Russian River Watershed Land Use History, Existing Conditions, and Field Investigations
Total Page：16
File Type：pdf, Size：1020Kb
CHAPTER 4 Russian River Watershed Land Use History, Existing Conditions, and Field Investigations This chapter is divided into four main sections with each addressing key issues. Section 4.1 describes historical and current land uses that have resulted in the existing conditions, and the mining and reclamation history of the Hanson gravel ponds. Section 4.2 describes existing conditions and physical processes affecting aquatic habitat. The results of the feasibility study field investigations detailed in Chapter 3 are presented and discussed in Section 4.3. Section 4.4 describes the results of fish assemblage sampling. 4.1 Watershed land use history 4.1.1 Watershed description The 110-mile long Russian River mainstem contains five major alluvial valleys. From the northern headwaters in Mendocino County to the estuary in Sonoma County, the valleys are Ukiah, Hopland, Alexander, Middle Reach, and Santa Rosa Plain/Laguna de Santa Rosa (Figure 4.1.1). The geology of the Russian River catchment is predominated by accreted sea floor sediment and uplifted volcanic deposits that are highly faulted and thermally altered (Bailey et al. 1964; Hart et al. 1983). According to the USDA Natural Resource Conservation Service (1972), the watershed has relatively high erosion rates. The regional Mediterranean climate of generally wet winters and very dry summers is punctuated by the El Niño storm cycle, often producing flood events during the wet season on approximately a 4- to 5-year frequency. Numerous parallel faults across the region result in patterns of valleys and ranges that are overlain by the natural drainage network. Each of the alluvial valleys has a geologic constriction at their southern downstream outlet that produces backwater hydraulic conditions during flood events that, over geologic time have left the valleys filled with alluvium (river-derived deposits of silt to gravel) ranging from 30 to 100 feet deep. The most frequent and deepest flooding occurs in the downstream end of the valleys near the outlet areas. The combination of climate and geology result in relatively high watershed sediment loads, particularly during El Niño storm events, and relative quiescence during the longer time periods between larger El Niño driven storms. Historically, this was the dominant geomorphic process that created the sediment deposition zones and resulting aquatic habitat patterns found in the valleys. 4.1.2 Watershed assessment As described in Chapter 2, a watershed assessment is the first step in restoration planning and project development (Beechie et al. 2008), as clear problem definition is essential (Skidmore et al. 2013). A watershed assessment for the Russian River evaluated the physical processes that form and maintain habitat for each physiographic section of the watershed in order to understand the potential significance of floodplain restoration at the Hanson property. The assessment, included in its entirety in Appendix B, is the framework for comprehending the extent of watershed modifications and resulting impacts on aquatic habitats and salmonid populations. Chapter 4: Hanson Russian River Ponds Floodplain Restoration: Feasibility Study and Conceptual Design | 4-1 Figure 4.1.1 The Russian River Watershed showing major streams and alluvial valleys. From north to south the valleys are Potter, the Ukiah, Hopland, Alexander, Dry Creek, and Middle Reach Valleys, and the Santa Rosa Plain/Laguna de Santa Rosa. Chapter 4: Hanson Russian River Ponds Floodplain Restoration: Feasibility Study and Conceptual Design | 4-2 The results of this watershed assessment underscore two significant findings: 1. Every major alluvial valley and associated former floodplains have been significantly impacted by various flood control measures. Development has effectively eliminated the major floodplain associated aquatic habitats from the ecosystem, with a few small exceptions representing the remaining strongholds for salmonids - the Atascadero Creek/Green Valley wetland, and Willow Creek with a formerly altered floodplain that has been passively restored to wetland habitat. 2. The major remaining floodplain wetlands - Laguna de Santa Rosa and the Russian River estuary remain only partly functional. For the estuary, this is due to water levels maintained through mechanical breaching below the floodplain elevation, and in the case of the Laguna de Santa Rosa floodplain, channelization has diminished its ecological functions. The Laguna can be sizable in winter, but use by salmonids is poorly understood. The significance of floodplain habitat for salmonid populations has become clearer as results of rearing trials and various experiments and studies have been published in peer-reviewed journals (Grosholz and Gallo 2006, Bellmore et al. 2013, Jeffres et al. 2008, Sommer 2001, Lister et al. 1997, Lindsey et al. 2015, Katz et al. 2013). To gain a better understanding of former ecosystem attributes within the Middle Reach Valley, NMFS funded an historical ecology study carried out by the San Francisco Estuary Institute (SFEI). The restoration of lost or diminished ecosystem attributes identified in the SFEI study were incorporated into goals and objectives used to evaluate restoration alternatives considered in this feasibility study. 