Is Green Better Then Grey? Evaluating and Assessing Nature Based Solutions

Nature Based Solutions (NBS) are increasingly applied in river interventions for obvious reasons: in general, they provide added value to the fluvial landscape that, in many cases, has been changed from pristine conditions centuries ago to an altered, engineered state to date. To assess the added value of NBS, however, is far from obvious. Based on an extensive literature study, we propose a novel framework to compare and evaluate NBS. The ideas are based on concepts that have been developed within the Dutch Delta program. Goal is to have a systematic and objective instrument that can be used to evaluate and demonstrate added value NBS, in favor of conventional ‘grey’ solutions. In the framework, design and implementation phase are separated.

The key elements in the framework are (1) Efficiency, related to the output (does the solution satisfy the specifications and principles of the design process?) (2) Effectiveness, related to the outcome (does the solution adequately answer the social challenge at the base of this measure?) (3) Social support, related to the process of stakeholder participation (have all the right steps been taken to ensure that the solution addresses all envisaged co-benefit?) and (4) Flexibility (how easy (and at low cost) can the solution be adjusted in view of the internal and external dynamics of the social challenge?). In the evaluation framework, indicators that characterize these key elements play an essential role.

Preferably, our framework is applied from the design phase, up to and including the implementation and monitoring phase (if available) of a NBS. The framework is tested on three NBS that are considered within the North Sea Interreg Building with Nature project. These projects are located in three different countries (Netherlands, Belgium and Scotland), deal with various governance structures and vary in scale. Application of the framework shows that NBS can indeed be assessed (and compared) on a numerical score (0-100%), where 100% indicates that the measure scores optimal on all key elements. Taking along an alternative, grey solution gives the possibility to compare the added value of a NBS and it’s grey equivalent. The results can be used to make an objective, comparative assessment between both alternatives.