OPW Guidelines & Schedules A - B Coastal Erosion Risk ...

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(ix) (x) (xi) It is important to note that existing coastal protection works, which are proposed to be replaced by new works, should not be included as a benefit although any assets being protected by existing works or scheme, e.g. a promenade, may be included as a benefit. The loss of infrastructure integral to the properties at risk from erosion e.g. power, phone, gas utilities and local access roads should not be included as an additional benefit. Where infrastructure is providing a service to an area free from erosion, but is itself threatened by erosion, then it should be included as a benefit in the form of provision of a least cost alternative. In respect of the loss of agricultural land, the current market value should be used together with a multiplier to capture the subsidy value of the land. A multiplier of 65% should thus be used. Methodology The simple methodology for calculating the economic benefits or Nett Present Value of Benefits for minor coastal erosion prevention schemes are outlined below in 3 steps. Step 1: Collect Relevant Data, Estimate <strong>Erosion</strong> Rates and Contours Identify and outline the extent of coastline affected by erosion from a site inspection and careful review of all relevant available information (historical aerial photography, beach photographic and topographic surveys, maps, charts etc). Estimate the annual average rate(s) of erosion. Prepare erosion contours at regular time intervals, typically 5 years, for a period of at least the expected design life of the scheme. Use smaller time intervals for high erosion rates (> 1.5 m/year). Step 2: Collect Valuation Data for Properties and Assets at <strong>Risk</strong> Identify and tabulate all erosion prone property, land and/or assets in the erosion prone area over the design life of the scheme. Determine or estimate the current erosion-free market value (MV) of each erosionprone property, land area and/or assets and their expected year of loss to erosion both with and without the proposed scheme. Allow a safety margin of typically 2 years to determine the time of loss (year) of the particular property, land and/or assets. In the case where a property or asset is not accessible or useable due to prior loss of access or utilities from erosion then the time of loss of this property or asset may be thus brought forward. Step 3: Calculate the Nett Present Value of Scheme Benefits The methodology involves the calculation of the discounted value of property, land and/or asset losses with erosion protection less those without a protection scheme. The result is a Nett Present Value of Benefits associated with the proposed scheme.
The calculation of such benefits may be carried out using the equations and method shown on Table 1 and as outlined below. The greater the life of the scheme, the greater the benefit, although losses further into the future are discounted more so than those in the shorter term. The properties, land and/or assets at risk from erosion identified in Step 2 are listed in column 1 of Table 1, together with their current market value (column 2) and estimated time to loss, in years, both with and without erosion protection scheme (columns 4 and 3 respectively). Once this information (shown green on Table 1) is available, the calculation of benefits is easily carried out using equations 1 to 3 shown below. Equation 1 is used to calculate the Present Value of Benefits without a scheme (PVb1) whilst equation 2 allows the Present Value of Benefits with a scheme (PVb2) to be calculated. The difference between these two benefits is the resultant Nett Present Value of Benefits (NPVb). The NPVb may be used to compare directly with the estimated scheme costs (both capital and maintenance) to derive an overall project Benefit /Cost ratio. Table 1: Sample of Benefit Assessment Tabulation & Calculation (An Excel version of this table is available to facilitate calculations) ____________________ Office of Public Works April, 2012
Page 1 and 2: OPW Guidelines for Coastal Erosion
Page 3 and 4: Schedule A : Scope & Terms of Refer
Page 5 and 6: 5. Prepare Detailed Current & Futur
Page 7: The feasibility of the preferred op

OPW Guidelines & Schedules A - B Coastal Erosion Risk ...

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