APPENDIX M RIPARIAN HABITAT DESCRIPTIONS FOR THE PROPOSED PROJET AREA

Transcription

1 APPENDIX M RIPARIAN HABITAT DESCRIPTIONS FOR THE PROPOSED PROJET AREA

2 1. Riparian Habitat along Local Area Rivers Rubicon River Rubicon River from Rubicon and Buck Island Reservoirs to Hell Hole Reservoir The Rubicon River downstream of Rubicon Reservoir is characterized by an incised channel with long stretches of bedrock and boulders confining small pools. Riparian vegetation along this reach consists of small, discrete patches supporting three vegetation communities: Mountain Alder, Lodgepole Pine, and Wet Meadow. Mountain alder (Alnus incana ssp. tenuifolia) was the dominant species in this reach (SMUD 2005). Rubicon River from Confluence with the South Fork Rubicon River to Oxbow Reservoir (Ralston Afterbay) The Rubicon River from the confluence with the South Fork Rubicon River to Oxbow Reservoir (also known as Ralston Afterbay) is a low-gradient river within a highly entrenched and confined channel. Boulders and cobble are dominant bed particle materials, although gravels are also plentiful, particularly in pools or other areas with reduced velocity. Riparian habitat occurs along more than 50 percent of the Rubicon River in this area, characterized by narrow continuous or discontinuous corridors supporting Alder-Willow-Cottonwood, and to a lesser extent, Alder-Willow vegetation communities. In general, the Alder-Willow vegetation community occurs in areas with bedrock and boulder substrates, while cottonwoods are part the vegetation community in areas with finer substrates and lower gradients (SMUD 2005). Gerle Creek from Loon Lake and Gerle Creek Reservoir to Confluence with the South Fork Rubicon River Gerle Creek below Loon Lake is a relatively small, primarily bedrock and boulder creek, with channel widths ranging from 10 to 40 feet wide. Riparian vegetation is present along most of the reach, consisting primarily of the Mountain Alder vegetation community, codominated by mountain alder, lodgepole pine (Pinus contorta), and various willow (Salix) species, depending on site conditions. Several large wet meadows are also present adjacent to Gerle Creek or within the floodplains of the creek in areas that are not bedrock-confined. Results of riparian studies conducted for the UARP indicated that riparian vegetation along several sub-reaches along Gerle Creek could be particularly susceptible to changes in streamflow resulting from UARP operations. (SMUD 2005). South Fork Rubicon River from Robbs Peak Reservoir to Confluence with Rubicon River South Fork Rubicon River is a small creek with channel widths ranging from 10 to 45 feet. The upper reaches of the creek have a moderate gradient and are composed of M-1

3 alluvial substrate. These reaches have a well-developed riparian corridor ranging from 4 to 65 feet wide and support Mountain Alder and, to a lesser extent, Willow vegetation communities. The lower reaches of the South Fork Rubicon River are steep and bedrockconfined and support only a few patches of Indian rhubarb (Darmera peltata) or small shrubs (SMUD 2005). Silver Creek South Fork Silver Creek from Ice House Reservoir to Junction Reservoir South Fork Silver Creek is approximately 15 to 41 feet wide just downstream of Ice House Reservoir, widening to 42 to 75 as it approaches Junction Reservoir. Riparian vegetation is found on the shoreline throughout most of this reach, characterized primarily by the Mountain Alder vegetation community, with smaller sections of Willow- Alder. Because the creek is set within a canyon, the riparian corridor, while often dense, is bounded by the canyon wall. The lower reaches of South Fork Silver Creek historically supported a conifer forest, which was destroyed in the Cleveland Fire of Several wetlands are present along South Fork Silver Creek, and may be connected with the creek at high flows. This includes a small wetland fed by drainage at the base of Ice House Dam that supports a population of Drosera rotundifolia (SMUD 2005). Silver Creek from Union Valley and Junction Reservoirs to Camino Reservoir Silver Creek downstream of Union Valley and Junction reservoirs is characterized by long stretches of bedrock that support limited riparian vegetation, composed of small, discontinuous patches of White Alder and Willow-Alder vegetation communities ranging from 3 to 35 feet wide (SMUD 2005). Silver Creek from Camino Reservoir to Confluence with South Fork American River Silver Creek downstream of Camino Reservoir is a relatively large (30 to 80 feet wide) stream that broadens to approximately 100 feet wide at the confluence with the South Fork American River. This stream reach is set within a deep, steep-sided valley. Riparian vegetation occurs in discontinuous stretches throughout the reach, limited by areas of bedrock and steep slopes. White Alder is the predominate vegetation community present, with small patches of Willow. The width of riparian areas ranges from 10 to 85 feet wide (SMUD 2005). Brush Creek from Brush Creek Reservoir to Slab Creek Reservoir Brush Creek is a small, steep, bedrock confined creek. No field data were obtained for this creek during studies conducted for the UARP. However, based on the steepness of the topography, riparian vegetation along Brush Creek is assumed to be minimal (SMUD 2005). M-2

