The Occoquan Watershed

George Mason University Campus Fountain, July 2010

©EOP

This morning I was looking for some local materials to include in the water course, and I chanced upon a good (if too small a scale) land-use map for the Occoquan Watershed (I hope to find a similar map at a bigger scale for use in a Power Point). Our Fairfax City house sits just slightly to the Potomac watershed (small streams draining directly into the river) side of the interfluve dividing the watersheds of the Potomac and the Occoquan. The GMU campus sits on the interfluve,and a part of the campus is on the opposite slope with water draining into small streams feeding the Occoquan (which itself eventually, just southeast of its eponymous town, flows into the Potomac).

Bull Run, one of the Occoquan's tributaries is very famous, for its small valley at the edge of Manassas City was the site of two of the more vicious battles of the Civil War. At the time of the Civil War and until quite recently the almost 1550 square kilometer basin of the Occoquan was predominantly rural with farmlands, wooded areas and only a few small towns and the small city of Manassas. Since the 1970s and especially since 1990 the watershed has  been rapidly urbanized with farm fields and pastures converted to townhouse projects and small "estates" along with the usual fast food and strip mall development. That has radically changed the timing and the quality of water run off into the Occoquan, for now much of the watershed is paved and impermeable even as urban uses add contaminants to the water flowing toward the river..

Prior to much urbanization the river became an important drinking water source supplying much of the urban water in Prince William County (including Manassas and Manassas Park cities) and some of the water consumed in Fairfax County, the two largest counties by population in Virginia. Altogether nearly 1,200,000 people are connected to water supply systems which use some Occoquan river water. A substantial dam impounds a tributary of the river and creates Lake Manassas, a water supply reservoir for its namesake city. Downstream another dam impounds the Occoquan Reservoir supplying much of Prince William County and large parts of adjacent Fairfax County. While other sources of water are used by both counties, the Occoquan could in an emergency supply most users. A bit further downstream yet near the town of Occoquan is one of the largest sewage treatment facilities in the Washington, DC metropolitan area, sending treated water into the Occoquan just before that river joins the Potomac.

A crucial element in the urban water supply of Washington, DC's Virginia slurbs, the Occoquan is also a major recreation resource for the area, and the undeveloped lands along its banks provide a substantial amount of open space. Unfortunately the stream is badly polluted in places, and runoff from developed areas makes it an endangered stream. The Prince William Conservation Alliance has an excellent webpage examining the issues of pollution in the Occoquan basin. The quality of water in the river is important for those of us condemned to live in Northern Virginia!

Watershed Map from Prince William Conservation Alliance.

Notes

Windmill, Pacific Ocean near Todos Santos, BCS, Mexico 2009

©EOP

Occasionally I shall post some random notes about issues, comments that do not fit together coherently. This is the first such posting.

This morning I was looking for some materials on local water concerns to use with the course, and I learned of a problem which was new to me. Fairfax City includes within its boundaries a sizable tank farm, a gasoline and diesel fuel depot. In 1992 there was a large underground spill that sent gasoline and other petroleum derivatives in a plume far downstream into the Mantua area of Fairfax County. That leakage cost a huge amount of money spent to clean up impacts in a scenic and generally uparket residential area. I had not paid attention to a much smaller leakage found in late 2009 which has not yet been fully cleaned up. The leak is fairly small, but it marks yet another insult to the land and waters of the Potomac Basin.

Several weeks ago I read reviews of James Lawrence Powell's Dead Pool (Berkeley: University of California Press, 2008, ISBN 978-0-520-25477-0), a  history and analysis of the dams on the lower Colorado especially Glen Canyon and Boulder Dams. The reviews were correct, for it is one of the most important books on water issues in the United States published in the past decade and should be required reading for almost everyone concerned with water supply in an era of population growth and climate change. The first few pages describing what might have happened if Glen Canyon Dam had failed in 1983 make for harrowing reading. The remainder of the book examines how the dams have shaped life in the southwestern corner of the continental US (and in adjacent parts of México) and what may happen as rainfall decreases due to climate change, reading almost as harrowing as the first few pages.