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Chris Chickadel

Principal Oceanographer

Affiliate Assistant Professor, Civil and Environmental Engineering






B.S. Oceanography, University of Washington, 1997

M.S. Oceanography, Oregon State University, 2003

Ph. D. Oceanography, Oregon State University, 2007


COHerent STructures in Rivers and Estuaries eXperiment

The experiment is a four-year collaborative project that couples state-of-the-art remote sensing and in situ measurements with advanced numerical modeling to characterize coherent structures in river and estuarine flows.

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Coherent structures are generated in rivers and estuaries when the flow interacts with bathymetric and coastline features or when density stratification causes a gradient in surface properties. These coherent structures produce surface signatures that can be detected and quantified using remote sensing techniques. A second objective of this project is to determine the extent to which these remotely sensed signatures can be used to initialize and guide predictive models.

The study site selected for Year 1 and Year 2 field operations was the Snohomish River in Everett, WA. Its annual mean flow of approximately 300 cubic meters per second is the third largest discharge into Puget Sound. The mouth of the river is defined by the city of Everett to the west (man-influenced) and Jetty Island to the east (natural). The river is dredged to a nominal depth of 5 m from the mouth at the south end of Jetty Island to approximately 12 km upstream, while the undredged depth is nominally 1-3 m. Thus the river profile is a compound channel, with the full 300 m width at Jetty Island containing the dredged channel of about 50 m width. The tidal forcing is strong, with the tidal range representing up to 2/3 of the river%u2019s mean depth. There is a bypass between the north end of Jetty Island and the mainland that connects to a mudflat area. During high tides, the river flow bifurcates between the main channel and this bypass, while at low tide very little flow occurs in the bypass. A sill extends from the north tip of Jetty Island to the southeast toward the opposite bank. The depth along this sill varies from 2 m to 5 m and terminates in a large scour hole in the middle of the channel with a depth of about 10 m.

This research is being conducted by a partnership of experts in remote sensing, numerical modeling, and estuarine dynamics from the University of Washington (Applied Physics Laboratory, Civil and Environmental Engineering, and Oceanography) and Stanford University (Environmental Fluid Mechanics Laboratory). The program is funded by a Multidisciplinary University Research Initiative (MURI) grant sponsored by the Office of Naval Research.

Tidal Flats

Under an ONR-sponsored Department Research Initiative researchers are studying thermal signatures of inter-tidal sediments. The goal is to understand how sediment properties feedback on morphology and circulation, and the extent to which such properties
can be sensed remotely.



2000-present and while at APL-UW

Thermal infrared multipath reflection from breaking waves observed at large incidence angles

Branch, R., C.C. Chickadel, and A.T. Jessup, "Thermal infrared multipath reflection from breaking waves observed at large incidence angles," IEEE Trans. Geosci. Remote Sens., 52, 249-256, doi:10.1109/TGRS.2013.2238241, 2014.

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1 Jan 2014

The infrared signature of breaking waves at large incidence angles was investigated using laboratory experiments and a radiometric model. Infrared imagery of the water surface at incidence angles greater than 70° shows multipath reflections for both spilling and plunging waves generated using a programmable wave maker. For the spilling breakers, the multipath signature was initially distinct from the breaking wave front roller signature but then merged to create a single large bright distributed target. For the plunging breakers, the roller and multipath signatures overlapped from the inception of breaking. The radiance of the multipath reflection was higher than the surrounding water for simulated cold sky conditions and lower for a simulated warm sky. A specular double-reflection model successfully predicted the presence of multipath reflection but the magnitude was sensitive to small uncertainties in geometry, wave slope, and input temperatures. The results show that multipath reflection from breaking waves is characteristic of large incidence angle infrared measurements and increases the area and magnitude of the infrared signature of breaking waves compared to the background.

Thermal observations of drainage from a mud flat

Rinehimer, J. P., J. Thomson, and C.C. Chickadel, "Thermal observations of drainage from a mud flat," Cont. Shelf. Res., 60, S125-S135, doi:10.1016/j.csr.2012.11.001, 2013.

