Setbacks from the crests of slopes along the North Saskatchewan River, Alberta

Abstract

Setbacks from the crests of slopes along the North Saskatchewan River valley between Edmonton and Fort Saskatchewan can be estimated from the ultimate angle of the slope and the rate of lateral river erosion. The ultimate slope angle depends on the slope stratigraphy and the position of the water table in the slope. Three slopes, in overburden, with a bedrock base and dominantly in bedrock, typically having groundwater tables at respectively the toe of the slope, halfway up the slope, and at the lower quarter of the slope height, are studied. Theoretical estimates of the ultimate slope angle in each type, from infinite slope analysis and from charts, agree with observations of the inclinations of abandoned slopes along the river valley. The procedure recommended presents a rational estimation of setback distances without extensive site investigations. Key words: setback, slope, ultimate angle, abandoned slopes, river erosion.