Iinuma Reclamation Lesson 1: Let's grasp the overview of Iinuma Reclamation and the appeal of what we will learn!

Iinuma Reclamation
This is a unit that almost all fourth-grade elementary school students in Ibaraki Prefecture study.

It's an example of reclaiming a large swamp, right?
It took 18 years before construction even started, didn't it?
They say the farmers signed a blood oath to commit to it.
It was Tame-naga Izawa's plan.
It's a story about successfully completing it by hand during the Edo period.

Teachers who know this much are truly impressive!

I understand the content, but the students don't seem to take much interest in it.
Even when I try to make it a research project, there aren't many good materials available.
I want to make it a lesson where everyone thinks together, but what should I have them think about?
Is there anything interesting about this unit?
It's difficult to teach...

I think such voices are heard quite often.

However, please rest assured.

Iinuma Reclamation is a unit that contains wonderful content for social studies.

When you study Iinuma Reclamation...

You will be amazed by the efforts of the people of the past.
You will also be amazed by the wisdom of the people of the past.
You will be amazed by the strength of the convictions of the people of the past.
There is content that will make students think desperately.
If you imagine the state of the reclamation, you can experience a sense of wonder.

And it is also a perfect subject for studying bottom-up democracy.

Let's think about the Iinuma Reclamation lesson together!

First, let's confirm the overview of Iinuma Reclamation.

Iinuma Reclamation is a highly successful example of reclamation work representing the Edo period, where water was drained from a swamp called Iinuma in the southwestern part of Ibaraki Prefecture to create vast rice fields.

Iinuma was a swamp with a topography surrounded by plateaus to the west, north, and east, with water flowing out into the Kinu River flowing to the south.

The reason Iinuma was a vast swamp lies in the fact that the riverbed of the Kinu River, where the water flowed out, was relatively high.
The elevation of the lowest part of the current Iinuma reclaimed land is approximately 7.4 meters.
The elevation of the Kinu River flowing to the south is approximately 11.6 meters.
It is thought that this difference in elevation was the depth of the swamp.

To drain the water of Iinuma...

To reclaim the swamp, the water stagnant in Iinuma had to be drained to a lower place.

Even if they tried to flow it toward the Kinu River, it could not be drained because the elevation was high.

The people of the Edo period must have known this from experience.
They thought of draining it into 'Sugo-numa' located at the tip of the plateau on the west side of Iinuma.

The current elevation of Sugo-numa is approximately 6.7 meters.
This is lower than the deepest part of Iinuma.
It is possible to drain it.

Therefore, they thought of digging a waterway to flow from 'Iinuma' to 'Sugo-numa'.

When considering the overview of the drainage channel in a cross-sectional view...

Looking at the cross-section of the area near Iinuma (near the blue line on the elevation map by color), we can see that to drain the water from Iinuma into Sugao-numa, it is necessary to dig a waterway about 10 meters deep for a distance of just under 3 km (about 2.7 km).

If we convert this depth into height, since one floor of an apartment building is about 3 meters, it would be equivalent to the height of a 3- to 4-story building.
They thought to dig this height (depth) over a length of just under 3 km.
Of course, it was done by hand.

Please think about it in terms of the area around your school.
If it were a distance of just under 3 km from your school, where would that be?
The depth is 10 meters.

It is a waterway 10 meters deep and just under 3 km long.
Try to imagine it all together.
The amount of soil to be excavated is an astronomical amount.
This was in an era without machinery.
How much labor would be required?

A picture imagining the state of this work is published in "Our Ibaraki Prefecture."
(Please look at the "imaginary illustration" in the supplementary reader.)
They are digging with tools by hand and carrying the soil out.
The names of the tools are also listed.
You can read what kind of tools they used and what kind of work they did.
It looks very difficult.

In this way, when you apply the scale of the construction to familiar concrete examples and then imagine the state of the work, the "greatness" of the reclamation project emerges clearly.
The children will surely be overwhelmed by the efforts of the people of the past.