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15 Jun 2013

Incised channels on tidal flats create a complex flow network conveying water on and off the flat during the tidal cycle. In situ and remotely sensed field observations of water drainage and temperature in a secondary channel on a muddy tidal flat in Willapa Bay, Washington (USA) are presented and a novel technique, employing infrared imagery, is used to estimate surface velocities when the water depth in the channel becomes too shallow for ADCP measurements, i.e., less than 10 cm. Two distinct dynamic regimes are apparent in the resulting observations: ebb-tidal flow and the post-ebb discharge period. Ebb tide velocities result from the surface slope associated with the receding tidal elevation whereas the post-ebb discharge continues throughout the low tide period and obeys uniform open-channel flow dynamics. Volume transport calculations and a model of post-ebb runoff temperatures support the hypothesis that remnant water on the flats is the source of the post-ebb discharge.

Frontogenesis and frontal progression of a trapping-generated estuarine convergence front and its influence on mixing and stratification

Giddings, S.N., D.A. Fong, S.G. Monismith, C.C. Chickadel, K.A. Edwards, W.J. Plant, B. Wang, O.B. Fringer, A.R. Horner-Devine, and A.T. Jessup, "Frontogenesis and frontal progression of a trapping-generated estuarine convergence front and its influence on mixing and stratification," Estuar. Coasts, 35, 665-681, doi:10.1007/s12237-011-9453-z, 2012.

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1 Mar 2012

Estuarine fronts are well known to influence transport of waterborne constituents such as phytoplankton and sediment, yet due to their ephemeral nature, capturing the physical driving mechanisms and their influence on stratification and mixing is difficult. We investigate a repetitive estuarine frontal feature in the Snohomish River Estuary that results from complex bathymetric shoal/channel interactions. In particular, we highlight a trapping mechanism by which mid-density water trapped over intertidal mudflats converges with dense water in the main channel forming a sharp front. The frontal density interface is maintained via convergent transverse circulation driven by the competition of lateral baroclinic and centrifugal forcing. The frontal presence and propagation give rise to spatial and temporal variations in stratification and vertical mixing. Importantly, this front leads to enhanced stratification and suppressed vertical mixing at the end of the large flood tide, in contrast to what is found in many estuarine systems. The observed mechanism fits within the broader context of frontogenesis mechanisms in which varying bathymetry drives lateral convergence and baroclinic forcing. We expect similar trapping-generated fronts may occur in a wide variety of estuaries with shoal/channel morphology and/or braided channels and will similarly influence stratification, mixing, and transport.

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Infrared-based measurements of velocity, turbulent kinetic energy, and dissipation at the water surface in a tidal river

Chickadel, C.C., S.A. Talke, A.R Horner-Devine, and A.T. Jessup, "Infrared-based measurements of velocity, turbulent kinetic energy, and dissipation at the water surface in a tidal river," IEEE Geosci. Remote Sens. Lett., 8, 849-853, doi:10.1109/LGRS.2011.2125942, 2011.

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1 Sep 2011

Thermal infrared (IR)-based particle image velocimetry (PIV) is used to measure the evolution of velocity, turbulent kinetic energy (TKE), and the TKE dissipation rate at the water surface in the tidally influenced Snohomish River. Patterns of temperature variability in the IR imagery arise from disruption of the cool-skin layer and are used to estimate the 2-D velocity field. Comparisons of IR-based PIV mean velocity made with a colocated acoustic velocimeter demonstrate high correlation. IR-based PIV provides detailed measurements of previously inaccessible surface velocities and turbulence statistics.

Mixing layer dynamics in separated flow over an estuarine sill with variable stratification

Talke, S.A., A.R. Horner-Devine, and C.C. Chickadel, "Mixing layer dynamics in separated flow over an estuarine sill with variable stratification," J. Geophys. Res., 115, doi:10.1029/2009JC005467, 2010.

