Jacob A. Morgan, PhD
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Field Observations Elwha River, Washington 
From 2011 to 2014 the 64 m high Glines Canyon Dam was removed from the Elwha River, making available nearly 90 years-worth of trapped bedload material. Using rod- and kyak-mounted rtk-GPS equipment, we conducted repeat annual topo/bathymetric surveys from 2014 to 2016 to characterize the effect of this increased sediment supply on a 1 km long reach located 5 km downstream of the former dam site. Our results show channel widening and general bed channel aggradation, especially on bars. Bar building coupled with bank retreat results in meander migration. Analysis of aerial images dating back to 1939 show that rates of channel widening and meander migration have increased since dam removal. Because the dam was genearlly operated as a run-of-the-river structure, and hydrology was consistent during this period, these changes can be attributed to the dam removal.
Brew, A.K., J.A. Morgan, and P.A. Nelson, 2015, Bankfull width controls on riffle-pool morphology
under conditions of increased sediment supply: Field observations during the Elwha River dam removal project,
in SEDHYD 2015: 10th Federal Interagency Sedimentation Conference and 5th Federal
Interagency Hydrologic Modeling Conference, Reno, Nev., 19–23 Apr.
Morgan, J.A. and P.A. Nelson, 2016, Hydro- and morphodynamics of riffle-pool
sequences in the middle Elwha River, Washington, USA, in Constantinescu, Garcia, and Hanes (Eds.), River Flow 2016,
Taylor & Francis Group, London: 1212–1217, doi: 10.1201/9781315644479-191.
Skin/Hill Gulch, Colorado 
The High Park Fire burned approximately 353 km2 in the Rocky Mountain foothills west of Fort Collins in June 2012. High frequency topographic stream surveys were conducted from 2012 to 2016 in two 15 km2 watersheds (Skin and Hill Gulches) to examine the geomorphic effect of the High Park Fire. Although the burn severity and general characteristics of the watersheds were very similar they showed very different responses. The original study was complicated by the occurrence of an extreme flood in September 2013. Geomorphic response was again disparate between the two watersheds. A look at the history of each watershed shows that Hill Gulch was subject to a large flood event in 1976 that did not affect Skin Gulch. Results show that the timing, magnitude, and sequence hydro-geomorphic events have a important bearing on response to disturbance.
Brogan, D.J., L.H. MacDonald, P.A. Nelson, and J.A. Morgan, 2019, Geomorphic complexity and sensitivity in channels to fire and floods in mountain catchments,
Geomorpology, 337: 53–68,
doi: 10.1016/j.geomorph.2019.03.031.
South Fork Nooksack River, Washington 
Text coming soon... |
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Physical Experiments 0.216-m Flume, Colorado State University 
We used a small-scale flume experiment to study how channel-width variations modulate changes in sediment supply. Sinusoidal width variations were loosely informed by width variations in the Elwha River and scaled down to a 9-inch flume. The flume was subjected to a sequence of sediment supply conditions all under steady discharge. The flume was first fed with a constant, "equilibrium" sediment supply. Following this the sediment supply was terminated. After reaching an dynamically equilibrated state the "equilibrium" sediment supply was returned. The channel responded to this series by an overall reduction in downstream slope with the terminated sediment supply, while bar-pool relief remained constant. Following this another sequence of sediment supply changes was imposed with a terminated supply followed by a large sediment pulse. It was expected that the sediment pulse would move downstream and primarily occupy the pool regions. However, the pulse moved downstream as a more-or-less continuous mass and evolved through primarily dispersive means.
Nelson, P.A., A.K. Brew, and J.A. Morgan,
2015, Morphodynamic response of a variable-width channel to changes in sediment
supply, Water Resources Research, 51(7): 5717–5734,
doi: 10.1002/2014WR016806.
1.219-m Flume, Colorado State University 
Two series of experiments were performed, one having constant downstream width and the other having sinusoidal downstream width variations. Both flume geometries were subjected to a sequence of: 1) steady discharge, constant sediment supply, 2) repeated hydrographs, constant sediment supply, and 3) repeated hydrograph, constant doubled sediment supply. The constant width channel developed alternating bars in flow with width-to-depth ratio lower than theory suggests should be possible. The doubled sediment supply results in a steeper downstream channel slope and higher Froude number in the constant width channel. The variable width channel adjusted to the increased sediment supply through a combination of reduced bar-pool relief and minimized cross-section elevation variability. Very little downstream slope adjustment occurred in the variable width channel following the increased sediment supply.
Nelson, P.A. and J.A. Morgan, 2018, Flume experiments on flow and sediment supply controls on gravel bedform dynamics,
Geomorpology, 323: 98–105,
doi: 10.1016/j.geomorph.2018.09.011.
Structure-from-Motion in Flumes, Colorado State University 
In order to examine the feasibility of and best practices associated with using Structure-from-Motion (SfM) photogrammetry in laboratory flumes, we performed a methodological study comparing SfM derived topography (processed using two different software options) with terrestrial lidar scanner (TLS) derived topography (collected using two different laser scanners). Data was collected for five different flumes and small sediment pan with a wide range of both dimensions and contained sediment grain size distributions. Elevation point clouds derived from SfM had spatial densities orders of magnitude higher than TLS derived point clouds. SfM errors relative to TLS were within the accuracy of the TLS instruments, suggesting that for laboratory settings SfM provides an accepable alternative to laser scanning. Results from the sediment pan suggest that higher angled imagery better captures interstitial space between grain, therefore better resolving sub-grain-scale topography. In order to capture sub-grain-scale topography camera parameters and position should be adjusted to obtain a minimum of 100 pixels per grain in the raw imagery.
Morgan, J.A., D.J. Brogan, and P.A. Nelson,
2017, Application of Structure-from-Motion photogrammetry in laboratory flumes,
Geomorphology, 276: 125–143,
doi: 10.1016/j.geomorph.2016.10.021.
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Numerical Simulations coming soon... |