Groundwater is the water beneath the surface of the ground that fills the spaces in the soil and gravel. An aquifer is a collection of groundwater that’s held within a permeable layer of rock, sand, or gravel. Aquifers can lie a few feet below the ground and be recharged with rain and floodwaters (Frannie learned that these are called unconfined aquifers) or be hundreds or thousands of feet inside the earth, trapped for hundreds of years beneath an impermeable layer like shale (confined aquifers).
Perhaps one of the coolest things about aquifers and the groundwater in them is the flow! Groundwater certainly moves down through the ground from the surface, but did you know it also flows horizontally? Like a river, groundwater will flow “downhill” or down the slope of layers that make up the aquifer. Unlike a river, groundwater takes much longer to travel. A drop of water in a river might be able to travel up to 7 feet in one second, but a drop traveling through the ground might take a couple of days to travel the same distance.
These time of travel calculations are very useful to hydrogeologists when they need to predict how quickly groundwater will move and where it’s going. Flow direction and time of travel can be affected by many things, including different points of discharge, which just happens to be the next bead on the bracelet!
Next time, Frannie will talk about different kinds of discharge and share the really cool connection between groundwater and volcanoes. See you then!