Water quality deterioration as a driver for river restoration: a review of case studies from Asia, Europe and North America

River restoration projects are carried out actively in several countries as an alternative flood protection measure, and also to improve/restore water quality and habitat diversity. The implication of various river restoration measures on water quality is seldom studied. In this review, case studies of restoration projects that aimed at water quality improvement were selected from four industrialized countries in three continents. The water quality concerns and the systematic development of legislative policies towards better water quality management in the different countries considered were assessed. The best management practices for river restoration with respect to water quality amelioration were evaluated with the perspective of the case studies selected. In the various case studies discussed, a combination of different restoration measures were implemented in tandem. The restoration measures were adapted to suit the local conditions and problems. A pre- and post-restoration investigation of the main success indicators was found to be an important criterion for the evaluation of the outcome of restoration projects. Successful restoration projects were found to focus on reduction of pollutant/nutrient input to the rivers, in addition to the implementation of suitable restoration measures. This has been achieved by public infrastructure development (like installation of storm water controls and sewage treatment plants). This review is aimed to act as an inventory for future restoration projects with water quality amelioration as their main target.