This mod adjusts water physics when digging sand near water in an attempt to prevent ugly appearances of flowing water. This means you can go dig up that sand you really needed without having to worry about ruining the environment.
Left: without the mod. Right: with the mod.
Note that this mod will create water for free, so it's not really suited for cases where water is meant to be limited.
How it works
It's super simple - when sand is broken next to water, instead of it becoming flowing water like it would in Vanilla, it becomes a source block even when the usual infinite water conditions aren't fulfilled. This allows you to dig up sand near water without worrying about being pushed around by water or leaving an ugly environment behind.
Additionally, it can also fill up more than one hole at once (though it does not go further than three blocks), in case you didn't start digging next to water at first.
It might be too simple and trigger in cases where it shouldn't - if you come across these, feel free to report them and I'll see if I can solidify the implementation to really only work on beaches, where it should.