A few unusual looking hirundines have been seen over the spray fields and percolation pond in the last week or so. They do not fit any species well and Russ Haselden on Surfbirds forum suggested they could be oiled Sand Martins which fit them very nicely. These birds superficially look like Brown-Throated (Plain) Martin (Riparia paludicola), which is a rare vagrant to the area, and could easily be misidentified as one if only poor views are obtained. Similar looking birds have also been seen in Kuwait and they may be quite a regular sight in the Middle East due to the large oil refineries etc here.
I apologise for the poor photographs, which were taken in late evening light. They do, however, show what the birds look like.