Gravel mining to reduce flood threats in the lower Fraser River has long been controversial because of the impact it has on fish habitat, with heavy equipment destroying spawning beds and refuge areas used by young salmon.
The provincial government has justified allowing contractors to "scalp" gravel bars by saying the practice lowers the river bed in areas prone to floods, arguing in effect that if you can save homes from being washed away, it is worth whatever collateral damage is done to salmon habitat.
But a new report by Michael Church, a world expert in geomorphology and hydrology, should give the government reason to rethink its safety-first strategy.
Mr. Church, a professor emeritus in the department of geology at the University of British Columbia, says rivers don't operate as simply as they appear to on the surface.
And mining the Fraser for gravel, he states in a paper being released this week, doesn't help prevent floods at all.
"It is claimed that gravel accumulation in the reach of the Fraser River between Laidlaw and Sumas Mountain is causing water levels to rise, hence increasing flood hazard in the reach," he writes. "Gravel certainly does accumulate in the reach. But the real concern is water level, and evidence indicates that channel alignment, not gravel accumulation is the main control of water level along the river."
Mr. Church writes that "scalping sediment from bar tops … has minimal effect on water conveyance and water levels."
But while cutting the tops off the bars doesn't reduce flooding, it does speed up the water flowing over the bars – and that is bad news for the small fish that rely on those areas for shelter during spring freshets.
"These [bars] are the 'escape' areas used by fish to avoid the high flood velocities of the main channel. The current method of sediment excavation reduces the area of escape terrain, while not significantly enhancing water conveyance," writes Mr. Church.
He says that some gravel removal might be beneficial, but in limited amounts in selected areas, where the hydrology of the river has been carefully studied. And he is concerned that the annual mining going on currently is taking out gravel faster than it can be replaced by new material washing downstream.
"The general rate of gravel accumulation is slow and does not justify regular gravel mining," he concludes.
In other words, Mr. Church has found that the quality of fish habitat is steadily being degraded in the lower Fraser by gravel mining – without improving flood controls.
That doesn't make much sense, says Mark Angelo, chair emeritus of the River Institute at the B.C. Institute of Technology.
"I think it's a really important study," said Mr. Angelo.
Mr. Angelo, one of the founders of an environmental initiative known as the Heart of the Fraser, said Mr. Church was commissioned to do the study to get an expert's opinion on the gravel-mining issue.
"We asked him to prepare this report because we wanted a scientific, objective analysis of the issues on the lower Fraser," said Mr. Angelo. "What he's telling us is that focusing on gravel extraction for flood control is too simplistic an approach. That's not the way to go."
He said a comprehensive management plan is needed for the lower Fraser, to ensure that existing habitat isn't further degraded.
"This river is a jewel. It's an Eden in our midst and we really need to do a better job of managing it," he said.
Mr. Angelo said his group will be circulating the report to all levels of government, hoping to end gravel mining in the Fraser.