Junichi Nishimata1,2), Hitoshi Miyamoto2) (1:Nippon Koei Co., Ltd , 2:Department of Civil Engineering, Shibaura Institute of Technology)

4. RESULTS and DISCUSSION

Table 1. Specifications of Tama RiverRiver NameTama River

Length138 kmBasin Area

1240 km2

Basin Population

446 million person

Basin Population density

3,600 person/km2

2.4

2.0 3030

2.0

1.6 2525

1.6

1.2 2020

1.2

0.8 1515

0.8

0.4 10

10

0.4

0.0 5

50.00-0.4 0-0.4
2014/12 2015/1 2015/4 2015/6 2015/8 2015/10 2017/12 2018/1 2018/4 2018/6 2018/8 2018/10
Downstream water temperature(#3)
Downstream water temperature(#1)
Upstream water temperature(#4)
Upstream water temperature(#2)
Equilibrium water temperature
Equilibrium water temperature
Treated water temperature
Water temperature difference / distance(#2-1)
Water temperature difference / distance(#4-3)

35

River, Equilibrium water temperature[℃]River, Equilibrium water temperature[℃]

The river studied in this paper was Tama River running through the metropolitan Tokyo. Forests are predominant
in the upstream part of the river basin, while, in the middle and downstream parts, the river basin has been heavily
urbanized since it has been located in the metropolitan Tokyo. There are 9 water treatment facilities located along
the main channel of Tama River, discharging treated sewage water with a constant water temperature of around
23 ℃.

2.4 35

35

30
25
20
15
105

DISTANCE FROM
RIVER MOUTH

DATA PERIOD

42-54km

12/2017-09/2019

Tama River Upstream,
Hachiouji

32-37km

12/2014-10/2015

MinamiTama

18-24km

12/2017-11/2018

WATER TREATMENT
FACILITYTRIBUTARYAkikawa
River

2.4

35

2.4

30

2.0
2.0

25

1.6
1.6

201.21.2

150.8

0.80.4100.40.0

50.0

Water temperature change per unit flow distance[℃/km]

2. STUDY FIELD AND RIVER WATER TEMPERATURE MONITORINGMIDDLE STREM(#9-#6)DOWN STREAM 1(#4-#3)DOWN STREAM 2(#2-#1)4.1. River temperature observation
Water temperature change per unit flow distance[℃/km]

・Back GroundIn recent years, there has been a concern that the global climate change and the artificial waste heat from urbanrivers will have a significant effect on terrestrial ecosystems at river sites1,2). River temperature is one of theimportant indicators that define the river environment.
・Purpose
The effect of the artificial waste heat of treated water on river water temperature was investigated for the Tama River.
Specifically, seasonal observations of water temperature observation data are compared in the middle anddownstream parts of the Tama River, and the water temperature formation factors are analyzed by using the heattransport equation.

SECTION

River, Equilibrium water temperature[℃]

1.INTRODUCTION

Table 2. Specifications of the three analytical sections

Downstream watertemperature(#6)
Upstream watertemperature(#9)
Equilibrium watertemperature
Treated watertemperature
Water temperature
difference /distance(#6-9)-0.4
2017/12 2018/2 2018/4 2018/6 2018/8 2018/10 2018/12 2019/2 2019/4 2019/6 2019/9-0.400
2017/12 2018/2 2018/4 2018/6 2018/8 2018/10 2018/12 2019/2 2019/4 2019/6 2019/9

Middle stream section
Down stream sections (left: down stream 1, right: down stream 2)
Figure 2. Time series of various water temperature quantities in the tree analytical sections

The (water temperature difference /distance) was quite small throughout the year in thedownstream section 1.On the other hand, for the downstream section 2, positive and negativevalues were switched seasonally. It was considered that the formation mechanism of river watertemperature had a great influence on the presence or absence of treated water inflows. In otherwords, it could infer that high temperature conditions were maintained continuously by the treatedwater inflow in the down stream section 1, while the river water temperature was naturally
changed due mainly to the thermal balance on the water surface in the down stream section 2.

