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Flood Hazard Maps
Flood hazard maps define floodway and flood fringe areas for the 1:100 design flood and are typically used by communities for planning or to help make local land use and development decisions. Flood hazard maps can also illustrate additional information for communities to consider, including incremental areas at risk for floods larger than the 1:100 design flood, such as the 1:200 and 1:500 floods.
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Definitions
Flood Hazard Area – The flood hazard area is the area of land that will be flooded during the 1:100 design flood. The flood hazard area is typically divided into two main zones, the floodway and the flood fringe, and may include additional flood fringe sub-zones.
Floodway – When flood hazard maps are produced for the first time, the floodway typically represents the area of highest hazard where design flood flows are deepest, fastest, and most destructive. When flood hazard maps are updated, the new floodway might not change and can be the same size as the previous floodway even when the flood area gets larger, to help maintain regulatory certainty for landowners.
Flood Fringe – The flood fringe is the part of the flood hazard area outside of the floodway. When flood hazard maps are produced for the first time, water in the flood fringe is typically shallower and flows more slowly than in the floodway. Depending on when a flood study was conducted, the flood fringe can also include high hazard flood fringe, protected flood fringe, or overland flow (flood fringe) sub-zones.
High Hazard Flood Fringe – The high hazard flood fringe identifies areas within the flood fringe with deeper or faster moving water than the rest of the flood fringe. High hazard flood fringe areas may be more prevalent in communities with updated flood hazard maps, but they are included in flood hazard maps from all newer flood studies.
Overland Flow (Flood Fringe) – The overland flow (flood fringe) is a legacy flood fringe sub-zone that identifies areas where flooding is expected but where there is uncertainty about flood levels and water depths. These areas are only defined in a small number of older flood studies and will be phased out as those studies are updated and replaced.
Protected Flood Fringe – The protected flood fringe identifies areas that could be flooded if dedicated flood berms fail or do not work as designed during the 1:100 design flood. These areas are not expected to be flooded but reflect areas of residual risk. Protected areas can be different for floods smaller or larger than the design flood.
Design Flood – The minimum design flood standard in Alberta is the 1:100 flood, which is defined as a flood whose flow has a 1% chance of being equaled or exceeded in any year. The design flood can also reflect 1:100 ice jam flood levels if they are more severe than 1:100 open water flood levels or be based on a historical flood.
Additional Information
Flood maps are not available in all communities and flood risks exist in areas without flood mapping.
Contact Us
For more information about flood maps and the provincial Flood Hazard Identification Program please visit www.floodhazard.alberta.ca or email us at epa.flood@gov.ab.ca.
Flood Inundation Maps
Flood inundation maps show areas at risk for different sized floods, including ice jam floods in some communities, and identify areas protected by flood berms. Because they map a wide range of floods, they are most often used for emergency response planning and to inform local infrastructure design.
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Additional Information
Flood maps are not available in all communities and flood risks exist in areas without flood mapping.
Older flood studies include maps for as many as three flood scenarios, and newer studies include maps for as many as thirteen scenarios, from the 1:2 flood to the 1:1000 flood. In areas where a selected flood scenario is not available for all studies, other flood scenarios may be displayed. Flood maps in the same area may be available for smaller or larger floods.
Contact Us
For more information about flood maps and the provincial Flood Hazard Identification Program please visit www.floodhazard.alberta.ca or email us at epa.flood@gov.ab.ca.
Alluvial Fan
An alluvial fan is a landform that develops from the deposition of sediment and other debris from mountain creeks as they flow from steep terrain to flat, wide valleys. Common alluvial fan processes are debris flow, debris flood, and low debris flood.
Alluvial Fan Inventory
The inventory includes information and boundaries of alluvial fans that may indicate the presence of hazards to infrastructure and Albertans in the mountainous regions of the province. Hazard types include events such as debris flows and debris floods. The alluvial fans were mapped using a combination of satellite imagery, air photo data, publicly available imagery, and fieldwork. The inventory focuses on alluvial fans near populated areas and infrastructure. However, the inventory is not an exhaustive list of all alluvial fans in the mountainous area of Alberta. The alluvial fan boundaries are approximate as these landforms are dynamic and subject to rapid change.
