What is the difference in the meaning between following sentences:
Riya was to pick strawberries yesterday but the downpour made the field too muddy. (source: modified from example from BBC learn English)
Riya was going to pick strawberries yesterday but the downpour made the field too muddy.
I've learned tha 'was to' is used for past plan'. But 'was going to' is also about past plan. So which form is used for past plan. So, what is the differences between the construction was/were to ... and going to ... ?
Note: I asked a similar question about the difference between “was to...” and “was to have” here, but this question is about “was to” and “was going to.”