Koyo New Town about 60 years ago and today

History of Koyo New Town

North of the city area of Hiroshima, around where the Ota River comes out of the mountains and runs down south, a tributary flowing from the northeast joins the main stream. The hill held between the two rivers, with its ridges and valleys finely interlocked, was for a long time a place of nothing but forest and paddies on the valley floors. Koyo New Town is what turned the top of that hill into a single housing area, and the nearest station is Kumura Station on the Geibi Line, which runs along the Ota River. Aerial photographs of five eras survive, from 1945-50 to 1987-90, and the intermediate stages in which the forest turns into surfaces of earth and fills with rows of residential buildings are held in them one photograph at a time.

The top of the hill and the valleys going down to the river differ in height at a glance. Of the five points measured in the frame, the lowest, the north, is 39.4 m, a value taken all the way down in the tributary's valley. The rest, the center at 56.6 m, the south at 61.1 m, the west at 62.6 m and the east at 68.2 m, all sit on the surface of the hill. Only the side facing the river is low, and the farther in you go from there, the higher the ground becomes. The long, narrow lowland along the river could draw water, so it was used early for paddies and settlements, and no sizable vacant land remains there. To prepare a sizable area of housing lots close to the city area, there was no place to choose other than the hilltop, where the paddies did not have to be destroyed.

Steps in each valley

The oldest photograph, 1945-50, is black and white and coarse-grained, but the skeleton of the terrain is if anything easier to read. The main stream at the left edge is not a single flow; thin streaks of water branch into many lines within a bright gravel riverbed. The tributary crosses the top of the frame and, toward the right, changes direction sharply to head for the main stream. The hill occupies about two-thirds of the frame, and the dark forest on the ridges, the valleys branching into the spaces between them and the pale steps on the valley floors can be told apart. Clusters of houses are limited to the mouths of the valleys and the sides of the road along the river, and beyond that there is only forest and steps.

The 1961-69 photograph is fine-grained, and even the inside of the hill can be read. The valleys branch into many lines toward their upper reaches, and long, narrow paddies are cut into most of their floors. The edges of the steps curve along the bends of the valleys, so the ups and downs of the hill appear directly as lines. The ridges are black, grainy forest, and along the tributary a settlement of several dozen houses strung along a road appears, with small white water surfaces that look like irrigation ponds behind it. On the hill of this era there is not a single block or wide road. When you open the location, this 1961-69 photograph is the first one lined up on the older side, and the more you switch to later eras, the more the valleys and forest decrease from the frame.

Surfaces of earth open up

Switch to 1974-78 and it is hard to believe it is the same hill. In the left half of the frame, now in color, several stepped graded surfaces have opened on top of the ridges, and bright beige ground on which only lot lines have been drawn forms steps. On one of these surfaces there is a group of small white buildings lined up regularly facing the same direction, showing that this is the section where buildings first went onto the hilltop. Another graded surface has opened toward the bottom of the frame, and here a wide road has gone through first. The surroundings are still dark green forest, and the boundary has no intermediate color. At the left edge the main stream lays a dark water surface beside bright sandbars, and on the upper part of the opposite bank, rows of houses are already densely packed. The order of climbing onto the hill after the riverside had been filled up forms a contrast within a single frame. The photograph of this era has bands where the brightness steps up or down along its seams, and they need to be read apart from differences in the color of the ground. The bright bare ground that appeared on the ridge at the upper right is also a point to watch from this era on.

Rows of residential buildings and unfilled land

In the 1979-83 photograph the hilltop is already a town. Left of the center, mid-rise residential buildings of the same shape and orientation repeat in diagonal rows, surrounded by blocks of detached houses with small roofs. In the middle there is a wide paved surface and a building with a large roof, showing that not only buildings for living but also places for people to gather were prepared at the same time. On the other hand, below the center, vacant land on which only a grid of streets has been drawn remains together. This distribution shows that the town was not built all at once, but that the graded surfaces were filled one after another. The bare ground at the upper right has spread whiter and larger than in the previous era. Yet at the top of the frame, the lowland along the tributary remains fields and paddies, and the reversed order in which the hilltop becomes a town first shows clearly in this era.

By 1987-90 that grid is also filled with houses. On the lower side of the frame, streets spreading in a fan and rows of houses following them appear, and the blocks wrap around to fit the shape of the hill. Sections with large roofs and earth sports grounds are dotted between the blocks, and the bare ground at the upper right has become a wide brown surface. Even so, the whole hill has not become a town. Several dark green bands tracing the valley floors remain between the blocks, and it can be seen clearly that the valleys left uncut turn green.

A hill where the green bands remain

In the latest aerial photograph too, this skeleton has hardly moved. The shapes of the streets and the positions of the rows of residential buildings can be overlaid on 1987-90; the change is in the replacement of buildings. Sections where the colors and directions of the roofs do not match are dotted about, and green is starting to return to the bare ground at the upper right. The main stream shows a muddy water surface and wide sandbars, and the position where the riverbed spreads is not very different from the old eras. The green bands of the valley lines also remain in the same positions. At the top of the frame a bridge spans the tributary, and a wide road extends from it toward the hill, so the use of the lowland, where only settlements and paddies were in the old eras, has also changed.

The record for a residential area in Kamezaki 1-chome on the hilltop, about 480 m from the location, begins at 133,000 yen per square meter in 1995. This first value of 133,000 yen in 1995 is also the highest in the record up to the 2026 official land prices (Chika Koji), and after that it kept falling, with 78,400 yen in 2015 and 2016 the lowest. In the 2026 official land prices it is 82,500 yen, a position that has come back only a little from there. On the hill side it is landslides and on the riverside lowland it is water: within the same frame, the hazard to prepare for differs. On the City of Hiroshima's hazard map you can check by type of disaster which assumptions are placed on which valley line.