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Definitions
Debris flow is a dense, fast-moving, channelized flow of water and debris, similar to wet concrete that poses a hazard to infrastructure and those living in mountainous environments.
Debris flood is a flood containing a moderate amount of debris. It is distinguished from a debris flow in that water controls the flow behaviour.
Low debris flood is a flood with a low amount of debris compared to debris floods. Low debris floods typically occur on creeks that are not steep.
Additional Information
For more information about alluvial fan flooding please visit https://www.alberta.ca/alluvial-fan-flooding
More information about alluvial fan terms, processes and hazards is available on the Alluvial fan terminologies, processes, and hazards
More information about alluvial fan inventory is available on the Alluvial fan inventory
Contact Us
Please email epa.flood@gov.ab.ca if you have any questions regarding alluvial fan flooding.
- -1 means the gradient is more than 3° and the creek is designated as mountain/steep creek
- 0 means the gradient is less or equal to 3° and the creek is not designated as mountain/steep creek
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Low:
- Dense vegetation, especially along the main stream channel flowing over the fan
- Previous channels, lobes or levees are difficult to discern from the surrounding fan environment
- Mature vegetation (coniferous forest greater than 50 years old) is dominant across the fan
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Moderate:
- Main stream channel may have sparse or inconsistent vegetation coverage
- Previous channels, lobes or levees are visible but may be partially or fully vegetated
- Immature forest vegetation (deciduous or mixedwood forest and shrubs less than 50 years old) is present in swaths across the fan, specifically near previous or active channels.
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High:
- Fresh deposits or eroded areas along and within the main stream channels flowing over the fan
- Clear distinction of previous channels, lobes or levees compared to adjacent fan environment
- Pioneer vegetation (lichen, moss, graminoids and shrubs less than 2 years old) or extents of bare sediment are present in and around the main channel of the fan
Watershed is the land area that drains rainfall and snowmelt to creeks, streams, and rivers, and eventually to outflow points such as reservoirs, lakes, bays, and the ocean.
Watershed length is the longest straight-line distance from the fan apex to the most distant point on the watershed boundary.
Watershed is the land area that drains rainfall and snowmelt to creeks, streams, and rivers, and eventually to outflow points such as reservoirs, lakes, bays, and the ocean.
Watershed relief is the difference between maximum and minimum elevation of a watershed.
Melton Ratio is a dimensionless ratio defined as the watershed relief divided by the square root of the watershed area. Melton ratio along with other watershed parameters generally defines the dominant process or hazard in a fan, for example, debris flows, debris floods and low debris flood.
Basin sediment supply condition presented as “supply-unlimited” and “supply-limited” basin.
- Supply-unlimited basins typically contain erodible deposits and/or landslides that continuously charge the channel with sediment and debris. These will trigger an event every time a hydro-climatic threshold is exceeded. Most debris-flood prone watersheds are supply-unlimited due to their alluvial beds in which large amounts of loose debris is stored.
- Supply-limited basins are typically rocky or heavily vegetated, with fewer sediment and debris sources for the main channel. These require time to accumulate debris before a rainfall and/or snowmelt event can trigger a debris flow.
Watershed is the land area that drains rainfall and snowmelt to creeks, streams, and rivers, and eventually to outflow points such as reservoirs, lakes, bays, and the ocean.
Watershed activity level is based on the recentness of channel deposits, evidence of erosion and whether the watershed sediment supply is limited or unlimited.
In debris flood dominated creeks:- Low: no recent channel deposits and mature tree growth to the active channel bank, the tree line is close to the watershed peak elevations. Supply-limited watershed, mostly bedrock controlled main channel with little alluvium present in the main channel or available to the few tributaries within the watershed.
- Moderate: deciduous tree bordering active channel, 1/3 of watershed above tree line, some active sediment sources along main channel. Supply unlimited watershed, main channel varies in width and is a mixed bedrock-alluvial channel.
- High: deciduous trees border the active channel, 2/3 of the watershed is above the tree line, numerous highly active sediment sources along main channel (i.e. debris slides, debris avalanches, raveling in lacustrine, glacio-fluvial, or morainal sediments. Supply unlimited watershed with a wide and debris-rich alluvial main channel.
