Monday, October 13, 2014

Chesapeake Bay Watershed has Plenty of Water this Year

The lead editorial in Science magazine last month began “The Western Hemisphere is experiencing a drought of crisis proportions. In Central America crops are failing, millions are in danger of starvation...” Editor Marcia McNutt goes on to illustrate the extent and severity of the drought and then to talk about the advances being made in measuring water availability using the Gravity Recovery And Climate Experiment (GRACE) satellites to measure large scale changes in groundwater and moisture from space and a new method for measuring groundwater extraction by measuring regional land uplift (Borsa et al., Ongoing drought-induced uplift in the western United States, Science vol. 345 issue 6204 page 1587). These new methods are allowing scientists to begin to measure the amount of groundwater extracted from an aquifer and the remaining water. This is a first step in managing surface and groundwater together. Both surface and groundwater are part of one connected system responding on different timescales to precipitation based on specific geology. The availability of water resources are not constant and certainly not unlimited.

We chose to live in this little corner of Virginia for the water (on my part) and proximity to my husband’s home or origin. While several counties of Virginia were abnormally dry this past September (according to the Drought Monitor), the dry area was south of us. Groundwater levels in the monitoring well down the road have been normal for most of the year. We seem to be doing just fine this year sitting as we do between the Potomac River and Bull Run and have plenty of water. The National Weather Service’s Middle Atlantic River Forecast Center (MARFC) reports a Potomac basin total precipitation of 28.3 inches of precipitation so far this year thought that is 2.3 inches below normal- 2.2 inches of that shortfall, was in September. Both MARFC and the NOAA are prediction a wet fall along the Potomac watershed and the south in general. Texas is finally seeing relief and recovery from their drought. The drought is California is expected to continue north of the Colorado River. 
from the climate prediction center

The Potomac River is the fourth largest river along the Atlantic seaboard and the lifeblood of our region. The Potomac River starts life as a spring at the Fairfax Stone in West Virginia. The river flows approximately 385 miles to the Chesapeake Bay increasing in size and flow from its tributary streams and rivers in West Virginia, Maryland, Pennsylvania, Virginia, and the District of Columbia growing to become the Bay's second largest Tributary. The River provides more than 500 million gallons of freshwater daily to those living in its watershed, in addition to irrigation water, and the more than 2 billion gallons of water a day for power plants.

The Potomac River is one of the least dammed large river systems in the Eastern United States. The combined storage capacity of all major reservoirs upstream of Washington, DC makes up less than 7% of median flow. Nonetheless, the Potomac River’s flow needs to be managed to assure the 500 million gallons per day the river supplies for drinking water to the region and the approximately 100 million gallons necessary for essential environmental services. The Interstate Commission on the Potomac River Basin (ICPRB) was created to manage and allocate the flow of the Potomac River. They reported last week, that despite a dry September recent rains have ensured that there is sufficient flow in the Potomac River to meet the Washington metropolitan area’s water supply demand without the need for water releases from the upstream reservoirs- Little Seneca and Jennings Randolph to keep the river at adequate flow.

The ICPRB manages the water withdrawals from the Potomac River by having Fairfax Water utilize their Occoquan Reservoir water treatment plant to maintain adequate flow to the Chesapeake Bay and having the other water utilities utilize their storage. The ICPRB reports it’s very unlikely (1-3% likelihood) that river flow will have to be augmented with water released from either the Little Seneca or Jennings Randolph reservoirs this year. Our region is well‐protected from a water supply shortage because of carefully designed drought‐contingency plans and continued strong precipitation. In addition to help maintain a consistent water supply, WSSC (the Maryland water utility) has their Patuxent reservoirs with a capacity of more than 10 billion gallons that is currently over 80% full and more reservoirs are planned for the entire system to ensure the water supply for the region can endure a prolonged drought. Back in the 1960’s during a severe and extended drought, when the population was only a fraction of what it is now, water withdrawals to supply drinking water to the three water utilities in the region from only the Potomac River reduced flows in the Potomac to such an extent that the River practically ran dry, leaving only mud between Great Falls and the tidal river.
Each fall when the Potomac is at its lowest flow the ICPRB maintains daily monitoring of the flow at Point of Rocks and Little Falls to always be prepared for the possibility that more serious drought conditions may develop in the upcoming weeks. At present, there is sufficient flow in the Potomac River to meet the Washington metropolitan area’s water demands, but the ICPRB remains diligent and watchful because weather as we know is changeable. 

from ICPRB
The U.S. Geological Survey (USGS) reports that groundwater levels are generally near normal for the region with both above and below normal levels scattered throughout the area. If your water is supplied by a well, you need to be aware of the factors that impact your water supply and regularly practice household water conservation to live within your water resources when necessary. Unfortunately, we do not have the ICPRB to help us manage our water resources and use. There are dry years and wet years and water will vary, though it is not always obvious. The groundwater aquifer you tap for water is not seen so you have to be aware of your water budget and live within it, something that transplants from the suburbs and city are not always aware of. 

My groundwater is very young, basically the groundwater levels in my well and the nearby USGS monitoring wells respond within a day to a rain storm despite being more than 100 feet deep. In many groundwater systems are not as directly tied to precipitation and so that is not true. Many well owners think of their water supply as unlimited until the well fails. Your well is not unlimited and you need to be aware of your water use. You need to be aware of the relationship between groundwater and surface water and how your well responds to drought and rainfall. During dry periods when my garden is in most need, my well is most vulnerable. I will only water my herbs and new plantings. Everything else in my garden has got to make it on what our climate provides (though I would probably try to save the cherry and plum trees in a drought- but not at the risk of my water supply).

USGS monitoring well 49V 1 shows a response to rainfall

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