Flood Mitigation: Channelization

What is channelization? 

Channelization is a method of river engineering that widens or deepens rivers to increase the capacity for flow volume at specific sections of the river. As a result, during flood times watercourses can move more efficiently and facilitate more water, which results in less damage to banks. Furthermore, channelization can provide erosion control and the rehabilitation of watercourses[1]. Despite these benefits, channelization can cause damage further downstream where efforts to widen or deepen the river were not undertaken. 

How does this option help to mitigate the impacts of a flood? 

River channelization occurs by dredging the river to facilitate more water. During a flood, this would mitigate damage to river banks and facilitate increased speed of the river flows. While this option could prove useful in specific areas of a river, there are concerns over the downstream and overall watershed impacts this option would have[2].

Is channelization already used in Alberta? 

Channelization has not been used in Alberta. Debris removal and river dredging, however, was performed in High River, Alberta to mitigate the impacts of a future flood. Dredging occurred in six different locations of the Highwood River to remove debris and excess mud and make room for the river to flow[3]. 

What are the costs to build and maintain?

Depending on the length and size of the river, costs of channelization and maintenance vary. 

How long does it take to build? 

Length of construction times varies depending on the size of the project and type of river channelization. For example, in High River dredging took two months with mechanical help[4].   

Operations lifetime expectancy? 

Channelization results in changes to the flow and direction of a river. While this mitigation option can limit the impacts of future floods, construction is not permanent given the natural and ever-changing flows of the river. 

What are the associated risks?

River channelization poses risks to the surrounding environment by impacting habitats, the aquatic ecosystem, and the natural function of floodplains. 

What are the environmental and watershed impacts of channelization?

River channelization results in the removal of sedimentation at the base of the river further increasing flow rates. Subsequently, habitat diversity is jeopardized due to the new flow of the river and natural pooling is disturbed which negatively impacts aquatic life[5]. 

Re-channeling a river requires actions such as river widening, deepening, dredging or re-aligning that impact the natural flow and ecology of a river. Removing or changing sediment deposition at the bottom of a river changes the velocity and flow of the water body. While this measure can alleviate flooding in one section of the river, it also enhances the speed of the river which can cause downstream flooding that can further impact the surrounding watershed[6]. 

Would river channelization help in a drought?

River channelization does not help in a drought.