Keeping the Reserve in Reservoirs

Aerial photos of Falls Lake during the height of the 2007-08 drought show Raleigh’s primary reservoir reduced to rivulets amid expanses of cracked, dry earth. Dr. Sankar Arumugam, an assistant professor in the Department of Civil, Construction and Environmental Engineering (CCEE), says seasonal climate forecasts could help ensure that reservoirs like Falls Lake never drop to critically low levels in future droughts. The forecasts could provide an advance assessment of the risk of running dry, he says, leading to better management of water resources.

“We need to look at the sustainability of our resources as population continues to grow. ”

Arumugam and his hydroclimatology research group developed computer models to forecast stream flows in the Neuse River basin. Using climate and streamflow data from 1991 to 2005, they discovered significant correlations between known climate patterns, such as El Niño-Southern Oscillation in the Pacific and sea surface temperatures in the tropical Atlantic, and the amount of water flowing into Falls Lake. The pattern in the tropical Pacific in the past two years, for example, led to below-normal inflows in early 2008.

Three-month streamflow forecasts could help assess early in the season the probability that water flowing into a reservoir will be above or below normal, Arumugam says. That would help water managers plan for the sweltering summer months, when demand for water usually peaks. Reservoirs can hold more water than the level at which they’re considered “full,” so if a dry summer is likely, downstream releases could be reduced in the spring to keep more water in the reservoir, Arumugam says. “Don’t just manage the releases to maintain an optimal lake level,” he says. “Look at what you need to keep in the reservoir to get you into the fall.”

Arumugam began devising such risk management strategies as a researcher with the International Research Institute for Climate and Society (IRI) in New York before joining NC State. A joint venture between the National Oceanic and Atmospheric Administration and Columbia University, IRI works to reduce vulnerability to climate uncertainties in fields like water use, agriculture, and public health. “Analyzing climate variability and incorporating it in models helps reduce uncertainty,” he says, “and lets you be aware of the risk in your decisions.”

“Don’t just manage the releases to maintain an optimal lake level. Look at what you need to keep in the reservoir to get you into the fall.”

Together with the North Carolina State Climate Office in the College of Physical and Mathematical Sciences, Arumugam is now developing streamflow forecasts for river basins statewide. He is also working with CCEE colleague Dr. Ranji Ranjithan on a unified management strategy for the Research Triangle region’s water resources, including Jordan Lake and Kerr Lake. “We need to look at the sustainability of our resources as population continues to grow,” Arumugam says. “It will help us allocate our water more efficiently.”

 

Dr. Sankar Arumugam says three-month forecasts of stream flows could help reservoir managers determine when to restrict downstream releases to ensure they have enough water to meet peak demand during the summer.

Falls Lake fell to record low levels during the 2007-08 drought, forcing Raleigh and nearby towns to implement water restrictions and to seek limits on the amount of water released into the Neuse River. Photo by The News & Observer.