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I I ! I , I is based on the difference between the reference flood water surface elevations at the grid cell and the index location. Figure 4-4 shows a grid cell upstream of the index location with a difference in refer- ence flood elevations of 3 feet. In this caSe the elevations of the grid cell elevation-damage function (elevation-damage function in which the zero stage coincides with the first floor elevation) are reduced by 3 feet to complete the translation process. (4) The resulting grid cell aggregated elevation-damage function (Figure 4-4) is then combined with the elevation-damage functions of other grid cells having the same land use category (land use 3) and which were previously aggregated to the index location (for damage reach 32). (Combined damage functions are separated based on land use categories so that damage calculations may be subdivided according to a particular interest). Figure 4-5 shows the aggregated damage potential- of the sample grid cell being combined with the existing (aggregated) damage potential at the index location for land use 3. If, for example, there are five land use categories in a particular damage reach and the damages for each grid cell in the reach have been aggregated to the index location, then a summary of the computed aggregated damage functions for the various land uses would appear as shown in Table 4-3. The total aggregated damage function (a summation of the individual functions) is also included. The aggregation procedure described is the Same for all DAMCAL runs, whether evaluating existing or alternative future conditions. The difference in the evaluation of nonstructural measures (described in the following para- graphs) is in the modification of the composite damage function or in the modification of the elevation axis of the elevation-damage function. 4-13