Research

Research Philosophy

My research focuses on answering questions that impact society through understand of natural water and wetland systems. My efforts focus on honestly evaluating problems scientifically and contributing the results to the earth science community. Ideally, these efforts will lead to more informed management decisions of our natural and human systems. Along the way, I hope to positively impact the research of those whose path I cross, through ideas, work, or encouragement.

Research Projects

Water Temperature Modelling

In 2007, while a graduate student at Berkeley, I joined a large collaborative effort (CASCaDE: Computational Assessments of Scenarios of Change for the Delta Ecosystem) funded by a California/federal government (Calfed) grant to study the impacts of climate change on the Sacramento-San Joaquin Delta. The project aimed to model every aspect of the delta, from precipitation and evaporation in the watershed, water routing, sediment supply, water quality, and biology over the next 100 years under a variety of scenarios.

I modeled the delta’s water temperature driven by inputs from downscaled climate models using a multiple linear regression, yielding R2 values between measured and modeled temperatures over 0.93 for all stations with at least one year of measured data. Calibrating the model using the historical record, I hindcast and forecast the Delta's water temperatures back to 1931 and forward to 2100, respectively. The output informed effects on pelagic fishes in the delta, showing temporal shifts in the seasonal spawning window as well as spatial shifts of the suitable habitat for these species. These results were well-received by the scientific community, but they were also cited in a review of the conservation plan for the delta.

Relevant publications and datasets:

1. Wagner, R. W., M. Stacey, L. Brown, and M. Dettinger. (2011) Statistical Models of Temperature in the Sacramento-San Joaquin Delta Under Climate-Change Scenarios and Ecological Implications. Estuaries and Coasts 34(3), DOI: 10.1007/s12237-010-9369-z

2. Cloern, J., N. Knowles, L. Brown, D. Cayan, M. Dettinger, T. Morgan, D. Schoellhamer, M. Stacey, M. van der Wegen, R. W. Wagner, and A. Jassby. (2011) Projected Evolution of California's San Francisco Bay-Delta-River System in a Century of Climate Change. PlosOne 6(9), DOI: 10.1371/journal.pone.0024465

3. Brown, L., W. Bennett, R. W. Wagner, T. Morgan-King, N. Knowles, F. Feyrer, D. Schoellhamer, M. Stacey, and M. Dettinger. (2013) Implications for Future Survival of Delta Smelt from Four Climate Change Scenarios for the Sacramento-San Joaquin Delta, California. Estuaries and Coasts 36(4), DOI: 10.1007/s12237-013-9585-4

4. Brown, L., Komoroske, L., Wagner, R.W., Morgan-King, T., May, J., Connon, R, and Fangue, N. (2015) Coupled Downscaled Climate Models and Ecophysiological Metrics Forecast Habitat Compression for an Endangered Estuarine Fish. PlosOne 11(1), DOI: 10.1371/journal. pone.0146724

5. Wagner, R.W. (2016) Hindcast of Water Temperatures in Sacramento-San Joaquin Delta from 1931-2009, DOI: dx.doi.org/10.6084/m9.figshare.3810807.v2

6. Wulff, M.L., Brown, L.R., Huntsman, B.M., Knowles, N., and Wagner, W., (2021) Data used in projected air and water temperatures for selected regions of the upper San Francisco Estuary and Yolo Bypass under 20 scenarios of climate change, U.S. Geological Survey data release, https://doi.org/10.5066/P9CXGU44.

Delta Evolution and Stability

Since graduating, I have worked as a post-doctoral scholar at the University of Texas on the Wax Lake Delta (WLD), a relatively small prograding system within the largely subsiding Mississippi River Delta (MRD). As a native of New Orleans, the dynamics of Louisiana’s coast is a problem that is close to my heart. I work with researchers from Louisiana, Texas, and around the U.S. to understand the morphodynamics of this delta to help inform plans to restore other areas of Louisiana to stability. I use airborne lidar to measure landscape change through time, demonstrating the timescales for the land to stabilize and to predict what the long term delta will look like. These answers will help us predict how much land can ultimately be maintained within the MRD.

