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- Title
The Influence of Knickpoint Development and Channel Incision on Riparian Vegetation in Semi‐Arid River Corridors.
- Authors
Johaneman, T. M.; Lininger, K. B.; Schook, D. M.; Pitlick, J.; Martin, M.
- Abstract
Hydrogeomorphic processes strongly influence riparian vegetation, but few studies have determined the influence of knickpoint development on these processes. We investigate the influence of knickpoint development and channel incision on flood inundation, channel morphology, and riparian vegetation on the Fremont River in Utah. We conducted topographic surveys (n = 30 transects) and plot‐based vegetation surveys (n = 336) in three 1 km‐long reaches with varying proximities to a human‐created knickpoint. We also developed 1D hydraulic models to assess flood inundation patterns. Our data indicate that knickpoint development affects riparian vegetation composition and abundance through its influence on geomorphic and hydrologic processes. The study reach located just upstream of the knickpoint (R2) had a deeper channel, flooded less frequently, and required higher flows to inundate the floodplain compared to the study reach located 5 km upstream of the knickpoint (R1). Overall mean vegetation abundance (percent cover) was higher in R1 (55.7%) than in R2 (30.1%), and R1 had more occurrences of wet‐adapted (facultative wetland and obligate) species than R2 (198 and 79, respectively). Vegetation in the human‐created abandoned meander reach near the knickpoint (R4) was predominantly dry‐adapted (upland) species. Cross‐reach comparisons and more than 3 m of incision in the knickzone since knickpoint creation indicate that knickpoint development has resulted in channel incision in R2, shifting its vegetation toward more dry‐adapted species reminiscent of the surrounding uplands. This work informs natural resource management practices for habitat in riparian ecosystems and can be applied to rivers in drier regions. Plain Language Summary: During construction of a road in the 1960s alongside the Fremont River, in Capitol Reef National Park, Utah, USA, a river bend was cut off and the channel was straightened. This decreased the river length and increased the slope, causing a waterfall to form and develop. We investigated the effects of the human‐created waterfall on channel form (width and depth), flooding, and vegetation. We used surveys to collect data for channel form and vegetation and simulated flood levels in each reach. We found that the development of this waterfall has caused changes to the river and floodplain up to 1 km upstream of the waterfall; the channel is deeper 0.2 km upstream of the waterfall, compared to a much shallower, less effected channel several kilometers upstream. A deeper channel has decreased the duration of overbank flooding, resulting in a shift from wetland vegetation species, which are better adapted to more flooding, to desert vegetation species, which are better adapted to less flooding and drier conditions. Drier conditions have also decreased the amount of vegetation present. This work will help inform future management decisions that could have impacts on channel depth, flooding, vegetation, and river ecosystem health. Key Points: Knickpoint development caused upstream channel incision, modifying vegetation abundance, and composition in a semi‐arid river systemChannel incision decreased flood inundation duration and increased the discharge required to inundate the floodplain in the impacted reachDecreased floodplain inundation has caused a shift in floodplain vegetation from more hydric and mesic species to more xeric species
- Subjects
UTAH; RIPARIAN plants; NATURAL resources management; FLOODPLAINS; ECOSYSTEM health; ROAD construction; DESERT plants
- Publication
Water Resources Research, 2023, Vol 59, Issue 10, p1
- ISSN
0043-1397
- Publication type
Article
- DOI
10.1029/2023WR034872