Floodplains are areas of land near natural drainage areas that are subject to periodic flooding from heavy rains or rapidly melting snow. A 100-year floodplain means that the odds of a flood occurring in that area are one every 100 years, or one in 100. The flood-way portion of a floodplain is the area that a river or stream moves across to take away water. You can get a special permit to build in a floodplain as long as the floor of your building is sufficiently above the floodplain level. But generally you cannot build in the flood way, since that would obstruct the flow of water.
Wetlands are marshy areas or other permanently wet areas.
The type of vegetation, such as marsh grass and cattails, that grows in the area as well as wildlife help identify such areas. Wetlands are protected by law to preserve natural resources for future generations. Your local building inspector has maps that show floodplains and wetlands. Churches can be built in just about all zoning districts, although churches generally prefer building in residential areas. However, there can be special restrictions for churches beyond the normal restrictions of a zoning district.