n terms of impact evaluation, studies often juxtapose two scenarios: “a comparison between what happened and what would have happened in the absence of an intervention.”11 However, due to constraints in availability of data and limited time, a longitudinal comparison was used to assess impact for this study. In analysing what happened, the evaluation first looked at the intended objectives of the project and the expected linkages between outputs and inputs within the economic, social and environmental contexts in which the project was being implemented. This understanding enabled the evaluators to assess the different levels and forms of actual impact of the project. Finally, to the extent possible, and given limited time and data availability, before and after comparisons of changes attributable to project intervention were conducted. This includes a comparative analysis on the protective impact of the mangrove forests in the Dai Hop commune. A longitudinal analysis was conducted of two level 9 typhoons which hit Dai Hop before and after 835 hectares (ha) of mangroves were planted. In 1987, the storm caused serious damage to a three km-stretch of the sea-dyke that needed to be repaired at a cost of 270,000 Swiss francs (CHF) (300,000 US dollars (USD)/218,000 euro (EUR)). Conversely, during the 2005 storm, the same dyke did not sustain any damage due to protective capacity of the mangrove forests.