Trinity River Geo-Physical Services

TRGV Crew collecting simultaneous ADCP and conventional Price AA meter streamflow measurements

The mainstem Trinity River drains a 2,036 square mile watershed (excluding the South Fork Trinity) joining the Klamath River at Weitchpec, some 43 miles above the Klamath’s entry into the Pacific Ocean. The Trinity River is the largest tributary to the Klamath River and historically produced large runs of Chinook (Oncorhynchus tshawytscha), Coho (Oncorhynchus kisutch) salmon and steelhead trout (Oncorhynchus mykiss). Impacts from industrial gold mining and logging in the early to mid-1900s substantially changed the mainstem and tributary channels. Placer mining overturned the streambeds and washed hillslopes into stream channels; while logging of highly erosive watersheds, such as Grass Valley Creek, introduced considerable quantities of sand into the mainstem. In 1955, Congress authorized construction of the Trinity River Division (TRD), a component of the Central Valley Project (CVP). The TRD consists of two large dams on the upper Trinity River, along with associated structures used to divert water out of the Trinity River Basin. Although Congress stated that the principal purpose of the TRD was to increase water supplies for irrigation and other beneficial uses in the Central Valley of California, Congress also directed the Secretary of the U.S. Department of the Interior (Secretary) to “… adopt appropriate measures to insure the preservation and propagation of fish and wildlife in the Trinity River Basin.” Both the construction and operation of theTRD have had severe effects on fish and wildlife habitats below Lewiston Dam.

In an effort to restore Trinity River fish and wildlife, the Secretary of the Interior directed the U.S. Fish and Wildlife Service to prepare the Trinity River Flow Evaluation Study in 1981. The TRFE produced recommendations “to fulfill fish and wildlife mandates” of the Congressional Act authorizing the Trinity River Diversion.  The study also provided the basis for the Trinity River Mainstem Fishery Restoration Environmental Impact Statement/Environmental Impact Report and the Record of Decision signed in 2000 (ROD). The ROD established the Trinity River Restoration Program (TRRP) with minimum water volume allocations based annually on water year type. The TRRP’s purpose is to restore and maintain the natural production of fish and wildlife populations in the Trinity River, downstream of Lewiston Dam.

Under the Trinity River Geo-Physical services contract, GMA fulfills the need for services covering physical data, including the following tasks:

  • Sediment Monitoring,
  • Stream Gaging and Discharge Records Computation,
  • Bathymetric Surveys,
  • Aerial Photogrammetry and LiDAR,
  • Other Geomatic Services, and
  • Data Product Synthesis.


Sediment Monitoring

Sediment transport monitoring by GMA, in various forms, has periodically occurred at a range of sites in the TRRP study area during the last thirty years. Sediment transport monitoring is intended to estimate the inputs and outputs to mainstem sediment budget cells, which support flow scheduling (e.g., determining flow magnitude and duration) and sediment management efforts (e.g., sediment budgeting and gravel management planning).

The monitoring stations were designed to provide sediment flux data for the four mainstem sediment budget cells between Lewiston Dam and Douglas City. The larger tributaries, Deadwood, Rush, Grass Valley, Indian, Weaver, and Reading Creeks, provide the majority of the natural sediment contributions for the mainstem within the study area. The downstream-most sediment budget boundary is located near Douglas City, where additional streamflow and sediment contributions (from Indian, Weaver, and Reading Creeks) significantly reduce the coarse sediment and streamflow deficits.

The overall objectives for each Spring Flow Release (SFR) are to determine the rate, volume (load) and texture of total sediment load at the four monitoring locations. GMA has developed an extensive cataraft-based sediment data collection programs that operate on large rivers in high velocity conditions.  GMA has successfully sampled on the Trinity River up to 11,000 cfs using this equipment. In addition to sediment data collection, GMA operates 3 continuous turbidity stations, 1 streamflow station and collects ancillary geomorphic data in relation to the SFR including; sediment monitoring site cross section surveys, pebble counts and water surface slope data.

In addition to sediment transport monitoring GMA is responsible for documenting or collecting data regarding the following;

  • Surface and Subsurface Substrate Composition,
  • Substrate Photo Monitoring,
  • Cross Section Surveys,
  • Water Surface Profiles, and
  • Water Velocity Surveys

Trinity River resource managers utilize the data that GMA provides to determine the relative effect of natural and anthropogenic influences on restoration goals such as complete sediment routing and the flushing of fine sediments from spawning features.

Bathymetric Surveys

GMA conducts various types of bathymetric surveys along the 42-mile Focal Reach of the Trinity R.  Surveys include As-built documentation of channel rehabilitation projects, geomorphic monitoring surveys used to track and evaluate gravel injections, and system wide surveys that are used to support a full range of scientific analysis such as fish habitat assessment, geomorphic monitoring and sediment transport, and restoration design.  Surveys are accomplished using a combination of boat-based sonar and land-based survey equipment and include all major side channels and channel margins that are necessary to develop a high resolution Digital Terrain Models (DTM’s).  Bathymetric surveys include quality assurance and quality control ground survey check points that are used for accuracy assessment and are regularly integrated with LiDAR datasets to produce Digital Terrain Models (DTM’s) that meet or exceed vertical accuracy standards for 2 ft. contours products   

Aerial Photogrammetry and LiDAR

GMA along with its project partners perform numerous types of aerial surveys along the Trinity R. including color-infrared orthophotography,  photogrammetry, and LiDAR surveys.  Data collection on the Trinity R. requires a multidisciplinary approach as projects range in size from less than 1-river mile to the entire 42-mile Focal Reach.  Smaller projects may utilize Small Unmanned Air system (sUAS) while larger projects require the data collection from full size aircraft.

Geomatic Services

Other Geomatic surveys that GMA provides for the Trinity River Project include:

  • Licensed Surveyor Services,
  • Terrestrial and Boat-Based Laser Scanning,
  • Oblique, Dimensionable Panoramic Photography of River Banks, and
  • Oblique, Dimensionable Structure From Motion (SfM) or River Banks

Synthesis Data Products

Synthesis products on the Trinity R. typically include integration and certification of various survey products to form highly detailed Digital Terrain Models (DTM’s).  Terrain models are developed for channel rehabilitation projects, site-specific geomorphic monitoring projects, gravel injections, tributary delta’s, and for the entire Focal Reach.  Synthesis data product development includes integration of LiDAR, sonar, and ground-based surveys to produce a certified DTM of the area of interest.  DTM’s are required to meet or exceed  vertical accuracy standards for 2 ft. contours and often exceed 1 ft. contours.  Synthesis products are delivered in a data package format that is well organized, documented, and accessible for rapid use by TRRP partners, stakeholders, and the public.