Flood maps · Ottawa

Ottawa flood maps: who makes them, what the river’s dams can and cannot do, and what the maps miss

Ottawa has two flood problems and they are mapped differently. The river one is the Ottawa River and the Rideau, and the spring of 2019 made it the one people remember. The other is a summer storm that overloads a creek or the sewers in a neighbourhood nowhere near a big river — which is what the Province activated disaster assistance for in parts of Ottawa after July 1, 2026.

This page sets out who makes Ottawa’s flood maps, what the conservation authority publishes for the city’s most vulnerable neighbourhoods, what the Province’s review of the 2019 floods said about mapping and about the Ottawa River’s dams, what the flood warnings mean, and what a flood map does and does not tell you about insurance and disaster assistance. The general guide to reading a flood map is on the flood maps page.

Who makes Ottawa’s flood maps

Ontario’s flood standard is set provincially, but the maps are local. The Province says most flood maps in Ontario are made by municipalities and conservation authorities. The authority that maps your street depends on which river or creek drains it; the Rideau Valley Conservation Authority publishes the neighbourhood maps below for parts of the City of Ottawa. The City’s own flood plain mapping pages could not be loaded for this page, so this site does not describe them.

Two things follow for a homeowner. First, the regulatory flood line on a map is a planning standard, not a forecast: it shows the land a defined flood would cover. Second, work in an area the conservation authority regulates may need a permit under Section 28 of the Conservation Authorities Act; the RVCA takes those applications in its watershed.

The RVCA’s neighbourhood maps

These are the most useful maps for an Ottawa homeowner in a flood-prone area, because they show patterns for both a minor and a major event rather than a single line. A minor-event map tells you what to expect in an ordinary bad spring; the major-event map tells you what the regulatory flood would do. If your street is on one, the RVCA’s advice is to make a plan before you need it:

The Ottawa River, and what the dams can do

This is the single most useful sentence in the 2019 review for anyone on the Ottawa River. The river has dams, and a board that coordinates them, and its name suggests it regulates floods. The Province’s Special Advisor on Flooding concluded that the name misleads: the reservoirs were built to generate power and do not have the storage to hold back a large spring flood. In a year like 2019, the water arrives whatever the board does. The review recommended dropping “Regulation” from its title, reviewing its almost 40-year-old founding agreement, and publishing its flood-operations data openly.

What the 2019 review said about mapping

The review’s mapping recommendations amount to a diagnosis: Ontario’s maps are made by many bodies, to guidelines that pre-date current technology, with no single custodian and no standing funding to keep them current. For the Ottawa River specifically, it tied updates to federal funding and to cooperation between Ontario and Quebec, because the river is the border. The federal government has since put $164.2 million into its flood mapping programme for 2024 to 2028.

What the flood messages mean

The RVCA offers flood forecasting alerts by email. If your property is on one of its neighbourhood maps, subscribing costs nothing and buys you time.

The flooding a river map does not show

That sentence is from Toronto’s conservation authority, but it describes every riverine flood map in Ontario, Ottawa’s included. A map of where a river goes says nothing about sewers that back up in a summer cloudburst. In Ottawa that risk is managed by the City’s Residential Protective Plumbing Program, which pays towards backwater valves and sump pumps:

The details are on the Ottawa page.

Insurance and disaster assistance

DRAO is not insurance and does not replace it. It pays for essentials, after insurance, at 90 per cent of eligible costs, and it treats sewer backup as insurable except for low-income households. Overland flood cover — the endorsement for river and surface water — is optional and priced by risk, which is where the flood map comes back in. The full rules are on DRAO and overland water coverage.

Questions people actually ask

Where to read next

• How to read any flood map
• Ottawa’s protective plumbing rebates
• DRAO
• Overland water coverage
• Edmonton flood maps