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I I I I I I I I I I I I I I I I I I I AYRES fil.SSOCGt1;,UIi='s Presenting Hydraulic Analyses Ayres Associates has extensive experience in making effective presentations of complex hydrologic and hydraulic issues. We teach numerous courses on these subjects for the Federal Highway Administration's National Highway Institute, including a HEC-RAS modeling course. We have also taught week long, 2-dimensional modeling workshops for New York and Florida State Departments of Transportation. Although not included as a cost in this task, this opportunity would be available for the study sponsors of this project. Ayres also has used 2-dimensional modeling for litigation support. This is because the flow visualization that can be produced using 2- dimensional modeling is much more meaningful and compelling to people who do not have technical backgrounds. In short, Ayres Associates has the technical expertise and resources to accomplish the 2-dimensional modeling and the experience in making this information meaningful to the general public. TASK 5: RISK ASSESSMENT The Risk Assessment Task will define the flood hazard (including GIS-based delineation mapping) for multiple and increasing flood levels to citizens, property owners, land speculators, government officials, and risk professionals (such as the insurance and lending industries). The elements of this task that follow will be used to define the flood hazard to the structures in the floodplain downstream of the canyon mouth. These efforts use the hydrologic and hydraulic models developed in previous tasks for the analysis. The flood hazard is defined based upon both economic and flood warning time indices. The methods and results for assessing the flood risk as well as a GIS coverage that includes the various risk indices will be described. A detailed risk assessment will be used to identify structures and locations subject to the greatest hazards and risks. This risk analysis will determine the frequency of flooding, the level of damage, and the overall risk for property damage and threats to life safety given flood flow conditions and emergency access. We will conduct a structure-by-structure risk assessment. This risk assessment will be for the existing, without-project, condition. The assessment will be formulated such that the data collected and the computer model configured can be used for future flood-reduction alternative evaluation. To do so, we will complete the following: 1. Identify at-risk structures in the floodplain and develop a database of the structure inventory. This database will include all structures within the 500-year floodplain as defined in Task 4. This floodplain is expected to include approximately 1,300 structures. Aerial photographs and County assessor tax records will be used to identify the structures. 2. Identify the occupancy type of each structure in the inventory based on County assessor tax records. 3. Estimate a first-floor elevation for each structure. If surveyed elevations are available, they will be used. If not, ground elevations for remaining structures will be estimated from the best-available topographic data. We will add an estimate of first- floor distance above grade to estimate first-floor elevations. 24