PUBLISHED: 29 November 2013

Flood Mitigation: Soft Engineering

What is soft engineering?

Traditionally, shore stabilizations have been constructed using hard engineering methods with materials such as steel and concrete to protect developments from erosion due to flooding. Soft engineering is a natural form of flood mitigation that builds along shorelines to protect areas from flooding. Often referred to as riparian zones, this technique establishes local vegetation along water banks to create shore stabilization through complex root structures.  Applied to water systems, soft engineering is proven to reduce erosion while at the same time protecting local habitats along river, lake and ocean shorelines[1].

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

Soft engineering systems built along rivers, lakes and oceans soften the land-water boundary and promote ecological value. Examples of soft-engineering include; afforestation where trees are planted closer to rivers to slow down flood waters, ecosystem management that integrates human and natural needs of the river, as well as planning to control developments along riverbanks[2]. Therefore, in times of flooding, infrastructure damage and costs remain low while the natural shoreline facilitates high water levels.

In relation to soft engineering practices and ecosystem management, the protection and management of healthy riparian areas that border bodies of water is of paramount importance. Riparian areas do not require bank stabilization or erosion control measures due to their ecosystem that acts as a transition areas between water and land[3]. 

Is soft engineering already used in Alberta? 

In Alberta, soft engineering has been utilized for some shoreline areas along the Bow and Elbow rivers in newer communities in the City of Calgary[4]

What are the costs to build and maintain? 

Soft engineering flood mitigation options are typically less expensive than hard engineering options due to the use of fewer materials, natural succession, and minimal construction costs. Major costs associated with soft engineering practices include the compensation of land to those landowners giving up property for flood mitigation and maintenance costs[5]. 

How long does it take to build? 

Soft engineering options such as constructing wetlands, creating flood designated areas and strengthening river banks through rebuilding riparian zones take little time to implement , however, depending on the soft engineered solution can take years to see the full benefit as natural ecologies return.  

Lifetime expectancy of soft engineering?

Continual maintenance of some soft engineering practices such as riverbank reinforcement is required to ensure longer lifetime expectancy. 

What are the associated risks?

While soft engineering options tend to work with water ways and pursue a natural approach to flood mitigation, this approach can take a long time to prove beneficial. For example, in order for river bank protection to be effective, a certain amount of vegetative growth must occur. The risk with this approach is that flooding can occur prior to river bank protection (or other soft engineering option) being fully constructed, resulting in more damage. 

What are the impacts on the surrounding watershed system and environment?

Soft engineering options help to regulate flooding and slow down flood waters. The controlling features of soft engineering measures, however, depend on the size of the flood and natural area. Impacts on the surrounding watershed system can be extensive in that lakes, ponds, wetlands, streams, rivers and groundwater can act as storage facilities for excess water in a flood[6]

Would soft engineering help in a drought?

Soft engineering protects natural areas. Enhancing a protected area of land where wetlands, forests and vegetation exists ensures regulated flows and water retention capabilities. 

[1] “River Flooding and Management Issues.” BBC-GCSE. Accessed December 9, 2013.

[2] Ibid.  

[3]“Riparian Areas.” Alberta Environment and Sustainable Resource Development. Accessed March 24, 2014.  

[4]“Calgary’s tools for conservation.” Accessed December 9,2013.  

[5] “Management Strategies.” BBC-GCSE Bitesize. Accessed January 21, 2014.  

[6] “Environmental Aspects of Integrated Flood Management.” World Meteorological Organization. Switzerland; 2006; pg. 25-28.