Water levels in an estuary typically rise and fall with the daily tides, but they are also affected by the weather. Periods of drought or excessive rainfall affect the amount of fresh water entering the estuary from rivers or runoff, and can easily change the physical, chemical and biological conditions in an estuary.
Depending on the source of pollution, the levels of toxins, bacteria, or nutrients may rise as runoff increases due to heavy rainfall. The concentration of dissolved and suspended materials in the water, or turbidity, may increase with runoff due to storms, or during periods of drought when there is a low volume of water in the estuary and winds and waves stir up the muddy bottom at low tide. In general, when water levels are too high or too low in an estuary for prolonged periods of time, the health of the estuary, and the plants and animals that live in it, are vulnerable to damage.
The NERRS SWMP uses electronic depth gauges to determine estuarine water levels throughout the year. To verify the accuracy of these sophisticated devices, researchers often go out and take measurements the old-fashioned way, by hand. (Photo: Hudson River NERRS site)