Belgium – Engineering services – Service contract concerning the revision of alert thresholds in the context of flood announcement, monitoring and forecasting, as well as their definition for Walloon municipalities impacted by flooding.

Opportunity description

The subject of the contract is the provision of services relating to the development and application of a consistent and reproducible methodology for the revision or definition of alert thresholds intended for flood announcement, monitoring and forecasting, as well as their definition for Walloon municipalities impacted by flooding. Description of the services to be performed: The first objective is to define and/or verify the consistency of the flow thresholds used by the Hydrological Management Directorate of SPW MI for flood forecasting and flood alerts. This involves validating, setting or revising: - The threshold values of flows causing the first overflows, as well as those corresponding to the justification for transitions to pre-alert and alert phases. The flow with a 100-year return period or that of the largest known flood will supplement the information equivalent to an extreme flood threshold; - The division of the Walloon territory into hydrologically homogeneous ‘watersheds / sections’ for the dissemination of pre-alert and alert phases. A consistent and reproducible methodology will be developed based on the methodology implemented to define vigilance levels in France. It must follow a basic three-component approach to define the thresholds: 1. Hazard: Physical characterization of flooding based on the return period and/or local hydraulic characteristics such as the flow corresponding to the 1st overflows and the most extreme historical flood. 2. Elements at risk: Assessment of the potential effects on people, property and activities. By determining thresholds for the number of affected elements at risk that trigger an alert phase, it will be considered that a threshold exceeded for one element at risk triggers this phase. 3. Context: Exceptional consideration of circumstantial factors. For each threshold value, a transition zone will also be determined to take account of uncertainties related to the characterization of the hazard and the elements at risk. Currently, for the territory of Wallonia, the DGH applies 3 phases (1st overflows, pre-alert and alert) for 42 watersheds / sections, relying on 45 hydrological forecasting points and approximately the same number of points where historical flow thresholds exist. Given the new developments underway at the DGH and needs during crisis periods, the method deployed here is expected to apply to 85 measurement stations referred to as “main” stations under this contract. The second objective is to define these four threshold values and their transition zones at municipal level so that each Walloon municipality crossed by one or more navigable and non-navigable category 1 watercourses (approximately 190 municipalities / 261) can establish its own local phases. For application of the methodology to the Walloon territory, the following points are expected at a minimum: - Geomatics approach based on overlaying flood extent or flood depth maps with elements at risk; - Approach based on the analysis of flood-related databases; - Approach relating to the collection of eyewitness accounts. Finally, the third and final objective is to determine, in a simplified manner, the 4 threshold values (1st overflows, pre-alert, alert and extreme flood) for all other active flow/water-level measurement stations on waterways and non-navigable category 1 watercourses (approximately 125 stations), by interpolating or extrapolating the thresholds rigorously identified at the 85 main stations. The main expected deliverables are: - 1 detailed methodological report validated by the Administration in word and pdf formats; - For each of the 85 main stations: o 1 analysis grid including the preliminary calculations and reports of the interviews that led to the setting of the 4 thresholds and their transition zones; o 1 threshold visualization scale; - A list containing the 4 interpolated or extrapolated thresholds for all the other 125 active stations on waterways and category 1 watercourses; - For each municipality crossed by one or more navigable and non-navigable category 1 watercourses (approximately 190): 1 analysis grid and 1 visualization scale per overflowing watercourse; - A geomatics database of the thresholds and the elements at risk exposed at each threshold; - A tool for consulting these deliverables in a geomatics environment; - Any intermediate result useful for the subsequent revision of these thresholds. In a first 8-month phase corresponding to the firm tranche of this contract, the methodology concerning hazards and elements at risk will be developed and applied to the watersheds of the Ourthe, Amblève, Vesdre and Mehaigne (22 main stations and 49 municipalities). Thresholds interpolated or extrapolated to the other measurement stations in these watersheds will also be produced. The second 16-month phase corresponds to the conditional tranche of this contract and concerns application of the method to the rest of the Walloon territory (63 main stations). For information purposes, the estimated value of