Biological Opinions - Bureau of Reclamation

Table 8.4 Potential emergent wetland habitat at the Williamson River Delta under different UKL elevations,
based on data in Elseroad (2004) and a GIS analysis of topographic data, and assuming no inundation of
emergent vegetation occurs below 4139.0 ft (1,261.6 m).
UKL
Elevation (ft)
4,143.0
(1,262.8 m)
4,142.0
(1,262.5 m)
4,141.0
(1,262.2 m)
4,140.0
(1,261.9 m)
4,139.0
(1,261.6 m)
Tulana Emergent
Wetland Area (ac)
Goose Bay Emergent
Wetland Area (ac)
Total Williamson River Delta
Emergent Wetland Area (ac)
1,080
1,560
2,640
(437 ha)
(631 ha)
(1,069 ha)
850
1,390
2,240
(344 ha)
(563 ha)
(907 ha)
580
1,080
1,660
(265 ha)
(437 ha)
(672 ha)
290
550
870
(118 ha)
(223 ha)
(352 ha)
0 0 0
At an elevation of 4,141.0 ft (1,261.9 m), approximately 1,600 ac (648 ha) of the potential
emergent vegetation habitat is available at the Williamson River Delta (Table 8.4). UKL surface
elevations at or above 4,141.0 ft (1,261.9 m) by the end of June occurred in one out of the 31
modeled years (year 1992; Table 8.1). By the end of July, lake levels drop another foot from
June levels (Table 8.5). The amount of emergent habitat available at the Williamson River Delta
in UKL declines from 2,640 ac (1,068 ha) at an elevation of 4,143.0 ft (1,262.8 m) to 870 ac
(352 ha) at an elevation of 4,140.0 ft (1,261.9 m; Table 8.4). At that elevation, any larvae not
present in the wetlands could be more vulnerable to entrainment at the outlet of the lake,
predation, and starvation. This would primarily affect SNS larvae because they are more
dependent on wetlands than LRS larvae (Terwilliger 2006; Simon et al. 2010, 2011). At that
elevation substantial larval mortality is likely because of the significant reductions in habitat that
would occur. However, elevations below 4,140.0 ft (1,261.9 m) at the end of July occurred in
only one year out of 31 modeled years (year 1992).
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