4.1.3 Historical ecology of the Middle Reach As noted above, San Francisco Estuary Institute was engaged to complete a reconnaissance-level historical ecology study of the pre-European Middle Reach Valley and channel conditions (SFEI 2014, Appendix B). SFEI located and compiled maps and photos from the early 1900s, and surveyor’s notes from the mid-1800s. This information, coupled with landscape descriptions from that era, provide important documentation of former ecosystem attributes. Prior to development of the Middle Reach Valley, the landscape was characterized by a broadly meandering, relatively shallow river channel flanked by sand and gravel bars often 1,000’ wide. Within that large, dynamically changing landscape was a rich array of seasonally important aquatic habitats including tributary and high flow channels, sloughs, and seasonally connected ponds and wetlands. The seasonal ponds (oxbow lakes formed from abandoned river channels) and a few deep perennial sloughs provided complex hydrologic structure within an extensive, dynamic, biologically complex, and likely highly productive floodplain. Floodplain inundation is the principal force determining productivity and biotic interactions in river–floodplain systems (Junk et al. 1989; Bayley 1991 and 1995) (Figure 4.1.2). Owing to their complex topography and relative proximity to the main river channel, these features likely provided extensive calm edgewater habitats in winter and spring, offering native species refuge from floods and predators as well as rich feeding areas. These former floodplains, annually integrated into the river system would have functioned as “nurseries” by providing habitat for fry recruitment and a wealth of opportunities for rapid growth of juveniles. In summer, some of the blind channel features, such as those labeled as sloughs, were probably sufficiently deep and well-connected to a cold water aquifer to provide thermal refuge for native fish species dependent on cold water habitats. Chapter 4: Hanson Russian River Ponds Floodplain Restoration: Feasibility Study and Conceptual Design | 4-3 Figure 4.1.2. Historical ecology of the Middle Reach Valley of the Russian River. The San Francisco Estuary Institute completed an historical ecology reconnaissance of the Middle Reach Valley. The photos illustrate the greater sinuosity of the river and the cutoff oxbows (meanders) that probably provided calm edgewater habitats in winter and spring offering refuge and feeding areas for salmonids. Each of the Russian River alluvial valleys and their floodplains likely possessed many of the habitat attributes revealed by the SFEI study for the Middle Reach Valley, because the geomorphic processes and conditions are comparable. 4.1.4 History of development and land use changes in the Middle Reach Early settlers, whose primary interest was agriculture, had been modifying the Russian River channel and its tributaries with fluvial engineering, concentrating and directing flood flows to excavate straighter and deeper drainage channels for a century prior to the first precision topography map (1933) and aerial photography (1942) of the valley. Historical valley forest land was cleared of conifers and hardwoods for livestock grazing (Ornduff 1974). A redwood sawmill operated at the mouth of Mark West Creek from 1820 to 1840 to serve the demand for building materials in the region (SFEI 2014); while hardwoods from the North Coastal Forest plant community were turned into charcoal to fuel the frontier’s energy demands. Today, hardwoods are sparse, and only a remnant stand of redwoods survives on the valley floor at Riverfront Regional Park. Although the Middle Reach Valley was already well into agricultural production with associated drainage and irrigation practices by 1950, the advent of earth-moving machinery following World War II triggered an unprecedented period of river channel and valley modification. The aerial photograph in Figure 4.1.3 from the mid-1950s looking upstream from the approximate location of today’s Riverfront Regional Park Chapter 4: Hanson Russian River Ponds Floodplain Restoration: Feasibility Study and Conceptual Design | 4-4 documents a recently dredged straight channel that severed three large-amplitude channel meanders winding