What river morphology after restoration? The methodology VALURI

Abstract

This paper proposes a tool which river managers may need to ascertain whether the key idea of River Restoration is valid, i.e. that rivers in more natural status are desirable not only for pure environmental reasons, but also to combat flood and geomorphic risk. The point addressed is how to predict the morphology and geometry that a river will assume after the application of a River Restoration project which foresees significant changes in the system of defence and exploitation works as well as morphological adjustments (e.g. reconnection of an incised main channel with the surrounding ex-floodplain). To this aim we developed a semi-quantitative methodology that integrates several differing criteria: from historical analysis of geomorphic evolution, expert-based mechanistic reasoning, checking with empirical qualitative formulas and analytical support from fluvial geomorphology and classic hydraulics. The development of the methodology has taken place on a case study along the 80 km of Chiese River, downstream of Idro lake, in northern Italy. Although the product to be considered is just a pilot one, we see it as a promising tool, which also opens several challenging questions suited for further fascinating research work.

Keywords:

• River management
• river restoration
• hydro-morphological risk assessment
• environmental cost–benefit analysis
• integrated evaluation
• Po-River basin (Italy)

Acknowledgements

We thank the State Archives of Milano, Brescia and Mantova, as well as Autorità di bacino del Po and AIPO for their invaluable collaboration.

This research would have not been possible without the support of Fondazione Cariplo ‘bando Qualità dell'acqua 2009’ to which we are very grateful. Support, data and suggestions provided by Autorità di bacino del Po have been a fundamental asset to conduct the whole study.

A special thank goes to the whole team and particularly to Lislie Zuñiga who carried out all the tedious and lengthy, but fundamental, GIS work required; another to Andrea Goltara who spent days delving at depth in the public offices’ archives with professional toughness, and one to Alessandro Frascati for his very interesting and supportive comments and the information supplied. We warmly thank, of course, the whole research team who has been invaluable to drive to real research results the original idea.

Notes

Another difference is that FISRWG (1998) assumes the existence of a unique relationship between river bed slope S, valley slope S _V and river sinuosity p (S = S _V/p), while the presence of artificial jumps, very frequent in anthropogenically impacted rivers – for instance, because of weirs for irrigation withdrawal – significantly modifies this relationship. Moreover, it does not utilize the analytical support from fluvial hydraulics described later on in this paper.