Evolving deltas: Coevolution with engineered interventions

Abstract

Deltaic environments are often densely populated with high socio-economic values, and thus are hotspots of climatic, environmental and anthropogenic change. Large scale engineered structures, such as dike systems, have played an important role in shaping both environmental and socio-economic conditions in deltas, with such interventions more likely where there is a high population and a wealthy economy. Engineered interventions interact with the morphological evolution of the delta, reducing or removing sedimentation and accelerating subsidence, increasing the consequences of flooding and necessitating further adaptation. They also encourage further development, reinforcing this feedback. Thus, in these cases, the deltaic landscape and associated livelihoods can be considered to be the result of a coevolution process between natural delta processes and human engineered interventions. This paper explores this hypothesis. It analyses the history of large scale engineering interventions and their implications in five representative, large, populated deltas across the globe (Ganges-Brahmaputra-Meghna, Yangtze, Rhine-Meuse-Scheldt, Mekong and Nile). The results demonstrate coevolution has occurred and indicate that the response type and the management approach of these engineered structures have significant implications for future delta development. To understand and manage unintended consequences and the development of lock-in trajectories in deltas, a systematic understanding of delta development, including these coevolution processes is essential.

Delta Challenges and Trade-Offs from the Holocene to the Anthropocene

“…The incremental nature of many of the trends is also apparent: they accumulate with time such as sea-level rise, loss of elevation and growth of flood defences (Tessler et al 2015). There is also a strong coupling between natural processes and engineering responses that can lead to co-evolution and lock-in (Welch et al 2017). Hence, deltas are complex systems and historical precedent is no longer a guide to the future.…”

“…The scale of the challenge for delta management in the Anthropocene would suggest that new and more integrated approaches are required. Deltas are inherently challenging systems to manage due to the high sensitivity to multiple drivers and the potential for co-evolution and lock-in (Welch et al 2017;Seijger et al 2018). As an example, construction of flood defences and drainage attracts development, excludes sedimentation and promotes subsidence of organic soils, increasing the consequences of flooding if the defences fail.…”

Sustainable Deltas in the Anthropocene

“…These trends are diverse and linked either directly or indirectly to human activities, consistent with the concept of the Anthropocene. While humans have been influencing deltas for thousands of years in some cases (Bianchi 2016;Welch et al 2017), these type of changes are now pervasive in low and mid-latitude populated deltas and dominate their evolution. Table 11.2 summarises some potential indicators of the Anthropocene transition in deltas from the analysis discussed in previous chapters.…”

“…This is what Seijger et al (2018) call the dual lock-in of deltas. However, environmental concerns of societies, especially in wealthy countries, can also have a bearing on delta development and planning (van Staveren and van Tatenhove 2016; Welch et al 2017). In such cases, the competing interests between hazard exposure, economic development, social welfare and environmental protection make delta planning more complex, and a clear understanding of trends, threats and trade-offs is essential (Suckall et al 2018;Chapter 9).…”

Hotspots of Present and Future Risk Within Deltas: Hazards, Exposure and Vulnerability

“…Historically, this has resulted in high levels of localised protective adaptation generating protected zones which encourage further development, placing additional populations and assets at risk (e.g. Welch et al 2017). However, risk is also fluid in nature, changing over time and in response to external influences.…”