While the training for hydrology and hydrogeology are completely different, in practice every hydrologist will do some level of hydrogeology and vice versa.
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I get this question all the time. To those in the industry, it’s the equivalent of mixing up geology (the study of earth and its physical processes) with geography (understanding maps). Two very different things.
However, read on and you’ll see why there is a lot of (understandable) confusion around these two fields.
Simply put, hydrology is a subcategory of engineering that deals with the physical properties of surface freshwater, such as lakes and rivers, and with its chemical interactions with environmental and man-made substances. Hydrogeology is a subcategory of geology that explores water moving through the pore spaces in rocks and soil layers beneath the land surface.
While the training for hydrology and hydrogeology are completely different, in practice every hydrologist will do some level of hydrogeology and vice versa. That’s because in the real world of consulting and managing environmental projects, there is so much overlap in the information and skills needed to analyze them that it just becomes second nature.
Perhaps that is why experience matters so much in our industry. Education only offers fundamental building blocks to solve problems that are narrowly focused and dependent on having lots of data. Those two combinations, a narrow focus and lots of data (a.k.a. lots of money!), are nearly impossible to encounter in real world settings.
Given this, most technologists will learn the other skill set on the job. Perhaps that is why who you train under has such a big impact on the skills, tools, and confidence you will acquire over your career. That is why hydrogeologists and hydrologists are often NOT interchangeable. However, while their specialization is not immediately transferable to outside studies, yet the fundamental understanding of science and physical water flow allows them to make the switch easily under a seasoned professional.
With the right on-the-job training, any hydrogeologist can function as a hydrologist, and any hydrologist can learn the functions of field hydrogeology.
Now, if you’re considering becoming a groundwater modeler, which is a specialization within hydrogeology, that is another subject entirely as explained in my article Why groundwater modeling?