4.1. Model analysis

Total heat flux
Tributary heat flux

The (water temperature difference / distance)
took a positive value throughout the year. In
particular, its value had maximal in winter.
This could be due to the large effect of theinflow treated water.

Water surface, Waterside and Wetted perimeter heat flux
Treated water heat flux

The values of the fluxes in Fig. 3 were devided by unit downstream
distance. In Fig. 3, the values during the period of fine weather
were collected and calculated for discussion. It was revealed from
3. ANALYTIC MODELFig. 3 that the total heat flux was larger in the middle section thanFigure 1. Tama River basin and the locations of river temperaturethat in the downstream section 1. It corresponded to themeasurements, discharge observatories and, water treatment facilities.
3.1. Basic equation
characteristics found in the (water temperature difference /This paper used the following one-dimensional thermal conservation equation as a basic equation of the riverdistance) relationship in Fig. 2. The heat flux of the treated water in
Total heat flux
winter was the largest in the middle section, while that in spring
temperature analysis3,4).
long-wave inflow
WINTER SPRING SUMMER AUTUMN YEARWINTERSPRINGSUMMER
AUTUMN
YEAR
Water surface, Waterside and Wetted perimeter heat flux
radiation discharge
was the largest in the down stream section 1. It could suggest that
Total heat flux
Tributary heat flux
Water surface, Waterside and Wetted perimeter heat flux
Treated water heat flux
𝜕𝑇𝑤𝜕𝑇𝑤
1𝑞𝑥
the season in which the effect of treated water was predominant
Tributary heat flux
= −𝑉+𝐻𝑤𝑏 +𝑇𝑤𝑙 − 𝑇𝑤(1)
Middlestream section
Down stream section 1
1.2
Treated water
heat flux
differed largely in each section. Furthermore, it also indicated in𝜕𝑡𝜕𝑥𝐶𝑤 𝜌𝑤 ℎ𝐴
1.0
short-wave
long-wave hyporheic
Figure 3. Seasonal distributions0.8of heat fluxes in the middle and down stream sections.
1.2
radiationreflection
Fig. 3 that the heat flux of the water surface, wetted perimeter, andexchange
1.0
0.6
rain
𝐻𝑤𝑏 = 𝐻𝑠 + 𝐻𝑎 − 𝐻𝑏𝑟 − 𝐻𝑙𝑎 − 𝐻𝑠𝑒 + 𝐻𝑏𝑒𝑑
(2)
surface inflow
0.8
0.4
lateral inflow had negative or nearly zero in summer and autumn in0.620.2
Tw: river temperature[℃], V: mean velocity[m/s], A: discharge section area[m ], Cw: specific heat atgroundwater
0.40.0
100%
100%
short-wave
the down stream section, meaning that the treated water inflow
constant pressure of water[J/(kg*K)], ρw: water density[kg/m3], h: water depth[m], Hs: short wave
long-wave reflection
0.2-0.2
222
radiation
0.0
radiation[w/m ], Ha: long wave radiation from air[w/m ], Hbr:long wave radiation from water[w/m ], Hla:
WINTER SPRING SUMMER AUTUMN YEARWINTER SPRING SUMMERwas
AUTUMN
onlyYEAR
contributed to the temperature formation.
80%-0.280%
latent heat transfer[w/m2], Hse: sensitive heat transfer[w/m2], Hbed: thermal flux from the wetted
WINTER SPRING SUMMER AUTUMN YEARWINTER SPRING SUMMER AUTUMN YEAR
tributarylatent heat
Figure 4 showed the ratios of each heat flux in the middle stream
22
perimeter[w/m ], x: longitudinal axis, t: time[s], qx: lateral inflow in unit length[m /s], and Twl: water
inflow
60%
sensible heat60%
section and the down stream section 1. In the middle stream
temperature from the lateral inflow[℃].
ground temperature40%
outflow
section, the effect of treated water on the river water temperatureexchange
40%
discharge
became most predominant in winter, and its ratio was reached to20%
3.2. Analytical method
20%70%. This result was also confirmed in the water temperature0%
The river water temperature change was estimated by using the analytical solution of Eq. (1) obtained by theanalysis in Fig. 2. On the other hand, in the down stream section 1,0% Total heat flux
-20%
method of characteristics. In this analytical solution, the river water temperature at the downstream end of the target
WINTER SPRING SUMMERAUTUMN YEAR
the model analysis revealed that the formation mechanism of theWater surface, Waterside and Wetted perimeter heat flux
Treated water heat flux
section was calculated when the water temperature and the flow rate were given as the upstream boundary-40%
Tributary heat flux
river water temperature was completely different in each season,
Tributaryheatflux
WINTERSPRING
SUMMER
AUTUMNYEARconditions.The heat fluxes on the water surface and the wetted perimeter were estimated by empirical bulk
Treatedwater
Total heat
fluxheat flux
though the river temperature change was quite small as shown in
WaterWater
surface,Watersideand
Lateralinflowheat
flux
surface, Waterside and Wetted perimeter heat flux
equations with the weather data from the AMeDAS system of the Japan Meteorological Agency. The water
depth
1.2
Fig. 2 (b). Namely, in winter and spring, the river water
Tributary
heatflux
MiddlestreamsectionDownstream
section
11.0
and the lateral inflow were determined by the least squares method of the observed and analytic temperatures
with
Treated water heat flux
temperature was kept constant by the balance between a warming
0.8
Figure4.
Ratiosofheatfluxesmodel parameters in the governing equations.
0.6
effect of the treated water and a cooling effect of the heat fluxes
1.2
0.4
1.0
from the water surface, wetted perimeter, and lateral inflow.
0.2
0.8
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2

