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SECTlONV Further there is destruction of floodplain ecology, and a loss of recreational opportunities. A value of thirty (30%) percent of total damage was used to Quan- tifythese "intangible" damages. The dollar amounts listed in Table V-l have been plotted against the excee. dence probability (Inverse of the return period) by reach to illustrate where the bulk of flood damages occur. Where heavy flood damages result from the more fre- quent floods, inadequate channel capacity is indicated. Where flood damages rise only in the less frequent floods, good channel capacity exists. The area beneath the flood damage curves represents the average annual flood damage. This is the average yearly cost of leaving the existing conditions as they are. listed in Table Y-l are the average annual flood damages summarized by reach. These are the "baseline" conditions against which the alternat ive plans are judged. FloodOamaqe The proposed improvements for the McClellands and Mail Creek Basins haVe been evaluated by comparing amortized improvement costs with the average annual flood damage costs. The magnitude of flood damages and costs for flood control improve- ments are directly dependent upon estimates of flood flows and limits of the res- pective floodplains. Given the flood hydrographs for floodS in a range of recur- rence intervals, dollar amounts for flood damage and costs for implementing pre- ventative measures are estimated bas€d on an analysis of the existing hydraulic conditions. The annual potential flood damage to public and private property within the floodplain is a function of the development within the floodplain. Unregulated, future development could spread to the floodplain areas and increase annual flood damage. With regulation, future flood damage potential should tend to decrease because of the limitations placed on construction in the floodplain. To analyze the effectiveness of proposed improvements, a baseline condition is used based on the existing channel conditions subject to floods generated by the estimated future drainage basin conditions. This approach is conservative, but because the drainage basin is urbanizing rapidly, it is reasonable. flood damage to property is estimated by catagorizing land use activiti€s within the floodplain. Foreachdesignflood,thefloodplainwasdelineatedand damage calculated according to land use category and flow depth. Structural damage was determined by estimating replacement costs for utilities, roads, culverts, and so forth. for residential and commercial structures, flood damage was estimated using proper~ valuations Obtained from local real estate listings and from indi- vidual property owner's information and then applying a damage factor according to t~ difference in the flood depth and the first flood elevation of the structure. The damage factor, were obtained from curves published by the Federal lnsurance AdministNtion, (r'efen"nce #4). Content ddmage for residentidl structures was es- timated by applying similar depth.related damage factors to forty (40%) percent of the estimated structural value. Forty (40%) percent of structure value for contents was used based on past inflation rates and appreciation rates in the housing industry. This procedure was used because updating content cost figures from the mid-1970's County tax records divided by 0.3 proved to be unrealistic in evaluating structure costs. Because of the isolated and sporadic nature of floodplain, a content data for commercial and industrial properties was obtained by interviewing individual management personnel on a casy-by~case basis. Flood damage estimated for each category and reach are listed in Table IV-i. These figures represent direct flood damages. Other "damages" occur during a flood whiCh are not so easily quantified. Probably the most significant haz~rds asso- ciated with the occurrence of a flood are the threats to the both physIcal and emotionalhealth,andsafetyofpeople. Additionally,thereareflood"damages" which result from inconvenience: interruption of traffic flows, obstruction of emergency vehicle movement, loss of sales by businesses dependent upon flood- damaged establishments for goods and services, and interruption of domestic services. " ~ ,-, V-I