Expect more erosion into reservoir, study says
ALLABEN — Bigger storms created by global warming are going to make it increasingly difficult for the New York City Department of Environmental Protection to keep its water supply clean, according to a study by a Yale University doctoral student.
The assessment was made in a Yale study that compared the impact from Tropical Storm Irene to previous weather events that sent eroded material down the Upper Esopus Creek.
“When there is an extreme event, which we are assuming to see more often, you have unlimited amount of organic material that’s coming into the reservoir,” Yale doctoral student Bryan Yoon said. “It is so much organic matter that’s coming out of the (watershed) system that we didn’t even expect the impact.”
YOON SAID the study had already begun in February 2011 and was intended to review the correlation between the amount of turbidity in the Ashokan Reservoir and city production of harmful chemicals from treatment processing.
“I was just going out to the watershed every other week or every time it was raining to get samples to test them and then we had Hurricane Irene which changed the focus of the research because sometimes you have something that’s so big that you didn’t expect your study to be able to capture that kind of event,” he said.
YOON HAD been sampling water upstream of the Shandaken Tunnel at Allaben when the tropical storm dumped 11 inches of rain in the region in late August 2011.
“The reason why I was studying over there is that there is a portal that is bringing extra water from the Schoharie Reservoir and the water that’s coming from the portal is more turbid, it’s got more organic material in it,” he said. “So I wanted to focus on a part of the watershed that I can actually know where the water is coming from rather than water that’s mixed.”
Yoon said the tropical storm represented 17 percent of the average annual rainfall and gave the Ashokan Reservoir an amount of dissolved organic material that represented 43 percent of its annual average load.
“If you look at the amount of rain we got in the Catskills it is just unprecedented,” he said. “It’s the biggest precipitation event we got in about 200 years or longer possibly.”
Yoon said the study disproves theories that having a lot of rain would help offset the amount of turbidity carried in the creek.
“PEOPLE USED to think or the scientists used to think that there’s some much water that there’s going to be dilution and there wouldn’t be an increase in organic matter,” he said. “I’m saying no, if the extreme weather events happen you will have more and more organic matter coming into the reservoirs.”
Yoon said the study is only intended to show there will be more material going into the stream with large weather events and does not deal with the ability of city officials to treat water.
“I know people in New York City are working really hard to tackle these issues and they know how to treat their water much more than I do,” Yoon said. “They know what they need to do when there’s more organic matter coming into the stream.”