I think that at the left is what's left of one of the water channels there, though most I saw
were higher up.  jordanjubilee.com says that these were covered by the silt and gravel washed down
from the streams over the centuries.
 Some were placed so that animals and people could both drink from them.

In fact, the level of the Siq was raised, as a result, by almost 2 meters (about 4.5 feet).
JordanJubilee.com writes:

"A few years ago the Swiss government paid for the restoration of the Siq;
the gravel and earth was dug away and the path resurfaced in concrete.  This took something
away from the romance of the passage, but it does make it possible to walk without keeping
one's eyes fixed on the ground."

On the other hand, note that the steps are uneven, so everyone was watching their step.