The Active River Area

Six landscape features make up the extent of the ARA. While there is often overlap between these features, each plays an important role in maintaining the ecological integrity of rivers and streams. 

The Floodzone is represented by three components of the Active River Area: floodplains, terraces and meander belts. While all attempts were made to map these components independently, the scale of the project area and the limited availability of high-resolution elevation data made it impossible to do so and as a result they were combined into a single floodzone feature. 

Floodplains are flat areas of land next to streams, rivers and lakes that are periodically flooded. They are typically composed of deep sediment deposited by flood waters. Habitats associated with floodplains include meadows, backwater swamps and floodplain forests. Well-connected floodplains also provide several ecosystem services, such as water flow regulation and storage, which protect communities downstream. 

Terraces are historic floodplains. Terraces typically run parallel, but at a higher elevation, to current floodplains. This is attributed to either higher volumes of water in the past, or a decrease in the stream or river elevation as it cuts into the valley bottom over time. Terraces are rarely covered by flood waters and tend to support communities of upland species. However, they play an important role in storing water during very large flood events and, depending on the frequency of these events, can also support natural communities of floodplain species.

A meander belt is the area where a stream or river channel naturally migrates over time. The width of a meander belt is directly tied to the topography that the channel runs through. On steep slopes or confined valleys, stream or river channels may be limited in their ability to move laterally, so the meander belt will be narrow. In broad, flat valleys, the meander belt can be very wide and curvy, with multiple braid-like channels. In this case, habitat diversity is high and often includes oxbow lakes, ponds and a variety of wetland types. 

Riparian (next to water) wetlands occur in low-lying areas on wet soils that support communities of water-tolerant vegetation. Riparian wetlands often support a high diversity of plants and animals. They also perform numerous ecological functions that support the integrity of freshwater ecosystems. Riparian wetland types include fens, sedge meadows, vernal pools, swamps, beaver flowages and shrub swales.

Steep slope material contribution areas are slopes with a greater than 15% grade along rivers that directly provide sediment and organic matter to stream and river channels. These areas form the basis of the aquatic food web and influence the distribution of aquatic habitats downstream. While they can occur anywhere in the watershed, they most often occur in the headwaters where the terrain is hilly or mountainous and rarely (if ever) flooded. 

Based on Active River Area modelling completed in the U.S., a cost distance function was used on the watercourse network data, using elevation and distance from the stream channel as the costs. As one moved away from the water channel, cost increased as distance and slope increased. Existing floodplain mapping was then used to determine appropriate cost-distance cut-off thresholds across the study area. For more details on the methods used to delineate the ARA, please see the report under the Attachments tab  here . 

The map on the right shows the results of the ARA modelling work. You can interact with the map and zoom in to your area of interest. Refer to the legend in the bottom left corner. Use the arrow icon in the top left of the map for full screen viewing and navigation.

The tables below summarize the total ARA extent and the percent cover for each province.  

Active River Area mapping has resulted in numerous applications. One is identifying priority areas to either conserve or restore riparian and freshwater systems. By understanding what land use types occur within the ARA, project managers and decision makers can better recognize opportunities for conserving large and intact floodplain and riparian habitats, as well as restoring areas where these natural systems have been altered by past land use.

The interactive dashboard to the right summarizes the landcover within the ARA within each  Canadian Hydrological Unit (CHU) level 12 watershed . Start by clicking the full screen icon in the top right corner. User instructions are in the "About" section on the right of the map.

Select your watershed of interest for more information. 

A major limitation of the analysis is the dependence on a coarse resolution 30m DEM. As a key foundational dataset that all of the results are based on, errors in flow direction are inevitable, as minute topographical changes that would naturally or un-naturally alter the flow of water across the landscape are missed. As previously mentioned, the 30m resolution DEM also did not allow for the separation of terraces and meander belts from the floodplains. 

The methods outlined in this analysis have since been  replicated    within two watersheds in New Brunswick using high-resolution LiDAR-derived DEMs as the elevation data. This has shown great promise in more accurately delineating the Active River Area. Using high-resolution elevation data (5m) also allowed for the separation of the floodzone into floodplains, terraces and meander belts.  

For more information on the Active River Area and other NCC freshwater conservation work related to the Freshwater Conservation Blueprint, please visit our Databasin website  here .

The completed Freshwater Conservation Blueprint offers a suite of freshwater planning tools for individuals and organizations of all sizes and sectors. By identifying and prioritizing freshwater systems that provide value to both people and wildlife, our hope is that these aquatic tools will promote collaboration in guiding sustainable development and conserving freshwater biodiversity throughout the region.