Abstract
The world's deltas are at risk of being drowned due to rising relative sea levels as a result of climate change, decreasing supplies of fluvial sediment, and human responses to these changes. This paper analyses how delta morphology evolves over multi-decadal timescales under environmental change using a process-based model. Model simulations over 102 years are used to explore the influence of three key classes of environmental change, both individually and in combination: (i) varying combinations of fluvial water and sediment discharges; (ii) varying rates of relative sea-level rise; and (iii) selected human interventions within the delta, comprising polder-dykes and cross-dams. The results indicate that tidal asymmetry and rate of sediment supply together affect residual flows and delta morphodynamics (indicated by sub-aerial delta area, rates of progradation and aggradation). When individual drivers of change act in combination, delta building processes such as the distribution of sediment flux, aggradation, and progradation are disrupted by the presence of isolated polder-dykes or cross-dams. This suggests that such interventions, unless undertaken at a very large scale, can lead to unsustainable delta building processes. Our findings can inform management choices in real-world tidally-influenced deltas, while the methodology can provide insights into other dynamic morphological systems.
Highlights
River deltas are iconic geomorphological features that provide ecosystem goods and services that support the lives and livelihoods of hundreds of millions of people worldwide [1,2]
We categorize individual drivers of environmental change into three broad classes: catchmentscale changes, global-scale changes, and local human interventions and we evaluate their impact on deltaic morphodynamic response
This research has shown that a quantitative numerical modelling approach may be applied to develop important insights about large-scale delta morphodynamics
Summary
River deltas are iconic geomorphological features that provide ecosystem goods and services that support the lives and livelihoods of hundreds of millions of people worldwide [1,2]. We categorize individual drivers of environmental change into three broad classes: catchmentscale changes (water and sediment fluxes supplied from the feeder catchment upstream), global-scale changes (sea-level rise), and local human interventions (with a specific focus here on common engineering interventions such as polder-dykes and cross-dams) and we evaluate their impact on deltaic morphodynamic response. To address this aim we explore a number of specific research questions as follows:
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