Why are streams classified?
Streams are classified
to help identify similarities and differences among streams, to assess
ecosystem health, and to help establish policies and regulations.
By grouping similar streams into categories, resource managers can
make better choices about how to protect or restore them. Streams
may be classified based on channel dimensions, hydrology, or the ways
humans use them (e.g., navigation, recreation, development, irrigation,
and water supply). For example, there are more stringent water quality
standards for rivers and streams that are classified for use as a
water supply than for rivers that are classified for navigation.
How are streams
There are several
classification schemes that can be used. Which one is right
depends on what the resource manager is trying to accomplish. Stream
order is one way to classify streams. The stream order classification
looks like branches on a tree. The initial channel where a small stream
first appears is referred to as a first order stream. When two first
order streams come together, they form a second order stream. With
each successive downstream junction, stream order increases. As stream
order increases, other characteristics change, such as channel shape,
drainage area, habitat, and biological communities.
Another method of
stream classification is the Rosgen system. Rosgens eight basic
stream types are based on a general description of the following characteristics:
geomorphological characterization (e.g., landform, soils, climate),
morphological description (e.g., channel pattern, width-to-depth ratio,
sinuosity, slope), stream condition (e.g., vegetation, flow, stability),
verification (e.g., sediment transport, fish biomass), and the size
and shape of the stream channel. For example, streams in steep terrain
tend to follow a fairly straight path and to have more characteristics
in common with one another than they do with low-gradient, curvy streams.
Knowing the stream type makes it easier for a resource manager to
predict the outcome of a certain practice, because similar rivers
and streams tend to respond to changes in similar and predictable
ways. The Rosgen method is commonly used for developing management
What is the connection
between rivers and watersheds?
A watershed is the
drainage basin or area from which surface water drains toward a lake,
stream, or wetland. Water in most streams and rivers originates primarily
from surface runoff on upland areas. Minnesota has eighty-one primary
watersheds within eight major river basins. For more information on
watersheds, see the Quick and Easy Answer Fact Sheet Everybody
Lives in a Watershed.
Why do stream banks
Stream banks erode
because the force of moving water (stream energy) lifts and carries
the silt, sand, gravel, and rocks downstream. Banks also erode as
groundwater seeps through the bank, loosening the soil. Changes in
water flow in the stream (e.g., flooding or drain tiling) or removal
of vegetation from the bank may increase erosion. For more information
on erosion see the Quick and Easy Answer Fact Sheet Minimizing
What is a hydrograph
and how do human activities change the hydrograph?
A hydrograph is a
graphical representation of the volume of water flowing past a particular
point in a stream over time. A hydrograph illustrates changes in streamflow
due to rainfall, snowmelt, drought, or water withdrawal. Human activities
and land use can significantly alter the natural patterns of stream
flow. Increasing impervious surfaces in the watershed, clearcutting
forests, drain-tiling agricultural fields, filling or draining wetlands,
diverting stormwater, and channelizing streams can increase both the
volume of flow and the speed with which runoff reaches a stream. Diversion,
irrigation, or other withdrawals can also change stream flow, reducing
baseflow and changing the characteristics of the river.
Who owns and manages
rivers and streams in Minnesota?
Like all public waters
in Minnesota, streams and rivers are owned by all Minnesotans. State
laws and local rules and ordinances regulate rivers and floodplains.
Various aspects of Minnesotas rivers are managed by agencies
at federal, regional, state, and local levels, including the U.S.
Army Corps of Engineers, U.S. Environmental Protection Agency, Minnesota
Department of Natural Resources (MDNR), Minnesota Pollution Control
Agency (MPCA), Metropolitan Council, watershed districts, and watershed
management organizations. The Minnesota Environmental Quality Board
(EQB) sets policies for rivers and streams in Minnesota. Federal agencies
administer the sections of the Clean Water Act addressing point source
discharges to the stream and alteration of the streambed by removal
or dredging of materials below the Ordinary High Water Level (OHW).
The MDNR regulates withdrawals from rivers and changes to the streambank
above the OHW. The MPCA sets water use standards and provides permits
for discharges to streams. Counties and other local units of government
regulate land uses adjacent to the stream and on the floodplain.
Although you may
technically own land adjacent to a stream, you must comply
with the regulations that are written to protect water quality and
quantity for everyone. Water withdrawn for uses such as public supply,
irrigation, and industrial needs requires a permit. Regulations also
exist for dams, impoundments, commercial fishing, and waste disposal.
Who can I contact if
I have questions or a problem related to river classification?
Check your local telephone
listing, the Who to Contact
section of the Minnesota Shoreland Management Resource Guide Web site,
or the Web sites listed below for:
What are some additional
resources related to river classification?
- Minnesota Rivers:
A Primer. 1999. M.E. Renwick and S. Eden. University of Minnesota
Water Resources Center
- Streambank Erosion
Gaining a Greater Understanding. 1991. D. Luethe and C. Bentley,
Minnesota Department of Natural Resources Division of Waters
- Stream Corridor
Restoration Manual: Principles, Processes and Practices. 1999.
Federal Interagency Stream Corridor Restoration Working Group