The first stage of the construction is completed with the completion of this waterway and the drainage of the swamp water.

Try to imagine it.
I think it took several years, but the local people all worked together to dig the waterway, and by doing so, they drained a vast amount of Iinuma's water.

How must the people have felt when they saw the water flowing through the waterway?
The people around the swamp must have seen the water level of the swamp dropping day by day.
How moved they must have been.
And after the water receded, a vast expanse of land appeared.
How much hope must have been visible, and how much courage must have been stirred up?
Perhaps tears of joy kept flowing?

To protect the Iinuma reclaimed land...

Although the reclaimed land was created in this way, just building a drainage channel is not enough to protect it.

The Iinuma reclaimed land is a terrain surrounded by plateaus.
There are always days when it rains.
Rainwater flows into the reclaimed land all at once.
Water also flows from upstream.
If it rains even a little heavily, water will accumulate on the reclaimed land.

If this happens, the rice fields will be submerged, and rice cannot be harvested.

It is necessary to prevent water from upstream from flowing into the reclaimed land.
It is also necessary to prevent water from flowing in from the surrounding plateaus.
And it is also necessary to quickly drain the water that has accumulated in the lowest part of the reclaimed land.

Therefore, the people of the past thought of countermeasures.

First, a drainage channel is dug in the lowest part of the center of the reclaimed land.
This is the Iinuma River.
This drainage channel connects to the waterway dug into the ground and has the role of quickly draining the water from the reclaimed land to Sugao-numa.

Next, a waterway and a sturdy embankment are built on the outer edge of the reclaimed land.
These are the Nishinire River and the Higashinire River.
These two waterways and embankments prevent the inflow of water from the plateaus around the reclaimed land.

What about the water flowing from upstream?
If it is allowed to flow into the Iinuma River, the water in Iinuma will easily overflow during heavy rain.
We do not want water from upstream to enter the reclaimed land.
Therefore, the water from upstream is divided into east and west upstream of the reclaimed land, and split into the Nishinire River and the Higashinire River.
By dividing it, the water volume decreases, making it easier to control the water.

Through these measures, the rice fields of the reclaimed land can be protected.

※ As for the order of construction, it is thought that the Higashinire and Nishinire Rivers were built first to reduce the water in the reclaimed land, followed by the excavation of the Iinuma River in the center.

The scale of the three waterways is...

In that case, the second phase of construction would involve excavating the Nishinire River and its sturdy embankment, the Higashinire River and its sturdy embankment, and a drainage channel in the center.

So, how long do the three waterways and embankments need to be?
This can be roughly measured from a current map.
Measure the straight-line distance from the junction of the Nishinire and Higashinire Rivers to the entrance of the drainage channel to Lake Sugao.
It would be good to have students prepare a map and measure it.
It is about 21 km.

The Iinuma reclaimed land is curved, and the outer edges have complex terrain, including valley rice fields. There are also sections where embankments were built to allow for grade-separated crossings of waterways.
Each of the three rivers must be longer than 21 km.
And three of them are needed.

21 km x 3 = 63 km.
In reality, they are even longer than that.
Try to imagine it.
How far is 63 km from the school where you work?
In reality, an even longer distance is required.
It would be good to have students measure this using a map as well.

How much effort would be required?
Since the waterways must be sloped, precise surveying is also necessary.
How did they do it?
It is an immense amount of labor. It is meticulous work.
And they did it by hand.

When students learn about things like this, they are moved from the bottom of their hearts by the efforts of people in the past.
Considering the labor involved, they can understand why people gathered at shrines and even created blood-sealed pledges.

The Iinuma reclamation was not something ordered by the shogunate; the people themselves requested to be allowed to build it, and it took 18 years to obtain permission.
And it was a great success.
They might also be moved by the greatness of people uniting and taking action, and by the wonder of humanity.
The episode of Tamenaga Izawa is also wonderful.
They will surely want to know the reason why they wanted to create rice fields so badly.

