Welcome to the surface processes and morphodynamics group in the Department of Civil and Environmental Engineering at Colorado State University. Our group uses a combination of analytical theory, numerical modeling, field observations, and laboratory experiments to investigate problems in the broad field of earth surface processes, including fluvial and hillslope geomorphology, sediment transport, hydrology, hydraulics, and landscape evolution.

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Peter A. Nelson

Peter Nelson is an Associate Professor in the Department of Civil and Environmental Engineering at Colorado State University. He received his B.S.E. in Civil and Environmental Engineering from Princeton University, and has a Ph.D. in Earth and Planetary Science from the University of California, Berkeley.

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Current students

Dan Brogan

Ph.D. student

Post-wildfire fluvial geomorphology.


Ryan Brown

Ph.D. student

Morphodynamic modeling of stratigraphic feedbacks on channel evolution; Sediment sorting in meandering channels.


Brian Murphy

Ph.D. student

Research focus TBD.

Jongseok Cho

Ph.D. student

Morphodynamic modeling of mixed bedrock-alluvial rivers.

Mike Gieschen

M.S. student

Geomorphic controls on surface water - groundwater exchange.


Andy Bankert

M.S. (2016)

Dynamic stratigraphy and alternate bars

Now working on modeling flow in rivers using smoothed particle hydrodynamics in our group at CSU.

Craig Baxter

M.S. (2018)

Modeling knickpoint migration in engineered systems.

Andy Brew

M.S. (2014)

Riffle-pool morphodynamics in variable-width channels

Now at Anchor QEA, Bellingham, WA

Tessa Hanson

M.S. (2016)

Flow and bed morphology in straight and curved channels

Now at River Design Group, Whitefish, MT

Travis Hardee

M.S. (2017)

Flow and fish passage over whitewater park structures.

Jacob Morgan

Ph.D. (2018)

Riffle-pool dynamics.

Now a postdoc at the University of Washington.


Robbie Queen

M.S. (2018)

Flow and sediment transport around run-of-river dams.

Tyler Rosburg

M.S. (2015)

Hydrologic effects of urbanization; influence of flow data resolution on sediment transport calculations

Now a Water Resource Engineer at ICON Engineering, Centennial, CO

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Active projects (click the tab for more information)

Sediment supply and sorting in meandering rivers

Collaborators: Tess Hanson (CSU), Ryan Brown (CSU), Giovanni Seminara (Genoa), Michele Bolla Pittaluga (Genoa)

North Cascades NP

Meandering river channels are one of the most iconic features in geomorphology and have long attracted the attention of scientists and engineers. In this NSF CAREER project, we intend 1) to investigate how channel curvature affects equilibrium patterns of bed topography and surface sorting, 2) to examine how changes in sediment supply affect sorting and bed topography in meandering channels, and 3) to explore the interactions of free and forced bars in meandering channels of mixed grain size sediment and variable sediment supply. This project includes a major outreach component consisting of summer programs developed in conjunction with the CSU Women and Minorities in Education Program and the Fort Collins Museum of Discovery, which will introduce K-12 students and the public to river science and will serve as a vehicle for recruitment and retention of students from underrepresented groups into STEM fields.

Sediment supply, width variation, and unsteady flow effects on riffle-pool dynamics

Collaborators: Jacob Morgan (CSU), Andy Brew (CSU), Tim Randle (USBR), Jennifer Bountry (USBR)


Riffle-pool sequences are a common feature of many gravel-bed rivers and provide important habitat for fish and other organisms. However, we have a poor understanding of how they are influenced by downstream variations in channel width, unsteady flow, mixed-size sediment, and changes in sediment supply. We are exploring these controls through a combination of numerical morphodynamic modeling, flume experiments, and field work on the Elwha River dam removal project.

