In general, the water table in a swamp is at ground level. The ground is saturated and water is evident on the surface of the ground. That's what makes a swamp a swamp. You wouldn't have to "dig...
none, though the orbit of the moon is SLIGHTLY efected by the sea, as the sea is affected by the moon, visa versa.
(i know that that isn't about the climate, but it may help!!!)