These measures pertain in areas including FEMA???s 100-year Floodzones, (areas that have a 1% chance of flooding every year, or in other terms, properties that have a 26% chance of flooding within a 30-year period), as well as smaller streams which have not been rated by FEMA. RCDs also protect or improve the water quality of streams by reserving vegetated areas to slow and infiltrate stormwater r