The Falaj is a traditional method of irrigation in Oman; some of which are quite basic as in this case, others can be complex with a very ridged control of how much water each individual gets.
Villages have a person who controls the amount of water supplied by using a form of ‘sun dial’ where the shadow cast by an upright stick times the amount each member of the community receives.
When a Falaj is required for moving water long distances, it will quite often be under ground for most of its length; getting the gradient and flow rate is a very skilled job.
See these links for a far more detailed description:
The Falajs – Written by Tor Eigeland.
The traditional Afalaj irrigation system.