- Low: poorly defined source areas; absence of fresh landslide scars, debris flows or channel deposits, low Active Area Ratio (a ratio of the total area of sediment sources to the total basin area), supply-limited watershed.
- Moderate: well-defined source areas; presence of some fresh landslide scars in soil or rock and some channel deposits, moderate Active Area Ratio, usually supply-limited watershed.
- High: numerous, well-defined, actively producing source areas in tributaries and along main channel; channel choked with debris, abundant fresh landslide scars in soils and rock, fresh channel deposits, high Active Area Ratio, supply-unlimited watershed.
Surface evidence for previous avulsions were based on vegetation evidence and the presence of relict channels, lobes, and deposits on the fan surface. These features can be detected, if present, on LiDAR hillshade; interpretations are less certain for areas without LiDAR coverage.
- Poor: relic channels (abandoned channels) on fan surface exist but are vegetated and difficult to discern.
- Moderate: relic channels on fan surface are clearly visible; swaths of young (<50 year) deciduous or coniferous vegetation exist in previous avulsion paths.
- Strong: obvious fresh avulsion paths exist, swaths of bare sediment or low (<2 year) pioneer vegetation exist on previous avulsion paths.
Channel confinement level is the degree to which stream channels are limited in their ability to move laterally. Channel confinement level is based on estimated bank height and the presence of areas where confinement could be reduced during an event, for example, channel bends, changes in channel gradient, and channel constrictions at road crossings.
- Low: minor or transient channel banks visible on LiDAR hillshade (likely <5 m deep), or obvious presence of locations where confinement could be reduced during an event (e.g. channel bends, changes in channel gradient, channel constrictions).
- Moderate: obvious (likely 5-15 m deep) channel banks on LiDAR hillshade, some presence of locations where confinement could be reduced during an event (e.g. channel bends, changes in channel gradient, channel constrictions or areas of potential blockage).
- High: obvious (likely>15 m deep) channel banks on LiDAR hillshade, no obvious locations where confinement could be reduced during an event (e.g. channel bends, changes in channel gradient, channel constrictions).
- Debris flow: a dense, fast-moving, channelized flow of water and debris, similar to wet concrete that poses a hazard to infrastructure and those living in mountainous environments. Debris flows contain a high percentage (greater than 30%) of sediment by volume and result in rapid sediment transport. The moving sediment controls the flow behaviour of these events.
- Debris flood: a flood containing a moderate percentage (up to 30%) of sediment by volume. It is distinguished from a debris flow in that water controls the flow behavior as opposed to the sediment.
- Low debris flood: a flood with a low proportion of debris compared to debris floods. Low debris flood typically occur on creeks that are not steep.
Hazard chance is the probability of a hazard occurrence within the watershed and fan. Hazard chance estimates are based on surface evidence of geomorphic activities. An active fan and watershed will have a higher relative hazard chance.
Hazard chance are represented as Low, Medium and High based on their return period, also known as a recurrence interval or repeat interval:
- Low: more than 100 years
- Moderate: 30 to 100 years
- High: less than 30 years
Avulsion is the sudden change in stream channel position in a fan due to partial or complete blockage of the existing channel by debris.
Avulsion susceptibility is the potential for avulsion. It is based on the channel confinement level and evidence of previous avulsions. It can be assessed through vegetation type and condition, presence of abandoned channels, and deposits on the fan surface.
- Low: fans with poor surface evidence or record of previous avulsions and having moderate to high channel confinements were assigned to the low avulsion susceptibility category.
- Moderate: fans with moderate surface evidence of avulsions and having moderate channel confinements, or fans with poor surface evidence of avulsion and low channel confinement were assigned to the moderate avulsion susceptibility category.
- High: Fans with strong surface evidence of avulsion events with moderate to low channel confinement, or fans with moderate surface evidence of avulsion events with low channel confinement were assigned to the high avulsion susceptibility category.
- A combination of higher channel confinement and higher or moderate evidence of avulsion is considered unlikely.
