A strategy to assess river restoration success

Abstract

1. Elaborate restoration attempts are underway worldwide to return human-impacted rivers to more natural conditions. Assessing the outcome of river restoration projects is vital for adaptive management, evaluating project efficiency, optimising future programmes and gaining public acceptance. An important reason why assessment is often omitted is lack of appropriate guidelines. 2. Here we present guidelines for assessing river restoration success. They are based on a total of 49 indicators and 13 specific objectives elaborated for the restoration of low-to midorder rivers in Switzerland. Most of these objectives relate to ecological attributes of rivers, but socio-economic aspects are also considered. 3. A strategy is proposed according to which a set of indicators is selected from the total of 49 indicators to ensure that indicators match restoration objectives and measures, and that the required effort for survey and analysis of indicators is appropriate to the project budget. 4. Indicator values are determined according to methods described in detailed method sheets. Restoration success is evaluated by comparing indicator values before and after restoration measures have been undertaken. To this end, values are first standardised on a dimensionless scale ranging from 0 to 1, then averaged across different indicators for a given project objective, and finally assigned to one of five overall success categories. 5. To illustrate the application of this scheme, a case study on the Thur River, Switzerland, is presented. Seven indicators were selected to meet a total of five project objectives. The project was successful in achieving 'provision of high recreational value', 'lateral connectivity' and 'vertical connectivity' but failed to meet the objectives 'morphological and hydraulic variability' and 'near natural abundance and diversity of fauna'. Results from this assessment allowed us to identify potential deficits and gaps in the restoration project. To gain information on the sensitivity of the assessment scheme would require a set of complementary indicators for each restoration objective.

Spatio-temporal heterogeneity of riparian soil morphology in a restored floodplain

“…Woolsey et al (2007) found that fish assemblage structure and composition were similar in embanked and restored reaches and concluded that the restoration of the River Thur failed to meet the objectives of near-natural abundance and diversity of fauna. Weber et al (2009) showed that hydrophysical habitat diversity had been improved by the widening but that the current geomorphological complexity was still considerably impaired at the restored reach in comparison with historical near-natural shoreline.…”

“…Assessing the outcome of these projects is essential for adaptive management, evaluation of project efficiency, optimization of future programs, and gaining public acceptance (Woolsey et al, 2007). However, restoration projects often lack post-restoration monitoring using standardized evaluation methods (with welldefined criteria and indicators), which would increase their cost-efficiency Sudduth et al, 2007;Bernhardt et al, 2005Bernhardt et al, , 2007.…”

“…This lack of monitoring is mainly due to lack of funding beyond the practical restoration project. Rapid yet informative, cost-effective monitoring tools are extremely sought-after; existing methods consider hydrology, physical and biological structures, and the landscape context Woolsey et al, 2007), but only include general elements with respect to soils.…”

Toward the use of testate amoeba functional traits as indicator of floodplain restoration success

“…The site was restored in 2002 through riverbed widening from 50 to 150 m. The major banks were stabilized by plantations of willows (Salix viminalis). Further information on this site is given in Woolsey et al [23]. We selected six habitats based on the functional process zones (FPZ) [24] proposed by Samaritani et al [25] to represent the different post-restoration successional stages present at the site.…”

Impact of flood deposits on earthworm communities in alder forests from a subalpine floodplain (Kandersteg, Switzerland)

“…To evaluate the success of floodplain restoration, a reference state to be reached by river restoration has to be determined [26] and a value assessment could be established by using reliable indicators of restoration evaluation. The most frequently used indicators to evaluate the success of river restoration aiming to increase biodiversity are based on vegetation and aquatic fauna [27]. So far, little is known about earthworms as bioindicators of restoration success.…”