Feedbacks between stratigraphy and river bed evolution

Collaborators: Ryan Brown (CSU), Andy Bankert (CSU), Rich McDonald (USGS), Jon Nelson (USGS)


Aggrading river systems create their own stratigraphy, which can be very heterogeneous in the cross-stream, downstream, and vertical directions. If conditions change such that a river becomes degradational and cuts through its self-formed stratigraphy, the potentially abrupt grain-size transitions associated with this exhumation may lead to feedbacks on morphodynamic evolution that are difficult to predict a priori. We are exploring these surface-subsurface interactions during channel aggradation and degradation, using flume experiments to guide the development of a 2D numerical model. We expect this work to improve our ability to model the dynamics of rivers and their stratigraphy, and ultimately to improve our geologic interpretation of the stratigraphic record.

Modeling hydraulics and fish passage at whitewater parks

Collaborators: Travis Hardee (CSU), Matt Kondratieff (Colorado Parks and Wildlife)


Whitewater parks are popular recreational amenities, especially in Colorado. These in-stream hydraulic structures typically create waves by constricting flow through a chute to increase velocities and form a hydraulic jump. These hydraulic conditions have been shown to potentially inhibit upstream fish movement. We are using 2D and 3D hydraulic models to compute a continuous and spatially explicit description of velocity and depth along potential fish swimming paths in the flow field, and the ensemble of potential paths are compared to fish swimming performance data to predict fish passage via logistic regression analysis.

Post-wildfire hydrology and sedimentation

Collaborators: Dan Brogan (CSU), Lee MacDonald (CSU), Stephanie Kampf (CSU)


Wildfires can dramatically change the hydrologic response of a watershed, leading to more overland flow and increased erosion rates for a given storm. Fires can therefore cause changes to hillslope and channel morphology, cause increased delivery of sediment to channels, impact water quality and aquatic habitat, and potentially influence landscape evolution. In the summer of 2012, the High Park fire burned 87000 acres of forest near Fort Collins, Colorado. We are using a combination of remotely-sensed topography, field observations of hillslope-scale sediment production, and Total Station, GPS, and terrestrial LiDAR surveys of channel geometry and channel network structure to better understand and quantify post-fire erosion rates at the watershed scale, sediment storage on hillslopes and sediment delivery to channels, changes in peak flows and channel morphology, and expansion and contraction of the channel network.

Geomorphic impact of run-of-river development

Collaborators: Jeremy Venditti (Simon Fraser University), Ted Fuller (Simon Fraser University), Wendy Palen (Simon Fraser University), Robbie Queen (CSU)


Run-of-river (RoR) hydropower projects have relatively small head ponds formed by small dams. The geomorphic impacts of these projects are thought to be small compared with large reservoir-based projects owing to their size and design, but the transient geomorphic response due to temporary sediment supply disruption is not well understood. We have been using morphodynamic models to explore potential downstream geomorphic changes due to installation of RoR projects so that we may better understand conditions that pose the greatest risk to aquatic habitat.

Structure-from-motion topography in field and laboratory settings

Collaborators: Jacob Morgan (CSU), Dan Brogan (CSU)


Structure-from-motion (SfM) photogrammetry has become widely used for topographic data collection in field and laboratory studies. We are using SfM extensively in laboratory experiments, and have conducted a rigorous analysis of SfM performance in lab settings. Our results show that SfM provides topographic data of similar accuracy to terrestrial laser scanning (TLS), at higher resolution and lower cost. We have suggested protocols for image acquisition and SfM software settings to achieve best results. In general, convergent imagery, taken from a higher angle, with at least several overlapping images for each desired point in the flume will result in an acceptable point cloud potentially capable of discriminating individual gravel particles.

Morphodynamics of bedrock-alluvial rivers

Collaborators: Giovanni Seminara (Genoa), Michele Bolla Pittaluga (Genoa), Jongseok Cho (CSU)


Bedrock rivers differ from their fully alluvial counterparts in that they are able to transport more sediment than what is supplied from hillslopes and upstream sources. We have been advancing our understanding of the morphodynamics of mixed bedrock-alluvial rivers by developing analytical and numerical models of flow, sediment transport, sediment cover, and bedrock erosion. These models have been used to explore how bedrock channel cross-sectional shape evolves in response to impacts from sediment particles eroding the underlying bedrock, how bars form in mixed bedrock-alluvial river bends, and how sediment cover is distributed across the channel bed.

