Hi Everyone! this is Kosame and Qisty writing (Yes, I am a new student in
Kawasaki Lab :D). This time we took a longer trip to the Fukui prefecture
visiting two dams. The difference was that this time, Kosame was attending as a
member of the committee, and one of the dams we visited was a dam that was under
construction.
(Sep 18th) Day 1: The Asuwagawa Dam
The dam is located in the Kuzuryu bashin of Fukui Prefecture because, in
recent years, there is often an embankment break caused by floods in Fukui City,
which has caused no small impact on the city's production and life, safety, and
other aspects. The Asuwagawa Dam is primarily designed for flood control. In
particular, the Asuwagawa Dam is a flowing concrete gravity dam, meaning that it
will completely close the gates during flood season to store the flood peak, and
open the gate outside flood season to allow the river to pass freely. It
features two gates, the primary measuring 5 m x 5 m and a smaller adjacent gate.
To release storage after flood event, they will first open the smaller gate
before the main gate to prevent a rapid rise in the downstream water level.
Asuwagawa dam is still under construction, with concrete placement about
40% complete and the diversion tunnel and water distribution facilities under
construction. The current production is achieving a height of 1 meter of the dam
body every week, with completion scheduled for 2028 before to the flooding test
in the subsequent year. Work will cease if rainfall above 2 mm per hour during
construction. Furthermore, as this is a gravity dam, a concrete strength of 10
N/mm² is theoretically adequate, whereas an arch dam requires more than 24
N/mm². Nonetheless, it is evidently challenging to produce lesser grade
concrete, since it tends to be excessively slumpy in practice; therefore, they
are constructing the dam with concrete of 20 N/mm² strength.
In construction, Asuwagawa dam uses new technologies to increase the efficiency of construction,
such as automatic concrete placement system and concrete consolidation
management system. Initially, they only utilize a cabled concrete bucket for
transportation. Due to the scarcity of cable crane operators, particularly those
with expertise, as the efficiency of the concrete pouring cycle is significantly
influenced by the operator's proficiency, alternative methods of concrete
transportation are being sought to enhance productivity and minimize overtime.
They implemented the utilization of premium belcon (the green sleeve), an effective method for
transporting concrete on gradients exceeding 45 degrees. The length possesses a
mechanism for shortening as the dam structure ascends. Notably, incorporating an
additional choice can reduce the cycle time by 10 seconds. Although this figure
may appear little, when aggregated over a whole 42-month concrete pouring
schedule, it can expedite the project by 1.7 months and yield substantial cost
savings in millions of yen (interesting!).
(Sep 19 th) Day 2: The Managawa Dam
The Managawa Dam is a concrete gravity arch dam that was completed in 1979 in the Kuzuryu Basin. It is primarily utilized for flood management and electricity production, with an annual output of 68,800 MWH in the Fukui region. The dam's discharge mechanisms are highly comprehensive. The system features a valve with a maximum flow rate of 30 m³/s for standard discharge, with two gates with a maximum flow rate of 500 m³/s serving as the primary discharge mechanisms. In emergencies, it can be discharged at a rate of 3500 m³/s through the gate at the dam's apex, a situation that has fortunately never occurred. The complete mechanism is as follows:
a. Regardless of rainfall, if the inflow to the dam is below 500 m³/s, the inflow is discharged into the downstream river without being retained in the dam.
b. In the event of heavy rainfall, if the inflow to the dam exceeds 500 m3/s, the downstream water release is consistently maintained at 150 m3/s to facilitate further water storage in the dam and mitigate downstream flooding.
c. If there is an unusually high rainfall and the dam's flood control capacity is maximized, an equivalent volume of input will be gradually released into the downstream river to prevent a fast increase in water levels.
d. Upon cessation of heavy rainfall, the inflow to the dam is reduced to below 500 m3/s. Upon confirmation of the downstream river's safety, the discharge flow rate will be incrementally elevated to 500 m3/s to expel the floodwater retained in the dam.
Clear sky!
This dam also features an aerator fountain to regulate the downstream surface water temperature, so preventing excessive rise that could jeopardize fish life and inhibit rampant phytoplankton proliferation. They stated that if the sunlight is positioned at the appropriate angle, a rainbow may be visible by the fountain!
(Sep 19 th) Day 2: Group work
We also conducted group work on how to further develop and utilize the Asuwagawa
Dam, particularly in tourism aspect to attract people and who the target will
be. Many interesting proposals have been proposed from different perspectives,
such as the cultural history of the Fukui area, the food culture, and the
characteristics of the dam. At the same time, due to the presence of many
practitioners, our program has also received comments from practitioners in the
industry.
After that, Kawasaki-Sensei gave a speech and asked us to hold a stance position (for 5 minutes I think?) to resemble a dam body, which should be strong during hard times to withstand rain and floods on its own. Then we gently rose, stood up, and exclaimed, "Banzai!"
On this trip we went to new locations and visited the Asuwagawa Dam under
construction and the already completed Managawa Dam. As young researchers, we
gained the latest methods of dam construction and learned about the problems
that might be encountered during dam construction. At the same time, we have
used our imagination to come up with many interesting ideas on how to use the
dam to benefit the region, and based on these ideas, industry practitioners have
discussed. Overall very pleasant and interesting! See you on the next blog!
The dam is located in the Kuzuryu bashin of Fukui Prefecture because, in
recent years, there is often an embankment break caused by floods in Fukui City,
which has caused no small impact on the city's production and life, safety, and
other aspects. The Asuwagawa Dam is primarily designed for flood control. In
particular, the Asuwagawa Dam is a flowing concrete gravity dam, meaning that it
will completely close the gates during flood season to store the flood peak, and
open the gate outside flood season to allow the river to pass freely. It
features two gates, the primary measuring 5 m x 5 m and a smaller adjacent gate.
To release storage after flood event, they will first open the smaller gate
before the main gate to prevent a rapid rise in the downstream water level.
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