A Warning against rapid building of dams…

River water always flows downstream.
There are many things that are carried with the flow of water in rivers.
River water displaces sand and rocks in the river bed.
When the speed of the current is high, water carries a lot of sand as well as small and large rocks.
When the speed of the current is low, the sand as well as the small and large rocks settle in the river bed.

When a river becomes dammed, the bottom of the dam creates layers of large rocks, middle sized rocks, small rocks, sand, fine sand, and silt, starting from the bottom to the top in this order. This happens due to the low current speed at the entrance of the dam.

Only water that is not carrying sand, large and small rocks moves sand and rocks from the bottom of the dam.
As a result, the river bed is lowered as sand and rocks are removed from the river bed. Only large rocks stay in the river bed.

The top of the dam becomes covered with sand and rocks. The speed of the water’s current becomes low and sand and rocks pile up above the dam.

Dams continuously form piles of sand and small rocks upstream

A dam that is covered with sand and rocks only allows fine sand and silt flow through it.

Only water full of sand and small rocks flow from a dam full of sand an small rocks

The bottom of the dam has only large rocks and it could cause mud slides when these large rocks shift.

【Sakakibara’s test video on youtube】

The bed rock is visible within a year due to the loss of sand and rocks.

The amount of sand and small rocks flowing from the dam increases: Aug. 7, 2009
The bed rock appears within a year, as large rocks in the dam are swept away: Nov. 2, 2010


A large rock on top of a sand pile


Large rocks at the bottom of the dam: Nov. 15, 2003
The bed rock appears as large rocks around the dam are swept away: Nov. 2, 2010


Jun. 13, 2012

Once the river bed has become lowered around the dam, the gap between the bank of the river and the bottom of the dam becomes enlarged. The gap causes the sliding of the bank of the river and surrounding trees.

The bank of a river starts collapsing as the river bed becomes lowered

The causes the sliding of surrounding hills and trees due to the lowered river bed.

The hill begins to slide as the river bed becomes lowered


The hill slides as the river bed becomes lowered

Driftwood and muddy water can often be seen flowing in rivers after a dam has been built. Large rocks sometimes flow in the river as well.
Dams are built to prevent accidents caused by the flooding of rivers. Ironically, dams may cause larger disasters downstream.

2003-08-14・加工済2・沙流川岡春部川・道路崩壊2003-08-14~15-B 076
This river is dammed upstream. The river bed became lowered downstream. When the water level became too high, the road collapsed. A car toppled over the edge and one person died while another person had gone missing


When the river over flowed, the road collapsed and three cars fell from the edge. One person died. There are many dams upstream of this river. The river bed downstream became lowered. Professor S from Hokkaido University said, “the river bed has not been lowered.”


The river bed is lowered. The bank of the river slid and the road collapsed.

The lowered river bed causes the lack of groundwater, water in water mills as well as river water.
Dams are also built to conserving water. Ironically, dams may cause water shortages further downstream.
It’s becoming harder for fish to find places to lay their eggs. Even when fish lay eggs, the eggs die from being swept away or covered with mud. The number of fish is becoming smaller and smaller.

Fish eggs as they get covered with the sand and silt on the bottom of the river


Building dams cause unknown damage to the environment.

We should not build dams so easily.
We should become more aware of risks of building dams.