Land Reclamation Impacts on Tidal Landscape Evolution

In the past 1000 years, the continuous need for fertile and strategically located land has led to the reclamation of intertidal areas. The direct and short-term impact of land reclamation is a reduction in intertidal storage space and the loss of ecological value. Its long-term impact on the tidal landscape is variable but surprisingly poorly known. In this contribution, we review the impacts of land reclamation in a wide range of physical environments. Land reclamation along exposed, muddy coastlines leads to erosion or accretion, depending on local transport conditions and sediment availability. Confined muddy coasts (typically estuaries) respond by progressive infilling of tidal channels, especially when their upper reaches have been reclaimed. More gradual reclamation along the length of an estuary can lead to tidal amplification, while reclamation at the estuary mouth may additionally lead to channel erosion. The response timescales may be very long (up to centuries) especially when controlled by positive feedback mechanisms between tidal dynamics and landscape evolution. Therefore, some of the present day land reclamations will influence or possibly control the evolution of the coastal landscape in the coming decades to even centuries. In sediment-poor coastal bays, the reduction in tidal prism mainly leads to lower exchange rates and, therefore, to a reduction in water quality. The framework introduced here facilitates the assessment of the past and future impacts of land reclamations in tide-dominated environments. This understanding is crucial to predict the response of land reclamation-impacted coastal systems to accelerated sea level rise.