I don't need to tell anyone that it's been a wet summer. Cumulative rainfall measurements at HRECOS stations are two to four times greater this year compared to last year. At the Schodack Island station, for example, we've measured 18.23 inches of rainfall since May of 2009 compared to 4.72 inches measured for the same time period last year.
This rain has impacted the Hudson River in multiple ways. For Part I of this investigation, we will explore how this wet summer has impacted the turbidity of the Hudson River.
Turbidity is a measurement of water clarity. At the HRECOS stations, our instruments shine a laser on the passing water and measure how much light is scattered by the suspended particles. The results are reported in nephalometric turbidity units (NTUs). Water with lots of reflective particles such as sediment, plankton, or solid waste, will have a high turbidity reading.For the three northern HRECOS stations, cumulative turbidity levels have been two to six times higher this year compared to last year. This is most likely caused by this year's increased rainfall.
During storm events, particles are transported to the Hudson River by its tributaries. The Hudson River watershed is roughly 13,000 square miles and is rich in materials left behind by receding glaciers. As water washes across this landscape, through streams and rivers, it collects the glacial material and other particles and transports them to the river. You've probably seen this transport in progress as chocolaty brown streams cascade beside the highway. In addition to sediment transport, the turbulent currents also churn up sediment from the river bottom. The end result is an increase in turbidity in response to storm events.
Rainfall this summer has both been more frequent and more plentiful. This has resulted in cumulative turbidity levels at Schodack Island, Tivoli Bays, and Norrie Point stations that are two to six times higher than last year.
In contrast, the southern HRECOS stations including Piermont and George Washington Bridge do not have higher cumulative turbidity levels compared to last year. This is likely because turbidity levels at the southern stations are influenced by marine sediments pushed in by the salt wedge.
The Army Corps of Engineers spends more than thirty million dollars every year removing sediment from New York / New Jersey Harbor. For this reason, it is important to understand the sources of sediment to the Hudson River. The USGS has partnered with HRECOS for this purpose. To view the USGS sediment flux project page, visit: http://ny.water.usgs.gov/projects/poused/index.html.
The next time it rains, open your computer and observe the real time impact on the Hudson River by clicking Current Conditions in the menu to your left.