GeoRisks
Identify and Mitigate Threats
Proactive Solutions for Mitigating Geologic Threats
There are countless GeoRisks and GeoHazards. Weathering is the chemical and physical breakdown of minerals and rocks; erosion tends to be the movement of weathered material. GeoHazards tend to be erosional, they are related in some way to the movement of materials. Dissolution of limestone is weathering, the collapse of the limestone roof into the dissolved room below it forming a sink is erosional. Magnet divides these GeoRisks into five subdivisions as follows:
Soil and Shallow Events – things like expanding clays / soils, sinkholes, saline seeps and liquefaction.
Collapse and Precipitous Transient Events – Things that happen suddenly, like a landslide or an earthquake
Erosional Events – Natural movement of materials downslope but also man-made intrusions such as highway cuts or land manipulation for other construction projects. These tend to accelerate the erosional process. In 2023 over 4500 new bulldozers were sold, everywhere around the world, bulldozers are cutting into banks, accelerating the erosional process.
Floods, fires, droughts and other atmosphere related events – From hailstorms, tornadoes and hurricanes to wildfires and floods. The devastation can be local to half a continent.
Contaminants – “Contaminants” has a negative connotation but is not always bad. Salt and pepper are contaminants on your eggs. Good or bad is typically tied to concentration. What is the contaminant and what is the concentration? Contaminant groups are Physical (example - turbid waters, brown earthy clay particles), Chemical (arsenic or sulfates or pesticides), biological (bacteria, virus, parasites), radiological (Radium/Radon/Uranium/ Thorium) and nutrient (like nitrates and phosphates).
Following are a few specifics:
Expansive Clays
It is often reported that these expansive clay issues are the most costly geohazard in the US. It is tied to certain types of clays and its behavior is subject to varying moisture content. Perhaps it is not recognized until a foundation is put down which changes the moisture regime of the underlying soil. This can result in the foundation either doming or dishing. Does the clay swell in the middle or the sides. Because it is not recognized ahead of time, it can result in much structural damage.
Floods
It has been reported that about half of the flooded homes in the Harvey Floods in Houston in 2017 were not in the designated flood zones. Why was this not recognized? There are two aspects to flooding, the watershed and the precipitation event. For the watershed, it can be divided into two parts also, geological and human influenced. For geological, things like size, slope, gradient, subsidence, infiltration / absorption, saturation, vegetation and season have a major effect on the concentration of water within the watershed. Humans are constantly building, constructing and affecting water runoff. A decrease in infiltration, from development increases the volume and concentration of water. The construction increases erosion and adds to the sediment supply which decreases the rate of downstream movement and causes both local and downstream effects. Extra sediment takes more room within the valley and raises water levels. The second aspect to flooding is the precipitation event itself, the storm. Does the storm move up the watershed, or down the watershed or across. What is the velocity of the storm, what is the intensity of the storm? These affect the concentration of water at any point within the watershed. There are three models to consider: (1) Natural water movement in a watershed; (2) Urbanization and human construction patterns; (3) Storm intensity and movement patterns. Each model is complicated, combining the models is even more difficult. And now it is easier to understand why Houston has many flooding issues, recognized and unrecognized. Any and all locations everywhere needs to be evaluated carefully with these aspects in mind.
Contaminant Modifications
Environmental changes have many affects. There is a phrase – “Dilution is the solution” and it has its place but can have issues also. For contaminants, if it rains more, it is more likely to dilute the contaminates but dilution in one place means contamination in another location. As rain decreases then soluble contaminants begin to become more concentrated. This could be seasonal, cyclical or a climatic thing. Polioencephalomalacia can kill cattle from the concentration of sulfates; Arsenic precipitation in a creek bed can send kids to the hospital on a dusty windy day. Test water and soils during wet periods for maximum contaminant content and test during dry times for maximum concentrations.
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