So I thought of this when reading the Malakim Desert Mechanics thread, and I think that spring is broken on flood plains, oases, and scrub. I think it should be changed so that if there is a flood plain or oasis, spring should convert the tile to grassland but destroy the feature. If it is cast on scrub, it should make a plains forest tile. That would create a tradeoff between leaving a moderately nice feature or gaining the ability to build improvements (or reducing unhealthy in the case of floodplains).
An oasis on plains doesn't make sense (at least as a good thing - in the real world we call that a swamp). Similarly, floodplains on plains or grassland is not reasonable - the ability to get high yields (see: Nile) is a direct result of silt deposition, which combined with the floods would kill any grass or hammerplants that tried to grow.
An oasis on plains doesn't make sense (at least as a good thing - in the real world we call that a swamp). Similarly, floodplains on plains or grassland is not reasonable - the ability to get high yields (see: Nile) is a direct result of silt deposition, which combined with the floods would kill any grass or hammerplants that tried to grow.