Status of and Perspectives on River Restoration in Europe: 310 000 EUR per Hectare of Restored River

The purpose of the present research was to analyze the available data on river restoration 14 projects. As the framework of our study, we conducted a structured international survey. We asked 15 selected entities and experts from among those responsible for river restoration in European 16 countries about the details and costs of European Union river restoration projects. We examined 119 17 river restoration projects that were implemented in Europe between 1989 and 2016; some of the 18 projects were still ongoing. We observed that the number of river restoration projects has been 19 increasing since 1989, which expresses society’s growing interest in improving the quality of aquatic 20 environments. We revealed that 56% of these European river restoration projects have been 21 implemented by dedicated entities and stakeholders, not as part of any structured, larger-scale river 22 restoration policy; this indicates that most European countries do not have integrated plans for river 23 restoration. Our analysis showed that 52% of the projects analyzed have been designed and 24 implemented without the participation of local stakeholders. It also showed that the budgets for 25 river restoration projects did not differ significantly across various time horizons from 1981 to 2016. 26 In our study, the average cost of restoring 1 ha of an average European river was 310 000 EUR (or 27 195 000 EUR if 4 outlying values are excluded). Considering these projects’ permanent assets and 28 including their amortization, for European river systems, we calculated the average unit price of a 29 river restoration’s value in terms of ecosystem meta-service to be 7 757 EUR · ha-1 · year-1 (4 875 EUR 30 · ha-1 · year-1 if 4 outlying values were excluded). 31

3 of 14 possible, we carried out a structured review of river restoration databases such as River Wiki [26] 98 and Onema [27]. The River Wiki database is funded by the Environmental Agency (England) and 99 administered by the River Restoration Centre (UK).

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The general analysis of the questionnaire consisted of summing up the answers for each query 103 and conducting standard statistical analyses. The collected structured data allowed for rough 104 calculations of the unit cost for river restoration in Europe, expressed in kEUR/ha. Although this 105 information provides only a very general approximation, we found it critical, as it is the most accurate 106 economic measure of a river's aggregated ecosystem services. This cost refers to the amount of funds 107 that stakeholders will pay to bring back a functioning riverine ecosystem that provides aesthetic 108 value as well as services such as biodiversity, self-purification, and sustainable flood/drought 109 mitigation.

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We obtained 105 questionnaire responses from 19 countries, of which 102 were reliable sources 112 of data for the analysis. This is response rate of 36%, which we considered sufficient for purposes of 113 our study. Altogether, we analyzed 119 river restoration projects in detail (Fig. 1) information about these projects is provided in the Supplementary Material. We are aware that other 115 countries have implemented river restoration projects, but to ensure that the results correspond to 116 the methodology, we did not count these countries' projects in our analysis.  We collated projects by the year when they were finished. The earliest project for which we have 123 data is from 1989. The most recent year we considered was 2016, but some of the projects were still 124 running and the end of that year. However, to keep the analysis clear, we assumed that, in such cases,

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2016 was the terminal year for these restoration projects. Either way, the number of European river 126 restoration projects in the countries for which we have data has clearly increased since the last two 127 decades of the 20 th century (Fig. 2).

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In the next step, we analyzed the setup of the river restoration projects. We attempted to 129 determine whether these projects analyzed were planned and implemented with the active 130 participation of the local authorities; whether their results were monitored to allow for adaptive 131 management; and whether the river restoration initiatives belonged to or result from any structured,

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large-scale river restoration strategy (e.g., a national river restoration plan). Less than a half of the part of large-scale (e.g., nationwide) river restoration policies, meaning that the majority of the EU 137 river restoration projects comprised the individually planned actions of interested entities (Fig. 3).

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Regarding the main goals of the river restoration projects, we revealed that an increasing number implemented (Fig. 4).

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Among the river restoration projects analyzed, the majority (51%) were designed and 155 implemented by regional authorities or by other entities working on a regional scale (Fig. 5). Europe. We observed (Fig. 6B) that the number of partially EU-funded river restoration projects has 183 been continuously increasing (Fig. 6A). Among the projects in the 1989-2000 period, none were 184 supported by EU funds (Fig. 6A and B).