Landslide dam is an earthen dam created when a landslide completely blocks a stream or river. Outbreak flood is the flood created by the landslide dam failure.
Outbreak floods susceptibility is the potential for landslide dam outbreak floods. It is based on evidence of past landslide, landslide dams, and presence of channel sections that are susceptible to blockage (i.e., channel constrictions).
- Low: absence of evidence of larger landslides reaching the valley floor, no evidence of previous landslide dams.
- Moderate: no evidence of previous landslide dams, presence of potential landslides with the potential to travel to the valley floor, presence of channel sections potentially susceptible to blockage (e.g. channel constrictions).
- High: evidence of past landslide dams, presence of large landslide scars with the potential to travel to the valley floor, channel sections potentially susceptible to blockage (e.g. channel constrictions).
Bank erosion is the removal and transport of riverbank material downstream. Erosion causes channel widening and can be severe during debris flow and debris flooding events.
Bank erosion susceptibility: the potential for bank erosion. Bank erosion susceptibility is based on signs of previous channel widening. In general, the higher ratings applied to channels with moderate or lower levels of confinement.
- Low: no visible evidence of channel widening, or unconfined channel where channel change is most likely to occur via avulsion.
- Moderate: signs of some channel widening (up to 2 times “normal” width, i.e. equilibrium channel width.)
- High: surface signs of previous channel widening > 3 times the “normal” width, i.e. equilibrium channel width.
Flood Forecast Maps
Flood forecast maps give context to advisories and forecasts by illustrating potential flood areas for smaller and larger flows than expected. These maps are not predictions of flooding for the current forecast flow range, but use pre-existing mapping for other flows to convey what areas could be at risk.
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Additional Information
Flood forecast maps are created using pre-existing flood inundation mapping from provincial flood studies. The maps may not be available for all areas with current advisories or flood forecasts.
The potential flood extents shown on the maps are not based on current flows or on any specific flows in the current forecast flow range, but are based on pre-existing mapping for other flows that are smaller or larger than the forecast flow range.
The intent of flood forecast maps is to provide emergency managers and other stakeholders with a general indication of what could be at risk based on a current flood forecast, but they are not a prediction of flooding. The maps show a potential range of risk using floods that are smaller and larger than what is expected based on a current flood forecast flow range.
For clarity and to prioritize illustrating the worst case potential flood condition, protected areas at risk behind flood berms are only shown for the larger flood.
Flood forecast maps are updated as forecasts change and as more information becomes available, both before and during a potential flood event. Please refer to the advisories and flood forecast information found at rivers.alberta.ca for official details on current conditions. For more information about local emergency preparedness and response, please contact your municipality or First Nation administration.
Contact Us
For more information about flood maps and the provincial Flood Hazard Identification Program please visit www.floodhazard.alberta.ca or email us at epa.flood@gov.ab.ca.
For additional and current flood forecast information please visit rivers.alberta.ca.
Flood Range Maps
Flood range maps compare two different sized floods and show what parts of a community can become at risk as flows change during a flood. Protected areas behind flood berms with residual risk are only shown for the larger flood being compared but they may also exist for the smaller flood.
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Additional Information
Flood maps are not available in all communities and flood risks exist in areas without flood mapping.
Older flood studies include maps for as many as three flood scenarios, and newer studies include maps for as many as thirteen scenarios, from the 1:2 flood to the 1:1000 flood. In areas where a selected flood scenario is not available for all studies, other flood scenarios may be displayed. Flood maps in the same area may be available for smaller or larger floods.
Contact Us
For more information about flood maps and the provincial Flood Hazard Identification Program please visit www.floodhazard.alberta.ca or email us at epa.flood@gov.ab.ca.
Flood Likelihood Maps
Flood likelihood maps illustrate cumulative flood risks over 30 years. Different sized floods can occur any year, but smaller floods tend to occur more often than larger floods over time. These maps show areas that are expected to be flooded and areas protected behind flood berms the same way.
Additional Information
Flood maps are not available in all communities and flood risks exist in areas without flood mapping.
Contact Us
For more information about flood maps and the provincial Flood Hazard Identification Program please visit www.floodhazard.alberta.ca or email us at epa.flood@gov.ab.ca.
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