PITTSBURGH – Snowfall turns reservoirs into wintery landscapes throughout the Pittsburgh District, with park rangers inviting visitors to build snow persons and venture into their trails for cross-country ski trips.
The snow offers immediate reservoir-recreational activities for those who love winter, but another benefit of snow extends well beyond the cold season.
“Snowpack acts as a sort of battery, storing water that eventually raises reservoir levels in the late winter and spring,” said Carl Nim, a biologist who works for the Water Quality section of the U.S. Army Corps of Engineers Pittsburgh District.
The upper Allegheny River area receives a snowpack of 12 to 24 inches each year, equivalent to one to two inches of rainfall.
The Pittsburgh District manages the land and water levels of 16 reservoirs. Dam operators lower the pool as winter approaches, and they allow water levels to rise as reservoirs prepare for summer. Releasing water is easy because each reservoir has a gated dam that opens, but filling the reservoirs relies on the weather.
“There is no spicket or a faucet we can turn on to refill our reservoirs. We use the snowmelt and spring rain to build from winter pool to summer pool,” said Megan Gottlieb, the Water Management unit lead for the Pittsburgh District.
Filling to summer pool is part of the annual plan to store water for later needs. Reservoirs help mitigate flood damage, improve water quality and support river navigation downstream.
Gottlieb estimates half of the water flowing into the reservoirs in the spring comes from snowpack, and the other half comes from rain and runoffs.
“Without a snowpack, it would delay our ability to fill to summer pool by at least a month or two,” Gottlieb said. “Or we run the risk of not reaching summer pool at all if it’s extremely dry.”
Nim, a biologist, said snowpack could benefit water quality as well. Cold water also holds more gases than warm water, meaning aquatic life benefits from its abundant dissolved oxygen.
“That’s definitely a water quality benefit since the reservoirs get filled with high dissolved oxygen water,” Nim said.
If snow melts slowly and gradually, it contributes to groundwater recharge without some of the harmful components that come with heavy rain, such as erosion and pollution. From a fishery perspective, snowmelts increase flow, and with warming weather, the change in temperature cues riverine fish for spawning.
“It’s a complex relationship between the correct amount of water flow and the correct water temperature that triggers fish spawning,” said Anthony Honick, a biologist with Water Quality.
However, a rapid snowmelt in developed areas could be damaging as well, Nim said. In developed areas, accumulated snow can store contaminants such as salt and metals entering the stream and impacting aquatic life and drinking water. The benefits of snow can vary from case to case based on context.
“Recharging the water table and keeping our streams and reservoirs full is probably the best benefit that snowpack has to offer,” Honick said.