Two story cob foundation below river

Hello ! Sorry for the english
First time threading.
I'm in North Patagonia, Argentina. Even more precisely, I am building Here

As you might see, there is an irrigation channel just OVER the place. This means, that water (in summer, right now is summer) wants to flow up the earth. I'm about two meters lower than the channel. If I dig to about 60 cm there is humid earth even though the terrain has been filled with gravel and urbanite and "stuff". In the other hand this gives a good drain to the place.

I discarded the chance of going with concrete or concrete slab, because I almost run out of cash. That is the traditional recomendation here. I bought about 6 trucks of soil that we call "Relleno calcareo" It is limey earth with some gravel and it is used to raise a platform to build on top. Im buidling 42 m2 and that is enough to raise abot 50 to 60 cm above ground.

Long story long. Im building two stories cob house; What should I make the foundations of? considering there is little chance of rain during year in a very dry climate but lots of winds and windy and high speed wind when there is wind blowing.

I thought urbanite masonry, but I am afraid of rising damp , am I right?. There is river rounded rock avaiable almost for free but... it is rounded.
I am now heading to build a gravel bag foundation, since river gravel is cheap. But will it stand a two story cob building with load bearing walls and a wood and cheap zinc sheet roof?. Could it work?
What about combining gravel filled tires with urbanite stem wall?

PLEASE HELP!

The title makes it sound like you want to build your foundation out of cob! I'm glad to see that is not the case

Round river rock certainly is not ideal for a foundation, but if you can keep it from spreading it may work well. I want someone more experienced with various stonework to chime in here... my local stone is generally flattish and squarish, perfect for building foundations without any mortar.

Can you break the rocks in half with a sledgehammer? Or are there any rocks which have been broken and have a somewhat flat side? If practical, that could give you a firm wide base to stack your round rocks on, with a lot of taper so the upper rocks don't want to slip out of place. If you can get a solid base, the round stones will actually give you the best separation from groundwater, as there will be fewer points of contact for water to wick up.