A measure of how much water is flowing past a point in time
Prior to 2003 WAV volunteers monitored streamflow using a variety of methods. To provide a consistent method for monitors in Wisconsin, WAV created a fact sheet and a corresponding data sheet for monitoring stream flow using methods adapted from Missouri Stream Teams.
How streamflow is measured:
These methods utilize a velocity-area approach to measuring streamflow (or volume of water passing a set point in a given period of time). That is, to determine flow, the monitors combine information about stream area with information about the velocity of the water at their site.
Monitors measure the area of the stream at their site by measuring the width across the stream and the depth at several locations across the measured width. They ultimately determine area by assessing a set 20-foot length of stream and multiplying this length by the average depth and the measured width. (Remember, area = length X width X depth.) To avoid a large error in the estimation of stream area at the site, monitors must be careful to locate a stream site that is uniform in width for the entire 20-foot length.
Monitors assess the velocity of the water in the stream by floating a tennis ball (slightly filled with water) along the 20-foot length of stream and timing its float from the upper end of the reach to the lower end. They can determine the tennis ball's speed in feet per second since they know how long it took to float a set length of stream.
Land use affects streamflow:
In urban areas, streamflow can be drastically altered with development. Normally, after a storm a stream's flow will increase to a certain level and then drop back to a base level, supplied by groundwater. With increased development, and thus an increase in the amount of impervious surface, streams may have lower base flow (since there is less water being input from groundwater due to limited infiltration through the expanse of impervious surfaces in the urban area) and higher peak flows and volumes following storms. The following chart shows how stream flow following storms can be altered due to increased amount of impervious surfaces in a watershed.
Domestic, agricultural, and industrial activities can also affect streamflow. For instance, dams might be shut to hold back water to create power during peak energy-demand periods and water later released in a surge, affecting habitat, temperature, and food resources for aquatic organisms.
How streamflow data may be used
DNR must determine stream size when permit requests are placed for wells. WAV streamflow data may aid staff in determining the average stream size in a given time period.