12. Post project evaluation
12.1. Post project evaluations demonstrate whether past investment has been worthwhile and has achieved its objectives. The exercise can be considerably eased if the fully documented original appraisal is readily available to evaluators. For example, it will be possible to compare actual performance against the sensitivity analysis in the benefit-cost analysis. This will enable a check on the areas of greatest uncertainty, to see whether variations in practice are within predicted limits.
12.2. In undertaking benefit-cost analysis as part of post project evaluation of flood risk management options, it can be difficult to identify realised benefits, which are based on the avoidance of losses which would have occurred had the project not been implemented. Hence, it is difficult to determine whether the actual benefits are equal to those predicted. It will usually, therefore, be necessary to judge success on the accuracy of related predictions such as the costs of construction and maintenance, rates of environmental enhancement or measures of residual damage.