Data regarding the waters of Four Mile Run can be divided into two broad categories: Water Quantity & Water Quality. As far as typical stream monitoring goes Four Mile Run can be regarded as rich in both.
Since 1952, the US Geological Survey (USGS) has maintained a stream gaging station on Four Mile Run at the Shirlington Road bridge. Prior to 1998 the gage was a simple crest-stage gaging station. In 1998 the station was converted to a Mean Daily Discharge Station recording stage, discharge and rainfall on five minute time intervals. (Also immediately after installation the station was recording temperature, although this has since been discontinued.) The USGS gage data for Four Mile Run is available online.
Just outside of the watershed is the National Weather Service (NWS) Weather Station at Ronald Reagan Washington National Airport (DCA). Current data from the DCA weather station
is served online by the National Oceanic and Atmospheric Administration (NOAA). Historical records from this station can be purchased
from the National Climatic Data Center.
NOAA has recently published new precipitation frequency data for the Ohio River Basin and surrounding states, including Virginia (and the Four Mile Run watershed). NOAA's precipitation frequency data
is available online.