Medium

What this scale means

Medium scale covers a catchment, a municipality or a city district: an area large enough that the interventions interact with one another and small enough that the institutions responsible for it can be identified individually. The decision is about a portfolio of measures rather than a single one, and the question is which combination, at which locations, delivers the objective at acceptable cost.

At this scale the assessment has to represent the connections between measures. Two retention areas in the same sub-catchment do not deliver twice the benefit of one, and a measure upstream can reduce the value of a measure downstream. It also has to represent the distribution of effects, because a change in flood depth across a city affects different neighbourhoods and different groups differently, and that distribution is usually what determines whether the proposal is accepted.

What to use

The integrative modelling framework is the instrument for this scale. It connects the hydrological response, the ecosystem services delivered, the damage avoided and the economic value in one structure, so that a portfolio can be tested as a whole and the interaction between measures is represented rather than assumed away.

The economic assessment framework provides the comparison: costs over the life of the intervention on one side, damage avoided and co-benefits on the other, with the counterfactual stated. The co-benefits valuation matters more at this scale than at any other, because it is usually the additional services — amenity, water quality, habitat, temperature — that make a portfolio acceptable to the municipality that has to approve it.

Adaptive planning is appropriate where the portfolio will be built in stages, which is the normal case. Measures that can wait are separated from those that cannot, and the triggers that would cause the plan to change are identified in advance along with the monitoring that will detect them.

Where it is used at NAIAD

Medium-scale assessment was carried out in most of the demonstration areas, and the city cases — Łódź, Copenhagen and Rotterdam — show the approach applied where the responsible authority is a municipality and the benefits are distributed across a resident population. The Glinščica catchment shows it applied where the unit is a catchment and the responsible bodies are several.