4 Upper American River South Fork American River from Slab Creek and Chili Bar Reservoirs to Folsom Reservoir The South Fork America River downstream of Slab Creek Reservoir is 35 to 150 feet wide. It runs through a deep river canyon and is primarily bedrock-confined. Riparian vegetation grows along most of the shoreline, ranging from a thin line of shrubs to areas as wide as 85 feet. Small areas of vegetation also occur within the streambed, rooted on sandbars. Riparian vegetation in this stretch is characterized primarily as White Alder, with smaller areas of Willow, Wet Meadow, Mixed Riparian Hardwood, California Sycamore, and Fremont Cottonwood vegetation communities (SMUD 2005). Middle Fork American River from Oxbow Reservoir to Confluence with the North Fork American River The Middle Fork American River downstream of Oxbow Reservoir (also known as Ralston Afterbay) is entrenched in a wide canyon, with bed materials ranging from boulders, to cobble, to gravel, and dominance of smaller materials increasing with proximity to the North Fork American River. This stretch of the Middle Fork American River is characterized primarily by the Alder-Willow-Cottonwood community, with the addition of black locust (Robinia pseudoacacia) in several locations. Riparian vegetation is distributed as a continuous narrow corridor along the channel and bar margins, and relatively dense except in areas that have experienced bank failures or other mass wasting events, or in areas of exposed bedrock (PCWA 2007). North Fork American River from Confluence with the Middle Fork American River to Folsom Reservoir Riparian habitats in undisturbed areas along the North Fork American River from the confluence to Folsom Reservoir are similar to those for the Middle Fork American River downstream of Oxbow Reservoir described above. However, riparian habitat downstream of the confluence is highly disturbed as a result of Auburn Dam construction activities and the annual seasonal pump station installation. The riverbanks in this area are characterized by unstable slopes and rock outcrops, which are largely unvegetated or have ruderal vegetation. Pockets of mature oak woodland vegetation have persisted where slopes were not graded or disturbed. However, there is only limited riparian habitat present in this area (PCWA and USBR 2001). 2. Riparian Habitat at Local Area Reservoirs Upper American River Reservoirs M-3

5 Vegetation communities mapped around upper American River reservoirs operated by SMUD and PCWA (e.g., Hell Hole, Loon Lake, Union Valley, Ice House, Chili Bar, and Oxbow (Ralston Afterbay) reservoirs) are predominantly upland communities (e.g., oak woodland, mixed conifer-fir, and chaparral communities). Steep slopes and well-drained substrates (or bedrock) constrain the occurrence of riparian vegetation around these reservoirs, although thin bands, small patches, or individual shrubs or trees characteristic of riparian settings (e.g., Salix spp.) may occur. The drawdown zones of these reservoirs are generally devoid of vegetation either because they are composed of bedrock, or as a result of frequent water level fluctuations (i.e., periodic inundation followed by subsequent desiccation). While the drawdown areas may support sparse riparian vegetation (i.e., small numbers of willow shrubs), they do not support significant riparian habitats that would be adversely impacted by an incremental reduction in reservoir levels (SMUD 2005, PCWA 2007). Folsom Reservoir The shoreline of Folsom Reservoir supports primarily upland vegetation communities, including non-native grassland, blue oak-pine woodland, and mixed oak woodland. The reservoir rim (i.e., draw-down zone) is devoid of vegetation, with the exception of willow shrubs that have established in several areas that are not subject to fluctuations in water elevations. The only contiguous band of riparian vegetation occurring at Folsom Reservoir is along Sweetwater Creek, on the southern end of the reservoir (City-County Office of Metropolitan Water Planning 1999). 3. Riparian Habitat along Regional Area Rivers and the Delta Lower American River The channel morphology and riparian communities along the lower American River have been highly impacted by human activities over the past century, including gold mining; gravel dredging, urban development, levee building, water diversion, and the construction of the Folsom and Nimbus dams. The upper reaches of the lower American River were generally bedrock-confined, and characterized by narrow bands of alder-dominated vegetation communities. Toward the confluence with the Sacramento, the American River transitioned to a low gradient, semi-confined channel. Nutrient-rich sediment deposition within the floodplains of this portion of the river supported wide bands of riparian vegetation dominated primarily by Fremont cottonwood and willow species. Development of levees and dams has since confined the river to a substantially narrower channel, greatly reduced the magnitude and frequency of flood flows, and disrupted the transport and deposition of sediments. M-4

