#84 Groundwater
April 17, 2008
This show originally aired on June 27, 2007 and was aired again on April 17, 2008 on “The Rivanna Rambler,” a weekly public affairs show airing every Thursday at 11:55 a.m. on WTJU 91.1 FM or wtju.net.
I was well into my adult years before I truly understood the nature and logic of water.
I grew up on the Assabet River in Massachusetts, the one that Henry David Thoreau explored with his brother 100 years before me. Its floodplain and wetlands were my childhood playground. Upstream, there was a marshy inlet that froze into a skating pond in the winter. Downstream acres of soggy, skunk-cabbage filled wetlands provided interest for many an after school hour. In the summer, the waters moved slowly, revealing a shallow brown bottom, fish, turtles, and freshwater clams. In the winter, the river rose high, sloughing the ice from its banks. Springtime floods often crept up the bank towards the low foundation of our house. The river’s cycle of the seasons was simply part of our lives –and I did not question the way water works.
I assumed that a river was filled by the tributaries that fed it, like our Assabet River joined the Sudbury to become the larger Concord River downstream – and that these, in turn, were fed by smaller streams and springs – and that the river flowed because the rain flowed over the land or into the river itself. Later, I encountered dry bed of the Ventura River as it approached the Pacific in a broad delta with windrows of cottonwood and willow marking the place where water, deep underground, was presumably still flowing. Curious, indeed.
It was not until I moved to Charlottesville that I began to notice and wonder about the changing level of water in the Rivanna. There was something about this Piedmont River, so prone to change, flashing high with summer rains, then sinking low as soon as the trees sucked it dry in the growing season, the banks deep and muddy, a river that I found hard to love in the best of seasons.
So it was rather shocking to me to learn that the level of the water in a watercourse corresponds roughly to the height of the water table in the adjacent soil and rock. From this simple but profound idea, I began to understand the connection between river, water, and the earth itself. And from this fundamental realization came an appreciation of the fact that the surface water in our rivers, reservoirs and runs is one and the same with the groundwater hidden below. And like surface water, deserves, for our health as well as that of the natural communities, to be protected both in source and quantity as well as quality.
Strictly speaking, the water table is the depth at which soil pore spaces become fully saturated with water. Groundwater is recharged from, and eventually flows to, the surface naturally – hence the natural discharge often occurring at springs, seeps, and streams. Unlike other parts of the country, Albemarle County does not have aquifers per se. Beneath the topsoil lies a layer of fractured bedrock called saprolite, through which rain water and surface flow seep, slow recharging the water stored in the fractures of bedrock below. Through this fractured bedrock, the water collects and even flows according to its own hydrologic regime along the hydrographic contours of groundwater. Roughly speaking it tends to flow mirroring the slope and direction of the corresponding topography above ground. When I paddle on the Rivanna, at one with the level of the river and its groundwater, I have tried to imagine this slow and mysterious flow of water hidden from view.
Those in our watershed who derive water from wells are perhaps more aware of groundwater than those of us who live in the urban ring and are supplied by water from the reservoirs. But it would be s mistake to think that groundwater and the water in our rivers are not connected – and that decisions about drinking water or disposing of wastes in septic versus sanitary sewers are fundamentally different. It is one system, one watershed that collects the water and sends it downstream, whether overland, in rivers, or through the soil, the best way to think about watershed is truly three-dimensional.