By: Theresa Boateng
Research on nature-based flood management is increasingly moving beyond the idea that adding more vegetation or green infrastructure will reduce flooding. A more specific proposition is emerging: restoring wetlands and floodplains can recover natural flood-management functions that have been lost or degraded through land-use change. These systems can provide space for excess water to be temporarily stored, slow the movement of floodwater and delay its release downstream. Recent modelling in Ghana provides particularly relevant evidence. In the Aboabo catchment of Kumasi, the restoration of floodplains and wetlands produced substantially larger reductions in modelled peak flows than simply creating wetlands in available spaces, demonstrating that the location and hydrological function of restoration are critical to its effectiveness [1]. Significantly, the research revealed that landscape plays a vital function in flood management infrastructure. A flood-management system does not necessarily have to move all rainfall away as quickly as possible; it can serve as a medium for temporarily holding water and releasing it more slowly. Restoring wetlands and reconnecting floodplains is one way of creating that capacity.
A wetland is more than an area containing water and vegetation. Hydrologically, it can function as a temporary storage system. Rainfall and runoff entering a wetland can be retained within surface depressions, vegetation, soils and connected water bodies. Some water may infiltrate or contribute to groundwater recharge, depending on soil, geological and groundwater conditions, while the remainder can be released gradually. Reviews of wetland-based flood management indicate that wetlands can modulate peak flows by storing runoff and releasing it over longer periods. However, their effectiveness depends strongly on characteristics such as size, design, location within the catchment and local hydrological conditions [2].
Floodplains perform a related but distinct function. They are expanses alongside rivers and drainage channels that can accommodate water when discharge exceeds the capacity of the main channel. Under natural conditions, a rising river can spill onto its floodplain, spreading water over a much larger area. This increases temporary storage and hydraulic resistance and can reduce the rate at which water continues downstream. Maintaining or restoring the connection between a river and its floodplain is therefore important because a floodplain that has been disconnected from the river by development, embankments or other physical barriers cannot perform the same storage function [3].
The hydrological mechanism can be understood by considering the flood hydrograph. In a highly modified catchment, rainfall may rapidly become surface runoff, particularly where permeable land has been replaced by roads, buildings and other hard surfaces. Runoff is then concentrated into drains and channels, causing discharge to rise rapidly and producing a relatively sharp peak. Where functioning wetlands and connected floodplains are present, some of that water can be temporarily stored, and its movement slowed before it reaches downstream areas. The resulting flood wave may have a lower peak, a delayed peak or a longer duration, depending on the characteristics of the catchment and the intervention.
This distinction is important because flood mitigation does not necessarily mean reducing the total amount of rainfall entering a catchment. Instead, the objective can be to change the timing, location and rate at which water moves through the system. Restored wetlands and floodplains can therefore operate through several interacting mechanisms: storing water, reducing flow velocity, increasing hydraulic residence time, providing opportunities for infiltration and delaying downstream discharge. A recent review of catchment-scale Nature-Based Solutions identifies flood detention, reduction of flood energy and diversion or redistribution of floodwater as fundamental mechanisms through which such interventions can reduce flood impacts [4].
The Ghanaian evidence is particularly useful because it shows why the concept must be applied strategically. Enu et al. examined changes in the Aboabo catchment between 1986 and 2023 and found that wetland cover had declined by 59%, while built-up areas increased by 134%. They then used the TELEMAC-2D hydrodynamic model to test different restoration scenarios and their effects on flood dynamics under different storm conditions [1]. The results were not uniform across the scenarios. The creation of wetlands simply in available spaces produced only 1–3% reductions in peak flow. A combined scenario involving floodplain restoration and wetland creation produced approximately 16–19% reductions in peak flow during prolonged storms, while another scenario which involved restoring the full floodplain network achieved approximately 24% reduction during short-duration events [1]. The more significant finding is that restoration becomes much more effective when it recovers a hydrologically important function in the right location. A wetland created simply because an undeveloped piece of land is available may have little influence on a major flood pathway. Reconnecting a strategically positioned floodplain, however, can provide substantial storage precisely where it is needed. Research conducted in Accra reinforces this principle of spatial targeting. Asare, Atun and Pfeffer developed a spatial multi-criteria approach for identifying locations suitable for different Nature-Based Solutions in Accra. Their analysis considered factors including land cover, proximity to rivers, soil texture, elevation and slope and demonstrated that different parts of the urban landscape have different suitability for flood-related interventions [5]. The implication is important: effective natural flood management cannot be reduced to a question of how much land can be converted into green infrastructure. It requires understanding how water moves through a catchment and where restoring natural storage will influence that movement.
For Ghana, this points towards a more deliberate form of restoration. Existing wetlands that still perform important storage functions can provide immediate value by retaining their capacity rather than allowing it to be progressively lost. Degraded wetlands may be restored where their hydraulic connection to runoff pathways remains meaningful. Floodplains can be considered for reconnection where they can safely accommodate excess water. Upstream storage can be particularly valuable where it can attenuate flows before they reach densely developed downstream areas. The objective is not necessarily to recreate every historical wetland or return every floodplain to its former state. It is to identify lost or degraded hydrological functions that can realistically be recovered.
