Date of interview: Monday, July 15, 2013
I stayed two nights in Tachikawa, Tokyo due to a dam mania exhibition at the Sagami Lake Exchange Center, and decided that it would be a waste to return home via the Chuo Highway, so I stopped by this Arima Dam to drive home via Chichibu. Lake Naguri is probably better known to the locals.
Aiming at the downstream face of the dike...
We went upstream along the river to look up at the embankment from below, but it was off-limits. Too bad. There is a day-trip hot spring facility called "Sawarabi-no-yu" near the dam, so it would be a good idea to soak in the hot spring while visiting the dam.
Looking upstream from the bridge near the off-limits chain
I had no choice but to photograph the situation downstream. This is the Arima River, a tributary of the Iruma River. The "Sawarabi no Yu" is glimpsed at the upper right.
Looking downstream from the bridge near the off-limits chain
Looking downstream on the other side. The river joins the Iruma River just there. Further downstream, families can be seen enjoying themselves on the riverbank. It seems to be a place of relaxation for the citizens of Hanno.
Arima Dam monument on the left bank
We came to the top level. It was crowded with visitors, probably because it was a holiday. The plantings seem to have been carefully managed.
View of the top edge from the left bank
The top end of the dam is also open to vehicles, except large vehicles. (Incidentally, the roads around the dam lake are closed to traffic from 9:00 p.m. to 6:00 a.m. the following day.)
Downstream view of the levee from the left bank
The Arima Dam is managed by Saitama Prefecture and was the first prefectural dam built. It is the only rockfill dam in Saitama Prefecture. The dam site was clean, but the embankment was a bit grassy.
View of the upstream face of the embankment from the left bank
The Arima Dam serves the purposes of flood control, maintaining the normal function of running water, and supplying water to the Hanno City Waterworks and the Prefectural Wide-area No. 1 Waterworks. The blue structure on the right bank is a selective intake facility consisting of seven high-pressure slide gates.
Water taken from the selective intake system is discharged from the water diversion system or the emergency discharge system, and there is a free overflow flood discharge over the selective intake system.
The flood discharge was not a chute type, but a tunnel type, and the NATM method was adopted for the tunnel construction. The tunnel was constructed using the NATM method for safety reasons due to the poor characteristics of the ground. Incidentally, this is the first tunnel-type flood discharge constructed by the NATM method in Japan.
There is no photo of the flood discharge...I visited the site that day without doing any preliminary research, so I did not know that there was a flood discharge and did not go through it. I would like to see it with my own eyes when I visit again someday.
View of the dam lake from the top
The water level is low on this day, but we assume this is because the water level has been lowered to the flood stage limit. The white building on the right is the administration office.
View downstream from the top
From the top end, the riprap grass looks more and more overgrown. Still, what does it look like from downstream?
View of the upstream face of the embankment from the right bank
Both upstream and downstream surfaces are neatly laid out with riprap by tension stone work, but it seems a shame that the grass has grown over it.
View of the top edge from the right bank
I was so sorry to have come all the way to the right bank and not seen the selective intake system and the flood discharge, as I write this article.
Downstream view of the levee from the right bank
The most distinctive feature is that it is a tunnel-type flood discharge dug by the NATM method, but apart from this, the embankment is a perfectly ordinary rockfill dam.
Arima Dam Management Station
Lastly, the Arima Dam control center, where I regret that I failed to photograph its greatest feature, the tunnel-type flood discharge dug by the NATM method, but I will close by saying that I now have a good reason to visit again.
Arima Dam Specifications
Location | Aza-Nukusa, Oaza-Shimonaguri, Hanno City, Saitama Prefecture |
River Name | Arakawa River System Arima River |
Objective | F (flood control, agricultural disaster prevention) N (unspecified water, water for river maintenance) W(Water for water supply) |
Model | R (Rock-fill dam) |
Bank height | 83.5m |
Bank length | 260m |
Dam volume | 1,690,000 m3 |
Watershed Area | 16.9 km2 |
Reservoir area | 34 ha |
Total storage capacity | 7,600,000 m3 |
Effective water storage capacity | 7,250,000 m3 |
Dam operator | Saitama prefecture (Kantou area) |
Main body constructor | Tobishima Corporation, Fujita Corporation |
Year of launch | 1969. |
Year Completed | 1985 |
Name of Dam Lake | Lake Naguri |
Other facilities/observations
Parking lot | ○ |
Toilet | ○ |
Park | × |
PR Exhibition Hall | × |
Fishing | ○○ (excluding no-take zones) |
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