This week at Science World, we looked at two topics about water for our third Earth and Space session: dam safety with hydro power, and hydrogeology (the study of groundwater). As with our other sessions, Dr. Phil Hammer and Tanya Stemberger were our guides, and we also had a guest speaker, Dr. Megan Sheffer from BC Hydro.
For our first topic, Dr. Sheffer told us about the use of dams in producing hydro power – power from falling/moving water. Most of the electricity we use in BC is produced from resources like local rivers. By building a dam, a reservoir of water fills on one side, and continuously flows out to the other side through large pipes called penstocks into powerhouses. Turbines in these powerhouses are driven by the moving water, changing kinetic energy into mechanical energy into electrical energy. These dams are made of a solid, non-permeable core, with an outer layer of fine-grained material like gravel, through which water can seep and enter the penstocks. If water tends to seep through one particular spot, the area around that penstock will undergo internal erosion, where the material weakens. If untreated, internal erosion can destroy a dam completely, which is why monitoring it regularly is so important. There are three ways to monitor water flow:
Temperature: fiber optic cables at the top (crest) and bottom (toe) of the dam measure the temperature of the water flowing through. If the temperature is different than normal or there is a large area of warm/cold water inside the dam, there might be a problem.
Electical resistivity: electrodes inject an electric current into the soil around the dam. Soil particles have a regular resistance to voltage, so if there is a change in resistivity, there could have been a loss of fine grains, meaning internal erosion.
Self-potential: electrodes measure the natural electric current produced by the kinetic energy of flowing water at different spots inside the dam. By comparing the differences between signels, we can determine if there are any areas with an abnormal current.
To ensure the top performance and safety of the dams, engineers need to inspect them regularly using all these methods. In this way, they can prevent the dams from breaking down, and help to provide energy for everyone in BC.
For our next topic, we discussed the importance of groundwater. 30% of the Earth freshwater supply comes from underground, through layers of rock and other material. Some materials are more porous (porosity), so they have more open space between them; some are more permeable (permeability), so water can easily flow through them. We did some experiments with a model (as shown in the featured image), where we put coloured “contaminants” into different wells of water. The contaminants reach the bottom of the well and seep into the ground around it, since the ground is porous and permeable. It then spreads through the ground water at an alarming rate and enters other wells and areas of surface water, as we can see in the picture. We then tried pumping out the contaminated water, and discovered how the water level underground (the water table) drops and creates a cone of depression.
This session reminded us of how important our water supply is in BC; it provides us with energy of all kinds, so we must handle it carefully and keep it clean at all times.