Past projects (click the tab for more information)

Design hydrology at stream crossings

Collaborators: Brian Bledsoe (U. Georgia), Dan Baker (CSU), Joel Sholtes (USBR), Tyler Rosburg (CSU), Travis Stroth (CSU)


The ubiquitous effects of land use change on stream hydrologic and geomorphic processes present an ongoing challenge for hydrologic design at the interface of built and natural environments. The purpose of this project was to develop a scientifically supported method for defining the design hydrology that may be applied to stream crossings or other channel modification/restoration efforts, along with an understanding of how that design hydrology might change with land use changes.

Sediment sorting and bed-surface patchiness

Collaborators: Bill Dietrich (Berkeley), Jeremy Venditti (Simon Fraser), Leonard Sklar (SFSU), and others


The beds of nearly all gravel-bed rivers, and many gravel-bed flumes, are frequently arranged into patches of distinct grain size and sorting. Some of these patches have been observed to persist over timescales of decades, while others are able to freely move downstream. Bed surface heterogeneity may also be a primary control on sediment transport rates, and because bed material exerts a strong control on the near bed hydraulic environment, patches may have important implications for aquatic ecology. Flume experiments my colleagues and I have conducted have provided insight on how sediment supply affects the development of freely mobile patches, and how temporally-stable fixed patches are a consequence of interactions between the fluid flow field, the sediment transport field, and bed topography. In collaboration with the USGS Geomorphology and Sediment Transport Laboratory, I have developed a two-dimensional morphodynamic model simulating the mixed-grain-size sediment transport and bed evolution and used it to show how patches interact with the evolving bed, and, through their effect on the flow field, considerably affect bed morphology. I also have drawn on work in the fields of graph theory and computer vision to explore how patches can be delineated from high-resolution grain size datasets.

Morphodynamics of tidal channels

Collaborators: Nicoletta Tambroni (University of Genoa)


Tidal channels are fundamental features of estuarine and lagoon environments. These channels often exhibit alternate bar morphology, which can have a significant impact on channel navigability and the distribution of ecological habitat. Recent theoretical and experimental work has raised some fundamental questions regarding the evolution of tidal channels, such as: To what extent does the morphology of tidal channels reflect their evolutionary history? Does the equilibrium condition of tidal bars depend upon the initial channel configuration? Is bar instability in tidal channels absolute or convective? And, ultimately, to what extent are bar characteristics actually predictable? My colleagues at the University of Genoa and I are exploring these questions through the development of a two-dimensional morphodynamic model that simulates bar formation and evolution in tidal channels.

Hydrology of urbanizing watersheds

Collaborators: Brian Bledsoe (U Georgia), Tyler Rosburg (CSU), Jim Smith (Princeton), Mary Lynn Baeck (Princeton), Andy Miller (UMBC)


Urbanization can have a dramatic effect on a watershed. The development of roads, buildings, and other impervious areas tends to increase runoff ratios and produce very rapid hydrologic response times. Much of the drainage network can be man-made, in the form of culverts and storm drains, and stormwater detention basins can change the timing and magnitude of flood peaks by delaying the transport of runoff into streams. Floods in urban environments are very real hazards as typical thunderstorms can produce extraordinarily high discharges. Urban stream channels then have to somehow cope with this flashy hydrologic regime, and often become ‘unstable’ by eroding or incising excessively. My collaborators at Princeton and UMBC and I have been using Baltimore County, MD, as a field site to study various aspects of urban hydrology and flood hydraulics. Our work is part of the Baltimore Ecosystem Study (BES), a NSF Long-Term Ecological Research site (LTER). Additionally, colleagues at CSU have been investigating how urbanization affects the entire distribution of flows (i.e., the flow duration curve), using several watersheds in the Puget Sound region as a test case.

