Because of climate change, seawater levels are expected to rise considerably, combining this with increased peak river discharges, results in significant strain on inhabited low lying parts of the world. The Rhine-Meuse estuary is a perfect example of this; a densely inhabited region in between the North Sea and multiple rivers.
The Dutch Delta Program researches the effects of climate change for the Netherlands and proposes multiple alternatives to reduce its effects. An alternative comprises of the implementation of large scale hydraulic interventions, in combination with keeping all dikes up to the norm.
Four alternatives are considered, being; A1: Closed seafront and keeping current water level, A2: Closed seafront, allowing an increase in water level, B1: Closable seafront and retaining river discharge distribution and finally B2: Closable seafront with an altered discharge distribution.

This research determines, and compares, the economic efficiency of the aforementioned alternatives considering different spatial planning scenarios. The economic efficiency of an alternative is calculated by summing the resulting benefits of the alternatives and dividing this by the cost of implementation.
A higher economic efficiency indicates that an alternative provides higher value compared to its cost of implementation, this is necessary to help decide if an alternative is worth considering for implementation. Estimating the impact that spatial planning strategies have on the economic efficiency of the alternatives helps in determining if such strategies need to be accounted for when performing efficiency determinations for similar large scale hydraulic measures. The benefit of implementing the alternatives consists of the resulting reduction in dike reinforcement cost and reduction in the region’s flood risk as compared to the baseline strategy. The baseline is the strategy to protect the Netherlands like it has been done i.e. reinforce dikes where the failure probability is close to becoming higher than the norm, combined with mainly utilizing closable flood barriers, also known as the open-closable strategy. All economic factors are converted to present value with a discount rate of 1.6%, alternatives are modeled to be implemented in 2100 and all the alternatives’ effects are considered up until 2200.

This study finds that, amongst the four considered alternatives, B2 appears to be the most economically efficient choice, next to that, alternative A1 has comparable economic efficiency. The efficiency is for a large part a result of the flood risk reduction for unembanked areas, which alternative A1 and B2 specifically, have as an effect. Alternatives A2 and B1 have an economic efficiency far below 1.0 for all spatial planning strategies; thus not worth exploring further based on the considered factors within this research. Spatial planning strategies have a significant influence on economic efficiency; alternative A1 and B2 become around 30% more efficient for the move to unembanked spatial strategy as compared to the densification one. And reversely, the strategy of developing rural land results in all alternatives having an economic efficiency of below 1.0; being cost ineffective.

In this research, three reference locations are used to determine the flood risk reduction of the alternative, the other economic factors are scaled (normalized) to be in proportion with the reference locations. If the flood risk reduction effects of the alternatives would be determined for the whole Rhine-Meuse Estuary the uncertainty of the applied method would be reduced. The flood risk reduction determination relies purely on water levels, their frequencies and corresponding damages, taking into account the alternatives’ effect on outside water level perseverance would lead to more precise flood damage estimations. The unembanked flood risk reduction is the governing factor for the economic efficiency of the alternatives making the (local) protection, of unembanked areas specifically, a possible highly cost effective strategy. This should be explored as a new alternative next to the four in this research, possibly made up out of components of the considered ones.