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4 Sep 2010

We investigate the generation of a mixing layer in the separated flow behind an estuarine sill (height H ~4 m) in the Snohomish River, Washington as part of a larger investigation of coherent structures using remote and in situ sensing. During increasing ebb flows the depth and stratification decrease and a region of sheared flow characterized by elevated production of turbulent kinetic energy develops. Profiles of velocity and acoustic backscatter exhibit coherent fluctuations of order 0.1 Hz and are used to define the boundaries of the mixing layer. Variations in the mixing layer width and its embedded coherent structures are caused by changes to both the normalized sill height H/d and to a bulk Richardson number Rih defined using the depth of flow over the sill. Entrainment ET and the mixing layer expansion angle increase as stratification and the bulk Richardson number decrease; this relationship is parameterized as ET = 0.07Rih-0.5 and is valid for approximately 0.1 < Rih < 2.8.

Available comparisons with literature for inertially dominated conditions (Rih < 0.1) are consistent with our data and validate our approach, though lateral gradients may introduce an upwards bias of approximately 20%. As the ratio H/d increases over the ebb, the free surface boundary pushes the mixing layer trajectory downward, reduces its expansion angle, and produces asymmetry in the acoustic backscatter (coherent structures). Three-dimensional divergence, as imaged by infrared video and transecting data, becomes more prominent for H/d > 0.8 due to blocking of flow by the sill.

Remotely sensed river surface features compared with modeling and in situ measurements

Plant, W.J., R. Branch, G. Chatham, C.C. Chickadel, K. Hayes, B. Hayworth, A. Horner-Devine, A. Jessup, D.A. Fong, O.B. Fringer, S.N. Giddings, S. Monismith, and B. Wang, "Remotely sensed river surface features compared with modeling and in situ measurements," J. Geophys. Res., 114, doi:10.1029/2009JC005440, 2009.

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3 Nov 2009

Images of river surface features that reflect the bathymetry and flow in the river have been obtained using remote sensing at microwave, visible, and infrared frequencies. The experiments were conducted at Jetty Island near the mouth of the Snohomish River at Everett, Washington, where complex tidal flow occurs over a varied bathymetry, which was measured as part of these experiments. An X band (9.36 GHz) Doppler radar was operated from the river bank and produced images of normalized radar cross sections and radial surface velocities every 20 min over many tidal cycles. The visible and infrared instruments were flown in an airplane. All of these techniques showed surface evidence of frontal features, flow over a sill, and flow conditioned by a deep hole. These features were modeled numerically, and the model results correspond well to the remote observations. In situ measurements made near the hole showed that changes in measured velocities correlate well with the occurrence of the features in the images. In addition to tidal phase, the occurrence of these features in the imagery depends on tidal range. The surface roughness observed in the imagery appears to be generated by the bathymetry and flow themselves rather than by the modulation of wind waves.

Vertical boil propagation from a submerged estuarine sill

Chickadel, C.C., A.R. Horner-Devine, S.A. Talke, and A.T. Jessup, "Vertical boil propagation from a submerged estuarine sill," Geophys. Res. Lett., 36, doi:10.1029/2009GL037278, 2009.

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20 May 2009

Surface disruptions by boils during strong tidal flows over a rocky sill were observed in thermal infrared imagery collected at the Snohomish River estuary in Washington State. Locations of boil disruptions and boil diameters at the surface were quantified and are used to test an idealized model of vertical boil propagation. The model is developed as a two-dimensional approximation of a three-dimensional vortex loop, and boil vorticity is derived from the flow shear over the sill. Predictions of boil disruption locations were determined from the modeled vertical velocity, the sill depth, and the over-sill velocity. Predictions by the vertical velocity model agree well with measured locations (rms difference 3.0 m) and improve by using measured velocity and shear (rms difference 1.8 m). In comparison, a boil-surfacing model derived from laboratory turbulent mixed-layer wakes agrees with the measurements only when stratification is insignificant.

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