Martijn van Staveren, Wageningen University, the Netherlands
Constructed hydraulic engineering works, such as dams, polder embankments, and canal systems, profoundly shapes a delta’s development trajectory.1 This can primarily be attributed to the physicalness of infrastructure intended to separate water from land, and fresh water from saline water. Extreme flood events aside, such costly infrastructure is unlikely to be moved or removed only a few years after construction. The infrastructure’s effects (which can be positive or negative) on the delta’s environmental ecosystem and human population will therefore be felt for decades, if not centuries.
A delta trajectory expresses how environmental dynamics, technological measures, and societal processes mutually interact. Environmental dynamics include seasonal differences between high and low water volumes flowing through a delta and sedimentation patterns. Technological measures include the different conceptual options and hydraulic capacities to develop certain hydraulic works. Societal processes involve the development of policy, institutional structures, and societal involvement in hydraulic choices. A composite delta trajectory follows out of the interaction between the three domains and may be oriented towards sustainable or unsustainable states, depending on factors such as a chosen time scale.
The impacts of hydraulic engineering on deltas’ development trajectories become visible with embankments and other protective infrastructure creating safer spaces, facilitating socio-economic development (urbanization, agro-industry, transportation) behind the embankments. This in turn creates demand for increased protection against high water. In the Dutch delta, an uncountable series of embankment heightening and strengthening has been going on in this way for centuries, in an iterative process with rapid socio-economic developments in protected areas. What started with simple embankment construction has resulted in a technological ‘lock-in,’ where growing socio-economic values in low-lying lands demand increasing protection through new, ever stronger embankments.
As another example in the Netherlands, a large scale storm surge barrier was constructed in the southwest delta region during the 1980s, in response to the devastating 1953 flood disaster. The barrier includes dozens of sluice gates, which are usually open and only close when a storm surge is expected. The physical, economic, but also emotional, value of the protective structure has created a form of path dependency. Despite the ‘open’ character of the storm surge barrier, the structure strongly impacts the delta’s environmental dynamics, such as tides, erosion, and sedimentation, which are addressed with stopgap counter measures. All long term delta management policies evolve around the enduring presence of the barrier, which is foreseen to last another 150 years.
It has been argued that several of the largest deltas are increasingly vulnerable or moving towards an unsustainable state (meaning that a delta becomes technically or economically untenable for human populations to live in). Recently, a prominent challenge to be addressed is the ‘sinking’ of deltas due to environmental and human-made processes such as natural soil subsidence, groundwater extraction, and reduced sedimentation deposition. From this particular perspective, many deltas are facing unsustainable futures where the land increasingly sinks further below sea level. Soil subsidence may go faster than sea level rise. In some delta regions this is already an urgent issue, in other deltas, it will take more time before it will be felt. 2
Given the ‘sinking’ of densely populated deltas on the one hand, and the technological lock-in and path dependency characteristics of existing hydraulic engineering works in those deltas on the other, addressing the issue of unsustainable trajectories is a challenging one. The question surfaces as to what flexibility exists to re-orient an unsustainable trajectory. Since hydraulic infrastructure shapes to a delta trajectory, can it also be employed to reorient an unsustainable one?
The field of eco-engineering may offer opportunities to re-orient unsustainable delta trajectories. Eco-engineering aims to improve the effectiveness of hydraulic engineering by incorporating (long-term) delta ecosystem dynamics in project designs. It acknowledges the potential of ecosystem dynamics, such as flooding and sedimentation, to contribute to long-term delta sustainability. Sea currents and delta wetlands or coastal mangroves have recently been applied in studied for their capacity of supporting coastal flood protection. In the Netherlands, sea currents slowly erode an artificial sand island in order to disperse sand particles along the coast, which compensates for coastal erosion on other nearby coastal locations. Delta wetlands and coastal mangroves are receiving increasing attention to flood wave attenuating or absorbing capacities, especially in Asia.
In connection, in several deltas around the world controlled flooding and its associated sedimentation processes are being restored at places where such dynamics have been halted for centuries. In the Netherlands over a dozen projects have recently been completed where controlled flooding has been re-introduced in polders (low-lying lands in use for agriculture surrounded by circular embankments, in which water levels can be controlled). The polder embankments are (temporarily) lowered, to restore or facilitate controlled flooding during particular times of the year. Obviously, if farmers reside in such areas they are pushed by the authorities to relocate.
The rationale behind such interventions is creating water safety (for other, nearby areas) by accommodating a flood peak, and nature restoration considerations. Controlled flooding contributes to the expansion of typical delta wetlands, both along the rivers and the tidal zone. Particularly in the tidal zone, sedimentation resulting from controlled flooding in a number of former polders has increased the height of the land considerably, creating a broader buffer between the sea and more inland (and deeper) polders. In the riverine region, seasonal flooding in a former polder contributes to one of the largest national wetland parks, but sedimentation is more problematic because it would hamper the hydraulic discharge capacity of the area (the fundamental reason to initiate the project in the first place).3
Restored controlled flooding and sedimentation currently takes place on a very marginal scale compared to the size of the broader delta systems. It is therefore difficult to argue that the practice on its current scale can fully reorient a delta trajectory towards a more sustainable state. Also, from a societal perspective, the practice has raised contentious debates since restoring controlled flooding goes against the Netherlands’ traditional culture of flood prevention, and sometimes leads to forced relocations of communities. Participatory processes for the creation and implementation of flood policy do not always accommodate the expectations of local populations residing in areas where controlled flooding is planned. Despite this complication, in policy circles the practice appears in various vision documents and will likely to continue to receive considerable attention in the future. A more thorough understanding of its technological, environmental, and social dimensions is therefore important when considering larger scale applications.
The main conclusion of our study is that hydraulic engineering works, once in place, outline a relatively rigid development path of a delta, or delta trajectory. Hydraulic engineering works display technological ‘lock-in’ and path dependency characteristics. However, there is scope for flexibility to re-orient an unsustainable trajectory towards a more desirable system state by means of eco-engineering or eco-technological add-ons to existing hydraulic engineering; thereby allowing ecosystem dynamics to be approached from different angles, and offering new conceptual long term thinking about deltas, flooding and sedimentation processes.
- Van Staveren, M. F., and J. P. M. van Tatenhove. Hydraulic engineering in the social-ecological delta: understanding the interplay between social, ecological, and technological systems in the Dutch delta by means of “delta trajectories.” Ecology and Society 21(1).
- Syvitski, J. P. M., A. J. Kettner, I. Overeem, E. W. H. Hutton, M. T. Hannon, G. R. Brakenridge, J. Day, C. Vorosmarty, Y. Saito, L. Giosan, and R. J. Nicholls. 2009. Sinking deltas due to human activities. Nature Geoscience 2(10):681–686.
- Van Staveren, M. F., J. F. Warner, J. P. M. van Tatenhove, and P. Wester. Let’s bring in the floods: De-poldering in the Netherlands as a strategy for long-term delta survival? Water International 39(5):686–700.
Martijn van Staveren is PhD candidate at the Environmental Policy Group, Wageningen University. His research focuses on the restoration of controlled flooding in polders and coastal zones of the Netherlands, Bangladesh, and Vietnam. He has complemented a background in civil engineering with an interest in ecosystem-based flood management and policy processes. He is primarily interested in the interaction between society, technological interventions and the environment when it comes to dealing with floods dynamics and deltas.
The views expressed in this article belong to the individual authors and do not represent the views of the Global Water Forum, the UNESCO Chair in Water Economics and Transboundary Water Governance, UNESCO, the Australian National University, or any of the institutions to which the authors are associated. Please see the Global Water Forum terms and conditions here.