What should be the height of the plinth level in flood-prone areas?

As rightly pointed out by Amol HFL could help you decide plinth level. Follow the local guidelines. HFL determination should be based on historic records with public authority. It is not just plinth level but even the access roads to your house or finish grade levels around your house or community should be developed by site improvement works to level well above HFL.

Hope this helps.

1. Plinth levels of all buildings should be 0.6 m above the drainage/flood submersion levels under the mean annual flood.
2. All the buildings should preferably be two or more storeys.
3. In single-storey buildings, a stairway must be provided to the roofs which could be used as temporary shelter for which roof should be made of flat type.
4. The roof levels of the single-storey buildings and the first floor level in double-storey buildings should be kept above 100-year flood levels.

For more detailed guidelines, follow the Building Materials and Technology Promotion Council

The average plinth height is up to 450mm is considered.

But in floor prone areas it is increased by 150mm as per requirement. After the study of the area plinth height should be considered.

So the average hight of the plinth in flood-prone areas is considered up to 600mm above from the HFL. (high flood level).