engleski

An index to assess the success of river and floodplain restoration

How should the success of river and floodplain restoration be assessed? We contend that the benchmark for restoration should be the river in its natural condition prior to modification. The pre-modification condition of the river represents the natural pseudo-equilibrium state in which the river accommodates and adjusts to catchment water and sediment fluxes. The resulting assemblage of river landforms (e.g. bars, channels, cut-banks, backwaters, floodplains) is in balance with the prevailing flood regime and sediment supply. Furthermore, these equilibrium forms are able to adjust to changes in e.g. flood magnitude and frequency via e.g. channel expansion and / or contraction. A restored river is one that has the capacity to adjust its form. It behoves river restoration to understand the history and trajectory of pre-modification channels, so that the 'right' river type can be restored. To assess the success of restoration, we propose the use of a natural character index (NCI). The NCI is simply the ratio between a parameter which describes the form and function of a river now and the same parameter measured at a point or points in time past. Example parameters include sinuosity, floodplain width, active channel width, bar area (at a given flow), riparian vegetation. Measurement of these parameters utilises a combination of aerial photos, archive maps and LiDAR-derived terrain models, the availability of which necessarily limits and determines what parameters can be used in assessment of a site NCI. LiDAR in particular provides an opportunity to comprehend pre-modification river and floodplain character. We illustrate the NCI concept and its potential for use in assessing restoration using examples from New Zealand, Spain and Croatia.

River ; Floodplains ; Equilibrium ; Natural Character Index (NCI) ; LiDAR ; New Zealand ; Spain ; Croatia

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