How to Measure Sea Level Rise and Groundwater Flooding

Sea level rise (SLR) vulnerability analysis of critical wastewater and transit infrastructure requires data collection at a temporal and geospatial scale small enough for planning and mitigation efforts. Flooding of wastewater infrastructure will increase with SLR, damaging pipes, pumps and causing sewer overflows and pipe backflows, creating human health exposure risks and environmental damage. Regular flooding of roads causes delays and damages transit infrastructure. Capital Improvement Projects (CIPs) for future wastewater and transit infrastructure projects are funded over 30-year cycles, and the next set of projects requires detailed field measurements to calculate projected SLR and groundwater flooding. SLR issues and infrastructure are discussed in [1-5]. Many general articles erroneously equate small increases in SLR with the equivalent topographic land contours. 

The two study areas were developed on filled wetlands along San Francisco Bay, California and have higher flood frequencies than dozens of similar nearby communities. They also reflect the intersection of areas with high flood vulnerability, with critical wastewater and transit infrastructure which fulfill Diversity, Equality and Inclusion (DEI) goals. I undertook field observations in both study areas in November and December 2020, during a period of extremely high tides (king tides), and noted groundwater flooding, stormwater backflow, surface flooding, and other associated SLR indicators that were identified and mapped. Area 1 - Atchison Village (AV), Richmond, California is a former WWII housing development, now a non-profit community with 450 units. AV is “severely economically disadvantaged,” where 27% of the houses regularly have emergent groundwater in crawl spaces. AV is surrounded by industrial sites (railyards, chemical plants, and a refinery) within 1.6 km. AV is affiliated with Rosie the Riveter WWII Home Front National Historic Park. “Lake Curry” forms at the intersection of two streets during heavy storms, preventing transit through the area. The NOAA SLR Viewer shows flooding in AV at this location only after 3-feet of SLR. Area 2 - Tamalpais Valley (TV), an unincorporated area in southern Marin County, becomes impassable at the Manzanita Interchange at U.S. Route 101. Flooding is a result of a complex combination of flood actors, including high tides, heavy rains, onshore winds, and subsidence. The adjacent Fireside Apartments provides 50 affordable living units for low-income seniors and families and individuals with special needs, including those transitioning from homelessness. The Fireside Apartments reflects the “multigenerational and diverse socioeconomic character of the community.” 

Research Question - How do we quantify, model and communicate the vulnerabilities of SLR and groundwater flooding on urban wastewater and transit infrastructure at a geospatial and temporal scale appropriate for local planning and mitigation?

Goal - The goal is to collect field data, characterize subsurface preferential pathway flow, and develop a hydrogeologic model for emergent groundwater, sewer, stormdrain, and road flooding to better understand the short-term impacts of SLR. The outputs aim to provide real-time advance warnings to agencies and residents of impending sewer overflows and road flooding and to identify sources of floodwaters.

Methodology - Effective measurement and management of SLR, groundwater flooding, and stormwater runoff requires quantification of various flood factors of the urban coastal water balance, such as precipitation, evapotranspiration, sewer flow, stormwater flow, surface flow, tidal elevations, barometric pressure, wind direction, and other factors. The sensor/logger locations will be surveyed vertically and laterally and will lie along four to five transects and will allow for variability within each study area for elevation, surfacing, subsurface soil permeability, vegetation, flooding potential, fill history, etc. I will use real-time ultrasonic touchless sensors to measure tide levels, surface flood elevations, and flow in sewer and stormdrain pipelines.  Real-time data loggers (loggers) will be installed in driven well points in utility trenches, buried stream channels and backfilled deposits (control locations). The loggers will continuously measure groundwater elevation, conductivity, temperature, pH, and other parameters. Comparison of the acquired data will help in evaluating SLR flood vulnerability of the wastewater and transit infrastructure in the two areas. The data will be evaluated using hydrogeologic models, and statistical models. A Bayesian Network will be developed as a tool for decision making. These data will be designed to (1) identify cause and effect of wastewater and transit infrastructure flooding, (2) develop flood prediction based on variable flood factor conditions associated with wastewater and transit infrastructure flooding, and (3) provide projected SLR flood information to agencies to inform SLR mitigation and CIPs for wastewater and transit infrastructure. The project is planned for five years, with three years of field data collected and analyzed.

