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September 2014 - Sixty-five percent of groundwater levels and 88 percent of monthly mean streamflows were in the normal range

Precipitation | Groundwater | Streamflow | Chesapeake Bay | Reservoirs | Archive of WC Reports

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Why is it important for the USGS to collect and analyze water resources data?

USGS water data are valuable to the public, researchers, water managers, planners, and agricultural users, especially during floods and droughts. These data can be used to assess how water resources respond to changes in climate. Scientists at the USGS have measured streamflow and groundwater levels in wells to assess water resources for over 125 years.

In addition to providing the most extensive set of historical streamflow and groundwater data available to the public, the USGS collects water data and quality-assures the data by employing standardized techniques across the country. The uniformity of the dataset allows for multi-state comparisons and other comparative statistical analyses that better inform policy makers of the possible water resource conditions they might encounter in the future.

The sites used in this water summary were carefully selected to show the response of streamflow and groundwater levels to precipitation. Ideally, these sites will show minimal effects from human influences. The streamflow and groundwater data are ranked in comparison to the historical record and summarized. Precipitation and reservoir data are also presented to give a more complete picture of the region’s water resources.

 

USGS September 2014 Water Conditions Summary

Sixty-five percent of the groundwater levels and 88 percent of the monthly mean streamflow values at sites used to monitor the response of water resources to changes in climatic conditions in Maryland, Delaware, and the District of Columbia were normal (between the 25th and 75th percentiles) in September.

September groundwater levels were above normal in 6 of 26 wells, including 2 wells above the 90th percentile. The groundwater level was below normal in three wells.

September monthly mean streamflows were normal at 29 of the 33 streamgages. Streamflow was below normal at four streamgages, and one of them was below the 10th percentile.

percentiles

A percentile is a value on a scale from 0 to 100 that indicates the percent of a distribution that is equal to or below it.

For example, a groundwater level in the 90th percentile is equal to or greater than 90 percent of the values recorded for that month.

 

September 2014 Precipitation and Weather

September rainfall was below the long-term average at the five National Weather Service (NWS) Mid-Atlantic weather stations. The highest September rainfall was in Georgetown, Delaware with 3.90 inches, and the lowest rainfall was in Arlington, Virginia with 1.11 inches.

The map below shows the departure from average at each of the five NWS weather stations.

*The NWS normal (long-term average) period used for determining records is from 19812010.

The NWS Middle Atlantic River Forecast Center’s 365-day precipitation data showed that all counties in Maryland, Delaware, and the District of Columbia were classified as average to above average except for Allegany County, Maryland. Three counties in Maryland (Baltimore, Harford, and Montgomery) were more than 10 inches over the 365-day average from September 2013 to September 2014. See the links below to view the NWS data. See the links below to view the NWS data.

September air temperatures were above normal at all five NWS Mid-Atlantic weather stations and ranged from 67.1 degrees Fahrenheit in Hagerstown, Maryland to 73.9 degrees Fahrenheit in Arlington, Virginia. 

*Note from the National Weather Service: September 2011 was the first month to incorporate the new 1981-2010 climate normals that were calculated by the National Climatic Data Center. The new normals replaced the 1971-2000 normals.


Sources:
National Weather Service MD and DC
National Weather Service DE
Middle Atlantic River Forecast Center (MARFC)








Groundwater

The USGS monitors groundwater levels in unconfined aquifers, providing observations that can be compared to both short-term and long-term changes in climatic conditions. Twenty-six groundwater wells were selected based on the following criteria:

 

September 2014 Groundwater Levels

Groundwater levels were normal (between the 25th and 75th percentiles) in 17 of the 26 wells used to monitor climatic conditions in Maryland and Delaware in September. Groundwater levels were above normal at 6 of 26 wells and two of the wells had groundwater levels above the 90th percentile. Groundwater was below normal at 3 wells in Allegany, Carroll, and Charges County.

In Delaware, groundwater levels were normal at the three observation wells

 

Click here to access the clickable groundwater map.

 

The groundwater level in observation well CL Ad 47 in Carroll County, Maryland dropped to below normal in September. Based on historical data for this site, the groundwater level is usually at its lowest in August, and typically begins to rise in September and October.

Click here to view five-year groundwater hydrographs for other wells.

 

These 5-year hydrographs show groundwater levels as a dark blue line, the minimum and maximum monthly values, and the normal range (between the 25th and 75th percentiles) as a white band based on the period of record. The maximum water level is at the top of the upper blue section and the minimum water level is at the bottom of the lower blue section in the graph. Each monthly measurement is colored according to the percentile rank in which it falls for the month.