Iinuma reclamation contains many elements that are deeply moving.

The three waterways have even more advantages!

The three waterways dug on the left bank, right bank, and center of Iinuma hide further advantages for rice cultivation.

In reclaimed land, it is absolutely essential to prevent flooding and waterlogging.
Flood control and water damage prevention.
These are the great enemies of rice cultivation.
For that reason, they installed waterways (Nishinire River and Higashinire River) to prevent water from flowing into the outer edges, and created a drainage channel (Iinuma River) in the center.

There is another great enemy of rice cultivation.
Drought damage.
Water shortages.
However, in the Iinuma reclaimed land, there is no need to worry about drought damage.
The Nishinire and Higashinire Rivers flow right next to the reclaimed land.
Moreover, they flow at a higher elevation than the rice fields of the reclaimed land.
Water can be drawn in at any time.
There is no need to worry about water.
There is no need for labor such as pumping up water.

The Nishinire and Higashinire Rivers also serve as irrigation canals.
This is still utilized today.

What would happen if the Higashinire and Nishinire Rivers had not been built?

In that case, the only place with constant water in the reclaimed land would be the Iinuma River.
Then, the edges of the reclaimed land (near the Higashinire and Nishinire Rivers) would be several meters higher than the Iinuma River, making it difficult to draw water from the Iinuma River, and it would be impossible to turn them into rice fields.
They would end up as fields for other crops.

Furthermore, building the three rivers has another positive aspect for rice cultivation.

In rice cultivation, "mid-season drainage" is also effective for growth.
Mid-season drainage is the work of temporarily draining water from the rice fields and drying the soil at the end of the period when the rice plants are increasing their stalks.
Mid-season drainage has the effects of promoting root growth, suppressing excessive tillering (an increase in the number of stalks), and improving the soil.
By performing mid-season drainage, the rice grows healthily and the harvest yield can be increased.

If there are three rivers, mid-season drainage also becomes easier.
This is because there is the Iinuma River below to drain the water from the rice fields.

In reality, it is difficult to think about "mid-season drainage" in class, but children understand that "water" is necessary for rice cultivation.
In other words, they understand the advantage of having an "irrigation water supply."

In the Iinuma reclaimed land, it has been possible to create an environment optimal for rice cultivation.

This water management system is exactly the same as the modern 'dry field' method of rice cultivation.
The wisdom of people in the past is truly astonishing.
There is an impressive point here as well.

Management of the reclaimed land that continues to the present day

Although the Iinuma reclamation was a great success in this way, due to the massive amount of ash fall from the eruption of Mount Asama during the Edo period, the central part of the reclaimed land remained a wasteland until the early Showa period.

Currently, as a flood control measure, a water pumping station has been established near the deepest part of Iinuma to manage flooding.
This is the Iinuma River Koda New Drainage Pumping Station.
Powerful pumps drain the water from the reclaimed land.
There are also floodgates.

Furthermore, another waterway has been developed from the Iinuma reclaimed land to Suganuma Marsh.
The waterway passes to the west of the Mitsukaido Golf Course.
This waterway flows along a winding path that takes advantage of the terrain.

A floodgate has also been built to prevent backflow from the Tone River.
This is the Hoshido Floodgate.
Just by looking at it, you can tell it is sturdily built.
When the water level of the Tone River is high, the floodgate is closed.

Thanks to these efforts, the Iinuma reclaimed land is maintained.

Such content is also important in social studies.

What do you think?
Have you understood that there is an appeal to learning about Iinuma reclamation?

☆ If this article was helpful, please give it a like (red ♡).

Please note that you are welcome to use the maps (created using the Geospatial Information Authority of Japan map) and cross-sectional diagrams published in this article in your classes.
Please contact me if you intend to use them for publication or as public materials.

☆ Following this article, 'Iinuma Reclamation' Lesson 2 introduces how to create a unit plan.

☆ I am sharing know-how for various subjects.

☆ I am introducing a new type of moral education lesson.