In the down-delta regions of WLD, change is greatest. Riverine sediment delivery is greatly outpacing the system's ability to remove it. Up-delta, the land is stable or even subsiding. These regions were initially very high, causing flooding frequency and sediment delivery to be lessened. As a consequence, in the areas, aggradation of new sediment is balanced or overcome by compaction of the older sediments that make up the land form. Analysis of the landscape change on Wax Lake Delta indicate that it aggrading towards a stable elevation on a timescale of 16 years. Higher elevations of the delta fluctuate around an equilibrium elevation due to change being driven by episodic aggradation and slower, steadier subsidence.

Relevant publications and datasets:

1. Wagner, R.W., Lague, D., Mohrig, D., Passalaqua, P., Shaw, J., and Moffett, K. (2017) Elevation Change and Stability on a Prograding Delta. Geophysical Research Letters (submitted)

2. Wagner, R.W. (2016) Wax Lake Delta 2009 Airborne Lidar, DOI: 10.5069/G95M63M8

3. Wagner, R.W. (2016) Wax Lake Delta 2013 Airborne Lidar, DOI: 10.5069/G9SF2T41

Fluid and Sediment Partitioning in an Active Delta

River deltas are formed where rivers debouche into receiving bays. Riverine sediments can accumulate over time, building complex subaqeous (under water) bathymetry, potentially forming subaerial delta landforms. The shape of these landforms feeds back onto the riverine sediment delivery system, as the sediments are partitioned across the delta's branches. This partitioning affects how much of the sediment is trapped in the delta (and therefore how much is exported to the coastal ocean) and controls the shape that the delta will take. Using a variety of methods (aerial photography of biogenic slicks on the water surface, airborne SAR (Synthetic Aperture Radar) images, and a real-time sensor network measuring water velocities and water quality parameters), my colleagues and I have analyzed how various factors affect the sediment routing into and through the system.

Relevant publications and datasets:

1. Shaw, J., Mohrig, D., and Wagner, R.W. (2016) Flow patterns and morphology in a prograding river delta. Journal of Geophysical Research - Earth Surface 121(2), DOI: 10.1002/2015JF003570

2. Shaw, J., Ayoub, F., Jones, C., Lamb, M., Holt, B., Wagner, R.W., Coffey, T., Chadwick, T.A., and Mohrig, D. (2016) Airborne Radar Imaging of Subaqueous Channel Evolution in Wax Lake Delta, Louisiana, USA. Geophysical Research Letters 43(10), DOI: 10.1002/2016GL068770

3. Ayoub, F., Jones, C.E., Lamb, M.P., Holt, B., Shaw, J.B., Mohrig, D., and Wagner, R.W. (2018) Inferring surface currents within submerged, vegetated deltaic islands from multi-pass airborne SAR. Remote Sensing of Environment 212, DOI: 10.1016/j.rse.2018.04.035

Future Research

I hope to continue to work in Louisiana rivers and wetlands. First, I wish the study the hydrodynamics of river plumes where they debouche into standing water. In the scientific literature, this is referred to as a turbulent jet and analogies are drawn with two dimensional jets produced in lab settings. However, many of these plumes are not shaped like their lab counterparts. This has huge implications for sediment deposition that occurs near the plume edges that will eventually form levees and on the effectiveness of the delta to retain riverine sediment. On the Wax Lake Delta, there are multiple river ‘mouths’ that demonstrate these hydrodynamics, and I know collaborators who have collected detailed bathymetry near them. I hope to use this data as well as simple analytical models to explain how a different deltas form levees. Further, I intend to study this problem numerically and in a lab setting. Second, I hope to study past Louisiana deltas through the sedimentary record. Wax Lake Delta is primarily built of sand, but the sediment load of the Mississippi and Atchafalaya Rivers is mostly mud. This has caused some researchers to propose that sand should be the focus of land restoration efforts (since it is easier to capture) while others propose that mud should be the focus (since it is more abundant.) Louisiana was built by these components, however, and the answer is in the sedimentary record. Much of Louisiana is built of mud, but sand packages can be readily found. An analysis of the spatial distribution of these facies accompanied by estimations of historical conditions of these regions will help decision-makers understand when one should design to capture sand and when one should capture mud. In the long-term, I hope to develop a research group that uses whatever tools necessary to answer questions critical to Louisiana’s future. These questions would focus on sediment and hydrodynamics, climate change, and transport and fate of environmentally important scalars (nutrients, carbon, etc.)