Riverine flooding occurs when water levels in rivers, streams, lakes, or other watercourses rise above their banks and inundate surrounding lands.

Flooding is a natural process that helps maintain healthy rivers and floodplain ecosystems. However, when development occurs within flood-prone areas, flooding can threaten public safety and damage homes, roads, infrastructure, and agricultural lands.

Within SNC's jurisdiction, flooding is commonly associated with spring snowmelt, heavy rainfall, and ice jams. Flooding can also occur during other seasons following prolonged precipitation or intense storm events.

Erosion is the natural process through which soil, sediment, and rock are worn away and transported by water, ice, wind, or gravity.

Along rivers and streams, erosion can gradually change the shape and location of channels, undercut streambanks, and contribute to slope failure.

Although erosion is a natural process, its effects can be accelerated by flooding, intense rainfall, changes in land use, vegetation removal, and human activities.

Erosion hazards generally occur along river valleys, streambanks, and shorelines where land may become unstable or erode over time.

Sensitive marine clays are fine-grained soil deposits that formed thousands of years ago when portions of Eastern Ontario were covered by the Champlain Sea.

These deposits, commonly referred to as Leda clay, are widespread throughout parts of Eastern Ontario, including areas within SNC's jurisdiction.

Sensitive marine clays can lose significant strength when disturbed, making certain deposits susceptible to slope failures and landslides.

Landslides may be triggered or influenced by several factors, including:

• • • Erosion at the base of riverbanks and valley slopes.
    • Increased groundwater levels and changes in drainage conditions.
    • Heavy rainfall and rapid snowmelt.
    • Excavation, construction, or the placement of additional loads near slopes.
    • Natural disturbances, including seismic activity.

In some circumstances, landslides involving highly sensitive marine clays can extend beyond the original slope failure, affecting areas farther inland. These events are known as retrogressive landslides.

Organic deposits are soils made up of accumulated and partially decomposed plant material. They are commonly found in wetlands, peatlands, and other low-lying areas. These soils, including peat, can create hazards because they are soft, unstable, and prone to settling.

Karstic limestone forms when water gradually dissolves limestone bedrock, creating underground cavities and openings. These areas can pose hazards where the ground becomes unstable or collapses, forming sinkholes.

Dynamic beaches are areas along shorelines made up of sand, gravel, and other loose materials that are constantly moved and reshaped by waves, wind, currents, and changing water levels. These areas can create hazards due to erosion, flooding, and shifting shorelines.