Course:EOSC311/2022/Geological Factors Impacting Urban Planning
Geological factors are often not discussed in urban planning discourse. This article seeks to argue why urban planners (or those interested in urban planning) should seek to understand the geology that lays beneath them. I argue that the safety and wellbeing of humans and their neighbourhoods rely on geology. To better illustrate my argument, I discuss concepts surrounding surficial geology, plate tectonics, and aquifers and their relevance to urban planning. To finish off, I present a case study example – the subsidence (the sinking of land) of the Pajaro Valley in California due to the over extraction of aquifers and the resulting compaction of fine-grained silts and clays.
Statement of connection and why you chose it
By 2050 over 68% of the global population will be living in urban environments (United Nations, 2018). Existing cities will grow and new neighbourhoods will be built and existing ones expanded. The practice of urban planning shapes how modern cities grow and expand (Legget, 1987). Urban planners shape the buildings and infrastructure that we live, work, and play in everyday (Earle & Panchuk, 2019). Yet, geology shapes the foundations our cities are built upon, contribute to natural hazards, and provide humans with the materials and resources to build our cities (Hudson & Cosgrove, 2019). Ultimately, geology significantly impacts both human wellbeing and our modern economy.
Main text
Section 1: Surficial Geology
A strong foundation is key to the construction of any neighbourhood – and a strong foundation is built upon good ground. When looking at surficial geology, one should look at the topmost geological layer. In the urban planning context, surficial geology will significantly impact how a site can be used. It should be noted that surficial geology makes up only one small aspect of the geological conditions urban planners should consider in their practice – but I think it is the most visible. For illustrative purposes, we will look at two areas of Metro Vancouver with different geologies – Sea Island and Lighthouse Park.
Modern Sediments – Building on Sand
Sea Island, home to the Vancouver International Airport sits on modern sediments (Turner & Clauge, 1998). These sediments were deposited by the Fraser River after the last ice-age 10,000 years ago (Turner & Clauge, 1998; Armstrong et al., 1990). At the human-scale, that 10,000 years ago is a very long time ago – but geologically that time frame is recent. As a result, the ground that makes up sea island is primarily comprised of sands and silts. It should be noted that at its current state, the modern sediments that comprise Sea Island are not considered sedimentary rocks. However, based on the known process of the formation of sedimentary rocks, I would expect that over geological time – the modern sediments of sea island may turn into sedimentary rock through continued compaction and cementation, and lithification (Earle & Panchuk, 2019). The geology of Sea Island creates unique challenges for urban planners and construction projects. Earthquakes resulting from tectonic activity (which will be discussed later) may result in the immediate shifting of the sediments – allowing water to flow freely in a process called liquefaction (Schmitt et al., 2017). During liquefaction, sediments become waterlogged and lose all of its strength (Schmitt et al., 2017). Such an event would be detrimental to the stability of buildings built on modern sediments.
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Strong Foundations – Bedrock
North of Vancouver is the. Unlike the relatively young modern sediments that form the foundation of Sea Island, the materials that form Lighthouse Park are much older. Comprised of basalts and andesites, these bedrock materials are solid igneous rocks that originated from volcanic activity over 17 million years ago (Turner & Clauge, 1998; Armstrong et al., 1990). The old solid bedrock provides a strong foundation for new development and is considered much more stable than modern sediments (Hudson & Cosgrove, 2019).
Plate Tectonics
Generally speaking, buildings are safer when they don’t move. However, depending where a neighbourhood is located – movement may be part of the environment. While bedrock geology quite literally makes up the foundation – planners need to understand plate tectonics to fully understand the risk that underlying geology has on neighbourhoods. Much of the western coast of North America lies on the Pacific Rim of Fire (see figure 1) – an area bordering the Pacific Ocean that is home to significant tectonic activity (US Geological Survey, 1999). Zooming into Vancouver, British Columbia the mountainous region is formed through the subduction of denser oceanic plate under the much lighter continental plate (Armstrong et al., 1990). This natural process, occurring kilometers below our feet contributes to the formation of mountains and volcanos – and the occasional earthquake. Occasionally fault lines will develop between two blocks of rock – which allows movement to naturally occur (Earle & Panchuk, 2019). Rapid movements will result in earthquakes while slower movements will result in creeps (Schmitt et al., 2017). Either phenomenon is bad for construction and must be adequately accounted for during development.
