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The activities in the 400 series provide credit for programs that improve regulatory maps or regulate areas to higher standards than the minimum NFIP program requirements. The effectiveness, or impact, of a mapping or regulatory program depends upon the area affected by that program.

In many cases, some elements of a community's program will not cover all of its floodplain or all of its watersheds. In these cases, an impact adjustment ratio must be determined based upon the ratio of the affected area to the total area.

In order to measure the impact of Activities 410, 420, 430, and 440, the community must determine how much of its floodplain area is affected by each element of its mapping or regulatory program. In order to measure the impact of Activity 450, the community must determine how much of its watershed area is affected by each element of its stormwater management program.

A few elements do not have impact adjustment ratios. If these elements are not effective throughout the community, no credit is provided. For example, in Activity 450, there is no credit for Erosion and Sediment Control Regulations unless they are enforced throughout the community.

A community has three options for determining the values of most of the impact adjustment ratios that are based on area.

Click on a link below to learn more about Impact Adjustments for Areas.

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