Long term changes to US Estuaries: A survey

Abstract:

Many locally-based studies have pointed to the effects of changed estuary geometry and altered fluvial and oceanic conditions on tides, currents, and transport. Some locations show a doubling or more of tidal range, while other locations show only slight or no change. However, few studies have surveyed or compared/contrasted more than a few estuaries, or assessed how prevalent changes are. In this presentation we use archival maps and reports from dozens of locations to first ascertain a basic question: how much have inlet widths and depths changed over the past 150 years, and how much have shipping channel depths been dredged, in both large and small harbors? To the extent possible, wetland loss is also surveyed. In addition, we use long-term river flow gauges from 20+ locations to estimate seasonal and long-term changes to river flow. Together, the changed geometry and river flow alter physical processes within each system, as observed for example in the inlet choking number or the friction number. The effects of alterations are elucidated by comparing/contrasting hundreds of tidal range estimates from the 19^th century and the present. This process identifies some estuaries (such as the Saint Johns River and Savannah River) in which large tidal changes have been unrecognized, and produces dynamical questions for further research. Similarly, we use water temperature measurements from ~15 estuary locations from both the 1880s and today to show that temperatures are generally increasing, in a seasonally dependent way. We conclude that anthropogenic changes of estuaries are ubiquitous, with effects that can be understood by investigating underlying physical processes.