Projects

This is a list of ongoing, nascent, and dormant projects, so that potential students, postdocs and collaborators have an idea of our group research. No project is ever fully "complete". As we discover answers to our research questions, many new questions inevitably arise! Therefore, dormant projects can always be revived. If something piques your interest, please contact Dr. Ludka as soon as possible so that we have time to seek out grant funding to support your project if needed. If you are looking for a research project in the near future, don't hesitate to contact Dr. Ludka to inquire about the status of active available projects and funding.

Harbor-Induced Circulation And Sediment Transport (HI-CAST) in Estuarine Systems

Elkhorn Slough, an estuary in Moss Landing, CA, has experienced significant erosion and loss of critical salt marsh habitat. The erosion is thought to have been initiated by the construction of the harbor mouth at Moss Landing in 1946, which exposed the estuary to more energetic tidal currents. Ebb currents leaving the estuary are stronger than the flood currents entering the estuary (Nidzieko 2010). Broenkow and Breaker (2005) hypothesize a positive feedback loop in which erosion increases the amount of water that flows into the estuary between low tide and high tide (the “tidal prism”), requiring a further increase in the tidal currents. This in turn promotes more erosion, continuing the cycle.

Dr. Ludka, collaborators Drs. Connolly and Orescanin, and students are testing this hypothesis with field observations and numerical modeling. Competing restoration strategies have been proposed to address the loss of salt marsh habitat (Largay and McCarthy 2010), prompting debate among local stakeholders due to limited scientific understanding of the underlying processes. New observations and modeling are needed to assess the potential impacts of the hypothesized feedback process on Elkhorn Slough and other estuaries.

Nidzieko, N. J. (2010) Tidal asymmetry in estuaries with mixed semidiurnal/diurnal tides. Journal of Geophysical Research, 115

Broenkow, W. W., and L. C. Breaker (2005) A 30-year history of tide and current measurements in Elkhorn Slough, California. Moss Landing Marine Laboratories Technical Report, 55

Largay, B., and E. McCarthy (2010) Management of Tidal Scour and Wetland Conversion in Elkhorn Slough: Partial Synthesis of Technical Reports on Large-Scale Alternatives. Elkhorn Slough Tidal Wetland Project, Elkhorn Slough National Research Reserve, Elkhorn Slough Foundation.

River Mouth Migration & Closure

Dr. Ludka is interested in the complex interactions (e.g. waves, coastal currents, river flow, tidal prism) that control river mouth migration and closure.

The migrating Tijuana River Mouth is less susceptible to closure than other nearby estuaries, yet when closures do occur, the consequences are more severe. Compared to other estuaries in southern California, the Tijuana River Estuary is relatively free of surrounding development, supporting a flourishing ecosystem including a number of endangered species. However during episodic rain events, the estuary transforms from one of the most pristine estuaries in the region, to the most severely polluted.

In addition to the declining levels of oxygen experienced in the waters of other intermittently closed estuaries along the coast during closure, pollution build up further threatens ecosystem functioning and is a local public health concern. Moreover, low lying homes on Sea Coast Drive of Imperial Beach are situated between the estuary and the ocean. These homes are prone to flooding from both water bodies, and contaminated river flooding is exacerbated when closure occurs. In March 2016 the Tijuana River Mouth closed for the first time since 1984. Dr. Ludka and colleagues found that El Niño wave conditions, coupled with six years of nourishment sand accumulation on the north side of the river mouth, likely contributed to the 2016 closure. As our understanding of river mouth dynamics improves, coastal management (e.g. nourishment, dredging, coastal structures) can be modified to better protect communities and ecosystems.

Ludka, B.C., Young, A.P., Guza, R.T., O’Reilly, W.C., Merrifield, M.A. (2022) Alongshore variability of a southern California beach, before and after nourishment. Coastal Engineering, 104223.

Ludka, B. C., Guza, R. T., & O’Reilly, W. C. (2018). Nourishment evolution and impacts at four southern California beaches: A sand volume analysis. Coastal Engineering, 136, 96-105.

