The Costs of SLR and Rainfall

The reliability of the assets within the area of interest starts with the design process in the asset management plan. Decision-making dictates how the assets will be maintained and effective means to assure the maximum return on investments. Through condition assessment, the probability of failure can be estimated. Assets can also fail due to a growing area that may contribute to exceeding its maximum capacity. Operation and maintenance of the assets are important in reassuring a longer life span as well as getting the most out of the money to be spent. Prioritizing the assets by a defined system will allow for the community to see what areas are most susceptible to vulnerability/failure, which assets need the most attention due to their condition, and where the critical assets are located in relation to major public areas (hospitals, schools, etc.) with a high population.

So what happens when conditions change?  Let’s say sea levels are rising and your land is low.  What would the potential costs be to address this?  Better yet, what happens if it rains? We looked at one south Florida community and the flood stage for each based on 3 storm events: the 1:10 used by FDOT (Assumes 2.75 inches in 24 hours), the Florida Building Code event that includes a 5 in in one hour event (7 in in 24 hrs), and the 3 day 25 year event (9.5-11 inches).

Of no surprise is that the flooding increases as rainfall increases.  Subsequent runs assumed revisions based on sea level rise. The current condition, 1, 2 and 3 ft sea level rise scenarios were run at the 99 percentile groundwater and tidal dates and levels.  Tables 2-5 depict the flood stage results for each scenarios.  The final task was designed to involve the development of scenarios whereby a toolbox options are utilized to address flooding in the community.  Scenarios were to be developed to identify vulnerabilities and cost effectiveness as discussed previously.

The modeling results were then evaluated based of the accompanying infrastructure that is typically associated with same.  A summary of the timelines and expected risk reductions were noted in the tables associated with storm and SLR scenarios.  This task was to create the costs for the recommended improvements and a schedule for upgrading infrastructure will be developed in conjunction with staff.  Two issues arise.  First, the community needs to define which event they are planning to address and the timelines as the costs vary form an initial need of $30 million to over $300 million long-term.  Figure 1 shows how these costs rise with respect to time.  The long-term needs of $5 million per 100 acres matches with a prior effort in Palm Beach County.

SLR costs

Figure 1  Summary of Costs over the 3 ft of potential sea level Rise by 2011, under the 3 storm planning concepts.


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