Gravel Augmentation Sites

New Gravel Augmentation Sites Proposed for 2023

Project Background

The Trinity River Restoration Program (TRRP or Program) is beginning a 30-day public scoping period to announce and explain the need to develop additional gravel augmentation sites upstream of Indian Creek on the Trinity River mainstem. We now request input from stakeholders and interested parties.

Following the 2000 Record of Decision (ROD), the U.S. Department of Interior (DOI) established TRRP to restore the fisheries of the Trinity River affected by dam construction and related diversions of the Trinity River Division of the Central Valley Project1.

Photo of gravel augmentation near Trinity River Hatchery in summer 2021

Gravel augmentation near Trinity River Hatchery in summer 2021

Administered by the U.S. Bureau of Reclamation (Reclamation), the TRRP is a partnership of federal and state resource agencies, Tribes, and Trinity County. The Program works to restore the processes and attributes of a properly functioning river to support the recovery of diminished salmon and steelhead populations while retaining Trinity and Lewiston dams’ deliveries of water and power to California’s Central Valley.

There are five primary components of TRRP’s river restoration work:

  1. Variable annual instream flows: releasing water from Lewiston Dam, based on the water year type2, to mimic natural Trinity River flows and interact with downstream areas to enhance conditions for all life stages of fish and wildlife. These variable annual instream flows are also known as “restoration releases.”
    • 2 TRRP uses five water year types to determine how much water will be available to the Trinity River each year. The five water year types are: Critically Dry, Dry, Normal, Wet, and Extremely Wet. A wetter water year means more water is available for restoration flow releases.
  2. Channel rehabilitation: reconnecting the river to functional and complex floodplains, side channels, and alcoves, and promoting alternate bar sequences and low-velocity habitat for salmonid fry. Channel rehabilitation also increases instream habitat complexity and enables the river to return to a more self-supporting alluvial system in both treated and untreated areas.
  3. Sediment management: reintroducing gravel (aka coarse sediment) to the river. Gravel augmentation replenishes spawning areas for salmon and provides other habitat benefits. Gravel entering the river system upstream of the dams is blocked from being transported to the Trinity River below Lewiston Dam, creating a gravel deficit over time. TRRP resupplies the river with gravel to counterbalance the Dam’s impact on gravel supplies that would otherwise be provided naturally. Current analyses show that gravel augmented by TRRP does not transport as far downstream as originally anticipated. Thus, these additional augmentation sites are under consideration to mitigate the ongoing gravel deficit in parts of the river.
  4. Watershed restoration: reducing the impact of land management activities in tributary basins (i.e., streams) of the Trinity River, primarily by controlling fine sediments that can harm aquatic life and by addressing barriers to fish passage in those tributaries.
  5. Adaptive management: monitoring river restoration actions, evaluating the outcomes from those actions, and informing methods to improve the effectiveness of future management actions.

TRRP proposes to expand the number of areas permitted for sediment management (Primary TRRP Component #3) in the Trinity River above the confluence of Indian Creek. A deficit of sediment (gravel and small cobble) occurs because Trinity and Lewiston dams not only trap water but also the supply of gravel and cobble from upstream areas. Gravel, cobble, and fine sediment supplied by the river’s tributaries, like Rush Creek, Deadwood Creek, and Indian Creek, for example, help balance the river’s ability to transport material to downstream areas. With a substantial portion of the watershed blocked by the dams that would otherwise supply sediment to the Trinity River, the river section closest to Lewiston Dam (near River Mile [RM] 112; Figure 1) transports gravel and cobble quicker than the river can naturally replace it. Trinity River analyses indicate that the deficit of gravel and small cobble extends downstream to Indian Creek3 (at RM 94), but current TRRP augmentation sites cannot adequately transport gravel throughout that section of river4. After the confluence of Indian Creek, other tributaries like Reading Creek, Weaver Creek, and Browns Creek supply enough gravel and small cobble to balance the “sediment budget.” For that reason, TRRP proposes new augmentation sites upstream of Indian Creek only.

