11th ISE 2016, Melbourne, Australia
EFFECT OF TEMPERATURE CHANGE DUE TO THE HYDROPEAKING ON
THE PHYSICAL HABITAT
Byungwoong Choi
Department of Civil & Environmental Engineering, Yonsei University,
e-mail:bw628@yonsei.ac.kr, Korea
Sung-Uk Choi
Department of Civil & Environmental Engineering, Yonsei University,
e-mail: schoi@yonsei.ac.kr, Korea
ABSTRACT
Since the upstream dam releases water only during the period of hydropower generation, the discharge in
the downstream reach tends to show fluctuations in a daily scale. The effect of short-term fluctuations of
water discharge or hydropeaking on the downstream fish habitat has been studied intensively. Most of
them used physical habitat simulations with habitat variables such as flow depth, velocity, and substrate.
However, in the assessment of such impact, the role of the water temperature should not be over-sighted.
That is, the temperature of water released from the upstream reservoir is likely to be lower in the summer
than that of the water in the downstream reach, and vice versa in the winter. The present study assessed
the impact of hydropeaking on the downstream fish habitat using the physical habitat simulations with
including the water temperature as a habitat variable. The study area is a 2.3 km long reach of the Dal
River in Korea, located downstream from the Goesan Dam. Pale chub (Zacco platypus) was selected as
the target species and a seven days period in summer was considered for the physical habitat simulations.
Hydraulic and water temperature simulation is carried out using Coastal Modeling System (CMS)-Flow
model. The Gene Expression Programming (GEP) model is used for the habitat simulation. Simulation
results indicate that hydropeaking flows decrease the habitat suitability of the target fish during summer.
1. INTRODUCTION
Flows regulated by upstream dams affect the downstream habitat in two different ways. The first is that
the upstream dam releases water only during the period of hydropower generations, resulting in the shortterm fluctuations of water discharge. This is called the hydropeaking. The second is the temperature of
water released from the upstream dam is likely to be different from that flowing in the downstream reach.
That is, in general, water released from the dam is warmer and cooler than that of flowing water in the
winter and summer, respectively. Ward and Stanford [1] called this phenomenon thermopeaking.
Hydropeaking is known to affect the downstream habitat adversely ([2], [3]). Similarly, thermopeaking
has major effects on biotic distributions by stimulating behavioral responses of flora and fauna ([4], [5]).
However, most previous studies have not taken into account of thermopeaking in the assessment of
hydropeaking flows on the stream habitat ([6], [7], [8]).
The purpose of this study was to investigate the impact of short-term fluctuations of water discharge and
11th ISE 2016, Melbourne, Australia
temperature on the downstream fish habitat. For this, a 2.3 km long reach located downstream from the
Goesan Dam was selected for the study area with Zacco platypus as the target fish. Physical habitat
simulations were carried out with including the water temperature for the habitat variable. The CMS-Flow
model and GEP model were used for hydraulic and habitat simulations, respectively. The Composite
Suitability Index (CSI) distribution and Weighted Usable Area (WUA) under hydropeaking operations
were provided and impacts of both hydropeaking and thermopeaking are discussed.
2. STUDY AREA AND RESEARCH METHOD
The study area is located downstream from the Goesan Dam. The dam was constructed in 1957 and has a
total storage of 1.53x106 m3. At the toe of the dam there is a 2,600 KW power plant, equipped with 2
Francis turbines, producing about 10.8 GWh-year. The study reach is 2.3 km long, extending from the
Sujeon Bridge to the Daesu Weir. The reach includes a bend, and the average slope is 1/650. The Goesan
Dam, 0.92 km upstream from the Sujeon Bridge, regulates the flow in the study reach.
Fish monitoring was carried out, revealing that dominant species in the study area is chub minnow (Zacco
platypus), followed by dark chubs (Zacco temmincki) and swiri (Coreoleuciscus splendidus) ([9]). In the
present study, the adult minnow was selected as the target life-stage and abundance data was used in the
evaluation of the physical habitat.
For hydraulic simulation, the CMS (Coastal Modeling System)-Flow model was used. ([10]). The CMSFlow model is based on the 2D shallow water equations for the flow and 2D depth-averaged temperature
equation for the water temperature. Gene Expression Programming (GEP) was used for the habitat
simulation ([11]). Choi and Choi [11] found that the HSCs by the GEP model are very similar to those by
the method of Gosse [12] and the GEP model predicts Habitat Suitability Curves (HSCs) better than the
Adaptive Neuro Fuzzy Inference System (ANFIS) model. Furthermore, Choi and Choi (2015) indicated
that the GEP model is robust and non-subjective compared the method of Gosse [12].
3. RESULTS
Figure 1(a) and 1(b) show the CSI distributions of Zacco platypus for the normal flow (Q185 = 7.23 m3/s)
and for hydropeaking flows, respectively. Figure 1(b) is the CSI distribution averaged over the period of
Aug. 24 – Aug. 30, 2009. For this figure, three physical habitat variables such as the flow depth, velocity,
and temperature were used in the physical habitat simulation. The average discharge released during this
period is 7.02 m3/s, which is similar to the normal flow.
Comparisons of the two figures lead to the impact of hydropeaking on the downstream habitat. The
hydropeaking operation induces not only short-duration fluctuations in discharge but decreases water
temperature below the dam. Consequently, the flow during the hydropeaking operation provides flow
depth and velocity smaller than preferred by Pale chub, which prefers the flow depths in the range of 0.3
– 0.5 m and velocities of 0.2 – 0.55 m/s. The range of preferred water temperature by the target species is
20 – 25oC. However the water temperature released by the dam was only 5.5 oC, much lower than the
preferred range. Thus, hydropeaking resulted in the decrease of the overall habitat suitability (Figure 1(b)).
The inclusion of the water temperature as habitat variable leads to a further decrease of the CSI for the
11th ISE 2016, Melbourne, Australia
target species.
Two WUAs from the physical habitat simulations with and without inclusion of water temperature as
habitat variable are given for the hydropeaking operation during Aug. 24 – Aug. 30, 2009 (Figure 2).
WUA increased temporarily during the hydropeaking operation due to the base flow of 0.05 m3/s being
too small without hydropeaking flow. However, the WUA during the hydropeaking operations (with
temperature) is, in general, smaller than the WUA for the normal flow. Specifically, the WUA for the
hydropeaking flows is about 27.3% of the WUA for the normal flow. It is also noteworthy that the
physical habitat simulation without the water temperature over-estimates the WUA seriously. This
indicates that the water temperature should be included in the habitat variables to see the impact of
hydropeaking on the habitat suitability.
(a) for the normal flow
(b) for the hydropeaking flow (averaged)
Figure 1. Distribution of CSI
Figure 2. Change of WUA with time
4. CONCLUSIONS
Physical habitat simulations were carried out to investigate the impact of both hydropeaking and
thermopeaking on downstream fish habitat. A 2.3 km long study reach, located downstream from the
Goesan Dam, Korea, was selected, and this study reach showed the dominance of Zacco platypus. The
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water temperature was used as a habitat variable as well as the flow depth and velocity. The simulated
results indicated that the CSI decreases significantly by hydropeaking of the upstream dam, and the
thermopeaking further decreases the CSI in the summer. The WUA due to both hydropeaking and
thermopeaking appeared to be seriously decreased in comparison to normal flow conditions.
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