River restoration through gravel augmentation

Collaborators: Bill Dietrich (Berkeley), Jeremy Venditti (Simon Fraser), Leonard Sklar (SFSU), and others


Stream reaches downstream of dams are starved of sediment supply. This inevitably leads to heavily armored beds with an overabundance of very coarse bed material. This armoring has ecological consequences, since salmon, for instance, prefer to spawn in gravels of an intermediate size range. One approach that river managers have adopted to address this problem is gravel augmentation, where large amounts of the material of the target grain size (the size salmon like) are added to the channel, effectively burying the bed. However, this is a temporary (and expensive) solution that lasts only as long as the added gravel can stick around. In collaboration with Bill Dietrich, Jeremy Venditti, Leonard Sklar, and many others, I have been exploring the hypothesis that the addition of sediment finer than the target grain size can alter the near-bed hydraulic environment such that the previously immobile coarse grains are mobilized. By removing the coarse surface and exposing the ecologically-preferable subsurface material, such an approach may be less costly than typical gravel augmentation with longer-lasting effects. Experiments that we performed at UC Berkeley’s Richmond Field Station confirmed our hypothesis. In our experiments, we also have addressed related questions concerning sediment pulse propagation in straight channels and channels with bars, and the effect of sediment supply on bar stability.

Mound springs on Earth and Mars

Collaborators: Michael Manga (Berkeley)


When springs occur in topographically flat, arid environments, they tend to form mound-shaped deposits through mineral precipitation processes. These so-called ‘mound springs’ occur relatively infrequently on Earth, but where they do occur they are generally important sources of water and can become focal points for unique ecological systems. The range of observed spring deposit morphologies suggest that mound springs follow a common evolution. Following insights gained from field expeditions to mound spring clusters in central Australia and in New Mexico, Michael Manga, Mary Bourke, Jon Clarke, and I have developed a model for the evolution of these deposits that relates mound shape to local subsurface hydrologic conditions. Because these mounds are essentially permanent features on the landscape, our modeling should allow us to use the mound shape to make inferences on historical local hydrogeology and paleoclimate. This may be especially useful on Mars, where high-resolution imagery of the planet’s surface has revealed features that are strikingly similar to terrestrial mound spring deposits. By applying our model to these features, we may be able to learn something about the hydrogeologic conditions that once existed in the martian subsurface.

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* denotes student author

Refereed Publications

26. *Bankert, A and PA Nelson, 2017, Alternate bar dynamics in response to increases and decreases of sediment supply, Sedimentology, doi:10.1111/sed.12399.

25. *Brogan DJ, PA Nelson, and LH MacDonald, 2017, Reconstructing extreme post-wildfire floods: a comparison of convective and mesoscale events, Earth Surface Processes and Landforms, doi:10.1002/esp.4194.

24. *Stroth, TR, BP Bledsoe, and PA Nelson, 2017, Full spectrum analytical channel design with the Capacity/Supply Ratio (CSR), Water, 9(4), 271, doi:10.3390/w9040271.

23. *Rosburg TT, PA Nelson, and BP Bledsoe, 2017, Effects of urbanization on flow-duration and stream flashiness: A case study of Puget Sound streams, Western Washington, USA, JAWRA: Journal of the American Water Resources Association, 53(2), 493-507, doi:10.1111/1752-1688.12511.

22. *Morgan JA, *DJ Brogan, and PA Nelson, 2017, Application of structure-from-motion in laboratory flumes, Geomorphology, 276, 125-143, doi:10.1016/j.geomorph.2016.10.021.

21. Cotrufo, MF, CM Boot, S Kampf, PA Nelson, *DJ Brogan, T Covino, ML Haddix, LH MacDonald, S Rathburn, S Ryan-Burkett, *S Schmeer, and E Hall, 2016, Redistribution of pyrogenic carbon from hillslopes to stream corridors following a large montane wildfire, Global Biogeochemical Cycles, 30, 1348-1355, doi:10.1002/2016GB005467.

