Groundwater major contributor to alpine watersheds: study
By Daniel Katz, Bow Valley Crag & Canyon
Monday, June 8, 2015 1:17:47 MDT PM
A team of scientists from the University of Calgary is conducting work to improve our understanding of how climate change affects river and stream flows in the mountains.
Since 2004, the scientists have been studying the snowpack and glacial melt around Lake O’Hara in Yoho National Park. The purpose of their research has been to understand the headwater and groundwater processes in alpine watersheds.
They discovered that, despite popular thinking that melting snow and ice feed directly into bodies of water in alpine environments, Lake O’Hara is actually between 30 to 70% fed by groundwater that has been stored over a long period of time in the soil, soaking up all the rain and meltwater like a sponge.
“So what happens is meltwater becomes groundwater immediately upon release from the snowpack, and then groundwater travels through the underground environment and eventually pops up into lakes and rivers,” said project co-ordinator Dr. Masaki Hayashi, professor of physical hydrology at the University of Calgary and a pre-eminent expert in the study of groundwater.
“That was unexpected because before we started our study, people including myself thought in the mountains you have lots of bedrock and there’s not a whole lot of capacity to store groundwater, but it turns out there’s a large capacity.”
The researchers also found that glaciers only directly contribute about 3% of water to the lake, with a slightly higher percentage in July and August. The recession of glaciers that is associated with climate change does not have such a direct contribution to water flows as previously thought.
“What we’re finding is the story is not that simple because with groundwater storage there is a capacity in the natural system to buffer the effects of climate warming,” said Hayashi. “People are worrying about snow melt coming early and there’s no water left in August, but that’s not going to happen because groundwater will continue to provide a flow of water in the rivers in August and September even until the winter.”
Groundwater was one of the main causes of flooding in Canmore during the 2013 floods, where it bled through the river berms and soaked into the soil, eventually leaking out onto the streets and in basements causing major damage.
Using water-level recorders, weather stations, ground wells, stream-flow monitoring stations and geophysical imaging, the scientists accumulated and correlated their data to make measurements on the water input and output of Lake O’Hara and and its headwaters and tributaries.
Climate change has been one of the factors blamed for the severe drought currently afflicting California, where record-breaking high temperatures and a smaller-than-average snowpack have left reservoirs running dry.
Over the longer term, climate change will have a profound effect on low-flows in the Rockies due to the evaporation of groundwater and snow melt, according Dr. John Pomeroy, Director of the Centre for Hydrology at the University of Saskatchewan.
“When we look at the Bow River over the last 100 years, the August stream flows have dropped by 25%,” he said. “It’s not that there’s less rain in August, it’s two things; 1) the glaciers are not as extensive as they were 100 years ago so glacier melt is a smaller contribution; But it also means that groundwater feeds into the river must be smaller as well.”
Low-flows can cause issues for municipalities at lower ends of the watershed, according to Pomeroy.
“If the river gets too low, in Canmore and Banff it’s not too bad because we’re at the top of the watershed. But further down you’ll get lower flows and it could cause restrictions on irrigation sometimes, or restrictions on municipal use, or lawn-watering, car washing, stuff like that.”
Hayashi’s work is critically important in helping scientists understand the amount of water available under drought conditions that may occur in the future, and also to mitigate damage caused by heavy rains that may lead to flooding, according to Pomeroy.