Excellent news in your update.

Having water during the dry summer months in a Mediterranean climate is a very valuable resource. Does your acequia run water all year?

Modern piping materials are the easiest way to control water flows, and one big advantage we have over "ancient" engineers.

Are you allowed to set up a siphon hose over your gate to take water? (Is that legal now, and would it NOT jeopardize your water usage amounts in future years?)

With a siphon, you could take easily controlled amounts of water, and have zero erosion risks down your slope.

Your large slope is also a benefit to you. Instead of pumping water to any of your usage sites, you can "gravity feed" water to any location on your property.

I think one option would be to build a single, large retention pond at a good location near the TOP of your slope. Fill it from the gate (or siphon pipe) as needed.

You can then run a large pipe (5 cm?) down the hill from your pond and to a large number of tees with control valves. You can then open any section of your irrigation pipes to water as you desire through smaller distribution pipes. You should probably do a search on "drip irrigation" methods and equipment. That is how I water the tree plantings on my very dry farm. It is VERY efficient for water usage, and can be installed easily by non-professionals.

Piping is much easier and cheaper to install and maintain compared to the construction work of building a series of ponds down the hill. However, ponds are certainly more beautiful!

For your main retention pond at the top of the slope, I would consider using a pond liner. They are not that expensive for the pond size you are considering, and it would guarantee that your pond did not leak (if installed correctly). The liner does need to be tucked into a little trench outside of the borders of the pond. If you have nice boulders available on site, that might be an attractive way to cover the edges of the pond liner and make a beautiful, hillside pond.

Every pond will eventually start supporting multiple living organisms, including mosquitos. In the U.S., we have a minnow called gambusia that love to eat mosquito larva so much, that their common name is "mosquito fish". However, many types of minnows and smaller fish will eat up your mosquito larva. Just make sure you use an approved indigenous fish species.

Just throwing out more ideas for you to consider for your big project. As you start to consider more detailed planning of your project, you can always keep coming back for more specific answers. There is usually an expert on the forum for almost every topic.