20. Kampf, SK, *DJ Brogan, *S Schmeer, LH MacDonald, and PA Nelson, 2016, How do geomorphic effects of rainfall vary with storm type and spatial scale in a post-fire landscape? Geomorphology, 273, 39-51, doi:10.1016/j.geomorph.2016.08.001.

19. *Rosburg, TT, PA Nelson, *JS Sholtes, and BP Bledsoe, 2016, The effect of flow data resolution on sediment yield and channel design, Journal of Hydrology, 538, 429-439, doi:10.1016/j.jhydrol.2016.04.040.

18. Fuller, TK, JG Venditti, PA Nelson, and WJ Palen, 2016, Modeling grain size adjustments in the downstream reach following run-of-river development, Water Resources Research, 52, 2770-2788, doi:10.1002/2015WR017992.

17. Nelson, PA, RR McDonald, JM Nelson, and WE Dietrich, 2015, Coevolution of bed surface patchiness and channel morphology: 2. Numerical experiments. Journal of Geophysical Research: Earth Surface, doi:10.1002/2014JF003429.

16. Nelson, PA, RR McDonald, JM Nelson, and WE Dietrich, 2015, Coevolution of bed surface patchiness and channel morphology: 1. Mechanisms of forced patch formation. Journal of Geophysical Research: Earth Surface, doi:10.1002/2014JF003428.

15. Nelson, PA, *AK Brew, and *JA Morgan, 2015, Morphodynamic response of a variable-width channel to changes in sediment supply, Water Resources Research, doi:10.1002/2014WR016806.

14. Nelson, PA, M Bolla Pittaluga, and G Seminara, 2014, Finite amplitude bars in mixed bedrock-alluvial channels, Journal of Geophysical Research: Earth Surface, doi:10.1002/2013JF002957.

13. Nelson, PA, D Bellugi, and WE Dietrich, 2014, Delineation of river bed-surface patches by clustering high-resolution spatial grain size data, Geomorphology, doi:10.1016/j.geomorph.2012.06.008.

12. Venditti, JG, PA Nelson, JT Minear, J Wooster, and WE Dietrich, 2012, Alternate bar response to sediment supply termination, Journal of Geophysical Research, 117, F02039, doi:10.1029/2011JF002254.

11. Nelson, PA and G Seminara, 2012, A theoretical framework for the morphodynamics of bedrock channels, Geophysical Research Letters, L06408, doi:10.1029/2011GL050806.

10. Nelson, PA and G Seminara, 2011, Modeling the evolution of bedrock channel shape with erosion from saltating bed load, Geophysical Research Letters, L17406, doi:10.1029/2011GL048628.

9. Nelson, PA, WE Dietrich, and JG Venditti, 2010, Bed topography and the development of forced bed surface patches, Journal of Geophysical Research, F04024, doi:10.1029/2010JF001747.

8. Venditti, JG, WE Dietrich, PA Nelson, MA Wydzga, J Fadde, and L Sklar, 2010, Effect of sediment pulse grain size on sediment transport rates and bed mobility in gravel bed rivers, Journal of Geophysical Research, F03039, doi:10.1029/2009JF001418.

7. Venditti, JG, WE Dietrich, PA Nelson, MA Wydzga, J Fadde, and L Sklar, 2010, Mobilization of coarse surface layers in gravel-bedded rivers by finer gravel bedload, Water Resources Research, W07506, doi:10.1029/2009WR008329.

6. Sklar, LS, J Fadde, JG Venditti, P Nelson, MA Wydzga, Y Cui, and WE Dietrich, 2009, Translation and dispersion of sediment pulses in flume experiments simulating gravel augmentation below dams, Water Resources Research, W08439, doi:10.1029/2008WR007346.

5. Nelson, PA, JG Venditti, WE Dietrich, JW Kirchner, H Ikeda, F Iseya, and LS Sklar, 2009, Response of bed surface patchiness to reductions in sediment supply, Journal of Geophysical Research, F02005, doi:10.1029/2008JF001144.

