Research Projects

Exploring the influence of large wood on bedload transport rates, bedload storage, channel morphology, and habitat complexity

Hydrophone (2 meter long pipe on channel bed) installed on the North Fork of Caspar Creek, CA. Photograph is looking upstream. The channel width is 4.4 meters at the gaging station. Bedload traps (with white covers) are located immediately downstream of the hydrophone. A turbidity probe is located immediately upstream of the hydrophone.

Major tree fall events occurred after timber harvesting on the North Fork of Caspar Creek, CA in the early 1990s. Over the following years, the wood was organized into wood jams. The wood jams have trapped substantial quantities of gravel. We are investigating how these jams store and release bedload. We are currently monitoring nine large wood jams with time lapse cameras. We recently installed a hydrophone, which measures gravel impacts on a pipe, downstream of the wood jams to investigate how the jams are modulating bedload transport. We intend to install additional hydrophones throughout the Caspar Creek watershed to monitor bedload transport.

USDA Forest Service geologist inspecting gravel storage behind a wood jam. Downstream is to the left. A time lapse camera is mounted to the tree on the right and monitors changes to the jam. A hydrophone measures bedload transport rates downstream of the jam.

Examining the influence of timber harvests on bedload transport

Looking downstream at the North Fork weir pond. The pond was drained for a sediment cleanout in 2018. The photograph was taken from the gravel delta. The weir pond has been surveyed annually since 1962. Richardson et al. (2020) used the weir pond surveys, pond sediment samples, and measurements of settled suspended sediment to reconstruct a 55-year record of annual bedload yields.

I am investigating how bedload transport responds to timber harvests at the Caspar Creek Experimental Watersheds in northern California. This work leverages previous measurements of annual weir pond volumes and suspended sediment yields to reconstruct a 55-year record of annual bedload yields for both the North Fork and South Fork of Caspar Creek. Weir ponds at the outlets of the watersheds capture bedload, organic material and settled suspended sediment. We have developed a novel method for reconstructing annual gravel yields by explicitly accounting for organic material and settled suspended sediment in the weir ponds (Richardson et al, 2020). By comparing the reconstructed gravel yields to yields predicted with a bedload transport model, we are able to determine how timber harvests have influenced bedload transport at Caspar Creek.

USDA Forest Service employees standing on a gravel delta at the upstream end of the North Fork weir pond. The photograph was taken after the pond was drained in preparation for a sediment cleanout in 2018.

Products

Richardson, P. W., J. W. Wagenbrenner, D. G. Sutherland, & T. E. Lisle (2020). Measuring and modeling gravel transport at Caspar Creek, CA to detect changes in sediment supply, storage, and transport efficiency, Water Resources Research, 56(6). https://doi.org/10.1029/2019WR026389

Richardson, P. W. & J. W. Wagenbrenner (2019). Assessing the applicability of the Wilcock 2-fraction bedload transport model at the Caspar Creek Experimental Watersheds, CA. Federal Interagency Sedimentation and Hydrologic Modeling Conference (SEDHYD) Conference. https://www.fs.fed.us/psw/publications/richardson/psw_2019_richardson001.pdf

The future of paired watershed studies and improving data availability

In a recently submitted paper to Hydrological Processes, my coauthors and I suggest that paired watershed studies have a bright future as experimental sites. In order for paired watersheds to maximize their usefulness to the scientific community and the public, data must be easily available online. At Caspar Creek, we have made a major effort to publish data through the USDA Forest Service online archive. Our archiving efforts are ongoing.

Map of North America showing operational paired watershed studies and nonoperational paired watershed studies. In some cases, nonoperational paired watersheds have been converted to experimental watersheds that no longer include a paired watershed component.

Products

Richardson, P. W., J. E. Seehafer, E. T. Keppeler, D. G. Sutherland, & J. W. Wagenbrenner (In revision). Fifty-eight years and counting of watershed science at the Caspar Creek Experimental Watersheds in northern California. Hydrological Processes.

Richardson, P. W., P. H. Cafferata, S. F. Dymond, E. T. Keppeler, J. W. Wagenbrenner, & J. A. Whiting (In prep). Past and Future Roles of Paired Watersheds: A North American Inventory and Anecdotes from the Caspar Creek Experimental Watersheds.

