Importance of Sediment Transport in the Saskatchewan River Delta

Nicole DollBlog, Featured

Overhead view of Sask River Delta

By Nicole Doll

Comprised of complex networks of river channels and water bodies that feed into various kinds of wetlands and forests, the Saskatchewan River Delta embodies an undeniably unique environment. Like many other deltas, the process by which it is formed is partly due to the transport and deposition of sediment. 

Deltas are distinct environments that form when rivers enter into another body of water, such as an ocean, lake, or even another river. The body of water that the river flows into is typically flowing at a slower rate, or not flowing at all (like a lake or an ocean). As the river flows into its new source and slows down, it empties all the sediments and nutrients it has carried with it over time. The sediments that are emptied into the new water source are critical for the surrounding ecosystem and create biologically productive areas. Over time, sediment that settles to the bottom of the terrain can form new landscapes.

Instead of flowing into another body of water like most deltas, the Saskatchewan River Delta empties into the land, forming an inland delta – which is rare of its kind. As the water flows over the land across multiple channels, along with it flows the sediment that gets distributed to wetlands, floodplains, forests, and marshes – replenishing the ecosystems of vital nutrients.

As the water flows over the land, new channels and wetlands are created, which creates rich habitat for a variety of species. The deposition of sediment is what allows the delta to be the distinctive ecosystem it is. 

Aerial image of multiple channels of the Saskatchewan River Delta, by Garth Lenz.

What exactly is sediment? 

Sediment is inorganic or organic matter that travels with water, wind, or ice. Ranging from tiny particulate matter (more typically), or rocks that can be carried during a high flow event such as a flood, sediment is usually derived from soil and rock, which have weathered or eroded from gravel, sand, silt, or clay. 

The process of sediment deposition is essential for the health of aquatic ecosystems, as it replenishes the surrounding land and water with nutrients. Not only does this create proper conditions for plant growth, but it creates food, habitat, and spawning areas that contribute to biologically rich areas that support a multitude of different species.

In the Saskatchewan River Delta, sediment deposition has been jeopardized since the 1960s, when the construction of the E.B Cambell hydroelectric dam disrupted the natural processes of the river.

How are dams able to impact the nutrient regime? 

Dams are able to effectively impound all kinds of sediment carried with the water, whether it be large rocks or tiny suspended particles. Downstream of the dam, the water becomes sediment-deficient and erosive. 

The lack of sediment carried to the ecosystem results in a depletion of nutrients and thus, a lack of growth and a less productive ecosystem that no longer allows species to thrive as they once did. Submerged vegetation has more difficulty growing, marshes and wetlands become stagnant, and habitat and spawning areas diminish. This affects all delta-users; insects, fish, birds, mammals, and of course, people who hunt and fish and rely on these waters for sustenance.

In addition, the sediment-depleted flow erodes banks downstream and speeds the rate at which the main channel widens and deepens, making it difficult for water to distribute to other parts of the land and feed into other channels and wetlands. This coupled with reduced peak flow in the spring means less water and nutrients that flood over the delta. 

The disruption of the nutrient regime has been one problem associated with the dam, but there are many others, such as the change in flow patterns. While many people benefit from the hydro dam, the downstream effects are broadly unknown by the general public. The communities that live downstream are faced with the consequences and robbed of their right to benefit from a healthy ecosystem. While there is no easy solution, locals in the area are working hard to steward the delta the best they can, while engaging with governments and various organizations on strategies to save what remains of the unique landscape.

Resources:

Sediment Transport and Deposition – Environmental Measurement Systems

Dam-induced and natural channel changes in the Saskatchewan River below the E.B. Campbell Dam, Canada