Woohoo! March 7-13 is Groundwater Awareness Week! (Yes, there is a Groundwater Awareness Week.) To get into the spirit of things, I decided to educate myself a bit about the relationship of Middle River to our groundwater aquifer system.
To start off, let’s review some basic earth science. An aquifer is an underground body of rocks with spaces between the rocks that fill with groundwater. Imagine an aquifer being like a rigid sponge. There are two terms that describe how an aquifer holds groundwater—porosity and permeability.
The rocks under our feet are full of cracks, fractures, and open spaces. For water to exist underground there must be empty spaces to hold it. The relative amount of space between rocks is called its porosity.
But the spaces between rocks can also be described by their connections to one another—which is its permeability. Highly permeable aquifers act as superhighways along which water travels underground. Since we live in the Valley and Ridge province of Virginia, it’s no surprise the aquifer that provides our ground water is called the Valley and Ridge aquifer.
If you could look at an underground cross section of an aquifer, the upper surface level of the water in the rocks—the point the water comes the highest—is known as the water table. If you dig a hole in the ground and the hole magically fills with water, it’s because you have dug down to the water table. The water table level fluctuates based on how much precipitation the land above the aquifer gets and also how much water is taken out of the aquifer via wells or springs.
There are different ways to get water out of an aquifer. The simplest way is to find a spot where the water table and the surface of the land meet. This is a spring— a place where the groundwater flows out onto the surface of the land all on its own.
The second easiest way is if you drill into an artesian aquifer. With an artesian aquifer, the layer of aquifer layer of rocks is squeezed between an upper and lower solid layer of rocks. The squeeze pressure on the aquifer pushes the water up the well, past the water table and to the surface. No pump needed.
But with most of the wells we drill, the underground water is not under pressure and does not rise above the water table, so you need a pump to bring the water all the way up to the surface.
The total amount of water in a river such as Middle River is a combination of groundwater that comes into the river via springs, and water from precipitation that runs off of the land surface and is pulled by gravity down to the river.
Precipitation runs down the less permeable shale and sandstone rocks of our mountains and enters the aquifer system through fractures or sinkholes of the more permeable limestone at the point where the mountains meet the valley edges. Once underground, the groundwater is pulled by gravity towards the lowest center of the valley.
The Shenandoah Valley floor is mostly made of limestone. Limestone erodes more easily in water than the mountain rock, which is why the magnesium and calcium content in our water is so high and why we get carbonate buildup on our plumbing. Groundwater spends a lot of time moving through rocks underground—sometimes thousands of years, so it has a lot of time to dissolve minerals from the limestone.
Principle Sandstone and Carbonate-Rock Aquifers in purple.
Middle River is fed by a lot of springs. Despite its many springs with cool water, Middle River remains largely a warm water stream (over 70 degrees Fahrenheit in the summer). In the upper Middle River, Cochran Spring adds over a thousand gallons per minute of cold water into Middle River as it courses downstream, giving many hope that with good conservation practices native Brook Trout will one day occupy its waters. Indeed, biologists have tried small stockings of fingerling Brook Trout along Route 602, but lack of shade and legacy sedimentation have been barriers to establishing a reproducing population of Virginia’s state fish.
Having many springs is the saving grace of Middle River. They add water to the river along its way, which dilutes the pollutants so that as the water flows downstream the water quality improves. Gardner Spring, a tremendous cold-water resource, enters the river near Franks Mill. Such a volume of groundwater surfaces here that it partially serves the City of Staunton's water supply.
And many have seen the beautiful waterfall on Middle River at Falling Spring Run, which can be seen from Shenandoah Valley campground.
Lastly, to celebrate Groundwater Awareness Week, if you like messing with maps… (and who does not?!!) the United States Geological Survey has a very cool interactive National Water Dashboard where you can look at real time data of water flow, nutrient data, water temperature and other water indicators for rivers, lakes and even wells. Check out this cool resource at https://dashboard.waterdata.usgs.gov/app/nwd/?aoi=default
Now, go celebrate! ~Kate
Sources consulted for this post:
United States Geological Survey (n.d.) Aquifers and Groundwater. Water Science School. Retrieved March 5, 2021 from https://www.usgs.gov/special-topic/water-science-school/science/aquifers-and-groundwater?qt-science_center_objects=0#qt-science_center_objects
United States Geological Survey (n.d.) Groundwater True/False Quiz. Water Science School. Retrieved March 5, 2021 from https://water.usgs.gov/edu/activity-tf-groundwater.html
Arthur, M., Saffer, D. & Belmont, P. (n.d.) Water Science and Society: Valley and Ridge Aquifer System. Pennsylvania State University. Retrieved on March 5, 2021 from https://www.e-education.psu.edu/earth111/node/922
United States Geological Survey (n.d.) Aquifer Basics. Water Science School. Retrieved March 5, 2021 from https://water.usgs.gov/ogw/aquiferbasics/sandcarb.html
Bugas Jr., P.E. (2020, November) Personal communication with Paul Bugas, Fisheries Biologist at the Department of Wildlife Resources, retired. https://www.friendsofthemiddleriver.org/the-river-today