Richardson, P. W., J. E. Seehafer, E. T. Keppeler, D. G. Sutherland, & J. W. Wagenbrenner (2021). Caspar Creek Experimental Watersheds Phase 1 (1962-1985) data (2nd edition), Forest Service Research Data Archive. https://doi.org/10.2737/RDS-2020-0017-2

Richardson, P. W., J. E. Seehafer, E. T. Keppeler, D. G. Sutherland, J. W. Wagenbrenner, K. D. Bladon, S. F. Dymond, & R. P. Cole (2021). Caspar Creek Experimental Watersheds Phase 2 (1985-2017) data (2nd edition), Forest Service Research Data Archive. https://doi.org/10.2737/RDS-2020-0018-2

Development of a new lava flow routing algorithm and topographic analysis of volcanic landscapes

Shaded relief map of the flank of Mt. Etna showing colormap comparison of  a MULTIFLOW model prediction and a lava flow in 2001 (black: match; blue: model underprediction; red: model overprediction). The flow is ~ 7 km long.

I developed a new lava flow routing algorithm (MULTIFLOW) with Leif Karlstrom that is both accurate and efficient. You can download the lava flow routing algorithm here. We used this model to investigate how landscape roughness influences lava flow morphology (Richardson & Karlstrom, 2019). In addition, we also investigated how volcanic processes more generally influence landscape evolution (Karlstrom et al., 2018).

Products

Richardson, P. W. & L. Karlstrom (2019). The multi-scale influence of topography on lava flow morphology, Bulletin of Volcanology, 81(32), 1-17. https://doi.org/10.1007/s00445-019-1278-9

Karlstrom, L., P. W. Richardson, D. O’Hara, & S. Ebmeier (2018). Magmatic landscape evolution, Journal of Geophysical Research Earth Surface, 123(8), 1710-1730. https://doi.org/10.1029/2017JF004369

The influence of climate and life on soil transport efficiency

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Ridges and valleys at Gabilan Mesa, CA. Soil transport efficiency can be determined for specific sites from analysis of ridgetop curvature and erosion rates.

I compiled estimates of hillslope transport efficiency and made new estimates. I found that hillslope transport efficiency increased rapidly with climate proxies such as mean annual precipitation and the aridity index, but ultimately the rate of increase diminishes at moderate precipitation rates and as vegetation becomes more established.

Products

Richardson, P. W., J. T. Perron, & N. D. Schurr (2019). The influence of climate on hillslope sediment transport efficiency, Geology, 47(5), 423-426. https://doi.org/10.1130/G45305.1

Investigating topographic asymmetry and the role of microclimates on landscape evolution

Image of Gabilan Mesa, CA (36.917°N, 120.760°W). Striking topographic asymmetry and large differences in vegetation on opposing slopes are visible. North-facing slopes have steeper gradients and denser vegetation than south-facing slopes.

This was the primary focus of my PhD thesis. The goal of this project was to leverage strong microclimatic differences on north-facing and south-facing slopes to improve our understanding of how climate influences landscape evolution. I used a mixture of field measurements, cosmogenic isotope analysis, and numerical landscape evolution modeling to investigate why topographic asymmetry developed at Gabilan Mesa, CA. Multiple ideas have been suggested, but few have been carefully tested until now. We found that infiltration rates on north-facing slopes are much higher than rates on south-facing slopes. We expect this difference lead to increased runoff and channel incision on south-facing slopes and is the primary driver of topographic asymmetry at Gabilan Mesa, CA. We considered a wide range of aspect-dependent erosional mechanisms and also suggested that other mechanisms may contribute to the development of topographic asymmetry at Gabilan Mesa.

Products

Richardson, P. W., J. T. Perron,  S. R. Miller, & J. W. Kirchner (2020). Modeling the formation of topographic asymmetry by aspect-dependent erosional processes and lateral channel migration, Journal of Geophysical Research Earth Surface, in press. https://doi.org/10.1029/2019JF005377

Richardson, P. W., J. T. Perron, S. R. Miller, & J. W. Kirchner (2020). Unraveling the mysteries of an asymmetric landscape at Gabilan Mesa, CA, Journal of Geophysical Research Earth Surface, in press. https://doi.org/10.1029/2019JF005378

Pelletier, J. D., G. A. Barron-Gafford, H. Guttierez-Jurado, E. S. Hinckley, E. Istanbulluoglu, L. A. McGuire, G. Niu, M. J. Poulos, C. Rasmussen, P. W. Richardson, T. L. Swetnam, & G. E. Tucker (2017). Which way do you lean? Using slope aspect variations to understand Critical Zone processes and feedbacks, Earth Surface Processes and Landforms, 43(5), 1133-1154. https://doi.org/10.1002/esp.4306

Please refer to my CV for a full list of publications.