In their seminal book titled Let the Water Do the Work: Induced Meandering, an Evolving Method for Restoring Incised Channels, authors Bill Zeedyk and Van Clothier explain how “rivers and streams that wend their way across long established valley bottoms tend to have functional floodplains” which are naturally occurring streamside features created by rivers to absorb the force of rising waters during flood events. “Flooding of the river onto the floodplain serves to attenuate flows, dissipate energy, deposit sediments … recharge the shallow alluvial water table, [and] nurture streambank vegetation.”
Floodplains are essential to the health of most rivers, especially in arid environments, because “without the relief afforded by floodplains, large flood flows … concentrate energy in the channel itself, causing increasing rates of bank and bed erosion,” ultimately resulting in channel incision. The authors assert that channel incision has affected many areas throughout the Southwest due to “deliberate channelization and straightening of stream channels for flood control, irrigation, agriculture and urban development.”
As channels “deepen more readily than they widen,” they eventually become isolated from their floodplains, resulting in the destruction of the channel’s natural pattern of meanders that have formed over time. According to Smart Water Magazine, “meanders are curves” in a watercourse formed as it “erodes the sediments of an outer, concave bank and deposits sediments on an inner, convex bank.” The word “meander” comes from the Greek Maiandros, the ancient name for a river in Asia Minor that is known today as the Menderes River in modern-day Turkey. Zeedyk and Clothier explain that it is “not known for certain why streams naturally meander.” But the phenomenon “has been observed worldwide” and is considered “the central tendency of streams.” Perhaps most interestingly, “there is a mathematical relationship between channel width and the distance between meanders that holds true for all streams,” write the authors.
One of the many natural forces at work in the formation of meanders is erosion, “the forced relocation of soil,” write the authors. “The flow of a stream is not composed only of water; it includes particles the stream is capable of moving that are either delivered to it from the adjacent upstream reaches and tributaries, or from its own locally eroding bed and banks.” Erosion not only dissipates energy as the force of the moving water is expended, it also results in the “sorting of particles” and the “distribution of substrate materials” through the deposition of “sediment by size in the appropriate layers.” Generally speaking, these layers range from fine-grained sediment above to coarse cobble and gravel below, each of which plays a role in the “dynamic equilibrium” of an evolving stream. For example, the cobble/gravel layer acts as a “contact zone” between the base flow from the alluvial aquifer beneath the stream and the “fine-textured strata above.” This contact zone “recharges the alluvial aquifer” during high flows or flood events, thus augmenting the available base flow and extending the period of its gradual, subsequent release into the stream.
The sorting action of erosion is also key to the propagation of riparian vegetation, which plays an important role in “bank storage” or the retention of water in the pores of the fine soil lining the stream. Also known as floodplain vegetation, riparian vegetation forces “flooding to occur more readily as a flood crest rises” and can result in “prolonged inundation of the floodplain,” explain the authors. These inundation events saturate the soil “to increasing depths, promoting infiltration and storing water in the alluvium.” This stored water then “seeps back” to the stream “and maintains base flow long after the flood pulse has passed.” According to Zeedyk and Clothier, this “temporary storage and release, if allowed to act over a long enough distance, is known to preserve or even recreate perennial flow in stream reaches that would be ephemeral without that vegetation.”
When it comes to riparian vegetation, the authors argue that there is a widespread misconception about its role in water loss. People often think that vegetation depletes the water in a stream. But Zeedyk and Clothier point out that there is a distinction between riparian and upland species of plants. “The water used directly by riparian plants for their own survival is balanced by the services provided to the ecosystem by the plant community. This is qualitatively different from the role of upland woody vegetation, which can become overabundant and desiccate the watershed.” Essential services provided by riparian vegetation include “shading the water surface and streambanks from the sun” thus reducing “water and soil temperatures during the summer months.” Thriving riparian vegetation “also moderates wind velocity” and curbs air circulation, thus decreasing “the rate of evaporation … from both the water surface and the moist ground,” explain the authors. “Well-vegetated, stabilized banks become groundwater infiltration galleries” that provide for natural filtering, improved water quality, modulated flood peaks, and extended base flows. The authors urge landowners to ask not only “How much water does riparian vegetation use?” but also “How much water does riparian vegetation create?” In their estimation, “maintaining riparian vegetation is a profitable water investment for the stream because the volume of groundwater infiltration and recharge it facilitates more than compensates for the water used by the plant community for its own survival.”
In order to address the channel incision phenomenon and restore floodplains, Zeedyk and Clothier have spent decades developing “Induced Meandering,” a method that aims “to assist the stream in its natural evolution, using the power of floods to shape the channel and banks over time.” According to the authors, “Induced Meandering strives to understand the river’s processes and immutable rules, and to be guided by the understanding that natural river forces are to be respected, never coerced.” This involves learning “to read the agenda of the stream” and “orchestrating the natural forces” to speed the stream’s recovery and enjoy “the benefits of a stable river sooner than would occur naturally.”
Let the Water Do the Work provides landowners with a variety of examples and cases studies, mostly located in New Mexico. Folks interested in exploring the possible application of Induced Meandering on their property can purchase the book at quiviracoalition.org or visit their local library, where the book is available through interlibrary loan.
