Winnipeg’s riverbanks consist of a combination of lacustrine clay-rich soils and alluvial deposits of layered clays, silts and sands. Clay soils are generally weak in strength and strongly affect riverbank stability in Winnipeg.
Overview of Winnipeg’s Riverbanks
- Lacustrine clays were deposited in proglacial Lake Agassiz between 11,500 and 8,000 years ago.
- The Red River and its tributaries were formed when Lake Agassiz drained into Hudson Bay causing channels in the clay.
- Over the course of many years, flooding deposited layers of clays, silts and sand.
- Postglacial erosion of the river valleys in Winnipeg resulted in steep, high riverbanks that were prone to bank failure.
- Riverbank development and man-induced factors can contribute to bank failure.
- Clay soils dominate the outside bends of the City’s riverbanks while alluvial deposits are located along the inside bends. Straight and transition sections of the riverbanks are typically composed of a combination of the two types of soils with alluvial over lacustrine soil deposits.
Riverbank Detail
1. Lacustrine Clay Banks
- Generally weak in strength
- Failure-controlled movements
- Incorporate large sections of the bank
- Tendency for deep-seated failures (from 40 – 50 feet below the ground to more than 200 feet from the river’s edge)
- Soil groundwater and river hydraulic conditions affect bank stability
2. Alluvial over Lacustrine Banks
- Exhibit bank movements, including erosion and failure controlled
- Shallow and deep-seated failures
- Potential for significant loss of riverbank
3. Alluvial Banks
- Exhibit higher strengths and therefore maintain a steeper gradient
- Erosion controlled banks
- Movements confined to the erosive face of the bank
- Assessment of bank erosion affected by river hydraulics, wave and ice action, precipitation, and soil cover
|
|
Last update: January 31, 2012
* Top of Page
