WHEN WE WERE IN the Western Cape of South Africa,  I  noticed streams running alongside roads in rural farming areas. Occasional small channels led off from them and into the fields of farms. At each junction of the main stream and a side channel, there were small plates that could be used  to temporarily dam the main stream to divert water into the channel leading to the fields.  

We are staying in Funchal, Madeira. Our guesthouse is high above the city centre and the seafront on a road that leads down an extremely steep hill.  On one side of the road there is a fast flowing stream. Every now and then, there are metal plates that can be inserted into slots on both sides of this stream to divert water into the property beside the water. This is just like what I saw in rural South Africa. Perhaps I should not be surprised by the similarity of the damming system, but I cannot recall having noticed it anywhere else I have visited.