In the Western Scheldt estuary, like in many estuaries, safe navigation, flood protection, and ecological targets require a balanced and sustainable sediment management. A thorough understanding of the morphodynamic functioning of the estuary and its response to changes in hydrodynamics (natural sediment transport) and large-scale interventions is imperative. This paper presents a detailed overview of over 65 years of morphological changes and a comprehensive sediment budget of the Western Scheldt estuary that is based on analysis of a unique series of frequent bathymetric surveys and historical data on human–sediment interactions of dredging, dredge disposal and sand mining. Solving the sediment budget reveals an annual sediment import of 2.2 million m3. The highest sediment imports occurred between 1980–1994 and 2005–2020 (2.9 and 3.7 million m3/year). A 1.3 million m3/year net export prevailed between 1994 and 2005. Natural variations in the hydrodynamics (e.g., tidal asymmetry and amplification) and sediment transports cannot explain the derived temporal variations in sediment import rates. Anthropogenic activities play a dominant role. Capital dredging of the main navigation channel has led to channel deepening and significantly increased dredge and disposal volumes. Disposal on tidal flats and in the secondary channel leads to a long-term storage of sand and, consequently, a local increase in bed level and a sand deficit in the remainder of the system that results in increased sediment imports. Large-scale disposal in the western part of the estuary can (temporarily) reverse the sediment exchange between the estuary and its mouth area, as observed between 1994 and 2005. Apparently, large-scale anthropogenic reallocation of sediment by dredging and/or disposal as part of navigation channel improvement, sand mining or nourishment essentially influences the morphological development of the Western Scheldt estuary. This reveals responsibilities as well as opportunities of sediment management for the Western Scheldt and similar estuaries worldwide.

Tidal inlets and the associated ebb-tidal deltas can significantly impact the coastal sediment budget due to their ability to store or release large quantities of sand. Nearly 300 million m3 (mcm) of sediments were eroded from Texel Inlet's ebb-tidal delta and the adjacent coasts following the closure of the Zuiderzee in 1932. This erosion continues even today as a net loss of 77 mcm was observed between 1986 and 2015. To compensate, over 30 mcm of sand has been placed on the adjacent coastlines since 1990, making maintenance of these beaches the most intensive of the entire Dutch coastal system.

Highly frequent and detailed observations of both the hydrodynamics and morphodynamics of Texel Inlet have resulted in a unique dataset of this largest inlet of the Wadden Sea, providing an opportunity to investigate inlet sediment dynamics under the influence of anthropogenic pressure. By linking detailed measurements of bathymetric change to direct observations of processes we were able to unravel the various components that have contributed to the supply of sediment to the basin, and develop a four-stage conceptual model describing the multi-decadal adaptation of the ebb-tidal delta.

Prior to closure of the Zuiderzee a dynamic equilibrium state (stage 1) existed with a stable ebb-tidal delta. The largest morphological changes occurred in roughly the first 40 years since the closure, and were dominated by the rotation and scouring of large tidal channels and landward retreat of the Noorderhaaks ebb shoal (stage 2; adaptation). Between 1975 and 2001 the general layout of main channels and shoals was stable, but large sediment losses continued to occur (stage 3; equilibrium erosional state). Since 2001, the erosion rates have significantly reduced to 2 mcm a−1 (stage 4; stabilisation).

Twenty-five years of data on ‘Dynamic Preservation’ prove that sand nourishments are well capable of keeping the coastlines adjacent to the Texel Inlet in place. Moreover, the abundant supply of sediment may also have compensated for the sediment losses on the larger scale of the southern part of the ebb-tidal delta, resulting in a recent stabilisation of its volume. This response illustrates the potential benefits of Dynamic Preservation not only for coastline resilience but also on the larger scale of the inlet system. Such knowledge is essential for future preservation, management and maintenance of inlet systems in the scope of climate change and accelerated sea-level rise.

The estuaries in the SW Netherlands, a series of distributaries of the rivers Rhine, Meuse and Scheldt known as the Dutch Delta, have been engineered to a large extent as part of the Delta Project. The Voordelta, a coalescing system of the ebb-tidal deltas of these estuaries, extends c.10 km offshore and covers c.90 km of the coast. The complete or partial damming of the estuaries had an enormous impact on the ebb-tidal deltas. The strong reduction of the cross-shore directed tidal flow triggered a series of morphological changes that continue until today. This paper aims to give a concise overview of half a century of morphological changes and a sediment budget, both for the individual ebb-tidal deltas and the Voordelta as a whole, based on the analysis of a unique series of frequent bathymetric surveys. The well-monitored changes in the Voordelta, showing the differences in responses of the ebb-tidal deltas, provide clear insight into the underlying processes. Despite anthropogenic dominance, knowledge based on natural inlets can still explain the observed developments. Complete damming of the three northern estuaries Brielse Maas, Haringvliet and Grevelingen resulted in a regime shift, from mixed-energy to wave-dominated, and sediments are transported in landward and downdrift direction. This results in large morphodynamic changes – sediments are redistributed from the delta front landward – but small net volume changes – a 0.1–0.2 × 106 m3 a−1 increase in volume over the period 1965–2010 – since the dams block sediment transport into the estuaries. Sediment volume losses of 106 m3 a−1 are observed on the ebb-tidal delta of the partially closed Eastern Scheldt and still open Western Scheldt estuary. As a result of a reduction of the estuarine tide in the mouth of the Eastern Scheldt, the north–south-running North Sea tidal wave has gained impact on its ebb-tidal delta, which causes morphological adjustments and erosion of the Banjaard shoal area. Moreover, the Eastern Scheldt ebb-tidal delta delivers sediment to its neighbours. The stable ebb-tidal delta configuration in the Western Scheldt, despite major dredging activities, illustrates that these large inlet systems are robust and resilient to significant anthropogenic change, as long as the balance between the dominant hydrodynamic processes (tides and waves) does not alter significantly.