3.3. Point-sources treatment as a boundary condition

0.0
0.6
-0.2
Regarding the heat inflow from treated waters and tributaries, the analytical section was divided into0.4
upperandWINTER
0.2
0.0condition
lower sections at the inflow point, and the analytical solution was applied to each section. The conservation-0.2

5. CONCLUDING REMARKSSPRINGSUMMER AUTUMNYEARWINTERSPRINGSUMMER AUTUMNYEAR・The influence of the treated water inflow extended to the entire river course of the Tama River.
・In particular, it revealed that the influence became larger in the middle stream section than in the down stream sections, and most predominant(Eq. (3)) of the heat flux before and after the division point was used as the inflow boundary condition of the divided
WINTER SPRING SUMMER AUTUMNYEARWINTER SPRING SUMMER AUTUMNYEARin winter.
downstream section

𝑄𝑟 𝑇𝑤𝑟 + 𝑄ℎ 𝑇ℎ
𝑇𝑤𝑓 =𝑄𝑟 + 𝑄ℎ(3)Qr: river flow rate[m3/s], Qh: treated water/tributary flow rate[m3/s], Th: treated water temperature (data from the Tokyo
Metropolitan Government) or tributary water temperature[℃], Twr: inflow river water temperature in the main river channel atthe division point[℃], Twf: river water temperature after the inflow [℃].

References
1.Robert; J.S. et al.: Horizontal cooling towers: riverine ecosystem services and the fate of thermoelectric heat in the contemporary Northeast US, Environmental Research Letters, 025010, Vol.8, Num.2, 2013.
2.Xin, Z. and T. Kinouchi: Analysis of stream temperature and heat budget in an urban river under strong anthropogenic influences, Journal of Hydrology, 489, pp.16-25, 2013.
3.Miyamoto, H. and Michioku, K. (2007): Monitoring and analysis of stream temperatures in a river basin, Annual Journal of Hydraulic Engineering, JSCE, Vol.51, pp.1105-1110 (in Japanese).
4.Miyamoto, H., Sugahara, Y. and Michioku, K. (2009): Analytic examination on principal factors of river temperature formation in upper, middle and lower streams of a river basin, Annual Journal of Hydraulic Engineering, JSCE,
Vol.53, pp.1153-1158 (in Japanese).