Drought Fact Sheet #8
Why Do Streams Go Dry?
Stream Management Involves the Entire Watershed
All of us have seen or heard of streams going dry.
It may be that one of the local streams no longer
flows all year as it once did. We also hear of great
rivers, such as the Rio Grande, that no longer flow
to the sea. Why do we see these changes?
Where Do Streams Come From?
We can’t really understand what happens with a
stream or river unless we first understand the basic
characteristics that are associated with streams. For
example, all streams reside in a watershed. Simply
stated, a watershed is a land area onto which water
flows toward a definable drainage point.
Sometimes the flow process is slowed down, for
example by a lake or a wetland. Sometimes it
speeds up, such as in a steeply sloped canyon. For
more information on the role of a watershed in the
overall hydrological cycle, refer to Drought Fact
Sheet # 2.
In arid regions, a good deal of the water in a stream
comes from runoff. However, in many parts of the
country, most of the water in a stream does not
come from runoff, it comes from groundwater.
Nearly half of all water in streams and rivers comes
from groundwater discharge (Payal Sampat, 2000).
Rain or snow falls on the soil, soaks into the
ground, then moves slowly toward the stream
bank. This process provides a natural filtering and
purification process. Streams receiving
groundwater are called ‘gaining streams’ (Figure
A). During dry times, or in dry areas, some of the
water in the stream goes the other way and
recharges water back into the ground as stored
groundwater. Streams discharging water to the
ground are called ‘losing streams’ (Figure B).
There are several key points in this seemingly
simple cycle. The stream relies on precipitation,
soil, vegetation, and groundwater for its flow; so
anything we do in the watershed to affect these
conditions has adverse impacts on the stream flow.
Figure A. Gaining Stream
Figure B. Losing Stream
A second key issue is that changes in the
groundwater will affect more than just the stream
flow; it will also impact the riparian areas that exist
all along the stream bank. Riparian areas rely on
the presence of water in the stream bank to support
vegetation, which stabilizes the stream bank and
helps to filter the surface water entering the stream.
For greater detail visit www.attra.ncat.org.
What Can Cause Streamflow to Decrease?
Once we view the stream as part of a watershed, it
is easy to see that there are many things that may
affect stream flow, including excessive stream
withdrawals, increased groundwater withdrawals,
alteration in runoff patterns and changes in climate.
Excessive stream withdrawals occur when cities,
industries and farmers draw water directly from
the river or stream for various purposes. Most
watersheds are commonly governed by a set of
laws that give priority to certain water users in an
effort to limit the depletion of the stream flow.
These laws are usually enforced at the state or
tribal level. For more information on water rights
you can contact your state water master or your
local water rights representative.
Another factor that can decrease the flow of a
stream or river is increased groundwater
withdrawal. Groundwater that is withdrawn from
the subsurface cannot recharge the river or stream
(Figure C). In some instances, this withdrawn
groundwater is used then returned to the river as
discharge from a pipe (see Drought Fact Sheet #3
for discussion of wastewater discharges). This
process reduces discharge from the streambank
and may impact riparian areas. Other users may
recycle the used water as irrigation water. This
process returns water to the groundwater supply,
which simulates the natural purification process
and provides natural discharge for riparian areas.
Figure C. Groundwater withdrawn from the subsurface cannot
recharge a river or stream.
In cities, as much as 65% of the surface area is
covered and runoff is diverted into drainage
systems that route the water to the nearest river or
stream. Believe it or not, this increased runoff can
actually cause the stream to become drier in the
long run; the water runs faster out of the
watershed during the rainy times, rather than
soaking into the ground and feeding the stream
during the dry times. Likewise, many agricultural
areas have been modified to increase the speed in
which surface water reaches the stream. If we
look at these activities from the standpoint of an
entire watershed we can see they create a short
circuit to the system. In recent years, wetland
preservation laws have been created under the
authority of the Clean Water Act to change many
of these practices. More information can be
obtained at www.wetlands.com/regs.
Changes in climate and rainfall patterns can also
impact stream flow. If precipitation amounts
decrease, there will be a change in the supply to
the watershed. The relative amount of rain to
snow is also important. These relationships are
discussed in Drought Fact Sheets #1 and #2.
What Actions Can Be Taken to Reduce the
Chance That a Stream Will Go Dry?
The answer to this question depends largely
upon the size of the watershed associated with
the stream or river in question. If the watershed
is small and completely within your community,
it may be possible to act through the local
community. If the watershed is larger and
incorporates several communities, it may be
necessary to act as part of a local watershed
council. Very large watersheds may involve
multiple states and it may be necessary to act
through the state legislative process. More
information can be found at www.epa.gov/owow/
watershed/approaches_fr.pdf.
The loss of stream flow is a very visible
illustration that changes have taken place in a
watershed. Drought planning must consider the
steps that will need to be taken to accommodate
the possible loss of this community resource.
We must also consider groundwater; drainage
systems; riparian zones; and impacts to cities
agriculture and industry. Watershed management
is a key factor in drought preparedness.
The NARC&DC would like to thank the USDA’s
Natural Resources Conservation Service for their
assistance in the development of this fact sheet.
All programs and services of the NARC&DC are offered on a non-discriminatory basis, without regard to race,
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March, 2006