Journal of Japan Society of Civil Engineers, Ser.
B1 (HydraulicEngineering),
Vol. JSCE,
68, No.Vol.56,
4, I_283-I_288,
2012.
Annual Journalof HydraulicEngineering,
2012, February

WATER AND ENERGY BUDGET ANALYSIS OF
AN URBAN RIVER UNDER STRONGANTHROPOGENIC INFLUENCE
Zhuohang XIN1 and Tsuyoshi KINOUCHI2
1Student Member of JSCE, Master Student, Dept. of Environmental Science and Technology, Tokyo Institute ofTechnology (4259 Nagatsuta-cho, Yokohama 226-8503, Japan)
2Member of JSCE, Dr. of Eng., Associate Professor, Dept. of Environmental Science and Technology, Tokyo
Institute of Technology (4259 Nagatsuta-cho, Yokohama 226-8503, Japan)

To reveal the anthropogenic influences on thermal environment in urban rivers, stream temperaturesfrom 1990 to 2010 of the Tama River were investigated. Both the long-term and longitudinal changes of
stream temperature, as well as flow rate, effluent temperature and volume, and water and energy budget
were revealed. Stream temperature in winter season increased significantly at points where thetemperature and discharge volume of effluents from wastewater treatment plants increased over the past
20 years. The different longitudinal variations in upstream temperature between winter and summer
seasons were found primarily due to the flow rate decrease. Water and energy budget analysis suggested
that the anthropogenic heat inputs from the wastewater were the dominant warming factor both in winterand summer seasons in downstream segments, while other factors such as groundwater recharges, andair-water and water-sediment interactions were contributing to suppress the stream water warming.

Key Words : human impact, stream temperature, wastewater effluents, water and energy budget

1. INTRODUCTION
Stream temperature is an important measure ofwater quality and ecosystem health affecting
physical, chemical and biological river processes. It
determines the ecosystem productivity and affects
the geographic distribution of aquatic life1). Thus, it
is essential to reveal the thermal behavior of river
systems under different environmental conditions
and human impacts.
Stream temperature depends on various physicalprocesses of heat energy added or lost to/from thewatershed, both natural and anthropogenic. Naturalprocesses mainly include tributary and groundwaterflows, and exchanges across the water surface andstreambed2). Human activities can affect stream
temperature through global climate change, ripariandeforestation and warm effluents discharge3).
Factors that influence stream temperature varyspatially and temporally, making comprehensive
understanding and prediction of stream temperature
variation a complex task.
Recent investigations in stream and rivertemperature give particular attention to the past andfuture trends, fundamental controls on thermal
behavior and thermal heterogeneity at different
spatial scales. Particularly, studies of how humanactivity may alter stream and river temperature
behavior have continued to command attention4).
This work has put forward a new discovery withrespect to the stream temperature variations on both
temporal and spatial scales of the Tama River inJapan, as a result of strong anthropogenic influence.
The objectives of this study are: (1) to reveal thestream temperature changes in recent 20 years, (2)to identify major causes of past changes of stream
temperature, (3) to analyze water and energy budget
in several segments for identifying significant
processes that determine temperature regime. Byutilizing these conclusions, scientific information
can contribute better to environmental management
and conservation.

2. STUDY AREA AND DATA SOURCE

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The Tama River is located in the east of Japan,

Fig.1 Study catchment showing the Tama River system,
mainstream, and locations of stream temperature
measurement, wastewater treatment plant and weir.

and has been a major river system running throughthe central Tokyo. The upstream region is basicallycovered by grass and forest whereas the downstream
region has been highly urbanized. The Tamawatershed consists of 60% forests, 31% urban area,
2% farmland, 1% paddy field and 6% others.
Stream temperature has been measured at 11
stream temperature measurement sites (S-1 through11) as shown in Fig. 1. At these sites, data of stream
temperature and flow rate from 1990 to 2010 wereavailable from the Ministry of land, infrastructure
and transport, Japan, with records of monthly
measurement which were taken 2 or 3 times in aparticular day in every month. The information
related to wastewater treatment plants (WWTPs),
such as monthly discharge volume from 1990 to2009 and monthly effluent temperature from 1993
to 2009 was provided by the Tokyo Bureau of
Sewerage. Meteorological conditions such as air
temperature, global short-wave radiation andsunshine duration were obtained from Japan
Meteorological Agency.