Geology & Plate Tectonics
Let’s think about surficial geology and plate tectonics together. The type of surficial geology a community is built upon will greatly influence the natural hazards a community will face. Some types of surficial geology such as modern sediments is significantly more susceptible to the negative impacts of earthquakes than bedrock. Understanding the risk rock types may pose in earthquake prone regions is critical to ensuring the safety and wellbeing of a community. Planners should be cognisant of surficial geology in land use planning practices to ensure the wellbeing and safety of both buildings and its occupants. This is especially important when considering the risks of natural hazards.
Section 2: Water & Geology
One of the fundamentals of life is water. Planners needs to consider where water can be obtained from and how water interacts with the existing geology. For instance, potable water – used for drinking, cooking, and cleaning is an increasingly scares resource, with some cities having to import potable water for urban use (Lerner et al., 2018). However, depending on the location of a neighbourhood – water might be below the surface in confined or unconfined aquifers.
Aquifers - Formation & Geology
An aquifer is a body of rock or sediment that has sufficient permeability and porosity to allow it to be used as a source of groundwater (Earle & Panchuk, 2019). Permeable materials such as aggregates of sand and gravel which contain interconnected spaces that are large and numerous enough to allow for the flow of water. Some aquifers are located under impermeable materials, defined as materials that do not allow or severely restrict the flow of water (Earle & Panchuk, 2019). Aquifers that are not covered by impermeable materials are classed as unconfined aquifers. Alternatively, groundwater may flow through the cracks, joints, and fissures of existing bedrock such as granites and basalts. These aquifers are known as fractured aquifers (Environment Canada, 2013) and are most common in mountainous regions.
Pollution
Communities can utilize groundwater aquifers as sources of water through the construction and usage of groundwater wells. A successful well must be deep enough to be below the water table and if the aquifer is confined – it also must penetrate any impermeable materials (Environment Canada, 2013). If done correctly the well will provide a stable and refilling source of drinking water. However, groundwater aquifers are susceptible to pollution (Worrall & Kolpin, 2004). Land-use planners should be cognisant of this fact when planning where industrial, manufacturing, or waste-treatment sites are to be built as pollution generated from these sources may find its way in the groundwater system (Worrall & Kolpin, 2004). This is especially important from an equity lens as historically – many sites that produce environmental harms are built near neighbourhoods that predominantly house communities of colour or low-income individuals (Park & Pellow, 2004). Planners should be cognisant when constructing developments to avoid the pollution of the groundwater aquifer system.
Case Study: California Aquifer Overuse
What Happened
As agricultural practices in the Pajaro Valley north of Los Angeles, United States grew – there was a need to provide water for both the growing agricultural sector and the equally growing residential population (Brandt et al., 2021). Groundwater provided through confined aquifers provided 90% of water resources for the region (Brandt et al., 2021). As demand for water grew, more water was extracted out of the aquifers resulting the sinking and compaction of the materials that comprise the valley floor (Brandt et al., 2021).
The Geology Involved
Pajaro Valley is a flat plain comprised of modern sediments - fine silts and clays deposited by nearby river systems (Brandt et al., 2021). With a warm climate, the valley is dry – requiring the need to freshwater to be extracted out of the aquifers to supply human demand (Brandt et al., 2021). The aquifers themselves are confined aquifers of fine-grain clays (Brandt et al., 2021). As groundwater is extracted from subsurface aquifers the topology above (silts and clays) settles as pressure is reduced (Brandt et al., 2021). This results in a process known as subsidence in low-lying areas. Unfortunately, the sinking of the ground results in the compaction of both the clays and silts – lowering the permeability of the aquifers thereby reducing the capacity for water retention (Brandt et al., 2021). The reduced water output of the aquifers due to both over extraction and compaction of the aquifers poses a significant risk to the wellbeing of human health and the economy (Brandt et al., 2021).
