Over the next few decades, managers of hydraulic engineering structures (such as locks, pumping stations and storm-surge barriers) face a significant replacement and renovation task. Rijkswaterstaat is currently drawing up a national forecast. To create a future-proof water infrastructure, we need to answer two questions: What is the best way to intervene? When is the optimal moment? It is not only the technical and economic life cycle that counts, but the functional performance of the engineering structure as well. How do you determine that?
A structure can reach the end of its life for a number of reasons. Thus far, we have looked mainly at the development of strength degradation (technical life span) and costs (economic life span) over time. But a structure that is technically still functional and has not yet been written off can sometimes no longer fulfil its function. It then reaches the end of its functional life span, e.g. due to changes in climate, use or policy. The floods in Limburg this summer, for example, show that we will need to take more intense rainfall into account in the future, and therefore higher discharges into the tributaries and the Meuse. In order to determine the functional life span of hydraulic civil engineering structures, the Wet Civil Engineering Structures Knowledge Programme has developed the Functional Life Cycle Methodology (MFL).
Functional Life Cycle Methodology
The MFL is still under development. The aim is to obtain a generic, practically applicable methodology for mapping the end of the functional life of a structure as part of the water system. An MFL-LIGHT assessment firstly filters qualitatively those functions that are most sensitive to expected developments – i.e. aspects such as climate change, changing transport demand and changing policies. Depending on the aspect being queried, more quantitative (time-consuming) analyses of the functional life span can then be carried out in a targeted manner (MFL-MEDIUM with available model calculations and MFL-HEAVY with new model calculations). These may be, for example, analyses to identify bottlenecks for shipping or in the discharge capacity.
The MFL-LIGHT assessment has now been successfully applied in three studies, according to the water authorities that have worked with this method: 1) Climate stress test of engineering structures in the main water system, 2) Weurt-Heumen regional analysis, and 3) Proof of concept for two cases in support of the national replacement and renovation programmes operated by Rijkswaterstaat. We explain the qualitative approach below, with highlights from the replacement and renovation programme.
Figure 1. Functional Life Cycle Methodology schematic
‘Meuse’ case study: proof of concept MFL-LIGHT
Rijkswaterstaat is working on a national forecast for the replacement and renovation of hydraulic engineering structures. To support this forecast, we applied the MFL-LIGHT assessment in a proof of concept for the ‘Meuse’ river system. The aim of this assessment was to estimate the end of the functional life span of the most critical functions within the system, in order to create a comparison with the estimated technical life span. The first step of the method consists of a situation outline of the structures and networks that they are a part of. The next step is to map the associated core tasks and functions for each object group (a group of the same types of engineering structure, e.g. ‘locks’). Then, based on expert knowledge, the sensitivity of these functions to ‘drivers’ is then looked at – future developments such as climate change, transport demand and changing policies.
In the method, an object group (= group of the same types of structure) for each function is given a sensitivity score per driver. A structure or sub-task can, therefore, have several sensitivities. The values of the sensitivity score (colour coded) are defined under Figure 2. This figure is an (abbreviated) illustration of how the method works. We have based the climate drivers on the upper limit of the Delta scenarios, the WARM2050 scenario. This scenario assumes more river supply in winter, less supply in summer, warmer summers and a limited increase in transport demand. Furthermore, we assume that the shipping class of the Juliana Canal will remain unchanged (it will remain a ‘Vb corridor’). The table for the Meuse was completed by regional experts working in water management and engineering structures.
Figure 2. Development of MFL-LIGHT for the Meuse (abbreviated version).
In the case of the Meuse River, four critical object-group-function-driver combinations stand out (red and orange blocks). One of these is the combination: locks in shipping lane – facilitating shipping traffic – decrease in river discharge in summer. It has a sensitivity score of -3. After all, as river discharge decreases in summer, low water will occur more often, causing more frequent lock restrictions, which will result in longer waiting times for shipping.
The outcome of the MFL-LIGHT assessment provides insight into the most important functions that will be under pressure in the future due to (climate) change.
‘Meuse’ case study: MFL-MEDIUM
The critical object group-function-driver combinations were then worked out in an MFL-MEDIUM assessment. The remaining life span of the structure was taken into account. On the basis of a literature study and interviews with experts, the function requirement was first made specific: at what threshold does the function no longer meet the requirements and how often may this occur? We then looked for a simple relationship between driver and function.
Figure 3 shows the results for the Meuse. Due to uncertainties in the Delta scenarios, we give a range here instead of a single point in time. The figure shows that the fixed bridges and locks in the shipping lane in particular limit the functional life span of this system. The fixed bridges are already in need of intervention, while the functioning of the locks in the shipping lane is expected to require intervention in 2030. However, it is not always possible to find simple relationships, and sometimes the information is simply not available (yet). In that case, new model calculations must be made with MFL-HEAVY.