Streamflow

Streamflow data are used for many purposes. A few of the most obvious uses are to assess water supply and the risk of droughts and floods. Streamflow data are also used to calculate loads of chemical constituents and assess how biological communities are affected by hydrologic conditions. The USGS operates the most extensive network of streamflow gages in the region.

The streamflow locations chosen for the monthly water summary were selected based on the following criteria:


Streamflow 2014 Streamflow

Monthly mean streamflows were normal at 29 of the 33 USGS streamgages used to monitor climatic response in Maryland, Delaware, and the District of Columbia in September. Normal is considered to be between the 25th and 75th percentiles.

Monthly mean streamflow was below normal at the Chicamacomico River in Dorchester County, Maryland and at 3 stations in Allegany and Garrett Counties in western Maryland.

In Delaware, all monthly mean streamflows were normal in September.

 

Click here to access the clickable streamflow map.

Monthly mean streamflow was below normal at the Chicamacomico River in Dorchester County, Maryland and at 3 stations in Allegany and Garrett Counties in western Maryland.

In Delaware, all monthly mean streamflows were normal in September.

The dark line in the 5-year hydrograph represents the monthly mean streamflow for this period and the white band shows the normal range (25th to 75th percentiles) based on the period of record. The maximum monthly mean streamflow is at the top of the blue shaded section, and the lowest monthly mean streamflow is at the top of the dark orange area. Each monthly mean measurement is colored according to the percentile rank in which it falls for the month.

Click here to view five-year streamflow hydrographs for other stations.

 

Estimated Streamflow to the Chesapeake Bay

The estimated monthly mean freshwater streamflow to Chesapeake Bay was normal in September 2014 at 20,200 ft3/s (provisional, and subject to revision). The average (mean) monthly streamflow for September is 36,900 ft3/s. The normal range for average (mean) monthly streamflow for September is between 17,200 ft3/s and 39,100 ft3/s, the 25th and 75th percentiles of all September values. These provisional statistics are based on a 78-year period of record.

Data and more information on the freshwater flow to the Chesapeake Bay can be found here: Chesapeake Bay Inflow. http://md.water.usgs.gov/waterdata/chesinflow/

Graphs and data are available on the “Estimated Streamflow Entering Chesapeake Bay” website.

Reservoir Levels

Available reservoir storage at the end of September in the Baltimore reservoirs (Loch Raven, Liberty, and Prettyboy) was 97 percent of available storage capacity, or a total of 75.67 billion gallons of water.

Total normal storage in the Triadelphia and Duckett Reservoirs, which serve parts of Howard, Montgomery, and Prince George’s Counties in suburban areas around the District of Columbia, dropped 10 percent to 82 percent of normal storage capacity in September, with 8.76 billion gallons of water. Not all of the water in the Patuxent Reservoirs is usable; for operational purposes, percent of normal storage capacity is used, but this value can exceed 100 percent of the usable storage.

September 2014

Percent available/
normal storage

Volume (billion gallons)

Source

Baltimore Reservoirs

Baltimore City - Environmental Services Division

Liberty
96%
36.72
 
Loch Raven
98%
21.20
 
Prettyboy
99%
17.75
 
Total
97%
75.67
 

Patuxent Reservoirs

Washington Suburban Sanitary Commission (WSSC)

Triadelphia
89%
4.96
 
Duckett
76%
3.80
 
Total
82%
8.76
 

 


More Information

Additional Archives
Water Conditions Reports: 2000-present

Maryland-Delaware-District of Columbia
USGS Drought Watch
USGS Water Summary
Streamflow
Groundwater
Chesapeake Bay National
USGS Streamflow and Groundwater levels
U.S. Drought Monitor from the National Drought Mitigation Center

Compiled by:

Wendy S. McPherson, USGS Hydrologist

 

Contact

U.S. Department of the Interior
U.S. Geological Survey

Wendy S. McPherson (wsmcpher@usgs.gov)

* If you want to receive notification of updates to the water conditions or receive the file, send an email to Wendy S. McPherson at wsmcpher@usgs with the following message: "Send monthly water conditions report."

Maryland-Delaware-D.C. Water Science Center
5522 Research Park Drive
Baltimore MD, 21228

Phone:443-498-5548

• Go to Water Condition Report Archives



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