Additional tasks include compiling pre-development ecosystem, urban development history, and land subsidence data for each study area and obtaining historic maps, historic aerial photographs, utility maps, geologic and soil maps, GIS agency maps, and topographic maps in collaboration with agency staff to identify accessible sensor/logger locations in critical road, sewer, and stormdrain locations to document when surface flooding (roads) or sewer or stormdrain pipe overflows are occurring (Task 1). Preferential pathways for groundwater such as buried stream channels, leaky sewers, or utility trenches will be located on GIS maps (Task 2). I will install multiparameter loggers (water elevation, conductivity, temperature, pH, etc.) in driven piezometers in utility trenches, preferential pathways, and in background fill (control) soil (Task 3). Weather stations and touchless ultrasonic meters will be positioned in sewer and stormdrain manholes, and tide and stream gauges will be installed (Task 4). I will initiate public outreach on the project and maintain data collection operations (Task 5). I will train local volunteers to assist with simple equipment malfunctions and to document flooding evidence with notes and photographs (Task 6). I will manage the incoming data (Task 7). I will provide quarterly project progress reports to my project leadership team for public meetings and distribution on websites, newsletters, and social media (Task 8). I will review the data, perform statistical analysis, and develop a Bayesian Network as a tool for predicting 2050, 2070 and 2100 SLR projections based on site-specific tide and water elevation data and flood factors (Task 9). I will prepare summary reports for technical publications, government forums, and public meetings of the procedures and lessons learned to share the information with others (Task 10).

Broader Impacts 

The methodology, approach, and tools developed during this research will allow wastewater and transit agencies in California and nationwide to make better choices on 30-year infrastructure plans where small-scale flood outcomes and SLR cannot be predicted with certainty. Public education, communication and outreach are an important part of the project. I have developed a public agency project leadership team specifically for my PhD project with commitments of participation from the executive director of the San Francisco Bay Area clean water agency, the mayor of the City of Richmond, the AV board of directors, the supervisor for southern Marin County, the general manager of the local sewer district (TCSD), the National Park Service, and others. The leadership team will help provide community input and valuable recommendations and their agencies will receive my progress reports, data, and findings. Public agency websites and my website (www.jamesajacobs.net) will share real-time water elevation and flood warnings with their communities. My communication plan includes project updates and results through quarterly Zoom/live meetings, publications, technical presentations, editorials, media, and social media venues. I will encourage citizen scientists to upload photos of flood events to my website. Where small-scale SLR and groundwater flooding can’t be predicted with certainty without site-specific data, this project will allow me to work with wastewater and transit agencies to help them make better choices on future 30-year infrastructure CIPs. 

References: [1] Befus et al., 2020, Increasing threat of coastal groundwater hazards from SLR in California, Nature Climate Change, 10, p. 946-952; [2] Habel et al., 2020, SLR Induced Multi-Mechanism Flooding and Contribution to Urban Infrastructure Failure, Sci. Rpts., Nature Res., 10:3796, 10 p.; [3] Hummel et al., 2018, SLR Impacts on Wastewater Treatment Systems Along the U.S. Coasts, Earth’s Future, AGU, 6, 622-633; [4] Plane et al., 2019, A Rapid Assessment Method to Identify Potential Groundwater Flooding Hotspots as SLR in Coastal Cities, Water, V 11, Issue 11 14; [5] San Francisco Estuary Institute (SFEI), 2019, SF Bay Shoreline Adaptation Atlas, Version 1.0, April, 262 p.

NOTE: Figures, maps, photos have been referenced as to their source, as best as possible.  Other  images are from County of Marin, City of Richmond, and other sources.   

Questions - contact James A. Jacobs at [email protected]