When most people think of a river, they think of the water itself. But the riverbank area, or riparian system, is also a vital part of the health of the river. A strong riparian area is beneficial to water quality, wildlife and to the ecological wellbeing of the river basin, including the prevention or reduction of erosion.
This vegetation plays a valuable role in helping to protect a river and the surrounding area.
“When these areas are intact with native vegetation, they slow the forces of floodwaters, help capture sediment, filter nutrients and slow runoff from upland sources,” according to the Passport to Texas radio series. “Yet land practices over the past 150 years have altered their natural state.”
Factors that have had a negative impact on riparian vegetation include mowing and uprooting it, excessive foot and vehicle traffic in these areas and excessive browsing (feeding) on the vegetation by both livestock and unmanaged wildlife, according to the TPWD.
When flooding occurs in areas throughout the basin, one of the casualties is the vegetation in the areas along riverbanks, which can include a tangled array of uprooted plants. Cleaning up that vegetation isn’t necessarily the best action to take, according to experts.
“One of the most important and critical components of a riparian area is fallen vegetation,” said Ryan McGillicuddy, a conservation ecologist with the Texas Parks and Wildlife Department, said on the department’s Passport to Texas radio series. “As fallen wood – woody debris – start to decompose, they add nutrients to the soil. They act as fish and wildlife habitat. They act as cages that protect new plants – the next generation of trees, the next generation of grasses. It provides a little refuge for those plants to get started before they’re browsed on by wildlife or they’re trampled by foot traffic.”
McGillicuddy said as long as vegetation along the riverbank is not posing some sort of safety risk, it is best to leave it where it is.
“Another thing it does is as flood waters do rise up and spill out of their banks, that wood can help slow down some of that water and help capture sediment. When the sediment falls out of the water, it’s actually building the structure of the banks, adding sediment and new layers of soil, as opposed to it being washed away.”
When riparian vegetation is thinned out, “it can contribute to higher peak flows for flooding,” McGillicuddy said. “And really, those areas become less resilient; they recover less quickly from disturbance events like floods.”
Those areas that lack healthy and adequate vegetation along riverbanks suffer far greater damage and erosion than areas with healthy and abundant riparian vegetation.
“What happens when you reduce the vegetation diversity and number of species is you lose some of the root stock that these native trees and grasses provide,” McGillicuddy said. “These species have very, very deep root systems that act like rebar holding the soil together.”
Areas deprived of their natural vegetation are much less resistant to erosion, which can result in significant land loss as well as unstable river and stream systems.
“If you have an intact, healthy riparian zone, it will slow the forces of floodwaters,” McGillicuddy said. But riparian zones also help enhance water flow during times of drought, he said, noting that these areas act like a sponge, and help add to stream flow when conditions are drier.
The benefits of protecting the vegetation in areas along the riverbanks are numerous, ranging from cleaner drinking water to flooding mitigation, enhanced recreation and land conservation. More information on the importance of riparian areas can be found here.