Young, A. P., Flick, R. E., Gallien, T. W., Giddings, S. N., Guza, R. T., Harvey, M., Lenain, L., Ludka, B.C., Melville, K.W., O’Reilly, W. C. (2018). Southern California coastal response to the 2015–2016 El Niño. Journal of Geophysical Research, 123(11), 3069-3083.

Modeling Beach Evolution

Beaches protect landward infrastructure from flooding and erosion, and provide habitat and recreational space that sometimes supports large tourist economies. Understanding both beach erosion and recovery is important to understand their impact on the services they provide. Like many beaches elsewhere, Southern California beaches experience a seasonal cycle. During the larger waves of winter, the upper beach tends to narrow while an offshore sandbar grows. In the summer the the sandbar erodes and the upper beach accretes. Dr. Ludka has tested models of wave-driven beach evolution and found that "equilibrium-type" models well capture the seasonal cycle on many (but not all) beaches. These models assume that the beach evolves toward an equilibrium shape determined by the offshore wave conditions. Whether the beach erodes or accretes depends on how it needs to evolve to reach the equilibrium condition. For example, if small waves had previously created a wide upper beach, moderately large waves would erode the upper beach. However if very large waves had already created a narrow upper beach, moderately large waves could accrete the upper beach. Future beach modeling work includes taking into account tides, different substrates (e.g. sand, cobble, bedrock), and the interaction of the beach with dunes and cliffs.

Montaño, J., Coco, G., Antolinez, J., Beuzen, T., Bryan, K., Cagigal, L., Castelle, B., Davidson, M., Goldstein, E., Ibaceta, R., Idier, D., Ludka, B. C., et al. (2020) Blind testing of shoreline evolution models. Scientific Reports, 10, 2137.

Kalligeris, N., Smit, P., Ludka, B. C., Guza, R. T., & Gallien, T. W. (2020). Calibration and assessment of process-based numerical models for beach profile evolution in southern California. Coastal Engineering, 103650.

Ludka, B. C., Guza, R. T., O’Reilly, W. C., & Yates, M. L. (2015). Field evidence of beach profile evolution toward equilibrium. Journal of Geophysical Research, 120(11), 7574-7597.

Beach Nourishment

Beach "nourishment" mechanically increases the width or volume of the beach using off-site sand. Nourishment is often used to provide recreational space, prevent flooding/erosion and prepare for rising sea levels. After placement, waves and wind redistribute the nourishment sand. Dr. Ludka has analyzed detailed observations of waves and sand levels, before and after nourishment, to understand the evolution and impacts of this commonly-used coastal management technique. Beach nourishment impacts coastal infrastructure, recreation, tourism, groundwater and ecosystems, and Dr. Ludka is interested in interdisciplinary collaborations that can provide a more holistic perspective on the complex interplay of these aspects.

Ludka, B.C., Young, A.P., Guza, R.T., O’Reilly, W.C., Merrifield, M.A. (2022) Alongshore variability of a southern California beach, before and after nourishment. Coastal Engineering, 104223.

de Schipper, M.A., Ludka, B.C., Schlacher, T.A., Raubenheimer, B., Luijendijk, A.P. (2020) Beach nourishment has complex implications for the future of sandy shores. Nature Reviews Earth & Environment.

Ludka, B. C., Guza, R. T., & O’Reilly, W. C. (2018). Nourishment evolution and impacts at four southern California beaches: A sand volume analysis. Coastal Engineering, 136, 96-105.

Ludka, B. C., Gallien, T. W., Crosby, S. C., & Guza, R. T. (2016). Mid-El Nino erosion at nourished and unnourished Southern California beaches. Geophysical Research Letters, 43(9), 4510-4516.

El Niño Coastal Impacts

During El Niño, Pacific winds and ocean temperatures are modified such that coastal California sea levels rise by a few decimeters. El Niño also modifies the location of Pacific storms, bringing recurrent large winter waves to the California coast that can further raise shoreline water levels by a meter or more through wave setup. The anomalously energetic wave conditions tend to intensify coastal erosion, compounding flood risk. The different wave approach direction also alters surf zone currents and sediment transport patterns. Dr. Ludka and colleagues work to characterize these extreme events to inform coastal protection efforts that include preparing for rising seas.

