The slope of the apron / parking bay is generally 1% or slightly less. The minimum we aim for is typically 0.4%. I think 2% is quite excessive; as a comparison, the runway transverse slope maximum is 1.5% for larger airplanes, and that is quite steep. To quote ICAO Annex 14:
3.13.4 Recommendation.— Slopes on an apron, including those on an aircraft stand taxilane, should be sufficient to prevent accumulation of water on the surface of the apron but should be kept as level as drainage requirements permit.
3.13.5 Recommendation.— On an aircraft stand the maximum slope should not exceed 1 per cent.
I can understand how the aircraft rolled 200 feet then stopped. That is the depth/length of a typical large aircraft parking bay. The drainage is designed for water flow down to a defined low point or line (such as a drainage channel), and it is quite likely that the parking bay sloped down at 1% and outwards from the terminal to the low end at the end of the bay (which acts as a drainage gully) and then the pavement sloped up again to the next high point such as the centreline of the taxiway. The aircraft stopped at the bottom of the slope.
To get the water away from the low point, the end of the bay is either sloped transversely so the water turns 90 degrees and flows away, or there is a slotted drainage inlet running along the width of the bay.
Cheers
Overrun