3. STREAM TEMPERATURE

Large part of the Tama River runs throughrapidly urbanized areas generating a great amount ofheat effluents from WWTPs. There are 8 WWTPs(W1-W8) distributed along the mainstream (Fig. 1).
W1-W3 and W4-W7 are located between S-3 to S-4
and S-4 to S-6 respectively. In our analysis, theeffect of W8 was neglected due to the relatively
minor discharge volume and close position to theriver mouth.
Fig. 3 illustrates the average of discharge
volume and effluent temperature from WWTPs in
winter months among 4 periods, which shows theoverall effluent temperature increase over the study
period. The increase trends of discharge volume
from W1-W3 and W4-W7 are also relevant, whichwere approximately twice amount in recent years
than that of 20 years ago. The long-term stream
temperature increase at S-4 and its downstream sites
in winter months (Fig. 2) is likely due to theincrease of both effluents temperature and discharge
volume from WWTPs. More quantitative discussion
will be given in the later part.

16

Discharge Volume (107m3/y)Stream Temperature (oC)

By analyzing the available data, both thelong-term and longitudinal stream temperaturechanges were identified.

4. EFFLUENT FROM WWTPs

14
12
10
1990-1995
1996-2000
2001-2005
2006-2010

8
6
4

5
4

2

3

4

5

6

7

8

9 10 11

Fig.2 Stream temperature variations at S-1 through S-11 in
winter months from 1990 to 2010.

19

3

18
2
1
0

S- 1

20

Effluent Temperature (oC)water temperature measurement sitewaste water treatment plantweirmainstream

The 5 or 6-year average of monthly measured
temperatures at S-1 through S-11 for winter months(December through February) were comparedamong four periods from 1990 to 2010 (Fig. 2). We
found that stream temperature in the most recent
period was much higher than that of the preceding
periods at S-4 to S-11, whereas at S-1 to S-3, no
obvious temporal change was observed, probably
due to unchanged land use conditions and cold
water released by the upstream dam. Longitudinaltemperature varied along the mainstream. An abrupt
increase occurred between S-3 and S-4, the highest
temperature appeared at S-6 and no obvious
longitudinal temperature changes were observed in
the further downstream region.
It is of great importance to identify the possible
causes related to significant stream temperaturechanges in recent years in downstream region.

W1+W2+W3
W4+W5+W6+W7
effluent temperature

1990-1995 1996-2000 2001-2005 2006-2009

17

16

Fig.3 Effluent temperature and discharge volume from WWTPs
in winter months from 1990 to 2009.

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18

Longitudinal stream temperature variation (Fig.
2) is probably caused by the distribution of
WWTPs. The clear discrepancy in stream
temperature was found between S-3 and S-4,
because of heat input from the WWTPs (W1-W3).
The highest stream temperature occurred at S-6
could be attributed to wastewater released from the
WWTPs (W4-W7), of which the discharge amount
was approximately twice of that from W1-W3. The
reason of lesser increase between S-4 and S-6 thanthat between S-3 and S-4 will be discussed in
section 7.

Flow Rate (m3/s)

16

6. RELATION BETWEEN AIR AND
STREAM TEMPERATURES
The significant stream temperature change foundin Fig. 2 may be partly due to regional warming
caused by urban heat islands since the downstream
region has been highly urbanized. To separate theinfluences of other factors from that of regional
warming, relationships between air temperature andstream temperature were investigated.

12
10
8
6

1990-1995
1996-2000
2001-2005
2006-2010

4
2
0

S- 1

2

3

4

6

8

Flow Rate (m3/s)

32

5. HYDROLOGICAL CONDITION

28

Summer Season

24
20
16
12
1990-1995
1996-2000
2001-2005
2006-2010

8
4

Stream Temperature (oC)

0

S- 1

2

3

4

6

8

16
Winter Season
141210
1990-1995

8

1996-2000

6
4

2001-2005
2006-2010

S- 1

2

3

4

6

8

28

Stream Temperature (oC)The stream temperature may be influenced byseveral hydrological conditions, such as flow rate
alteration which mainly influences the heating or
cooling rate due to human and natural heat inputs.
Flow rate and stream temperature in winter andsummer (July through September) seasons atselected stations are shown in Fig. 4 respectively.
Flow rate decreased abruptly between S-1 and S-2,
because there are two weirs used for water
withdrawal for agriculture and drinking purposes,
and then it became larger due to wastewater
discharge and tributary inflows. Flow rates display
similar variation along the mainstream between
winter and summer seasons, whereas the stream
temperatures are quite different, particularly in the
upstream region (S-1-3). This pattern is possibly
caused by interactive influence of radiation and flowrate alteration. In summer season, stream
temperatures are more sensitive to the heat input by
short-wave radiation during low flows5), thus the
upstream temperatures were inversely related to
stream flow. On the contrary, stream temperatures in
winter season were relatively stable between S-1-3
even the flow rate decreased considerably, probably
due to small net radiation inputs.
In winter season, stream temperatures during
1996-2000 were quite similar to those in 2001-2005.
This is probably due to the lowest flow rate of
1996-2000, which enhanced the heating by warmer
effluents.