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The level of EU co-funding for river restoration projects has increased from 43% (in 2000-2005) 186 to 65% (in 2010-2015). In the last time frame analyzed (2016 onward), the rate of EU co-funding 187 decreased to 52%. However, the last time frame analyzed is still not complete, as it does not cover a 188 full 5-year period. In the years analyzed, the total budgets for river restoration projects did not differ 189 significantly ( Fig. 6C and Tab. 2). There was only a significant difference between two periods, as 192 Table 2. p-values of the T-Test of the differences between total budgets of river restoration projects in

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Once considering the total budgets of the river restoration projects and the areas of their 200 influence (lengths and widths restored), we calculated these projects' average unit value per hectare 201 of restored river (Fig. 7). We revealed that, on average, the cost of restoring 1 ha of river was 310 000      al. [29]; for instance, the number of river restoration projects implemented in Europe continues to 247 increase. In our analysis of the structure of river restoration projects, we noted that less than half of 248 all the projects (42%) were part of a larger restoration strategy. Therefore, the majority of river in some cases, 95%; Fig. 6), which has led to enhanced cooperation between NGOs and regional (or 263 national) official entities (Fig. 5). However, without structured strategies and planned cooperation 264 between NGOs and national (or regional) authorities, river restoration projects will likely remain 265 hobbyists' activities rather than comprehensive country-level actions that would produce measurable 266 improvements in degraded rivers' statuses.

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Although Wohl et al. [29] reported that most river restoration projects are oriented at one river implemented with the active participation of local communities (Fig. 4). This status frequently led to

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We estimated the average unit costs for EU river restoration projects, expressed in EUR · ha -1 ,

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and although we calculated these values with a relatively small sample, there were few statistically  due to legal accordance, similar levels of amortization apply to such assets throughout the EU, the 305 average cost of river restoration projects per hectare per annum would be 7 757 EUR · ha -1 · year -1 (310 306 kEUR · ha -1 · 40 years -1 ), which is equal to roughly 8 920 USD · ha -1 · year -1 . Excluding the four outlying 307 values referred to above, the unit costs of river restoration were 4 875 EUR · ha -1 · year -1 (5 606 USD · 308 ha -1 · year -1 ).

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These values represent the price that European society wishes to pay (technically, has already 310 paid) to restore river functions. Hence, we consider this value to be the monetary dimension of 311 healthy rivers' ecosystem meta-service. Due to each river restoration project's complex aims and 312 measures, it is difficult to calculate the elementary values of a particular ecosystem's services (e.g., a 313 restored river as a new habitat for fish), but the given annual unit cost of restoring 1 hectare of a river 314 system is likely to represent the average long-term value of that river's services.

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Interestingly, the calculated unit cost of river restoration may now be referred to as the value of 316 riverine ecosystem meta-service and is similar to the average worldwide unit value of ecosystem 317 services that de Groot et al. calculated for rivers and lakes combined [35] (4 247 USD · ha -1 · year -1 ; 318 ranging from 1 446 USD · ha -1 · year -1 to 7 757 USD · ha -1 · year -1 ). At the same time, the calculated 319 value is a bit higher than the quantities for some single-ecosystem services calculated in individual 320 studies (such as flood retention, as calculated by Grygoruk et al. [21] and priced at approximately 500 321 EUR · ha -1 · year -1 or 590 USD · ha -1 · year -1 ), but lower than the ones calculated by Costanza

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However, along with increases in sustainable growth and outstanding recent advances in ecological 357 engineering, the awareness of the need for a high-quality environment will also rise [46-47], so we 358 believe this negative scenario will not come to pass.

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We analyzed 119 river restoration project from 19 EU countries, revealing that the number of 361 river restoration projects has been increasing over the time frame analyzed (1989-2016). We also 362 observed that the complexity of these river restoration projects has increased; in addition to the 363 restoration measures in river channels and floodplains, more catchment-scale initiatives are now 364 being implemented. We also revealed that majority of river restoration projects were not done in the 365 framework of any larger (e.g., country-scale) policy, meaning that most are individual actions 366 implemented by groups such as regional authorities. We also observed an increasing involvement of calculations, we estimated the average unit cost of river restoration per hectare to be 7 757 EUR · ha -1 376 · year -1 (8 920 USD · ha -1 · year -1 ). We stated that this value reflects society's willingness to pay for a 377 healthy river. Therefore, the calculated value can be referred to as monetary expression of river stakeholders (e.g., NGOs) to apply for external funds to pay for local river restoration initiatives. Such 384 programs would broaden the involvement of local stakeholders and decentralize river restoration 385 initiatives, thus enhancing local stakeholders' responsibility for their rivers. At the same time,

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countries should implement national programs to address river restoration on nationwide scales to 387 provide planned and structured catchment-scale actions.

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Acknowledgments: We sincerely thank all the experts from 19 European countries that participated in the 389 survey.

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Author Contributions: All authors contributed equally to manuscript preparation.

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Conflicts of Interest: The authors declare no conflict of interest.