Can forests protect us from flooding?
By Monica Allaby, Posted on September 29, 2020
Climate change is causing more frequent and extreme storms. For much of Canada, this will likely mean more flooding. Flood damages in Canada exceeded $1.8 billion between 2009 and 2017. Here in New Brunswick, the province has been forced to access federal disaster relief funding more than any other jurisdiction in Canada. Recent data shows that in 2014 alone, flood damage exceeded $39 million for New Brunswick. In addition to its economic impacts, flooding has negative impacts on the social and mental health for those affected.
There are ways to reduce the risk of flooding — things like storm-water ponds, flood gates, and rain gardens can help us adapt. But what if one of the most important solutions to flooding was already all around us? What if forests could protect us?
Though relatively unexplored compared to wetlands, forests show great promise for mitigating flood damage. Let’s take a look at the research!
What the research shows
Research has found that there are significant increases in peak flow, the maximum amount of water that moves through a stream or river during a rainfall event, when more than 50% of the nearby forest is removed from the landscape. This can also cause permanent changes to stream morphology (the shape of rivers or streams and the path that they follow) and have lasting effects on an ecosystem.
After a forest is harvested and vegetation starts to grow back, streams begin to recover to a more normal flow. On average, it takes 10-12 years for the rate of stream flow to return to normal. However, rainfall is not the cause of flooding. In the spring, melting snow poses an additional flood risk, increasing the water flow downstream as melting snow flows into streams and rivers. The impacts of forest clearing on snow-melt may last for more than 15 years!
Intensive forest management over multiple years degrades soil conditions on the land. When a forest is harvested, the important organic matter on the forest floor is often removed or destroyed, exposing the mineral soil beneath. This degraded soil loses its ability to slow flooding and erosion from significant rainfall events which, in turn, contributes to higher risk of flooding downstream.
Removing forests from the landscape causes a decline in the flood mitigation services that these ecosystems can provide. Without the protective cover of trees, snow can melt faster and rain flows into waterways unchecked.
Healthy forests, resilient communities
With the support of the Intact Financial Corporation, Community Forests International is studying, protecting, and restoring the flood reduction value of more than 1,000 acres of forest in the Canaan-Washademoak Watershed, which drains into the Lower Wolastoq River. The watershed has seen significant land use changes in modern history, where mature forest cover has been cleared for agriculture, settlement, and transportation.
The goal of our project is to create an economic case for using natural infrastructure for flood mitigation in New Brunswick, and in similarly impacted regions throughout the Maritime Provinces. This project will provide working examples of forest protection and restoration for flood risk-reduction, and at the same time, show that forests are more valuable when they are kept standing.
Successful adaptation to climate change requires innovating how we value and manage natural infrastructure, like forests. Healthy forests help to build resilient communities.
Community Forests International is grateful to Intact Financial Corporation the for generously supporting this work.
References:
Moudrak, N., Feltmate, B., Venema, H., Osman, H. (2018). Combating Canada’s Rising Flood Costs: Natural infrastructure is an underutilized option. Waterloo, Ontario: Intact Centre on Climate Adaptation, University of Waterloo.
Guillemette, F., Plamondon, A. P., Prévost, M., & Lévesque, D. (2005). Rainfall generated stormflow response to clearcutting a boreal forest: peak flow comparison with 50 world-wide basin studies. Journal of Hydrology, 302(1-4), 137-153.
Jewett, K., Daugharty, D., Krause, H. H., & Arp, P. A. (1995). Watershed responses to clear-cutting: effects on soil solutions and stream water discharge in central. New Brunswick. Canadian Journal of Soil Science, 75(4), 475-490.
Talbot, J., & Plamondon, A. P. (2002, June). The diminution of snowmelt rate with forest regrowth as an index of peak flow hydrologic recovery, Montmorency Forest, Quebec. In Proceedings of the 59th annual Eastern snow conference. (pp. 85-91).
Prepas, E. E., Burke, J. M., Whitson, I. R., Putz, G., & Smith, D. W. (2006). Associations between watershed characteristics, runoff, and stream water quality: Hypothesis development for watershed disturbance experiments and modelling in the Forest Watershed and Riparian Disturbance (FORWARD) project. Journal of Environmental Engineering and Science, 5(S1), S27-S37.