Pairing instream restoration with disturbances to restore headwater meadows and reduce downstream sedimentation
My colleagues and I are using ecologically-focused, process-based techniques to restore meadows in the Sierra Nevada. We are focusing on meadows impacted by recent wildfires and leveraging post-fire sediment fluxes in conjunction with low-tech restoration structures (for example, beaver dam analogues) to mend degraded meadows.
We are monitoring three meadows in the Plumas National Forest and three meadows in the Sierra National Forest. For each region, we will restore a degraded, fire-impacted meadow and a degraded, unburned meadow. We will also monitor a degraded, fire-impacted control meadow. We will monitor sediment transport, groundwater and surface hydrology, meadow ecology, and changes in stream morphology. The monitoring began in summer 2021 and the restoration is planned for summer 2022. Post-restoration monitoring will continue for multiple years.
Exploring the influence of large wood on bedload transport rates, bedload storage, channel morphology, and habitat complexity
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. Publications are forthcoming.
Examining the influence of timber harvests on bedload transport
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.
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 Caspar Creek Experimental Watersheds, the future of paired watershed studies, and improving data availability
An experimental timber harvest was recently completed at the Caspar Creek Experimental Watersheds. A selective harvest was completed in the South Fork and a wide variety of pre- and post-harvest monitoring was implemented. You can read about it in Dymond et al. (2021).
In a manuscript recently submitted to the Journal of American Water Resources Association, 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. You can read about recently archived data in Richardson et al. (2021).
Richardson, P. W., P. H. Cafferata, S. F. Dymond, E. T. Keppeler, J. W. Wagenbrenner, & J. A. Whiting. Past and Future Roles of Paired Watersheds: A North American Inventory and Anecdotes from the Caspar Creek Experimental Watersheds. Submitted to the Journal of American Water Resources Association (JAWRA).
Dymond, S. F., P. W. Richardson, L. Webb, E. T. Keppeler, I. D. Arismendi, K. D. Bladon, P. H. Cafferata, H. E. Dahlke, J. Harrington, J. A. Hatten, D. Longstreth, P. Ode, C. G. Surfleet, & J. W. Wagenbrenner. A Field-Based Experiment on the Influence of Stand Density Reduction on Watershed Processes at the Caspar Creek Experimental Watersheds in northern California, Frontiers In Forests and Global Change, 4:691732. https://doi.org/10.3389/ffgc.2021.691732
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). Fifty-eight years and counting of watershed science at the Caspar Creek Experimental Watersheds in northern California, Hydrological Processes, 35(6), e14207. https://doi.org/10.1002/hyp.14207
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
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).
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
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.
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
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.
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.