Riparian monitoring of wadeable streams on the Fremont River, Capitol Reef National Park, 2009?2021

The goal of Northern Colorado Plateau Network (NCPN) riparian monitoring is to deter-mine long-term trends in hydrologic, geomorphic, and vegetative properties of wadeable streams in the context of changes in other ecological drivers, stressors, and processes. This information is intended to provide early warning of resource degradation and determine natural variability of wadeable streams. This report summarizes NCPN monitoring of the Fremont River in Capitol Reef National Park (NP) from water years 2009 to 2021. The focus of this report is to (1) examine patterns in water availability at one monitoring reach from 2010 to 2021, and (2) present geomorphology and vegetation data from four reaches monitored from 2009 to 2021. Vegetation sampling and geomorphology surveys were completed at varying intervals throughout the time period; this report looks at changes within single reaches and establishes a baseline for future comparisons. There are four monitoring reaches established on the Fremont River: (1) F-01, approximately 2.5 kilometers upstream of a knickpoint (sharp change in channel slope) and associated waterfall that emerged following construction of State Highway 24 in 1964, (2) F-07, in a large oxbow that was cut off due to the highway construction, (3) F-04, approximately 1.5 kilometers downstream of the knickpoint, and (4) F-14, approximately 4.8 kilometers downstream of the knickpoint. Geomorphic and vegetation surveys took place at all reaches. Hydrologic monitoring occurred only at F-01. From 2001 to 2021, the entire range of flows recorded at a gaging station on the Fremont River upstream of the park near Bicknell, Utah, decreased, with the steepest decreases occurring in the highest flow percentiles. Continuous hydrologic monitoring at reach F-01 in the park from 2010 to 2021 showed perennial flows in the Fremont River, with lower flows during the irrigation season (April 1?October 31). The irrigation season was also characterized by greater evapotranspiration, which may be exacerbated in the future due to higher air temperatures. Lower observed inputs and greater evapotranspiration suggest the Fremont River is at risk for progressively lower flows over time. While overbank flows occurred infrequently in the monitoring reach, inhibiting cottonwood recruitment, groundwater levels remained shallow enough to support mature cottonwood trees. Protecting spring snowmelt flows of 94 cfs (the average annual maximum 14-day rolling mean at reach F-01), or greater should maintain the current wetland vegetated zone. Maintaining the hydrologic record was challenging due to high-magnitude flood events and turbid flows; the park should consider a gaging station for an accurate discharge record. Geomorphic surveys showed net sediment deposition at reaches F-01 and F-14 in the channels, banks, and floodplains from 2009 to 2021, with more deposition occurring earlier in the study period. A large flood event in 2013 resulted in high flows and deposition of close to one meter at F-01. Only localized erosion occurred, and thalweg surveys showed that stream channels were either stable or increasing in elevation. Reach F-07, the abandoned oxbow, exhibited little geomorphic change over the study period. Riparian vegetation was characteristic of a Fremont cottonwood woodland, with canopy closure up to 30% and a mixed understory of shrubs and herbaceous species. Obligate wetland vegetation cover of 5%?10% was present at reaches F-01, F-04, and F-14. Reach F-07, in the oxbow, has transitioned to an upland system, with little to no canopy cover and no obligate wetland species. While mature cottonwoods were present in reaches F-01, F-04, and F-14, there was limited evidence of seedlings or saplings graduating into larger size classes. Cottonwood seedlings are primarily resprouts from beaver-browsed trees, although one seedling recruitment event was observed in 2014, following high flows in late 2013. Protecting some cottonwoods with chicken wire may help protect the larger size classes and maintain a mixed-age woodland. Exotic plant species cover was less than 10% in reaches F-01, F-04, and F-14. Efforts to control Russian olive (Eleagnus angustifolia) along the Fremont River appear to have been successful in these reaches. In reach F-07, exotic plant cover ranged from 9% to 25%, with notable spikes in Russian thistle (Salsola tragus) and cheatgrass (Bromus tectorum) in 2010 and 2011, respectively.