shallowing

Shallowing is the process by which the depth of a water body or other feature becomes more shallow. In hydrology, geomorphology, and related disciplines, it describes a trend toward reduced depth in lakes, rivers, estuaries, or coastal shelves. Shallowing can result from sediment deposition that builds up the bed, progradation of shorelines, or tectonic uplift that raises land relative to the water surface. It may also follow changes in water inflow, climate, or land use that reduce the transport or removal of sediments.

Causes and contexts: In freshwater systems, sediment input from rivers, delta growth, and human activities such as dam building can promote shallowing by trapping sediments in reservoirs or upstream reaches. In coastal and estuarine environments, long-term sediment supply and littoral drift can shoal bays and inlets. Biological processes such as plant growth and biofouling can also contribute by trapping sediments and stabilizing sites.

Implications: Shallowing can reduce habitat complexity, increase water temperature, alter light penetration, and degrade habitats used by fish for spawning or refuge. It can affect nutrient cycling, evaporation rates, and the availability of navigable depth for boats, pumps, and infrastructure.

Measurement and monitoring: Depth changes are tracked with bathymetric surveys, depth soundings, sonar mapping, and, for large basins, satellite altimetry and time-series shoreline/topography data.

See also: shallowness, bathymetry, sedimentation.