Capital works projects, particularly the modification of coastal rivers, are becoming increasingly significant to economic activities worldwide as a response to climate-driven changes and urbanization. The benefits of channel modification projects can be realized quickly, but the altered movement of sediments in the river channel can lead to unintended morphologic changes decades later. An example of this is the closure of the San Bernard River mouth, located on the central coast of Texas, which was clogged by sediments in the 1990s as a result of two major projects in the area: the diversion of the Brazos River channel (1929) and the construction of the Gulf Intracoastal Waterway (GIWW) (1940s). The objective of this study was to document the delayed geomorphic response to the projects using historical aerial imagery and provide a snapshot of flow pathways in the area using measurements collected in situ. Results showed that the GIWW was the main conduit for river flow as it bisects the San Bernard 2 km inland of its river mouth, reducing discharge in the terminal limb of the river. Due to reduced flow, the river mouth became clogged with wave-transported sediment supplied the Brazos River which had been diverted to within 6 km of the San Bernard. With no connection to the sea, altered sediment and flow pathways have led to numerous hazards and costly corrective dredging projects. To optimize the cost-effectiveness of channel modification projects their long-term impact must be considered as managers continue to adapt to ever-changing coastal zones.

Arctic continental shelves, including the Alaskan Beaufort Shelf (ABS), are experiencing declines in sea ice coverage leading to increasingly energetic sea states and coastal erosion. In this study we investigated the morphologic response of the ABS to increasing wave energy, and how shelf profile adjustments modify wave energy propagating toward the coast. We developed a 2D cross‐shelf morphodynamic model using Delft3D and tested shelf response to a present‐day wave climate and a future Arctic wave climate projected under the RCP8.5 climate‐change scenario. Simulations lasting 1000 years were conducted for relatively steep (Flaxman Island, AK, slope 0.0008) and flat (Harrison Bay, AK, slope 0.0003) cross‐shelf profiles. We found that morphologic evolution and regulation of future waves depends primarily on existing shelf morphology. On the steeper profile, RCP 8.5 waves drove sediment erosion at 0–15 m water depth and redeposition at 15–30 m water depth. Over 1000 years, this redistribution of sediment from the inner to middle shelf resulted in a 7.6% reduction in wave heights at the 2 m isobath. This morphologic adjustment represented a regulatory feedback in which shallowing of the middle shelf led to attenuation of waves reaching the inner shelf. In contrast, effective wave attenuation across the flatter and wider Harrison Bay section limited cross‐shelf transport and morphologic change under both wave climates. Together our results suggest that coastal changes in response to the growing Arctic wave climate may be dependent on shelf morphology, and even mitigated in some regions by morphologic adjustment.