Review on costs and benefits of river restoration. Data were collected in a database to empirically investigate the costs of river restoration measures throughout Europe. Also, a summary of restoration planning and the specific measures which can inform the future development of cost-benefit analysis and their application were introduced. A non-exhaustive review of peer-reviewed literature and technical reports was conducted to elicit the effects of individual measures, providing a basis for the analysis of restoration benefits.

The non-exhaustive review of river restoration measures showed that it is extremely difficult to predict the impacts of specific river restoration measures on a European-level. The river type, based on geomorphological and functional process units, as well as the specific anthropogenic pressures are relevant for choosing suitable restoration measures. Practical limitations such as land availability, project budget, and/or stakeholder consent limit the spatial extent to which rivers can be restored. Programmes of Measures should address the type and scale of pressures in a river basin, provide long-lasting improvements, and be robust against the impacts of climate change. Independent of the type of restoration measures, considering the hydrogeomorphological processes affecting a river restoration site and implementing this information into the project design is critical to elicit the maximum ecological benefits from measures (REFORM D5.1).

Many successful river restoration measures have been reported, which support improvements to hydrology, hydromorphology, water chemistry, biota, or ecosystem services. The findings of the non-exhaustive literature review on the ecological benefits of restoration measures to the WFD Biological Quality Elements macrophytes, macroinvertebrates, and fish are presented. Although this type of clear-cut and generalized information is useful to river managers and decision makers, it does not encompass the full spectrum of complexity and uncertainty surrounding restoration impacts. The response of biota to habitat improvements may be confounded or delayed by many factors, including: migration barriers, the lack of a colonizing source population, the isolation of restored habitat reaches, long-term recovery processes, the creation of inappropriate/unsuitable habitat conditions, or biotic interference resulting from competition, predation, or invasive species. Also, the impacts of large-scale pressures which are not addressed by reach-scale restoration can override the hydromorphological improvements made by reach-scale restoration measures (e.g., catchment land use, water quality, missing source populations, etc.). Careful treatment of the environmental framework conditions and site-specific socio-economic constraints is necessary to elicit the ecological benefits of river restoration.

The cost database created was designed to gather data on the costs of the reported measures while also collecting sufficient information to enable marginal cost-benefit and cost-effectiveness analyses by way of statistics on effectiveness and monetary benefits (REFORM D5.2, forthcoming). The cost database contained cost data for 766 restoration projects from Germany (n=454), Spain (n=228), the United Kingdom (n=54), and the Netherlands (n=30). Cost data were reported as total investment cost per unit for the implementation of individual measures. Fifty-nine percent of the data (all German data) were estimated costs (n=454), while the remaining 41% from ES, NL, and the UK were actual reported total unit costs from restoration projects (n=312). To provide a finer spatial resolution to the restoration measures in the database and to enable a scaling-up of costs, effects, or benefits (D5.2, forthcoming), project data were assigned a river typology, based on the river types developed within REFORM D2.1.

Most of the projects in the database were conducted in single thread, alluvial gravel or sand rivers. The majority of the hydromorphological measures reported in these countries concern in-channel habitats, floodplains, and longitudinal connectivity. Measures dealing with sedimentation and river planform (depth and width variation) also make up a noteworthy percentage. The four countries included in this study reported very different restoration portfolios, and the types of measures implemented in each country do not necessarily reflect the state of their river systems.

In all cited stated preference elicitation studies, the economic benefits of the hydro-morphological river restoration are proxied through the environmental benefits and services provided by restored river ecosystems and/or riparian zones. As a rule, a restoration project is considered as a bundle of use and non-use ecosystem services, which makes it very difficult to extract separate values for particular services or even their groups. The most commonly considered services (benefits) are higher wildlife and aquatic life diversity, provision of drinking water, improved water and air quality, flood protection, carbon sequestration, erosion protection, better river appearance and recreational amenities of a riparian forest, better possibilities for swimming, boating, and fishing activities, and nitrate and phosphorus cycling and retention. The majority of reviewed studies, 23 out of 30, assume that the main beneficiaries of river restoration are local households and use different forms of contingent valuation studies or discrete choice experiments to elicit their valuation of the restoration projects.