Whether water plant area is qualified for this credit?

Yes, I would say so.

I am working on a project with the same characteristics mentioned above.

There is a detention pond which was calculated to be flooded only in extreme situations.

Adapted vegetation will be plant in the detention pond area, which qualify the area for the credit purposes. However, as only water tolerant grass will be planted, the area might be considered as a monoculture planting.

According to the reference guide, monoculture plantings cannot contribute to the credit requirements even if they meet the definition of native or adapted vegetation.

The detention pond area represents only 4% of the total vegetated area. The remained vegetated areas do not configure monoculture planting. Considering this situation, is the detention pond area qualified for the credit purposes?

Anderson, can you provide some more details on the rest of the vegetation planned for the site? What percentage of the remaining vegetation (outside of that planted in the detention pond) will be adapted or native?

The total vegetated area is equal to 652,148 sf.

The detention pond area is equal to 26,086 sf, which represents 4% of the total vegetated area, as mentioned above.

The remaining vegetation area, outside of that planted in the detention pond, is equal to 626,062 sf. From which 385,083 sf will not be irrigated, since it is an existing reforestation area. The remained area, 240,979 sf, will be irrigated. 100% of both areas will be adapted or native plants.

Thanks for the additional info Anderson. What is your site area? To meet the credit requirements you need to have the larger of either 50% of the site area (excluding building footprint) or 20% of the site area as native or adapted. Unless there is a large portion of hardscape as part of your site, if 100% of your vegetated area outside of the detention pond is planned for adapted / native vegetation, even with the monoculture detention pond, it looks like you would be ok to meet the requirements.