Winter Season

14

26

Summer Season24
22
1990-1995
1996-2000
2001-2005
2006-2010

20
18
16

S- 1

2

3

4

6

8

Fig.4 Flow rate and stream temperature in winter and summer
seasons respectively. Each plot indicates a 5 or 6-year
average of monthly measured data.

The relations between air temperature andstream temperature at S-1, S-4 and S-6 from 1990 to
1995 and from 2005 to 2010 are compared in Fig. 5.
The data in the figure were based on monthly stream
temperature measured at each site and weekly
average of air temperature recorded on an hourly
basis at Ome (for S-1) and Fuchu (for S-4 and S-6)
of AMeDAS. The averaging period for the airtemperature was a week prior to the monthly stream
temperature measurement, because the weekly
average was more strongly correlated with stream
temperature than any other intervals6).

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o

Stream Temperature ( C)30

7. WATER AND ENERGY BUDGET

S-1

25

The analysis of water and energy budget for four
segments (S-2-3, S-3-4, S-4-6 and S-5-6) was
conducted to quantify the processes (Fig. 6) that
affect the stream temperature.

20
15
10
1990-1995
2005-2010

5
0

0

5
10 15 20 25o
Air Temperature ( C)30oStream Temperature ( C)

30

S-4

25

Fig.6 Components responsible for water and energy budget ineach segment.

20
15
10
1990-1995
2005-2010

5
0

0

5

10
15
20
25
o
Air Temperature ( C)30oStream Temperature ( C)

30

S-6

25
20
15
10

1990-1995
2005-2010

5
0

0

5

10
15
20
25
o
Air Temperature ( C)30

Fig.5 Relations between air temperature and stream temperature
at S-1, S-4 and S-6 during two periods.

At S-1, the relations between air temperatureand stream temperature were overlapped in thesetwo periods. Stream temperatures were lower than
air temperatures at air temperatures above about
15oC, probably due to the shading covers in
upstream region and cold water released from thedam in warmer seasons. By contrast, stream
temperatures at both S-4 and S-6 were higher inrecent years (2005-2010) than those of previous
years (1990-1995), particularly at air temperatures
below about 15oC. This is likely due to the strong
anthropogenic heat inputs caused by the increased
wastewater temperature and discharge volume incolder seasons. When air temperatures were above
about 15oC, stream temperatures at S-4 and S-6
were more close to air temperatures, which indicatesthe insensitive change of stream temperature towastewater influences in warmer seasons because
the natural flow is normally larger (Fig. 4) and thestream temperature is similar to that of wastewater.

A general description of water budget is given as
(1)
where
is the outflow at downstream section,,,
are inflow at upstream section, andfrom tributaries and WWTPs respectively.
indicates integrated flows of other factors (i.e.,
evaporation, groundwater flow and water
withdrawal). In equation (1),, ,andare measured river flow or discharge volume from
WWTPs, andis calculated by.
The balance equation of heat transport in eachsegment is expressed as
(2)
where
is the outflowing heat at downstream
section,,,are inflowing heat at
upstream section and from tributaries, WWTPs andnet radiation respectively.
indicates
integrated heat exchanges caused by other factors(i.e., air-water and streambed-water interaction,
groundwater flow and water withdrawal, etc.). The
heat flux () is defined as
(3)
where
is the heat capacity of water (TJ/m3/K),
is the measured river flow () ordischarge volume from WWTPs ( ) (m3/h),isthe measured stream or effluent temperature (K).
The heat flux caused by net radiation ( ) isexpressed as
(4)
where
is the water surface area (m2), calculated
from google earth image.
is the net radiation,
which is derived from equations (5)-(9) 7),8).
(
)
(5)
(6)
[
(
) ]
(7)
[
(
) ](8)(9)
whereis the global short-wave radiation(TJ/m2/h),is the albedo of the water surface

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Fig.7 Water and energy budget for each segment in winter and summer seasons.

