPERATURE IN THE RIVER KUPA CATCHMENT AREA
Fluctuation of annual water temperature values is compared with fluctuations of average annual
discharge and average air temperature values. Analysis was performed for two characteristic
stations in the catchment area - station Kupari for which the air temperatures were measured at the
Parg meteorological station (Fig 3) and station Kamanje for which air temperature data were
obtained at the Karlovac meteorological station (Fig 4).
20
8,5
18
0
16
temperature ( C)
discharges (m 3/s)
8
7,5
14
12
7
10
discharges Kupari
w ater
temperature Kupari
air temperature Parg
6,5
8
6
6
67 69 71 73 75 77 79 81 83 85 87 89 91
years
Figure 3. Fluctuations of average annual water temperature, air temperature and discharge values
for Kupari-Kupa station
14
90
13
12
0
80
temperature ( C)
3
discharges (m /s)
100
11
70
10
60
9
50
discharges Kamanje
w ater
temperature Kamanje
air temperature
- Karlovac
8
40
7
67
69
71 73
75
77
79 81
83
85
87 89
91
years
Figure 4. Fluctuations of average annual water temperature, air temperature and discharge values
for Kamanje-Kupa station
It can be noticed that for both analyzed stations, values of single analyzed parameters have simillar
fluctuations. At the Kupari station trend of annual discharge values fluctuation is 0.45% and at the
Kamanje station is -0.9%. Trend of air temperature values fluctuation for Kupari is -0.19% annualy
and for Kamanje is 0.11%. Trend of water temperature values fluctuation for Kupari is -0.05%
annualy and -0.51% annualy for Kamanje station. Mutual correlation analysis was also performed
for each analyzed parameter. It was determined that correlation is weak between average annual
discharge and water temperature values fluctuations (linear correlation coefficient for Kupari station
is -0.04 and for Kamanje station -0.27), average annual discharge and air temperature values
fluctuations (-0.29 for Kupari and -0.28 for Kamanje station) and average annual air and water
temperature values fluctuations (0.24 for Kupari and 0.28 for Kamanje station).
We have also performed analysis of distribution of water temperature, air temperature and discharge
values during the year for the same stations. Fig 5 shows the results for the Kupari station and Fig 6
the results for the Kamanje station. It can be emphasized that there is a strong correlation between
same parameters from both stations regarding the monthly distribution during the year. For
example, linear correlation coefficient between average monthly discharges at the Kupari and
Kamanje stations is 0.94, for average monthly water temperature is 0.97 and for air temperature is
0.98.
25
18
12
15
10
8
10
6
4
5
2
0
0
-2
1
2
3
4
5
6
7
months
8
9
10
11
12
0
14
temperature ( C)
20
3
discharges (m /s)
16
discharges Kupari
w ater temperature
- Kupari
air temperature Parg
120
24
100
19
80
14
60
9
40
4
20
0
temperature (0C)
3
discharges (m /s)
Figure 5. Fluctuations of average monthly water temperature, air temperature and discharge values
for Kupari-Kupa station
discharges Kamanje
w ater
temperature Kamanje
air temperature Karlovac
-1
1
2
3
4
5
6
7
8
9
10
11
12
months
Figure 6. Fluctuations of average monthly water temperature, air temperature and discharge values
for Kamanje-Kupa station
It was determined that correlation between fluctuations of certain hydrological parameters exists on
each analyzed station. Average mean monthly discharge values and water temperatures for Kupari
station have the correlation coefficient of -0.67 and for Kamanje station -0.83. Average mean
monthly discharge values and air temperatures have the coefficient of -0.71 for Kupari station and 0.74 for Kamanje station. Average mean monthly air and water temperatures have the coefficient of
0.97 and 0.98 for Kupari and Kamanje stations respectively.
4. CONCLUSIONS
Paper presents the results of hydrological analyses of water temperatures recorded in the Kupa river
catchment area. They suggest that, on average annual water temperature level, exists significant
correlative connection just of data obtained on relatively closely located hydrological stations that
have pretty close air temperatures also. Analysis of frequencies and durations of daily water
temperature values determined great differences in their appearance regime characteristics.
Analyzed trends of fluctuations of average annual water temperatures in the Kupa river catchment
area are relatively simmillar and they show a slight tendency in decrease of values.
Analysis of fluctuations of average annual water temperatures, air temperatures and average
monthly discharges during 25 year period determined that there is no significant mutual correlative
connection. But, such connection was noticed at a level of average monthly data when distribution
during the year was analysed. It was determined that the highest water temperature values in the
Kupa river catchment area were present exactly in these months with lowest values of inflow.
These results of analyses of water temperatures in the Kupa river catchment area suggest the
complex nature of water temperature regime character of the catchment area. Therefore, regarding
the great importance that water temperature has for the water chemistry and for biological processes
in the stream, it is necessary that, when hydrological analyses of certain events are performed, water
temperature should also be taken into consideration what is necessary for keeping sustainable
ecological balance of the water system.
5. LITERATURE
1. Bonacci,O.: Metodologija odre|ivanja ekolo{ki prihvatljivih najni`ih protoka (Biolo{kog
minimuma). (Methodology of determination of ecologicaly acceptable lowest discharges (Biological
minnimum)). Faculty of civil engineering, University of Split (unpublished), Split, 1997.
2. Chow,V.T.: Handbook of Applied Hydrology. McGraw-Hill, New York, 1972.
3. Rubini},J, O`ani},N.: Prirodne hidrolo{ke zna~ajke povr{inskih vodnih pojava @upanije
primorsko-goranske (Natural hydrological characteristics of surface water phenomena in `upanija
primorsko-goranska district). (unpublished), Rijeka, 1997.
4. Srebrenovi},Z.: Kompleksno ure|enje sliva Kupe - knjiga 3.1 - Postoje}i vodni re`im sliva Kupe
(Complex regulation of the Kupa river catchment area - Book 3.1 - Existing water regime of the
Kupa river catchment area). VRO Projekt (unpublished), Zagreb, 1988.
kontakt adrese autora:
Josip Rubini}, dipl.in`.gra|.
HRVATSKE VODE, VGI Labin, Zelenice 18, 52220 LABIN
dr.sc. Nevenka O`ani}, dipl.in`.gra|.
HRVATSKE VODE, VGO Rijeka, Ciottina 17b, 51000 RIJEKA
Gordana Bu{eli}, dipl.in`.mat.
Dr`avni hidrometeorolo{ki zavod, Gri~ 3, 10000 ZAGREB
mr.sc. Janja Milkovi}, dipl.in`.fizike
Dr`avni hidrometeorolo{ki zavod, Gri~ 3, 10000 ZAGREB