Augmentation helps to restore healthy river attributes to the dammed Trinity River. In a natural river system, a river’s channel bed is frequently mobilized during high flows. When the gravel and small cobble of the riverbed is mobilized, gravel and cobble bars are scoured and redeposited. Augmentation is intended to increase the availability and quality of physical habitat in the river channel by promoting scour and fill processes that, through flow, maintain bars, pools, juvenile rearing habitat, spawning beds, and other elements of channel complexity. As long as the dams are in place, there will be a need to add material (e.g., gravel and wood) that would otherwise be provided naturally from the blocked watershed area above the dams.

The purpose of this notice is to invite you to provide input, site-specific suggestions, or concerns you may have about the project during a public scoping period, pursuant to 40 CFR § 1501.95. This scoping notice includes a general description of the New Gravel Augmentation Sites (Proposed Action), with options, and the purpose and need of the project to encourage your informed participation.

  • 5 Council on Environmental Quality (CEQ) National Environmental Policy Act Implementation Regulations. 40 CFR Parts 1500–1508 (2020).
New Gravel Augmentation Sites Goals and Objectives

Currently, TRRP augments gravel at five permitted sites below Lewiston Dam (Figure 1). For augmentation purposes, we propose to add as many as nine new sites. From upstream to downstream, the new sites being investigated include Dark Gulch, Bucktail, Trinity House Gulch, China Gulch, Steelbridge, and Vitzthum Gulch (Figure 1). The potential benefits of augmenting in new areas of the Trinity River upstream of the confluence of Indian Creek include:

Photo of Chinook over spawning gravel (photo credit Thomas Dunklin).

Chinook over spawning gravel (photo credit
Thomas Dunklin).

  • Providing material to the river that will create a more natural bar, riffle, pool sequence.
  • Creating bars and pools in the river channel by encouraging the scour and fill processes that form them.
  • Providing additional juvenile rearing habitat in the river channel as opposed to floodplain rearing habitat that is only made available during high flows.
  • Creating and maintaining spawning beds for redd formation by adult salmon.
  • Improving the overall elements of channel complexity.
General Description of Proposed Action

Gravel would be introduced in proximity to proposed new gravel augmentation sites based on site-specific annual recommendations from the TRRP’s Physical Workgroup ( While annual gravel placement recommendations would depend on the water year, location, and site-specific needs, in general, gravel from 0.375 inch to 5 inches in diameter would be added during winter or summer placement. Gravel additions would generally range from 500 to 2000 yds (50 to 200 trucks full) at a location.

Depending on access agreements reached with local landowners at proposed locations, gravel would be trucked into sites for winter or summer placement, or processing of local material (e.g., tailings piles) may provide gravel in some proposed locations without trucking. Gravel augmentation might also include larger cobbles to support long-term gravel bar development and habitat in the area.

Depending on the source of gravel to be added, TRRP would work with locals to minimize the impact of trucking on their neighborhoods. Trucking speeds would be kept slow and hauling schedules would be timed to minimize residential impacts. If used, County or private roads would be maintained, and public safety would be supported by signage and other safeguards.

Figure 1: Map of current augmentation sites (in blue) and proposed augmentation sites (in red).

Figure 1: Map of current augmentation sites (in blue) and proposed augmentation sites (in red).

Possible Impacts

The Public Draft EA for this proposed management action will address potential impacts to:

  • Water clarity during placement
  • County-maintained roads and the public during gravel transportation through neighborhoods along
    the river
  • Local communities from noise during rock processing and placement
  • Cultural resources and historic properties
  • The fishery, wildlife, vegetation, and wetlands
  • Other impacts determined during analyses and scoping
Proposed Project Schedule

To Comment on this Gravel Augmentation Scoping Proposal:

  • Please provide all comments by April 17, 2022, to be fully considered by TRRP staff.
  • Send your comments via mail to:
       Gravel Augmentation Sites Scoping
       C/O TRRP
       P.O. Box 1300
       Weaverville, CA 96093
  • OR send your comments via email to Be sure to include the word GRAVEL in your email’s subject line.
Public Scoping:
March 17 – April 17, 2022

Draft EA for public comment:
Fall 2022

Final EA and Decision:
Fall-Winter 2022 – 2023

Proposed implementation:
Use of newly permitted augmentation sites for processing mine tailings or placing rock in the river could begin as early as winter 2022/2023.