INFLUENCE OF BATHYMETRIC CHANGES ON HYDRODYNAMICS AND SALT INTRUSION IN ESTUARINE SYSTEM¹

Abstract

A vertical (laterally integrated) two‐dimensional numerical model has been applied to study the hydrodynamic characteristics and salt water intrusion in the Tanshui River estuarine system. The cross‐sectional profiles measured in 1978 and 1994 are schematized for model simulations. Detailed model calibration and verification have been conducted with water surface elevations, tidal current, salinity distributions, and residual velocities measured. The overall performance of the model is in qualitative agreement with the available field data. The model was then used to study how hydrodynamics and salt water intrusion change in response to changes in bathymetry. The model simulations indicate that more tidal energy propagates into the estuarine system in 1994 because of the substantial increase in river cross‐sections. The limits of salt intrusion in 1994 extended farther inland than those in 1978. On the other hand, the extent of mangrove wetland in the lower estuary has increased over the past 20 years and is likely a result of the increased salinity in the estuary.

Restore or retreat? saltwater intrusion and water management in coastal wetlands

“…For example, mangrove encroachment was observed after dredging the Tanshui River in Taiwan, and substantial changes to tidal range and SWI occurred after dredging in the Pearl River in China (Liu et al. , Yuan and Zhu ). In addition, many rivers have been straightened to improve transportation and flood control (Bechtol and Laurian ).…”

“…Optimization modeling was also applied to allocate surface and groundwater resources to balance social, economic, and environmental demands in the Pearl River Delta in China, which is experiencing SWI (Liu et al. ). The model developed by these authors could be used to propose modified surface water withdrawals during the dry season to limit SWI.…”

Untangling complex shallow groundwater dynamics in the floodplain wetlands of a southeastern U.S. coastal river

“…is often difficult because of complex interactions between surface water, groundwater, and porewater in a variably saturated matrix with heterogeneous soils, vegetation, and topography. For example, depth, duration, frequency, and salinity of floodplain inundation are functions of tidal range; distance from the ocean; distance from the river channel; local elevation (microtopography); volume of freshwater flow; and the direction, volume, and salinity of groundwater fluxes [e.g., Wang, 1988;Liu et al, 2001;Melloul and Goldenberg, 1997], as well as soil hydraulic characteristics and floodplain vegetation properties.…”

Linking River, Floodplain, and Vadose Zone Hydrology to Improve Restoration of a Coastal River Affected by Saltwater Intrusion

“…Coastal zones also provide at least half of all global ecological services (Costanza et al, 1997) and generate billions of dollars annually from fisheries, recreation, and tourism (Niemi et al, 2004). Environmental pressures facing coastal wetlands come from natural and anthropogenic sources, and these stressors often overlap and have synergistic effects (McCarthy et al, 2001). Saltwater intrusion is an example of such a pressure.…”

“…Estimated sea level rise alone has the potential to eliminate as much as 22% of the world's coastal wetlands by 2100 (Nicholls et al, 1999), although regional impacts would vary (Michener et al, 1997). Anthropogenic drivers of saltwater intrusion include land drainage (e.g., Holman and Hiscock, 1998); pumping of coastal freshwater aquifers (e.g., Sadeg and Karahanogulu, 2001); reduction in freshwater discharge from dam construction, water withdrawals, and other water diversions (e.g., Johnson, 1997); and hydraulic structures and land use changes within watersheds (e.g., Wang, 1988;Liu et al, 2001;Bechtol and Laurian, 2005). When anthropogenic and natural drivers act together, saltwater intrusion can lead to rapid and catastrophic loss of coastal wetlands (Wanless, 1989).…”