Laboratory 9: Runoff Measurement and Analysis
1. LEARNING OBJECTIVES
Learn the processes and factors that influence runoff.
Explore the relationships between precipitation and stream response.
2. BACKGROUND INFORMATION
Rivers, lakes, reservoirs, and dams provide more than 75% of the water used in the U.S.
Surface water systems are also used for recreational purposes and in many cases are important
transportation conduits. The importance of surface water in the development of the U.S. is
illustrated by looking at a map of the nation. Virtually all cities with populations exceeding
150,000 are located on rivers, and many smaller communities are located on rivers and lakes.
There are about 2 million streams and rivers in the U.S., including the mighty Mississippi
River, which is the fourth longest river in the world at 3,710 miles long. Of the world’s 11
freshwater lakes with the largest surface area, 4 are located in the Great Lakes system
(Superior is 1
, Huron is 5
, Michigan is 6
, and Erie is 11
). In addition to the Great Lakes,
we have many thousands of smaller lakes, dams, reservoirs, and ponds. These include 25 lakes
with surface areas greater than 100mi
and more than 200 with surface areas larger than 10 mi
All of these water bodies depend on the phenomena of runoff.
Runoff is all water transported out of the watershed by streams. Some of this water may have
had its origins as overland flow, while much may have originally infiltrated and traveled
through the soil mantle to streams as throughflow. In addition, water that infiltrates and goes
down into groundwater may later emerge far downstream through seeps and springs to add to
streamflow. At that point, it also becomes runoff.
While runoff is usually benevolent, under extreme conditions of rainfall or land use it can
cause extensive damage by eroding soils and stream banks; carrying off valuable agricultural
nutrients and pollutants; destroying bridges, utilities, and urban developments; and causing
flooding and sediment deposits in recreational, industrial, and residential areas along stream
systems. The hydrologic effects of deforestation, agriculture, and surface mining have been
manifested since European settlement. Since World War II, we have seen a dynamic reshaping
of our landscape by rapid urbanization and more intensive agriculture. These activities have
changed hydrologic responses, soil erosion, and sedimentation in watersheds. For example,
urbanization of farmland and forests causes more rapid runoff, higher peak discharges, and
larger runoff volumes.
2.1 Runoff characteristics