Cumulative Runoff Graph Explanation
 |
Cumulative runoff graphs depict: |
| Average daily: Cumulative sum of average daily values (not runoff for "average" period) | |
| Lowest year: Cumulative sum of daily values for lowest runoff period | |
| Current provisional: Cumulative sum of daily values for this period (not final) |
The seasonal runoff graphs depict cumulative runoff in acre-feet that occurred from April 1st until September 30th (the end of the water year) at a given USGS streamflow-gaging station. The cumulative runoff for the current (2003) water year (solid red line) is compared to an “Average daily” cumulative runoff (area under the blue curve) and to the “Lowest year” cumulative runoff on record for that station (area under the tan curve). It is important to note that the “Average daily” runoff amounts are not derived from a single average year. Rather, they are calculated by using the average daily runoff values that have been recorded at that station while it has been in operation. Thus the data used to generate the curve are derived from multiple water years. The “Lowest year” runoff curve is constructed from data collected during the single year having the lowest annual runoff during the time that the station has been in operation. All of the graphs are specific to individual USGS streamflow-gaging stations. The USGS operates a network of streamflow-gaging stations across the United States.
Acre-feet An acre foot is the volume of water that would cover one acre to a depth of one foot and equals 43,560 cubic feet or 325,851 gallons.
Water year The 12-month period October 1 through September 30. The water year is designated by the calendar year in which it ends and which includes 9 of the 12 months. Thus, the year ending September 30, 2003, is called the “2003 water year.”
The URL for this page is: http://wy.water.usgs.gov/projects/drought/runoff04/files/explan.htm