Floodplain Restoration

Introduction

The Butte Creek Floodplain Reconnection and Channel Restoration Project will restore over two miles of floodplain and side channel rearing habitat for juvenile salmonids. The project covers the Honey Run unit of the 287-acre CDFW Butte Creek Canyon Ecological Reserve, which was acquiredfrom a gravel mining company after the flood of 1986. Butte Creek is one of only three Central Valley streams that has a population of Central Valley Spring-run Chinook Salmon. The project reach is immediately downstream from the Spring-run spawning grounds in Butte Creek Canyon. This section of Butte Creek is a highly disturbed landscape following nearly a century of gold dredging and gravel mining that extensively manipulated the floodplain and rerouted the channel.

Gold dredging occurring between 1902 and 1949 left piles of gravel tailings and an inverted floodplain soil profile ill-suited to high quality riparian forest. Subsequent gravel mining of these areas from the 1950s through 1970s created deep off-channel pits that create stranding, temperature, and predation hazards for salmonids. The project seeks to (a) expand the floodplain with a restored natural soil profile and healthy floodplain forest; (b) improve hydraulic connectivity between the river channel and this restored floodplain habitat; and (c) increase the effective channel length while creating side-channel rearing habitat for spring-run Chinook salmon.

The Friends of Butte Creek team evaluated aerial photos, hydraulic model results, lidar data, and channel geometry to select promising opportunities for restoring floodplain areas, restoring remnant side channels and reconnecting these areas to its floodplain. Project sites are in the historic Butte Creek floodplain and side channel depressions, where restored channels and floodplain improvements are more likely to persist into the future.

The lower reaches of the rearing areas of Butte Creek are a mixture of disturbed landscapes previously mined for gold, gravel and rock. The disturbance happened over a 100-year period from the 1849’s to the 1950’s. Activities included small to very large mechanical manipulations of the floodplain. Large scale dredging equipment and modern gravel extraction tools literally turned the entire floodplain profile upside down. Butte Creek was more-or-less in the way of the various mining operations and was pushed and diked from one side of the floodplain to the other. As the gravel extraction ended in the 1950’s, the land was left with numerous tailing piles (mining tailings), many large dredger ponds, failing roads and bridges scattered across the area. Most recently much of the privately held gravel extraction area was turned over to the CDFW’s Wildlife Conservation Board (WCB) which created the CDFW Butte Creek Ecological Reserve. This 287-acre reserve covers the floodplain from Highway 99 to approximately one mile south of the Honey Run Covered Bridge Park. In addition to this public land, the Butte Creek Ecological Reserve (BCEP) is contiguous upstream of the WCB reserve and adds 93 acres to this proposed restoration of the floodplain of Butte Creek. Formerly managed by CSU Chico, this preserve was transferred to the Mechoopda Indian Tribe of Chico Rancheria in 2022.

The wide riparian corridor, confined within Butte Creek Canyon, is highly disturbed by a history of gold dredging and gravel mining. In addition to gravel-bedded river channel areas vegetated with riparian woodland, a significant portion of the floodplain is occupied by gold dredge tailings that have been subsequently gravel-mined. These areas are isolated from the active channel, devoid of native vegetation, and contain large areas of seasonal and perennial standing water.

Source: CSU Chico Northeastern California Historical Photograph Collection

Dredger on Butte Creek just above the reserves, 1910

Source: CSU Chico Northeastern California Historical Photograph Collection (sc29540)

Butte Creek Canyon, looking upstream from Skyway

History

The history of mining in this area began during the Gold Rush in the mid-1800s. Gold mining initially occurred on the reach between Centerville and Helltown, starting with placer mining and then transitioning to hydraulic mining and drift mining of Tertiary gravels. The use of power shovels and washing plants began in the early 1900s. Dredging operations took place from around 1902 to the early 1920s, then again in the 1930s, and finally from 1945 to 1949 (Clark, 1976). Typical outcomes of these dredging operations include a reversal of the floodplain profile. Dredges excavate soil material from the top down, beginning with the coarse surface gravels and ending with finer materials including clays that were underlying the gravels. Depositing the tailings in reverse order, the finer materials end up closer to the surface, creating a layer of fines overlaying highly permeable coarse gravels. As described by Kondolf and Williams (2002):

Dredges move across the landscape on a pond of their own creation. As the head of the dredge chews into the floodplain, the tail end of the dredge disgorges the larger cobbles and gravel into piles of “tailings” at the other end of the pond. In this way, the dredge works the pond across the floodplain, leaving [a] characteristic series of elongated piles. . . . The finer sediments are sluiced for gold within the dredge and discharged into the pond, where they settle to the bottom, to be covered later by the tailing piles as the dredge moves along. As a result, the alluvium is inverted; the soil and fine-grained sediments normally at the surface and interspersed through the alluvial sediments are buried, leaving barren piles of relatively uniform cobble across the landscape (Kondolf and Williams, 2002, p. 66).

Butte Creek was also diked and its channel moved to the side of the floodplain to make way for gravel mining operations. Piles of mine tailings were deposited in the floodplain, creating poor quality habitat. Pits and ponds, dug below the water table such that they fill with water, have been left in place. Not only do these features pose a stranding hazard for fish, but they also have significant and potentially deleterious geomorphic impacts: located adjacent to the active channel, they can readily be captured by the channel during high flows, which occurred in the project site during the floods of 1986. In general, Butte Creek along the project reach is highly unstable and prone to jumps, channel avulsions, and cutoffs during high flows.

Fisheries

Butte Creek is one of only three Central Valley streams that has a population of federally and State threatened CV Spring-run Chinook Salmon (Spring-run). Butte Creek is also habitat for threatened CCC Steelhead (steelhead). CDFW has specifically identified portions of Lower Butte Creek as a high priority for assessment due to ongoing poor habitat, water quality and quantity concerns and recorded observations of mortality of both upstream migrating salmon and downstream migrating juvenile salmon and steelhead.

Butte Creek has also been identified as a priority area for salmon and steelhead habitat restoration under the CVPIA Near-term Restoration Strategy (NTRS). Butte Creek juvenile salmonid habitat restoration as related to survival is identified in the NTRS as Action 7: “Improve survival in Butte Creek in downstream areas.” The Project would address NTRS Action 7 by restoring over two miles of historic juvenile salmonid floodplain and side channel rearing habitat along Lower Butte Creek that was debased by intensive gravel and gold mining in the late 1800s early 1900s. Salmonid growth associated with floodplain habitat has been shown in several studies to increase survival into adulthood (Sommer et al. 2001, Sommer et al. 2005). As juvenile rearing habitat is restored throughout the Lower Butte Creek floodplain, chances of survival for juvenile salmonids on their way to the Pacific will increase due to better habitat (for feeding and cover) early in their journey (Limm et al. 2009).

Along with restoring up to 320 acres of floodplain habitat, the Project would create or improve hydraulic connectivity between the river channel and this restored floodplain habitat. In addition, this area of the Butte Creek meets Reclamation’s goals for their CVP Habitat and Facility Improvement Program whose main aim is to protect, to restore, and to enhance fish, wildlife, and associated habitats.