Tidal Channel Reference Model

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delineation of delta islands and channels - South Fork Skagit

Tidal channels naturally form in marshes and allow for the movement of water and fish. The geometry of naturally formed tidal channels is consistent and controlled by the size of the marsh island. Using delta island area, parameters like tidal channel length, number of side channels, number of channel mouths, can be predicted. This project measures existing tidal channel networks in Puget Sound. A second phase of work examines the available aerial photo record for sites where there has been accidental or intentional breaching or removal of dikes, and observes the rate of channel formation following restoration of tidal flow.

Following early work in the Chehalis Estuary (Hood 2002) and the Skagit Delta (Hood 2007), SRSC with support from ESRP and NOAA Restoration Center is completing a reference model for Puget Sound tidal channels. This project will support the following activities in the delta restoration community:

  1. Design of channel restoration projects based on delta island area.
  2. Quantification of the recovery of delta function as a proportion of total potential function.
  3. Use of channel parameters as a tool for estimating fish rearing services, allowing estimation of restoration project benefits and comparison of alternative restoration designs.
  4. Quantification of pilot channel excavation as method for accelerating recovery of function.
  5. Prediction of the effects of restoration context on recovered channel geometry

Relationship to other Topics and Efforts

This is a product of the River Delta Adaptive Management Strategy, and is anticipated to support more robust evaluation of project effectiveness under the Delta metrics project. This work is improving our understanding of Delta salmon utilization and Delta hydrodynamics and channels, and more specifically Development of tidal channels following restoration.

Predicting Rate of channel development for restoration sites and natural breach sites

Documents and Presentations


  • All delta island systems in Puget Sound with naturally formed channel systems are measured at 14 study sites—including all river deltas as identified by Simenstad et al 2011, not including the Duwamish, Puyallup, Deschutes, Samish, Dungeness and Elwha, Separating Nooksack and Lummi, and including Tahuya and Union Rivers.
  • Using regression models, island area is used to predict channel geometry including: total channel length, largest channel length, total channel area, number of channels mouths, number of first order channels in the largest network, outlet width, and number of tributaries to the largest channel.
  • For most metrics, island area explained a large portion of the variation in channel measurements. Residual error was highest in predicting channel count and outlet width, and among pocket estuaries.
  • While slope (the scaling function) was not significantly different among sites, the intercept varied among sites (some sites consistently had higher channel measurements for the same island area).
  • Tidal range and wave height appears to explain much of this difference among sites, with higher tidal range increasing channel metrics, and higher wave height decreasing channel metrics.
  • The area of channel, partially indicative of delta salmon utilization has a non-linear relationship to island area, such that larger projects are likely to provide more habitat services per acre than smaller projects, such that restoration of one 200 acre marsh will provide more services that restoration of two 100 acre marshes.