The occurrence of floods is influenced by natural factors (weather, terrain, vegetation, soils) and human activities. Floods can result in physical devastation, perils to human safety, threats to human health from contamination of water and the spread of water-borne diseases, detrimental effects on ecosystems, and severe economic losses to individuals and society.

There are two main causes of flooding, the first cause presented below is coastal flooding with storm surge playing a major role, and the second is inland flooding with stormwater runoff, snowmelt, and ice jamming playing key roles.

Coastal Flooding

  • Storm surge is a temporary increase in sea level due to incoming storms and strong winds.
  • Storm surges can occur during low or high tides.
  • During a storm surge, waves can wash over lands that do not usually experience wave action.

Inland Flooding

  • Inland flooding includes open-water floods from regional moderate-intensity rainfall and snowmelt, local floods from inadequate storm-water drainage or high water tables, flash floods from rapid watershed response to high-intensity precipitation events, flooding because of full or partial flow obstruction (e.g., ice jams), and surges owing to failure of upstream flow obstructions.
  • Inland flooding from stormwater runoff occurs when heavy rainfall creates large volumes of water that overwhelm drainage networks (culverts, etc.) that are to small to handle the flush of water.

Regional Variances

In Nova Scotia, inland flooding can be caused by torrential rainfalls, sudden thaws, and failure of infrastructure. Flood-plain areas include those along the Musquodoboit River, the Sackville and Little Sackville Rivers, East River (Pictou), Antigonish-area rivers, and Truro-area rivers.

In Prince Edward Island, inland flooding is primarily the result of heavy precipitation, often as a result of extra-tropical storms (remnants of hurricanes).

In New Brunswick, inland flooding is primarily the result of sudden heavy rain or rain-on-snow events, ice jamming, or a combination of these factors. The areas most prone to inland flooding (in terms of flood area and potential flood severity) are along the Saint John River from Fredericton to Lower Jemseg, the Kennebecasis River (and tributaries) from the Sussex area to Hampton, and Marsh Creek in the City of Saint John; past flooding events have occurred along many rivers and streams throughout the province.

Looking for regional specific flood-risk mapping? Please explore below:

A coastal scene with cliffs in the midground and background. Text above reads "New Brunswick", and there is a map of NB in the right of the image.
An oceanfront city. Text at the top reads "Newfoundland and Labrador" and there is a map of NL in the left of the image.
A lighthouse and beach in front of an ocean sunset. Text above reads "Prince Edward Island", and there is a map of PEI at the top of the image.
A photo of the Cabot Trail, Cape Breton, Nova Scotia. The words "Nova Scotia" are displayed across the top and are centred. A green graphic of the province is on the centre right of the image.