Dam of Marib (unique national wonder) - what traits should I give it?

For my Sabaean Kingdom civ I've decided to go with the Dam of Marib as a unique national wonder (for lack of any historical records of their military!).

I'm not sure what bonuses to give it so I'm opening this topic for suggestions. I plan to make it require an Aqueduct in all cities and for its bonuses to be based around population growth. At the moment I'm thinking of giving it a free source of fresh water, an increase to food yields for farms in the city radius on desert and plains tiles and a build only in cities on deserts/plains clause. Naturally the civ will have a desert start bias.

Comments and suggestions?

How about this - "+1 Food on desert tiles near this city. Acts as a source of fresh water". Essentially what you're got, and that would be my initial thought anyway. Slightly boring, but still fairly powerful.

The fresh water bonus seems like a no-brainer, as far as other bonuses are concerned how about +? Growth for every river tile?