(0.06),
is the emissivity of the water surface(0.97),
andare long-wave downward andupwardradiation(TJ/m2/h),istheStefan-Boltzmann constant (TJ/m2/K4/h),andare stream temperature and air temperature (K),is the atmospheric emissivity under clear skies,
is the cloud cover ratio, andis the fraction ofsunshine hours. The
in equation (2) iscalculated by.
The water and energy budget for each segment(Fig. 7) is calculated using equations (1)-(9). The
data used for calculation were the monthly measured
stream temperature and river flow, monthly effluent
temperature and discharge volume from each
WWTP along with the short-wave radiation andsunshine duration collected at the central Tokyo andair temperature measured at Fuchu. The number of
events that were taken into account in each segment(shown in parentheses in Fig. 7) was based on thedata availability and all the events selected are undernormal flow condition. Table 1 displays theconsideration of factors in our analysis. The
numbers on the left/right in the column indicate theTable 1 Consideration of factors in each segment.

segment
S-2-3
S-3-4
S-4-6
S-5-6

Qi, Hi,Qw, HwQt

Ht

Q other , H other

○

○ 0/0

△ 1/2

△ 0/2

✕

○

○ 3/3

△ 0/2

△ 0/2

✕

○

○ 4/4

△ 3/4

△ 3/4

✕

○

○ 1/1

○ 0/0

○ 0/0

✕

Qo , Ho ,Hr○: fully considered and calculated using observed data△: partially considered and calculated using observed data✕: not directly quantified and calculated using Eqs. (1) and (2)number of WWTPs and tributaries that wereconsidered in our analysis/existed in the segment
respectively. The other factors such as weirs used
for water withdrawal were not directly quantified
due to the data limitation. Moreover, the flow ratesof tributaries that were not measured tended to besmall and negligible.
In segment S-2-3, the water budget result
indicates thatwere almost balanced by thetributary inflows. The differences between

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and
were smaller in winter and comparatively
larger in summer, probably due to the larger
tributary inflow in summer seasons. Thus, insegment S-2-3, the water and energy transport
processes are likely to be dominated by tributary
inflow and the net radiation. In segments S-3-4 andS-4-6, which are under strong anthropogenic
influences, the discharge volumes and heat inputs
from WWTPs occupied large proportions of waterand energy increases in most periods, whereas theeffects of the net radiation and tributaries wererelatively small. In both segments, theprimarily indicates the energy losses throughsensible and latent heat, groundwater recharge andwater withdrawal. The heat losses were quite larger
in segment S-4-6 than that in segment S-3-4, which
may result in the lesser increase in stream
temperature between S-4 and S-6. In segment S-3-4,
were quite small, which may be caused bytributary inflow, water withdrawal and groundwater
recharge. In segment S-4-6,
is probably
caused by groundwater recharge and water
withdrawal.
To better understand the effects of groundwater
flow, budgets analysis in segment S-5-6 was alsostudied. The energy loss caused by groundwater
recharge () is estimated using equation (3), in
which,
is regarded equal toandisstream temperature. The calculation result showsthatis close to, which suggests thatthe groundwater recharges took place andcontributed a lot to the water and energy losses insegment S-5-6.

8. CONCLUSIONSThis study mainly investigated the long-termand longitudinal changes in stream temperature in
the Tama River system, using data on stream
temperatures, flow rates, effluent temperatures andvolumes, air temperatures, global short-wave
radiations and sunshine durations.
Stream temperature increase in winter season
was detected at sites that had considerable increasein both effluent temperature and discharge volume
over the study period. The flow rate decreased
sharply between S-1 and S-2, resulting in different
longitudinal stream temperature changes in the
upstream region between winter and summer
seasons. The relationships between air temperatureand stream temperature at S-1, S-4 and S-6 for two
periods indicate that the major cause of stream
temperature increase was the wastewater released
from WWTPs.
The budget analysis helps to understand thecontribution of each component in water and energy

transport processes in each segment. Tributary andnet radiation were found to be the dominant factors
in upstream segment of S-2-3. In segments that
under anthropogenic impacts, the water and energychanges were largely contributed by wastewater
inputs from WWTPs. Specifically, groundwater
recharges were confirmed to be the major cause ofwater and heat losses in segment S-5-6.
To improve the urban water environment andcontrol on the warming of stream temperature,
several countermeasures can be taken. To control
the water temperature during wastewater treatment
process may be an effective way as most WWTPs
value the removal of chemicals and nutrients. The
use of warmer wastewater as heat sources and reuseof treated wastewater are also recommended as they
can save energy and reduce the effluent release.
Other alternative methods for wastewater treatment
are also suggested such as man-made wetlands andstabilization ponds9).
ACKNOWLEDGMENT: This work has been
financially supported by the Tokyu Foundation for
Better Environment. The authors express sincere
gratitude to the Tokyo Bureau of Sewerage forproviding data related to WWTPs.
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