Rishir Water Works ... ?

Anybody know what these structures on what appears to be dry creek beds coming off of Rishiri?  There are similar structures on other dry creek beds to the north and south as well.

Attachments:

Dammed Dry Wash.kmz (831 B)

Hi, Scraps,

The usual reasons for these sorts of structure are to either prevent water runoff after rain in arid areas to conserve the water; or, as I suspect in this case, to mitigate the effects of flash floods.  It's a relatively large catchment and pretty steep-sided and you can see how water run-off has carved deep valleys down the sides of the mountain, channeling and confining any water that does run down them.  I imagine that these streams are usually dry, as you point out; but under heavy rainfall, they'll become raging torrents.  All of these valleys have to cross the road that runs right round the perimeter of the island and I think the main purpose of the dams is to slow down and contain somewhat these torrents that would otherwise damage the roads and bridges.

There also looks to be considerable amounts of rock debris coming down as well, so by slowing down the water, perhaps the dams also help to cut down erosion and contain the debris.

Cheers,

Frank