this contract falls within a range from €400,000 to €1,200,000 excluding VAT. The subject of the contract is the provision of services relating to the development and application of a consistent and reproducible methodology for the revision or definition of alert thresholds intended for flood announcement, monitoring and forecasting, as well as their definition for Walloon municipalities impacted by flooding. Description of the services to be performed: The first objective is to define and/or verify the consistency of the flow thresholds used by the Hydrological Management Directorate of SPW MI for flood forecasting and flood alerts. This involves validating, setting or revising: - The threshold values of flows causing the first overflows, as well as those corresponding to the justification for transitions to pre-alert and alert phases. The flow with a 100-year return period or that of the largest known flood will supplement the information equivalent to an extreme flood threshold; - The division of the Walloon territory into hydrologically homogeneous ‘watersheds / sections’ for the dissemination of pre-alert and alert phases. A consistent and reproducible methodology will be developed based on the methodology implemented to define vigilance levels in France. It must follow a basic three-component approach to define the thresholds: 1. Hazard: Physical characterization of flooding based on the return period and/or local hydraulic characteristics such as the flow corresponding to the 1st overflows and the most extreme historical flood. 2. Elements at risk: Assessment of the potential effects on people, property and activities. By determining thresholds for the number of affected elements at risk that trigger an alert phase, it will be considered that a threshold exceeded for one element at risk triggers this phase. 3. Context: Exceptional consideration of circumstantial factors. For each threshold value, a transition zone will also be determined to take account of uncertainties related to the characterization of the hazard and the elements at risk. Currently, for the territory of Wallonia, the DGH applies 3 phases (1st overflows, pre-alert and alert) for 42 watersheds / sections, relying on 45 hydrological forecasting points and approximately the same number of points where historical flow thresholds exist. Given the new developments underway at the DGH and needs during crisis periods, the method deployed here is expected to apply to 85 measurement stations referred to as “main” stations under this contract. The second objective is to define these four threshold values and their transition zones at municipal level so that each Walloon municipality crossed by one or more navigable and non-navigable category 1 watercourses (approximately 190 municipalities / 261) can establish its own local phases. For application of the methodology to the Walloon territory, the following points are expected at a minimum: - Geomatics approach based on overlaying flood extent or flood depth maps with elements at risk; - Approach based on the analysis of flood-related databases; - Approach relating to the collection of eyewitness accounts. Finally, the third and final objective is to determine, in a simplified manner, the 4 threshold values (1st overflows, pre-alert, alert and extreme flood) for all other active flow/water-level measurement stations on waterways and non-navigable category 1 watercourses (approximately 125 stations), by interpolating or extrapolating the thresholds rigorously identified at the 85 main stations. The main expected deliverables are: - 1 detailed methodological report validated by the Administration in word and pdf formats; - For each of the 85 main stations: o 1 analysis grid including the preliminary calculations and reports of the interviews that led to the setting of the 4 thresholds and their transition zones; o 1 threshold visualization scale; - A list containing the 4 interpolated or extrapolated thresholds for all the other 125 active stations on waterways and category 1 watercourses; - For each municipality crossed by one or more navigable and non-navigable category 1 watercourses (approximately 190): 1 analysis grid and 1 visualization scale per overflowing watercourse; - A geomatics database of the thresholds and the elements at risk exposed at each threshold; - A tool for consulting these deliverables in a geomatics environment; - Any intermediate result useful for the subsequent revision of these thresholds. In a first 8-month phase corresponding to the firm tranche of this contract, the methodology concerning hazards and elements at risk will be developed and applied to the watersheds of the Ourthe, Amblève, Vesdre and Mehaigne (22 main stations and 49 municipalities). Thresholds interpolated or extrapolated to the other measurement stations in these watersheds will also be produced. The second 16-month phase corresponds to the conditional tranche of this contract and concerns application of the method to the rest of the Walloon territory (63 main stations). For information purposes, the estimated value of this lot falls within a range from €400,000 to €1,200,000 excluding VAT. Procedure: open. Review the original TED notice for the complete requirement, lots, amendments and attachments.