PI-39 Commonly Asked Questions About Utah's Great Salt Lake and Ancient Lake Bonneville

One of the two 15-foot-wide by 20-foot-deep culverts in the rock-fill portion of the causeway. Photo taken during low lake level (1960-1962).

How has the railroad causeway affected the Great Salt Lake?

The rock-fill causeway has had two major effects on the Great Salt Lake, both related to restricted circulation of water between the north and south arms: (1) the south arm has maintained a higher water level than the north, and (2), the north arm has become saltier than the south. 

Great Salt Lake, Bonneville Salt Flats, and elements of the state's two flood-control programs: the causeway breach (1984) and the West Desert Pumping Project (1987).

These conditions persist despite two 15-foot-wide by 20-foot-deep open culverts that were built into the causeway to facilitate water and boat movement between the two arms, and despite a 300-foot-wide breach (opening) which was cut through the causeway near Lakeside in 1984 as a flood-control measure.

The level of the south arm is higher than the north arm because river water enters the south arm at a faster rate than lake water can move  northward through the causeway and its openings.

Since the construction of the solid-fill causeway, the salt content (salinity) of the north arm has become greater than the south arm.  This is due to the following: (1) the south arm receives nearly all of the freshwater tributary inflow to the lake, and (2) the north arm is fed mainly by south arm salty water seeping through the causeway and flowing through the culverts and the breach opening. 

Currently, the north arm of the lake is near its salt-saturation point (24-26 percent) and is about twice as salty as the south arm (12-14 percent).