With these results, authorities can think more precisely about possible means of intervention. More detailed analyses can indicate, for example, whether the limited clearance of a fixed bridge would be better resolved by demolition – and accommodating the road traffic via another bridge – or by replacement with a higher bridge. Both interventions have a different impact on the system and its environment. Furthermore, ‘end of functional life span’ does not necessarily mean that the object needs to be replaced in its entirety – sometimes a minor modification such as installing an additional pump may be sufficient.
Figure 3. End of functional life span range for the most important object group-function-driver combinations for the Meuse system.
Challenges and uncertainties in MFL
When interpreting the results from the MFL-LIGHT, it can sometimes be difficult to identify the functional relationship between different object groups. For example, a system requirement may be that the water level in a canal bank must be maintained within a certain range. Often, multiple structures (pump, lock or weir) contribute to maintaining that water level. Quantitative insight into this kind of cohesion within the water system is often absent.
When establishing the end of a functional life spanwith MFL-MEDIUM/HEAVY, defining the requirements or ambitions is a challenge. For example, what is the maximum permissible waiting time at locks? How much is an authority willing to invest in sticking to an ambition of no more than two days’ waiting time per year? Is the action perspective with a less stringent requirement of 10 days per year acceptable? The same question can be asked of pumps. What is the minimum required availability and reliability? And how does this relate to current performance? The current performance of structures is not always monitored.
Another challenge in determining the end of a functional life span is that simple relationships are not always available. Model calculations will have to be performed to show current performance and make forecasts about the future, and these can be time-consuming. Good model schematics, in which the coherence within the system is appropriately taken into account, are not always available. In addition, forecasts involve uncertainties. Calculating the vertices of the Delta scenarios helps to map a range for the end of functional life span. An estimate can also be made of accelerated sea level rise scenarios, such as those recently presented by the KNMI and IPCC. Focused and periodic measurement of the functional performance of the system is expected to lead to a better understanding that helps to reduce uncertainty.
Further development of MFL
The phased approach in the Functional Life Cycle Methodology has clear added value for water authorities when deciding on replacement and renovation tasks. MFL-LIGHT can be used immediately. However, not all the requisite information will be available for application of MFL-MEDIUM and MFL-HEAVY. Water authorities can contribute by collecting information on how the current structure is performing in relation to requirements and ambitions. The Hydraulic Civil Engineering Structures Knowledge Programme 2021-2024 helps to map the required (further) development of models to visualise future bottlenecks; how does the system perform under the future scenario (drivers) outlined?
Nienke Kramer, Joost Breedeveld and Ida de Groot-Wallast (Deltares), Hans van Twuiver and Evert Jan Hamerslag (Rijkswaterstaat)
References
- Deltares, 2018, Deltascenario’s voor de 21e eeuw century (revised 2017), H.A Wolters, G.J. van den Born, E. Dammers, S. Reinhard, 2018a, Deltares, Utrecht, https://media.deltares.nl/deltascenarios/Deltascenarios_actualisering2017_hoofdrapport.pdf
- Kennisprogramma Natte Kunstwerken, 2020, Kennisprogramma Natte Kunstwerken, Handleiding Toolbox Functionele Levensduur, Joost Breedeveld, Nienke Kramer, Ida de Groot-Wallast, Deltares report, December 2020, 1200741-079-HYE-0001, 56 pag. https://www.nattekunstwerkenvandetoekomst.nl/producten/relatie-object-systeem/functionele-levensduur/item101
- Rijkswaterstaat, Klimaat stresstest objecten HWS – Bezien vanuit het perspectief van Ruimtelijke Adaptatie, Hidde Boonstra, v1 final, 1 May 2020
- Rijkswaterstaat, Regioanalyse Vervanging en Renovatie (VenR) Weurt-Heumen: analyse van de VenR-opgave voor de sluiscomplexen Weurt en Heumen van het Maas-Waalkanaal, Version 1.0, 2020
Summary
In view of the design life span of a large proportion of hydraulic engineering works, water authorities expect to have to make many investment decisions concerning replacement and renovation over the next few decades. These decisions are an important moment of choice; they provide an opportunity to consider desirable changes in the (multifunctional) infrastructure with a view to the future. Within the Hydraulic Engineering Works Knowledge Programme 2017-2020, Rijkswaterstaat and Deltares have developed a methodology that takes into account the decrease in (functional) performance over time and thus estimates the functional life span. This article outlines the method using the river ‘Meuse’ system as an example.
