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The general increase of human activities, including the exploitation of the hydraulic and sediment resources of rivers, has caused extensive coastal erosion throughout the world, especially during the last 150 years or so. The true costs and impacts of this erosion have not been reflected in the price of providing commodities such as sand and gravel. These impacts and their estimated costs are presented using information from the states of Washington, Oregon, and California on the Pacific Coast of the United States of America.

The coastal erosion causes and their relative importance are site specific, changing from place to place. In the Portuguese Northwest coast, namely between Douro River and Nazaré, coastal erosion is mainly due to sediment supply reduction from Douro River. The present study analyzed the anthropogenic impacts on the river, identifying the type and time history of Human actions, the flow changes and the impact on the sediment transport along the years. Numerical formulations of sediment transport estimation allow defining the relative importance of the different interventions on the Douro River and its basin. The major importance of the dams constructed in the Douro River basin led to laboratory works on a hydraulic flume, evidencing the sediment transport reduction related with the lower flow velocities caused by the reservoirs of the dams on the upstream side.

Four inlets (Johns Pass and Blind Pass; and New Pass and Big Sarasota Pass) in two multi-inlet systems along the West-central Florida coast were studied. Johns Pass, New Pass, and Blind Pass are dredged every 4-9 years, whereas Big Sarasota Pass has never been dredged. The goal of this study was to investigate the morphodynamics of the four inlets and the influences of channel dredging on the flow patterns over the ebb tidal delta and sediment bypassing. Time-series aerial photographs and bathymetric maps starting from the 1920s were analyzed to assess the pathways of sand bypassing and morphodynamics at the inlets. The Coastal Modeling System (CMS), computing wave, current, sediment transport, and morphology change of tidal inlets, was applied and reproduced the observed medium-term morphology changes. CMS is then used to investigate influences of channel dredging on inlet morphodynamics.