Glendon Desk Assignment: Role of Wetlands in Mitigating Flooding

Wetlands are the areas that act as a natural sponge to halt and slowly release the flood water, rain, groundwater and snow melt. They play an important function in our global ecosystem. Wetlands reduce the degree of flooding and also decreases soil erosion by stopping  the flow of sediments. Wetlands are termed as “Earth Kidneys” and “Biological Supermarkets” because of their capacity to hold harmful pollutants and rapid flow of flooding (Ming, Xian-guo, Lin-shu, Li-juan, & Shouzheng, 2007).

Wetlands play a critical role in:

–  slow release of stored water to prevent flooding

– acting as a filter to stop the flow of contaminants and sediments

– Providing a natural habitat to wildlife

– Improving water quality

wetlands_2.png

Graphic source: 2005: WaterScape Bowen Island, Turner R.J.W. et al, Geological Survey of Canada Miscellaneous Report 88

Simmy and myself were dicussing  impacts of wetland destruction and found how natural wetlands and their restoration helped in mitigating flood in Texas and Florida as well as around the whole world. Texas is a city which had experienced the most deaths and loss due to flooding as compare to any other state (Brody, Zahran, Highfield, Grover, & Vedlitz, 2008). Urbanization of the city, rooftops, carparks led to the destruction and removal of many wetlands. Brody et al studied that 3.15 inches of rainfall in October 1997 in Texas caused USD 15,000 of reported damage in De Witt County, where only five wetland-altering permits were allowed.  The scientists found that four years later, when there were 17 wetland alteration were granted, and the same amount of rainfall caused USD 150,000 of damage (Broody et al, 2008).

How wetlands reduce flooding and erosion:

Wetlands not only prevents flooding but also protect the crops from water logging. They also prevent droughts and improves water quality. Water quality is basically improved by the removal of nitrates via denitrification (Mitsch & Gossilink, 2000). The ecosystem, dead or living plants and vegetation slows down the water currents, increase the rate of transpiration and shade water (Mitsch & Gossilink, 2000).Protecting wetlands also help cities and municipalities to save their revenue and resources on flooding. 

A study was done in Smith Creek watershed which is 60 km from the city of Yorkton in southeastern Saskatchewan to show the direct link between wetlands and flooding. It was found  that the wetlands area in this watershed has decreased from 24% to 11% between 1958 and 2008. They also found that in 2011, the flood levels reduced by one third due to the complete restoration of the wetlands but the flooding increased by 78% when there was a drainage. This shows how wetlands act a reservoir when there is a change from winter snowmelt to summer dry weather.

1 - Smith Creek.jpg

The figure above shows how wetland restoration reduces flooding in Smith Creek Yorkton.

Wetlands protection from storm and floods:

Coral reefs, mangroves, tidal flats and deltas are coastal wetlands that provides a  physical barrier against high tidal waves and storms to reduce the water’s height and speed of flow. Protection of wetland vegetation, which includes mangroves and saltmarshes bind the shoreline together and reduce  soil erosion from heavy storms and high oceanic tides. It was seen in Chignecto Harbour Ramsar Site in Nova Scotia that saltmarshes and vegetation absorb the excess water flow and protecting the surrounding habitat and wildlife environment from severe destruction.

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Saltmarshes, in Chignecto Harbour Ramsar Site in Nova Scotia, help to absorb and slow floodwaters

How to protect and restore wetlands:

Wetlands play a huge role in maintaining water cycle in our global system. They can be restored through consistent monitoring and assessment. There should be strict restrictions on  waste dumping in wetlands and their buffers, as well as by reducing the discharge of untreated storm water into natural wetlands.There is a technique called “living shoreline” which uses the plant roots for soil stabilization to protect waterfront property and  also to stabilize riverbanks shore line.

Wetlands can be protected through land use planing and using aquatic buffers as mentioned in ‘Adopting watershed tools to protect wetlands’ article by Karen Cappiella. Expansion of wetland buffers and connecting them with their habits also protects the wetlands. They can also be restored through better site designs which minimizes the different  wetlands crossing and interference into each other.

References:

Brody, S. D., Highfield, W. E., Ryu, H. C., & Spanel-Weber, L. (2007). Examining the relationship between wetland alteration and watershed flooding in Texas and Florida. Natural Hazards, 40(2), 413–428. https://doi.org/10.1007/s11069-006-9003-3

Mitsch, W. J., & Gossilink, J. G. (2000). The value of wetlands: Importance of scale and landscape setting. Ecological Economics, 35(1), 25–33. https://doi.org/10.1016/S0921-8009(00)00165-8

http://archive.ramsar.org/pdf/info/services_01_e.pdf

https://auma.ca/advocacy-services/programs-initiatives/water-management/watershed-management/wetlands

http://www.wetlandprotection.org/protect-wetlands.html

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