2.1. Study Area
The SRR is located in south-central Utah and is a tributary of the Green
River in the upper CRB (Figure 1). Like many desert river tributaries in
the arid southwestern United States, the SRR has experienced a number of
anthropogenic perturbations like dams, diversions and intensifying
climate shifts. These impacts have significantly altered its natural
hydrograph of high-magnitude, long-duration spring snowmelt-driven
floods and short-duration, monsoon-driven floods in late summer and
early fall (Webb & Betancourt, 1990; Fortney, Schmidt, & Dean, 2011;
Laub et al., 2013). The presence of reservoir and water-diversion
systems upstream on the SRR’s three tributaries causes the SRR to be one
of the most overallocated basins in Utah, where these reservoirs can
hold back all spring runoff with exception to those years with abundant
snowfall and snowmelt (Fortney et al., 2011). Another significant impact
to the SRR riverscape includes the invasion of nonnative tamarisk and
Russian olive (Elaeagnus angustifolia ), which has contributed to
vertical accretion of fine sediments, enhanced streambank stabilization,
channel narrowing and planform simplification (Manners, Schmidt, &
Scott, 2014). The loss of a natural flow regime, as well as the invasion
of nonnative vegetation, has caused the SRR to change from heterogenous,
diverse and multi-threaded system to a highly aggraded, simplified and
homogenous riverscape (Walker & Hudson, 2004; Pennock et al., 2021;).
Specifically, between 1938 and 2009, the system has narrowed 83% in the
lower 90 km, and the floodplain has vertically accreted between 1.0 and
2.5 m (Fortney et al., 2011). Reduced flow and exacerbated channel
simplification have also collectively altered habitat for native and
endemic fishes, significantly reducing the quality and availability of
complex habitat required for spawning, feeding, resting and rearing
necessary for their persistence (Bottcher, Walsworth, Thiede, Budy, &
Speas, 2013; Walsworth, Budy, & Thiede, 2013).