This is also why restoration should be considered at the scale of the catchment rather than as isolated sites. Water does not respond to administrative boundaries or individual projects. Runoff generated upstream can accumulate downstream, and the effectiveness of one intervention can depend on what happens elsewhere in the drainage network. A recent systematic review of Nature-Based Solutions for catchment-scale flood mitigation similarly concludes that performance depends on physical characteristics such as catchment size, slope, topography, geology, river networks, land use, intervention location, event magnitude and climate conditions [4].
There are, however, clear limits to what restored wetlands and floodplains can achieve. Their storage capacity is finite. Once soils and surface storage areas become saturated, additional rainfall will continue through the catchment. Consequently, the effectiveness observed during one storm cannot automatically be expected during a much larger event. Research on larger catchments indicates that while there is empirical evidence for Nature-Based Solutions improving processes such as infiltration, floodplain reconnection and water storage, performance at larger scales and under more extreme floods remains less certain and is often assessed through modelling [6].
The physical condition of the system also matters. A polluted or sediment-filled wetland may have reduced hydraulic functionality; a floodplain isolated from its river cannot provide the same storage capacity as a connected one; and highly urbanised areas may simply lack sufficient space for large-scale restoration. Soil properties, groundwater levels, rainfall characteristics and antecedent moisture conditions can also determine whether infiltration or additional storage is actually achievable. These constraints mean that restoration must be assessed using hydrological and hydraulic evidence rather than assumed to be effective simply because an intervention is labelled “nature-based.”
This does not make wetlands and floodplains an alternative to hard engineering in every circumstance. Instead, their strongest potential may be as part of a hybrid flood-management system. Restored wetlands and floodplains can store and attenuate water; smaller urban interventions can reduce or delay runoff closer to its source; and drains, culverts, channels and other engineered systems can convey the water that remains. The assessment of flood management in Accra similarly identifies potential for integrating Nature-Based Solutions into existing flood-management and spatial systems rather than treating them as completely separate approaches [7]. The practical significance of this approach is therefore a change in how flood infrastructure is understood. Conventional infrastructure primarily manages water through conveyance and controlled storage. Restored natural systems can provide another form of infrastructure: distributed storage and flow regulation embedded within the landscape. The two approaches perform different functions and can complement one another.
For Ghana, the evidence does not justify the claim that restoring wetlands and floodplains is the single answer to flooding. It does, however, provide a credible scientific basis for treating the restoration of natural flood-management functions as one practical intervention worth testing and developing. The strongest lesson from the Ghanaian research is that effectiveness depends less on simply adding “more nature” and more on restoring the right hydrological function, in the right location, at the right scale. The Aboabo results demonstrate the potential magnitude of this difference, while research in Accra demonstrates how spatial analysis can help identify where particular interventions are physically appropriate [1,5].
Ultimately, restoring wetlands and floodplains is about giving water somewhere to go before it reaches terrains where it causes damage. Where natural storage has been lost, restoring it can slow the flood wave, temporarily retain excess water and potentially reduce downstream peak flows. It will not remove the hazard posed by extreme rainfall, nor can it replace every component of a flood-management system. But where the physical conditions are appropriate, restoring these natural systems offers Ghana a scientifically grounded way of making the landscape itself part of the infrastructure used to manage floodwater.
References
[1] Enu, K.B., Merk, F., Su, H., Rauch, M., Zingraff-Hamed, A., Broich, K., Förster, K., Pauleit, S. & Disse, M. (2025). A scenario-based analysis of wetlands as nature-based solutions for flood risk mitigation using the TELEMAC-2D model. Nature-Based Solutions, 7, 100236. (ScienceDirect)
[2] Ferreira, C.S.S., Kašanin-Grubin, M., Kapović Solomun, M., Sushkova, S., Minkina, T., Zhao, W. & Kalantari, Z. (2023). Wetlands as nature-based solutions for water management in different environments. Current Opinion in Environmental Science & Health, 33, 100476. (ScienceDirect)
[3] Jakubínský, J. et al. (2021). Managing floodplains using nature-based solutions to support multiple ecosystem functions and services. WIREs Water, 8(5), e1545. (Wiley Online Library)
[4] A bibliometric analysis and overview of the effectiveness of Nature-based Solutions in catchment scale flood mitigation (2025). Nature-Based Solutions, 7, 100235. (ScienceDirect)
[5] Asare, P., Atun, F. & Pfeffer, K. (2024). Spatial Multi-Criteria Analysis for Discovering Nature-Based Solutions Location for Urban Flood Mitigation in Accra. Applied Spatial Analysis and Policy, 17, 207–239. (Springer Link)
[6] Dadson, S.J. et al. (2021). How can we plan resilient systems of nature-based mitigation measures in larger catchments for flood risk reduction now and in the future? Water Security, 13, 100091. (ScienceDirect)
[7] Asare, P., Atun, F. & Pfeffer, K. (2023). Nature-Based Solutions (NBS) in spatial planning for urban flood mitigation: The perspective of flood management experts in Accra. Land Use Policy, 133, 106865. (ScienceDirect)
