A Methodology for the Management of Estuarine Restoration Plans at the Regional Scale based on Classification Techniques

A major challenge for environmental managers is the planning of the restoration of estuarine areas, moreover when several estuaries covering a large region are involved. These restoration plans must be designed by finding a balance between two opposing factors: a complete restoration of the area, i.e. the return to its natural conditions, and the maintenance of its current socioeconomic uses. At the regional level this balance can be obtained by choosing to recover some areas and not others. This work introduces a methodology to help decision-makers in the planning phase of restoration plans by providing an objective tool that measures the level of restoration achievable by different actions.

The new approach is based on a classification of the areas to be restored according to some characteristics that represent the possible hydrodynamic and morphodynamic effects that the restoration action may induce on the rest of the estuary. The four parameters chosen to classify the restoration actions are: (1) the change in tidal prism induced by the restoration of the zone, (2) the distance between the area to be restored and the estuary mouth, (3) the tidal wave phase lag and (4) the flood potential of the area to be restored.

The classification procedure combines self-organizing maps (SOM) and the K-means algorithm. This combination allows to easily represent multi-dimensional maps in two-dimensional plots while obtaining a concise final classification. The methodology was applied to a total of ten estuaries along the entire coast of Cantabria (Northern Spain), totaling 139 potential restoration areas, where a Spanish Ministry of the Environment Recuperation Plan is underway. The methodology classifies the 139 areas of restoration into five clusters.

Empirical relationships were used to estimate the effects the restoration of each cluster may induce on the estuary’s various morphodynamic elements (cross-sectional area of the estuary mouth, area of tidal flats, volume of tidal channels and volume of the ebb tidal delta), giving managers an overall view of the potential effects of the restoration in each zone and providing a basis on which to plan these actions.