Takeaway for Planners
Planners should be cognisant that aquifers provide a stable source of water for differing agricultural, commercial, and residential uses. Depending on the source of groundwater, the aquifer may naturally refill itself on a stable cycle. Planners should also be cognisant that depending on the geology and location of the aquifer, pollutants may find itself enter the groundwater system. If the aquifer is a confined aquifer, these pollutants may remain underground for a long time. Lastly, planners should be cognisant that overuse of confined aquifer systems may result in the sinking of the ground in a process known as subsidence.
Conclusion / Your Evaluation of the Connections
This article only explored a few geological facets that planners should consider in the practice of urban planning. However, many more factors exist and should be considered depending location. Through evaluating Sea Island and Lighthouse Park I hoped to have shown surficial geology is both interesting and also a contributor to the risk natural hazards such as earthquakes and liquefaction play onto neighbourhoods. Through the dive underground into subterranean aquifers I hope to show that aquifers, while a very important source of water – is also an over extracted resource with devastating consequences. These consequences are useful for planners in practice when making decisions on where new neighbourhoods should be built, or whether to recommend a new garbage dump be constructed on modern sediments. I hope planners (or those interested in the planning profession) will take it upon themselves to become more versed in geological concepts. At the very least – increase the appreciation for the geology that provide the foundation of our modern world.
References
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Brandt, J. T., Earll, M. M., Sneed, M., & Henson, W. (2021). Detection and Measurement of Land-Surface Deformation, Pajaro Valley, Santa Cruz and Monterey Counties, California, 2015–18. US Geological Survey.
Earle, S., & Panchuk, K. (2019). Physical Geology (2nd ed.). BC Open Textbook Project.
Environment Canada. (2013). Water Sources: Groundwater. Environment Canada; Government of Canada. https://www.canada.ca/en/environment-climate-change/services/water-overview/sources/groundwater.html
Hudson, J. A., & Cosgrove, J. W. (2019). Understanding building stones and stone buildings. Boca Raton Crc Press.
Legget, R. F. (1987). The value of geology in planning. Geological Society, London, Engineering Geology Special Publications, 4(1), 53–58. https://doi.org/10.1144/gsl.eng.1987.004.01.04
Lerner, A. M., Eakin, H. C., Tellman, E., Bausch, J. C., & Hernández Aguilar, B. (2018). Governing the gaps in water governance and land-use planning in a megacity: The example of hydrological risk in Mexico City. Cities, 83(31), 61–70. https://doi.org/10.1016/j.cities.2018.06.009
Park, L. S.-H., & Pellow, D. N. (2004). Racial Formation, Environmental Racism, and the Emergence of Silicon Valley. Ethnicities, 4(3), 403–424. https://doi.org/10.1177/1468796804045241
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United Nations. (2018). 68% of the world population projected to live in urban areas by 2050, says UN | UN DESA | United Nations Department of Economic and Social Affairs. Www.un.org. https://www.un.org/development/desa/en/news/population/2018-revision-of-world-urbanization-prospects.html#:~:text=68%25%20of%20the%20world%20population
US Geological Survey. (1999). Ring of Fire [This Dynamic Earth, USGS]. Pubs.usgs.gov. https://pubs.usgs.gov/gip/dynamic/fire.html
Worrall, F., & Kolpin, D. W. (2004). Aquifer vulnerability to pesticide pollution—combining soil, land-use and aquifer properties with molecular descriptors. Journal of Hydrology, 293(1-4), 191–204. https://doi.org/10.1016/j.jhydrol.2004.01.013
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