4. Nelson, PA, JA Smith, and AJ Miller, 2006, Evolution of channel morphology and hydrologic response in an urbanizing drainage basin, Earth Surface Processes and Landforms 31: 1063-1079, doi:10.1002/esp.1308.

3. Smith, JA, ML Baeck, KL Meierdiercks, PA Nelson, AJ Miller, and EJ Holland, 2005, Field studies of the storm event hydrologic response in an urbanizing watershed, Water Resources Research 41, W10413, doi:10.1029/2004WR003712.

2. Smith, JA, AJ Miller, ML Baeck, PA Nelson, GT Fisher, and KL Meierdiercks, 2005, Extraordinary flood response of a small urban watershed to short-duration convective rainfall, Journal of Hydrometeorology 6: 599-617, doi:10.1175/JHM426.1.

1. Hicks, NS, JA Smith, AJ Miller, and PA Nelson, 2005, Catastrophic flooding from an orographic thunderstorm in the central Appalachians, Water Resources Research 41, W12428, doi:10.1029/2005WR004129.

Peer-reviewed book chapters, reports, and conference proceedings papers

9. Nelson, PA and N Tambroni, 2017, Indagini numeriche sulla morfodinamica delle barre alternate in canali in marea, in Atti dell’Istituto Veneto di Scienze, Lettere, ed Arti, D’Alpaos, L (ed), Istituto Veneto di Scienze, Lettere, ed Arti, Venice, pp. 3-28.

8. McDonald RR, JM Nelson, R Fosness, and PA Nelson, 2016, Field scale test of multi-dimensional flow and morphodynamic simulations used for restoration design analysis, River Flow 2016, Constantinescu, Garcia, and Hanes (Eds), Taylor and Francis Group, London, 1390-1398.

7. *Morgan JA and PA Nelson, 2016, Hydro- and morphodynamics of riffle-pool sequences in the middle Elwha River, Washington, USA, River Flow 2016, Constantinescu, Garcia, and Hanes (Eds), Taylor and Francis Group, London, 1212-1217.

6. Bledsoe, BP, DW Baker, PA Nelson, *JS Sholtes, *TT Rosburg, and *T Stroth, 2016, Design hydrology for stream restoration and channel stability at stream crossings, Final Report for NCHRP Project 24-40.

5. Venditti, JG, PA Nelson, RW Bradley, D Haught, and AB Gitto, 2015, Bedforms, structures, patches, and sediment supply in gravel-bed rivers, Gravel Bed Rivers 8.

4. *Brew, AK, *JA Morgan, and PA Nelson, 2015, Bankfull width controls on riffle-pool morphology under conditions of increased sediment supply: field observations during the Elwha River Dam Removal Project, SEDHYD 2015, Reno, Nevada, 19-23 April. PDF

3. Venditti, JG, PA Nelson, and WE Dietrich, 2008, The domain of bedload sheets. In Parsons, D, T Garlan, and J Best (eds), Proceedings of Marine and River Dune Dynamics III, International Workshop, April 1-3 2008, University of Leeds, UK, 315-321. PDF

2. Clarke, J, M Bourke, P Nelson, M Manga, and J Fonseca, 2007, The Dalhousie mound spring complex as a guide to Martian landforms, processes, and exploration. In Mann, G (ed), Proceedings of the 7th Australian Mars Exploration Conference, Mars Society Australia, Clifton Hill, Victoria. PDF

1. Dietrich, WE, PA Nelson, E Yager, JG Venditti, MP Lamb, and L Collins, 2005, Sediment patches, sediment supply, and channel morphology. In Parker, G and MH Garcia (eds), River, Coastal and Estuarine Morphodynamics: RCEM 2005, 79-90. PDF

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Peter Nelson
Department of Civil and Environmental Engineering
Colorado State University
1372 Campus Delivery
Fort Collins, CO 80523-1372

Phone: +1 (970) 491-5247
Email: peter.nelson@colostate.edu