1. Introduction

This expansive study, initiated by Geneva Industrial Services (SIG) in partnership with the Territorial Department, represents a collaborative endeavor spearheaded by the Office of Works and Environmental Studies (BTEE) and B+C Engineers SA. It brought together a multidisciplinary team of six entities, including engineers and specialists in various fields. The study’s primary objective was to establish a comprehensive decision-making framework for sediment management at the Verbois Dam. This framework was designed to facilitate informed decision-making by systematically identifying and evaluating key components of sediment management strategies [1].

Emphasizing a holistic approach, the study incorporated a detailed impact analysis and assessment module (illustrated in Figure 1). This module integrates various evaluation tools, including quantified evaluation grids complemented by informative graphical representations such as fever and radar curves. These tools provide a nuanced understanding of the environmental, technical, and socio-economic implications of sediment management practices.

Notably, the study abstains from endorsing specific strategies or providing weighted conclusions. Instead, it presents a transparent and objective analysis, offering a range of scenarios through meticulously commented and quantified data. This approach ensures that decision-makers are equipped with unbiased, comprehensive information, enabling them to consider a spectrum of possibilities and implications before arriving at sustainable and effective sediment management strategies [2].

The outcome of this study is expected to significantly contribute to the field of sediment management, particularly in the context of dam operations. It provides a replicable model for addressing complex environmental challenges, balancing technical feasibility with ecological and societal considerations.

Figure 1: Sediment removal scenarios from the Verbois dam(Services Industriels de Genève GIS basic data)

Traditional scientific and technical research focusing on flushing in the Geneva Rh\^{o}ne has predominantly concentrated on specific aspects such as fish survival and sediment quality. While these studies have been instrumental in deepening understanding of critical parameters and advancing sediment management techniques, they often fell short in providing an integrated perspective that encapsulates economic, societal, and environmental dimensions. Addressing this gap, our study undertakes a holistic analysis of various flushing-emptying scenarios in the context of sustainable development. This approach emphasizes early risk detection and conflict identification, thereby enhancing strategies for sustainable progress [3].

To tackle the multifaceted nature of this challenge, a specialized expert group was convened. This group, comprised of seasoned professionals, undertook an objective evaluation of data and insights provided by the Services Industriels de Gen\`{e}ve (SIG) and the Territorial Department. Their collective expertise facilitated a nuanced and comprehensive understanding of the intersecting factors influencing sediment management and its broader implications [4].

2. Material and Methods

The study progression follows distinct steps

The methodology employed in this study involved a meticulous selection of domains and identifying key components, each influenced by various factors. This process entailed the careful selection of sustainability criteria, drawing upon the Swiss Federal Council’s 2002 guidelines for sustainable development, while tailoring these criteria specifically to the nuances of flushing-emptying processes [5].

The study then proceeded with an in-depth analysis of effects, which offered valuable insights into the impacts and potential enhancements associated with different scenarios. This step was crucial in understanding the various implications of each variant under consideration.

Finally, the study conducted a comprehensive sustainability evaluation. This involved correlating the observed effects and identifying any conflicts, all within the tripartite framework of sustainable development. This evaluation aimed to discern the pros and cons of each project variant, while also pinpointing areas for potential improvement. By doing so, the study strived to present a balanced view, encompassing the intricate interplay of environmental, economic, and social factors integral to sustainable development.

3. Scenarios

The study encompasses six sediment management scenarios, with a detailed focus on three “main scenarios” subject to study and hydraulic modeling during Aquavision 2005 and Aquavision 2006. The remaining “bis” scenarios are interpreted by the interdisciplinary group[1, 2].

4. State Reference, Limits, and Assumptions

The baseline for evaluation in this study is established using the post-emptying conditions of 2003, as primarily recorded in the 2003 Rh\^{o}ne monitoring report by Services Industriels de Gen\`{e}ve (SIG, [6]). The geographic and temporal scope of the research encompasses the segment of the Rh\^{o}ne in Geneva, stretching from the Junction to the Chancy-Pougny dam, with a focus on the post-2003 drainage conditions extending up to the year 2050. The hydraulic and morphological assumptions employed in this study are derived from documentation provided by AquaVision Engineering S\`{a}rl. This includes insights from the AquaVision 2005 study, as well as findings from their summary report released in 2006[6]. It is important to note that this study did not involve any new field investigations, as it was confined to the parameters of the given mandate.

