She said it started rushing in at 9.30am, and continued to rise until 11.30am on Thursday.
"It just poured in for the next two hours until it was half a metre high."
Roper quickly moved stock off the ground with the help of her husband, his staff member, and a stranger who was stuck in traffic due to the flooding, but she said there was still considerable damage.
The shop is located just outside of Greymouth, and Roper said they are used to floods, but this was unlike anything they had seen.
"We've seen big floods before, and we always knew there'd be another one, but this one was really different.
"Usually they are slower, like over a few hours, but this one was just half an hour, and it was here. Quite unexpected."
Flooding, power outages and road closures all took effect across the West Coast yesterday after an orange MetService rain warning was in place overnight.
More heavy rain was expected tonight in Buller and Westland until 1am today.