The replacement of the George Massey Tunnel with a bridge could have a negative impact on the irrigation water quality for Delta farmers.
Potential changes in the hydrology of the Fraser River with a new bridge is one of the issues local farmers want examined.
A study is getting underway following concerns raised by the Delta Farmers' Institute. The group is wondering whether the increased depth and length of dredging will have the same effect as removing a dam that currently restricts the intrusion of the "salt wedge" up the Fraser River.
Salt wedges occur in estuaries like the Fraser River delta where ocean water meets fresh water. The term salt wedge refers to the denser ocean salt water that pushes up the estuary. Some mixing with fresh river water occurs but in general the denser salt water tends to remain on the bottom of the river and fresh river water flows on top of the saline water.
Farmers say there's a great deal of uncertainty when it comes to the future of the agricultural water supply in the lower Fraser River.
"Concerns about changing salinity levels in the Fraser River are not limited to Delta alone. Many farms in Richmond also rely on the south arm of the Fraser River to provide irrigation water for agriculture. For some farmers it is their only source of water," DFI vicepresident Clarence De Boer stated in a letter to Delta requesting participation and funding for the study.
Delta's irrigation water intakes in the Fraser River are affected by the migration of the salt wedge up the river when river flows are reduced, but the DFI notes the current understanding of salinity behaviour in the river is incomplete.
There's a need for a better understanding of the salt wedge behaviour throughout the entire river channel and particularly as it relates to the deeper portions, according to a Delta staff report that concurred with the DFI's concern.
The Delta agricultural community is concerned that allowing the salt water wedge to move further upstream will affect water quality at the 80th Street intake.
Delta council has agreed to contribute $10,000 toward the $75,000 analysis.
Noting Delta has already been working with farmers to monitor salinity in the irrigation water, Coun. Ian Paton said Delta's upgraded irrigation system so far hasn't had much in the way of problems with the salt content. However, Westham Island does not have the benefit of that irrigation system, so it depends on flood gates which feed the area's ditch system, resulting in a higher chance of salt water.
"This time of year, the farmers basically closed down these gates, they don't want any water coming in from the Fraser River because it just has too much salt content in it," Paton said.
