Rewilding Our Rivers: The Riparian Edge by Lauren Eden
So far in the Rewilding our Rivers Discussion Series, we have discovered the importance of healthy soil systems and wetlands in the attenuation of water during flooding events. The previous two blogs talked about how soils rich in organic matter hold and retain more water, and how wetlands function like sponges across the landscape absorbing surface water runoff subsequently replenishing aquifers. In addition to ensuring that Alberta’s soils and wetlands are healthy, riparian zones also play a beneficial role in flood mitigation.
The riparian edge is where aquatic and terrestrial ecologies interface; formed by the merging of land and a river, lake, or stream. As unique ecosystems, riparian zones provide a vast array of ecological goods and services including decreased soil erosion; storing and recycling of organic matter; providing habitat for fish and wildlife; and improving water quality through the removal of nutrients such as nitrogen and phosphorus from surface and subsurface water. The functioning of these many goods and services is highly dependent on the width of riparian vegetation; at minimum a riparian zone should extend over the stream bank and 5 to 10 metres onto the floodplain.
The riparian zone flood mitigation claim to fame is the ability to slow down the speed of water via energy transfer to the vegetated root structures along the banks of the watershed. As flood waters speed over the vegetated banks, the plants resist the flow and dissipate the energy. Then, as the water’s velocity slows down it is able to infiltrate the soil system leading to groundwater recharge and the storing and recycling of nutrients. The strength of the root structures of the trees and grasses stabilizes stream banks and reduce flood flows, resulting in the reduction of downstream flooding.
These aquatic terrestrial edges also act as a buffer in times of drought by recharging aquifers leading to year round higher water tables.
Unfortunately the riparian buffer has been encroached upon. A study in 2012 found that only 5% of Calgary riparian zones were healthy. Concrete channelization, human activity, development, and our desire to live closer to water has led to increased manufactured landscapes that destroy dense riparian ecologies. One only needs to look along our river ways to see the decline in healthy vegetated banks, characterized by eroded slopes with minimal trees, shrubs and native grasses. The destruction of this buffer zone also creates greater vulnerability, as the ecosystem no longer has the structure to dissipate high-energy water flows and instead literally crumbles away.
The ecosystem goods and services that healthy soil, wetlands and riparian ecologies offer us are essentially free. All we have to do is get out of the way and let nature’s intrinsic intelligence do the work. The earth’s memory is astounding. The seeds of these local ecologies are stored in our soils and if human-made obstacles were removed, and water was able to freely flow. Ecological succession would begin and before long native terrestrial ecologies would regenerate along our riverbanks. It almost sounds too simple to say no. But with all choice comes trade-offs. It would mean changing how we value and develop our landscapes. Waterfront property would now have vegetated shores, agricultural lands would need to reforest water lines, and concrete river banks would need to be rebuilt using soft-engineering practices.
Like the riparian zone, we are at the edge of changing valuation systems. In the face of extreme weather events, we now must learn to adapt and respond to Mother Nature. Restoring resiliency to our ecologies in turn restores our community resiliency by providing us with natural mitigation measures for both flood and drought.
There have been some proactive steps taken in Alberta to protect and restore our riparian edges. The Government of Alberta has published the Stepping Back from the Water document, a guide for developing near water bodies, and funded the Bow & Beyond Initiative that works to regenerate riparian zones with private land owners. Numerous water stewards, organizations, and municipalities across the province are also working hard to ensure the protection and restoration of these important ecological edges. Some examples include the Nature Alberta’s Living By Water project, Cows and Fish’s publication Riparian Areas a User’s Guide to Health , and Alberta Conservation Association’s riparian restoration projects .
But can we do more?
British Columbia has implemented a Riparian Area Regulation that protects the features, functions and conditions that are vital in the natural maintenance of stream health and productivity. Should we as Albertans learn from our western neighbours and implement something similar? And what would riparian protection look like in Alberta? Understanding that ultimately it is the health of the terrestrial edge that provides the buffer to flood flow volumes.
Lauren Eden is a Researcher at Alberta WaterSMART.