I recall studying such things at University (Engineering School) and although I do highways now and not beaches I recall the effects of breaking a coastline in the way that these 2 developments have done when there is a longitudinal current (almost always is) is that sand builds up on the upstream side, and gets eroded on the downstream side.

My prediction for the Palm (not so much for the burj) is that in time (nature left to it's own devices of course) that the Plam will become more the shape of the letter P when viewed from the land side and the beach to the east will be eroded away - eating into the original beach.