In its simplest concept discharge means outflow; therefore, the use of this term is not restricted as to course or location, and it can be applied to describe the flow of water from a pipe or from a drainage basin. If the discharge occurs in some course or channel, it is correct to speak of the discharge of a canal or of a river. It is also correct to speak of the discharge of a canal or stream into a lake, a stream, or an ocean. (See also Streamflowand Runoff.)
The data in the reports of the Geological Survey on surface water represent the total fluids measured. Thus, the terms discharge, streamflow, and runoff represent water with the solids dissolved in it and the sediment mixed with it. Of these terms, discharge is the most comprehensive. The discharge of drainage basins is distinguished as follows:
- Yield. Total water runout or crop; includes runoff plus underflow.
- Runoff. That part of water yield that appears in streams.
- Streamflow. The actual flow in streams, whether or not subject to regulation, or underflow.
Each of these terms can be reported in total volumes (such as acre-feet) or time rates (such as cubic feet per second or acre-feet per year). The differentiation between runoff as a volume and streamflow as a rate is not accepted.
Science in Your Watershed. (n.d.). Retrieved March 02, 2017, from https://water.usgs.gov/wsc/glossary.html