5. Areas and Components Determining Factors

The study inventories elements potentially influenced by flushing scenarios, categorized into four main areas: Hydraulics, Solid Transport, and Sediments; Operation, Maintenance, and Safety; Industry and Navigation; Nature, Landscape, and Leisure. The consortium and steering group identified key points known as “determining components” (fig 2), which are analyzed, evaluated, and commented upon during the effects analysis of different operating methods. The chosen scale within this work is a homogeneous cardinal scale with an increment of 1 (or 0.5 when necessary) ranging from “-2” for the most negative effects to “+2” for the most positive effects. This scale is applied uniformly to all determining components, regardless of quantifiability. For efficiency, a general analysis was chosen in this study due to time constraints, as it is impractical to present all elements systematically and rigorously in their quantitative and/or qualitative forms.

Figure 2: Determining components retained for the analysis of effects.

Similarly, their transposition onto the cardinal scale involves indicators, standards, and benchmarks currently absent. It was also considered reasonable to justify the results of the expertise using key elements of the project and the context that strongly influence the criterion in question.

6. Appreciation Value, Analysis, and Evaluation Methodology for Effects Analysis

The adopted rating scale is relative, accounting for the difference of one scenario compared to the others. The score magnitude reflects the change’s magnitude, with a score of 0 corresponding to the 2003 post-emptying reference state, well-documented by the 2003 Rh’ne monitoring (SIG [6]).

7. Criteria Sustainability

The sustainability assessment utilized criteria based on the 2002 Strategy of the Federal Council, Central Indicators for the sustainable development of cities and cantons (FSO, OFEFP, ARE [5]), and the thematic fields and indicators of the Bernese Compass for sustainable development (BVE [3]). Twelve sustainability criteria (4 per sustainable development dimension) were employed, each described in Figure 3.

Figure 3: Extract from the sustainability analysis table

8. Results and Analysis of the Effects of the 3 Scenarios

The analysis of effects presents results summarized in tables and an overall qualitative synthesis with fever curves (Fig. 1). Due to space constraints, only an extract from the effects analysis table (figure 4) is presented here to demonstrate the approach and form of analysis.

Figure 4: Extract from the effects analysis table

9. Synthesis

Scenario 1 “Three-year Hunt”

Positive aspects include easier management of the Rhone and effective solid transport management, but with very negative impacts on wildlife.

Scenario 2 “Passive”

Environmental equilibrium is quickly reached, promoting biodiversity and leisure activities. Negative aspects involve operational and maintenance challenges and increased flood risks.

Scenario 3 “Active Flood”

Favorable for still water fish species, it limits flood risks but poses challenges to wildlife. Planning and safety during floods may cause coordination issues with Rh’ne users.

10. Scenario Optimization Track

Three optimization avenues for each scenario are defined post-analysis, aiming to resolve identified problems but necessitating additional studies and simulations for precise control of implications. This involves optimizing flushing, avoiding sensitive wildlife periods, and studying the implications of modifying the reservoir’s flushing water tipping point.

11. Conclusion

This exploratory study represents an initial phase in identifying key elements for optimizing sediment management from the Verbois dam. Utilizing current data, simulations, and expert opinions, the study tested the tool through analysis of three scenarios. While providing valuable insights, refinement of the scenarios is essential, incorporating alternative scenarios to approach an optimal and sustainable sediment management solution for the Rhône.

References

1. AQUAVISION. 2005. Dam of Verbois – Study hydraulic And morphological, AquaVision Engineering Sàrl, Ecublens, 139p.
2. AQUAVISION.2006. Verbois Dam – Hydraulic and morphological study – Summary report. AquaVision Engineering Sàrl, Ecublens, 53 p.
3. SBVE 2004. The compass Bernese of development sustainable – Guide, Bern, 14p.
4. ADVICE FEDERAL SWISS. 2002. Strategy 2002 for sustainable development, Bern, 41 p.
5. OFS, OFEFP, ARE.2003. Sustainable development in Switzerland – Indicators and comments, Neuchâtel, 92 p.
6. GIS.2006. Monitoring 2003 of the Rhône. SIG, Geneva.