What will happen in the future with the decline in Lake Biwa water level? The stone wall of Sakamoto Castle Kayaking class is also affected

This is a standard gag phrase that indicates that Lake Biwa is the "water of the Kansai region", but in fact, the water in Lake Biwa is decreasing.

As of the morning of the 5th, the water level was minus 69 cm. Shiga Prefecture is just a few steps away from minus 75 centimeters, which is the time to set up a "drought countermeasure headquarters".

Why is it decreasing? What will be the impact in the future?

"Lake Biwa is a little thin"

NHK filmed the area around Lake Biwa from the sky on the 4th.

Among them, Shirahige Shrine in Takashima City, Shiga Prefecture, is famous for its torii gate that floats in the lake, but as the water level drops, the lower part of the torii pillar, which is usually hidden, becomes visible.

In addition, the piers of the Lake Biwa Bridge, which connects the east and west of Lake Biwa, are also in a state where the parts that are usually hidden under the water can be seen.

"Okunosu" is connected to the land

About 200 meters off the coast of Lake Biwa in Kohoku Town, Nagahama City, there is a small island-like state called "Okunosu", but due to the decrease in water level, it is now connected to the shore of the lake.

According to the nearby Kohoku Wild Bird Center in Nagahama City, "Okunosu" is usually home to wild birds such as swans and warblers, and when the water level of Lake Biwa drops by about 50 cm, a road several meters wide appears between it and the shore of the lake.

When NHK filmed the helicopter from above, a number of people were walking along this unusual road.

So that you can walk to the site of the "Taiko Well"

In addition, on the shore of the lake near the ruins of Nagahama Castle in Nagahama City, Shiga Prefecture, you can walk to the site of a well called "Taiko Well", which is usually under the water.

The "Taiko Well", which is said to have been used in Nagahama Castle, built by Toyotomi Hideyoshi, was found when the water level of Lake Biwa dropped in Showa 14 (1939), and since it is usually submerged under the water, a stone monument about 2 meters high has been erected to show its existence.

According to Nobuo Yamaoka of the Yutaka Park Management Office in the ruins of Nagahama Castle, the base of the stone monument is usually submerged in water, but as the water level drops, it becomes possible to approach it on foot, and if you go around the back of the stone monument, you can see words such as "Showa <>".

Nobuo Yamaoka of the Yutaka Park Management Office
: "It has become a walking distance and is now a photo spot.

Damage also caused damage to the screw of a fishing boat

On November 11, Shiga Prefecture established the "Water Level Decline Liaison and Coordination Council" for the first time in two years to investigate the impact on fisheries and tourism, and Governor Mikazuki announced the results of the survey at a regular press conference on the 27th.

In some ports, the height difference between the quay and the boat has increased, affecting the boarding and disembarking of people and the loading and unloading of cargo, and the screws of fishing boats have been damaged by hitting stones and other objects on the bottom of the lake.

Governor Mikazuki of Shiga Prefecture
: "At the moment, there has been no major impact on the lives of the people of the prefecture, but we will continue to monitor the situation.

Why is the water level dropping?

After Typhoon No. 8 traversed the region in August, the water level of Lake Biwa was plus or minus 7 compared to the standard.

However, after that, there was no consistent rainfall, and the total precipitation in September and October was as follows.

▼ Hikone City 0 mm (less than half of normal) ▼ Otsu City 9 mm (about two-thirds of normal)


As a result, the water level of Lake Biwa has gradually begun to decline.

In late September, it was about minus 10 cm, but in late October it dropped to minus 139 cm, and in late November it dropped to minus 216 cm.

And as of 3 a.m. on the 2th, it is minus 9 centimeters.

For this reason, the Lake Biwa River Office of the Ministry of Land, Infrastructure, Transport and Tourism, which regulates the water flowing out of Lake Biwa at the Seta River Wash Weir on the south side of Lake Biwa, has been limiting the amount of water, which can be hundreds of tons per second at times, to 9 to 15 tons per second since September.

This is the minimum amount required to cover the water used downstream in Osaka and Kyoto.

The Lake Biwa River Office says, "We will continue to work to control the decline in the water level of Lake Biwa by controlling the discharge rate while coordinating with related organizations."

According to Shiga Prefecture, if the water level drops to minus 75 cm in the future, a "drought response headquarters" will be set up and a wide range of calls will be made to conserve water, and if the water level drops to minus 90 cm, the national government, Osaka Prefecture, Kyoto Prefecture, etc. will consider restricting water intake.

In the past, the school pool was no longer available.

In Lake Biwa, when the water level has dropped in the past, it has affected the lives of citizens.

In 1994, when there was a drought due to lack of rain, the water level reached a record high of minus 1 meter 23 centimeters.

Lake Biwa (1994)

In downstream areas, water withdrawal restrictions of 10% to 20% were imposed, which affected the lives of citizens, such as making it difficult for houses on high ground to get water out and making it impossible to use school pools.

If the water level drops to minus 75 centimeters, the prefecture will set up a "drought response headquarters" to call for further water conservation.

It is expected to remain at a two-year low since 2021, so it will be necessary to keep an eye on the situation.

What is the height of Lake Biwa's "water level of 0 meters"?

According to Shiga Prefecture, the water level shown as "Lake Biwa water level" is the average value of the values of five water level observatories in the lake, with the height of the observatory on the south side of Lake Biwa as "0 meters", and the amount of water equivalent to 5 cm of water level is about 1.68 billion liters.

The standard water level of 0 m is almost the same as the height of the castle tower of Osaka Castle.

Since Lake Biwa is located in the upper reaches of the river flowing into Osaka Bay, the height of this "water level of 0 meters" is almost the same height as the castle tower of Osaka Castle when viewed from downstream of the river.

In addition, it is said that the height of this "water level of 0 meters" is the water level that was judged to be "not to go down any further" when the observatory was set up in the Meiji era.