The Influence Of Hydrogeomorphic Characteristics On Riparian Vegetation Along The Fremont River, Utah.
Abstract
Complex interactions between geomorphic form and flooding influence riparian vegetation communities in the semi-arid western USA. On the Fremont River in Capitol Reef National Park, Utah, road development created a knickpoint after cutting off a 1.2 km meander bend, causing an upstream oversteepened reach. The continued development of the knickpoint could threaten infrastructure and has likely altered channel morphology and riparian vegetation through local base level fall and upstream migration. However, research on the influence of knickpoint development on channel-floodplain hydrologic connectivity and riparian vegetation is limited. Using topographic and vegetation surveys, we investigated the influence of knickpoint development on upstream flood inundation and vegetation communities in four 1 km-long reaches: an impacted reach just upstream of the knickpoint, a reference reach 5 km upstream of the knickpoint and a reference reach 0.7 km downstream of the knickpoint, and a reach in the cutoff meander that is no longer connected to the river. We surveyed floodplain and channel morphology and channel slope along ten cross-sections in each reach. We established vegetation plots along each cross-section, identifying species and estimating percent cover, bare ground, and litter. Using survey and discharge data, we modeled inundation extent and frequency using a 1D HEC-RAS model, linking hydrologic characteristics to riparian vegetation. Results indicate that knickpoint development likely has had an effect on upstream channel morphology and vegetation. In the impacted reach, the channel has a lower width-to-depth ratio, vegetation plots have more bare ground, and vegetation species consist mostly of xeric and some mesic species; opposite trends are present in the less-impacted reach upstream, which also has more hydric species present at a greater range of distances from the channel. The abandoned reach resembles the adjacent semi-arid upland. This shows that the diversion and knickpoint have likely caused incision that has propagated upstream, affecting lateral hydrologic connectivity, patterns of inundation, and riparian vegetation. Results of this study will directly inform park management decisions and enhance our knowledge of biogeomorphic interactions in river corridors.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFMEP25C1339J