Young, A. P., Flick, R. E., Gallien, T. W., Giddings, S. N., Guza, R. T., Harvey, M., Lenain, L., Ludka, B.C., Melville, K.W., O’Reilly, W. C. (2018). Southern California coastal response to the 2015–2016 El Niño. Journal of Geophysical Research, 123(11), 3069-3083.

Barnard, P. L., Hoover, D., Hubbard, D. M., Snyder, A., Ludka, B. C., Allan, J., … Serafin, K. A. (2017). Extreme oceanographic forcing and coastal response due to the 2015-2016 El Nino. Nature Communications, 8(14365).

Ludka, B. C., Gallien, T. W., Crosby, S. C., & Guza, R. T. (2016). Mid-El Nino erosion at nourished and unnourished Southern California beaches. Geophysical Research Letters, 43(9), 4510-4516.

Coastal Water Level & Flooding Predictions

Dr. Ludka has had the to opportunity to work with wave modeling experts to create coastal water level and flooding predictions. Flooding along the continental U.S. West Coast most often occurs when high tides combine with large waves that are generated by near or distant storm winds. Beach state estimates and global, regional, and surf zone wave models are tested against observations and are combined to create water level predictions. The water level predictions are also tested against observations to assess accuracy and improve the forecast, which is used to help coastal communities prepare for flooding.

Merrifield, M.A., Johnson, M., Guza, R.T., Fiedler, J.W., Young, A.P., Henderson, C.S., Lange, A.M.Z., O’Reilly, W.C., Ludka, B.C., Okihiro, M., Gallien, T.W., Pappas, K., Engeman, L., Behrens, J., & Terrill, E. (2021) An early warning system for wave-driven coastal flooding at Imperial Beach, CA. Natural Hazards, 108, 2591–2612.

Fiedler, J.W., Young, A.P., Ludka, B.C., O’Reilly, W.C., Henderson, C., Merrifeld, M.A., Guza, R.T. (2020) Predicting site-specific storm wave run-up. Natural Hazards, 104, 493–517.

Sand Mining

Dr. Ludka helped write a report about the impacts of a beach sand mine while working at the California Coastal Commission. The CEMEX Lapis mine in Southern Monterey Bay was the last operating beach sand mine in the United States, and it fully shut down in December 2020. The Southern Monterey Bay has some of the highest rates of long-term shoreline retreat in the state (Hapke et al. 2006). The mostly unarmored landward migrating coast often maintained wide beaches as the dunes eroded and fed the beach (Thornton 2016). Dr. Ludka is interested in how the coast is recovering now that the sand mine has been shut down.

Hapke, C. J., Reid, D., Richmond, B. M., Ruggiero, P., & List, J. (2006). National assessment of shoreline change Part 3: Historical shoreline change and associated coastal land loss along sandy shorelines of the California Coast. US Geological Survey Open File Report, 1219, 79.

Thornton, E. B. (2016). Temporal and spatial variations in sand budgets with application to southern Monterey Bay, California. Marine Geology, 382, 56-67.

Satellite Derived Bathymetry

Coastal bathymetry (underwater topography) is useful for navigation, sea level rise and storm impact predictions, and characterizing geology and ecosystems. Much of the world's shallow coasts are unmapped or poorly mapped because typical methods are often expensive, labor-intensive and/or dangerous. Access to data is an issue of equity. Low income coastal communities often lack beach and bathymetry elevation data and resources to adapt to rising seas, yet contributed the least to global carbon emissions.

Using multiple satellite images captured in different wavebands (e.g. Sentinel-2 imagery), coastal water depths across the globe can be estimated based on the physics of how different wavelengths of light are attenuated in the water column. Due to variations in water clarity, substrate type, and other factors, additional data is needed to calibrate the method for sub-meter mapping accuracy. New water-penetrating LiDAR measurements from the IceSAT-2 satellite can now be used to calibrate the depth estimates. Karan Sunil and Dr. Adrian Borsa developed a data processing pipeline that Dr. Ludka is helping to build upon. Dr. Ludka is also interested in working with local coastal knowledge keepers around the world who can direct and utilize this work.

Header Photo: Ocean Beach, San Diego California