6 Riparian vegetation along the lower American River is likely in a state of ongoing and dynamic adjustment to human-influenced hydrologic and geomorphic conditions. Currently, a large portion of the lower American River in this reach is characterized by riparian forests dominated by Fremont cottonwood and willows. In addition, backwater ponds and lagoons are present throughout the reach, resulting from both natural gravel deposits and artificial dredging. Examples of these ponds are located at Sacramento bar, Arden Bar, Rossmoor Bar, and between Watt and Howe avenues (Sands, et al., 1985). Vegetation around these ponds is characterized primarily by mixed-age willow, alder, and cottonwood. (City-County Office of Metropolitan Water Planning 1999). Lower Sacramento River Historically, the Sacramento River was bordered by thick riparian forests dominated primarily by Fremont cottonwood, sycamore, and willows, with valley oak woodland covering the higher river terraces. However, beginning in the mid-1800s, riparian vegetation along the lower Sacramento River was removed for timber and agricultural development (e.g., pastures, orchards, vineyards, and row crops). In addition, water development projects, including channelization, dam and levee construction, bank protection, and flow regulation have altered the riparian system and contributed to vegetation loss. Levees along the approximately 60-mile length of the lower Sacramento River from the confluence with the American River to Collinsville were constructed immediately adjacent to the river, and riparian vegetation is therefore generally absent or consists of single rows of Fremont cottonwood, sycamore, or willow trees (Gibson, 1975). Sacramento-San Joaquin River Delta Located at the confluence of the Sacramento and San Joaquin rivers, the Sacramento-San Joaquin River Delta was once a large tidal freshwater marsh. Beginning in the 1800s, levees were built along river channels, and the land was drained to allow for agricultural development. As a result, the Delta today consists of 57 separate tracts or islands bounded by water. Lands on these islands are primarily agricultural fields, bordered by disturbed, non-native grasslands. Remnant native habitats include riparian vegetation, similar to that described above for the lower Sacramento River, as well as freshwater and brackish tule (bulrush) marshes. (City-County Office of Metropolitan Water Planning, 1999). Upper Sacramento River and Feather Rivers The upper Sacramento River (upstream of the confluence with the American River) and the Feather River are part of the CVP and SWP system located upstream of the lowest point of diversion considered in this Proposed Project. However, because the Proposed M-5

7 Project could potentially result in operational changes to these facilities, a brief description of the riparian resources of these waterways and reservoirs is provided here. As stated previously, the Sacramento River was bordered historically by extensive riparian forests dominated primarily by Fremont cottonwood, sycamore, and willows, with valley oak woodland covering the higher river terraces. Since then urbanization and agricultural conversion have been primary factors eliminating riparian habitat. Water development projects, including channelization, dam and levee construction, bank protection, and streamflow regulation have altered the riparian system and contributed to vegetation loss. However, remnant riparian habitats remain along the upper Sacramento River corridor from Shasta Dam to its confluence with the Feather River, and particularly along the river from Red Bluff to Colusa. Levee systems along this portion of the river are absent or are constructed more than one-half mile from the river, allowing the river to meander and fostering more natural river processes which, in areas not cleared for agriculture, support riparian habitats (Gibson, 1975). Feather River riparian forests downstream of Oroville Dam are fragmented and narrow compared to historic riparian forests. The majority of the trees associated with the riparian forests of the Feather River are broad leaved and deciduous. A wide range of riparian conditions exist along the Feather River floodplain. In many areas constrained by levees, urbanization, or agriculture, riparian vegetation may be a thin band of trees only one tree canopy wide with little to no understory. In other areas where the river is less constrained, large patches of riparian habitats exist. The dominant riparian vegetation types are similar to those of the Sacramento River (State of California Department of Water Resources 2004). 4. Riparian Habitat along Regional Area Reservoirs Shasta, Trinity, and Whiskeytown Reservoirs Habitats associated with these the Shasta, Trinity, and Whiskeytown reservoirs include primarily upland habitats such as ponderosa pine forest, non-native grassland, oak-pine woodlands, and chaparral. Much of the vegetation surrounding the reservoirs consists of forested habitats, with small enclaves of oak woodlands, grasslands, and chaparral, particularly near the dams. Pine forest habitats are located on the upland banks, and slopes of the reservoirs are dominated by ponderosa pine (Pinus ponderosa), Jeffrey pine (Pinus jeffreyi), Douglas fir (Pseudotsuga menziesii), madrone (Arbutus menziesii), and incense cedar (Calocedrus decurrens). Chaparral occurs in openings in the forest, and is characterized by several native shrubs such as manzanita (Arctostaphylos patula) and various species of ceanothus (Ceanothus sp.). Non-native grasslands and oak-pine woodlands are similar to habitats described for Folsom Reservoir. Similar to Folsom Reservoir, the draw down zone of these reservoirs are generally devoid of vegetation and M-6

8 contiguous riparian communities are not present in these areas; therefore, the draw down zones do not provide valuable plant communities or habitats (City-County Office of Metropolitan Water Planning, 1999). Oroville Reservoir Vegetation around Lake Oroville above the full-pool elevation consists of a variety of upland communities including tolerant mixed oak woodlands, foothill pine/mixed oak woodlands, and oak/pine woodlands with a mosaic of chaparral. Native riparian habitats were, and still are, restricted to narrow strips along drainages, consisting mostly of alders, willows, and occasional cottonwoods and sycamores. The annual water level fluctuations within the drawdown zone of Lake Oroville result from various natural precipitation/runoff events and project operations for water supply, hydropower generation, and flood control. These water level fluctuations create a harsh environment for establishment of plant cover within the drawdown zone. Loss of soil to wave action, periodic inundation; followed by severe desiccation have resulted in a generally barren drawdown zone (State of California Department of Water Resources 2004). M-7