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Management of Streamside Zones on Municipal Watersheds 1
Edward S. Corbett 2 and James A. Lynch 3
Abstract.--Riparian zones playa major role in water
quality management. Water supply considerations and maintenance of streamside zones from the municipal watershed manager's viewpoint are detailed. Management impacts affecting
water quality and quantity on forested municipal watersheds
are discussed in relation to the structure of the riparian
zone.
INTRODUCTION
The principal rivers and lakes on which many
of the major cities in the United States were
first settled also served as the source of water
supply. As pollution became a problem or as water
supply plants were damaged by floods, many of them
had to be relocated to secondary streams. Many
municipalities had the foresight to obtain large
uninhabited areas in which to construct water supply reservoirs. These watersheds were generally
protected by planted or natural forests and produced a relatively pure water supply (Ring 1977).
timber harvesting, recreation and educational
opportunities, increased water yields, and others
as enumerated by Corbett et al. (1975).
In the Northeast, 2,000,000 acres (809,400
ha) of watershed land are owned or controlled by
more than 750 municipalities, private water companies, and state and federal agencies. Forty-one
percent of this acreage is municipally owned, 13
percent is owned by private water companies, and
36 and 10 percent are under state and federal control, respectively. Ownership of an entire drainage basin for water-supply purposes is uncommon
(Corbett 1970). Douglass (1983) estimated that 4
to 5 percent of the land base in the Northeast and
the South is in municipal watersheds.
Today, municipal watersheds are receiving
increased use because of their environmental setting and proximity to population centers. These
impacts particularly concern the municipal watershed manager who must balance the supply and quality of water against the demands for products and
services. Public pressure and municipal needs are
producing a new, more open policy toward watershed
use.
Forest management, maintenance of buffer
zones on the edges of reservoirs and streams, and
control of urbanization and agricultural development are approaches used to maintain water quality
in upland reservoirs.
Riparian ecosystems are
ecotones between aquatic and upland ecosystems.
And as Odum (1979) points out, riparian zones have
their greatest value as buffers and filters
between man's urban and agricultural development
and his most vital life-support resource, water.
The primary function of municipal watersheds
is to provide domestic water supplies (often including those for local industries). They may be
privately or publicly owned. The municipal watershed includes drainage-basin lands, protection
land around reservoirs, and well fields and their
recharge areas. These special watersheds are valuable community assets. Municipal watersheds can
provide many goods and services in addition to
high-quality water. These include income from
WATER-YIELD CONSIDERATIONS
Research on forested watersheds clearly demonstrates that water yield can be increased through
forest harvesting practices. The greatest potential for water yield augmentation appears to be on
watersheds that have the biophysical potential to
produce water for high value purposes and can be
managed under sound multiple use management, such
as municipal watersheds (Douglass 1983, Ponce and
Meiman 1983).
1Paper presented at the 1st North American
Riparian Conference, Tucson, Arizona, April 16-18,
1985.
2principal Hydrologist, USDA Forest Service,
Northeastern Forest Experiment Station, University
Park, Pa. 16802
3Associate Professor of Forest Hydrology, The
Pennsylvania State University, School of Forest
Resources, University Park, Pa. 16802
Water yield can be increased by periodically
harvesting timber on portions of municipal water-
187
of any sound watershed management plan. Excessive
nonpoint-source pollution may alter forest productivity, contribute to stream eutrophication,
affect aquatic biota, and cause drinking water
supplies to deteriorate.
sheds. In the Northeast, water yield the first
year after heavy cutting will increase by 4 to 12
inches (10.2 to 30.5 em), or approximately 109,000
to 326,000 gallons (412.6 to 1233.9 m3 ) of water
per acre cut (Lull and Reinhart, 1967). Of special value is the increase in low summer flows.
Regrowth after 5 years can reduce the water-yield
increase by two-thirds; partial cuttings under
all-age management have a much smaller and a
shorter-lived effect on water yield than do heavy
cuttings.
A review of methods used to predict
potential water yield augmentation from various
forest management practices was published in the
Water Resources Bulletin (AWRA 1983).
Information from experimental watersheds is
sufficient to determine the probable effects of
timber harvesting on water quality (Aubertin and
Patric 1974, Corbett et al. 1978, Lynch et ale
1985).
The most significant impacts involve
changes in water temperature, turbidity/sediment
levels, and concentrations of dissolved nutrients.
Best Management Practices
Where municipal ownership of watershed land
is substantial, vegetation management can have a
significant influence on the amount of water
yielded to a reservoir system, so vegetation conversions and planting programs should be carefully
evaluated. On the Baltimore, Maryland, municipal
watershed, research has shown that conversion of
open land to eastern white and loblolly pines
decreased water yield by 238,000 gallons (900.8
m3 ) per acre per year (Corbett and Spencer 1975).
This is equivalent to a layer of water almost 9
inches (22.9 cm) deep. Establishment of a mixed
hardwood forest on an open-land watershed would
not reduce water yield as much as a pine forest.
Swank and Douglass (1974) found that 15 years
after a mature hardwood forest was converted to
white pine, annual streamflow was reduced about 20
percent below that expected for the hardwood
cover.
Several control strategies or best management
practices (BMPs) used to minimize or prevent these
impacts are described in detail by Lynch et ale
(1985). Water quality data collected during the
first 2 years after a commercial clearcutting in
central Pennsylvania show that the BMP approach
was sufficient to control most nonpoint- source
pollution during and following logging. Although
slight increases in turbidity and sedimentation
were observed, the increases could be traced to
windblown trees that had been uprooted near an
intermittent stream channel. A properly designed
buffer zone along this intermittent stream would
have reduced the erosion hazard from the windblown
trees. Increases in streamwater temperature were
generally slight and possibly beneficial to the
aquatic ecosystem.
Nutrient concentrations
remained well below maxima mandated for drinking
water.
Harvesting and/or converting riparian zone
vegetation has resulted in small to insignificant
increases in streamflow (Hibbert 1967), but the
environmental consequences may outweigh small
increases in water yield. On the Newark, New Jersey, Municipal Watershed a streamside vegetation
control treatment had been practiced to remove
vegetation that dropped its leaves into streams,
causing color and chemical build-up in the raw
water, and also to prevent the accumulation of
debris that might cause stream blockage. An experiment simulating this treatment, conducted on a
small portion of this watershed, showed that removing the streamside vegetation was not effective in
increasing water yield. There was a definite
reduction in diurnal streamflow fluctuation during
the growing season, indicating that transpiration
losses had been reduced (Corbett and Heilman
1975).
Stream Temperature, Turbidity,
and Sedimentation
Of particular importance to municipal watershed managers during and after forest management
operations is the control of turbidity, sedimentation, and stream temperature. Problems associated
with increased turbidity and sedimentation include
reduction in reservoir storage and stream channel
water-carrying capacities, water-quality impairment and public health hazards, increased cost of
water treatment, reduction in aquatic habitat productivity, and a reduction in hydrologic amenities.
In 1977 the national drinking water standards
for turbidi ty4 were strengthened. The new standards placed an additional burden on watershed
managers. The regulations that became effective
in June 1977 changed the turbidity parameter from
a secondary (esthetic) to a primary (health) standard. The reason was a concern that microorganisms might be protected from inactivation by disinfectants by their association with particulate
matter. The type of turbidity can also affect
disinfection efficiency.
On the Baltimore Municipal Watershed, hardwood vegetation along the main and secondary channels on a small sub-basin was cut back from the
streams for 30 to 125 feet (9.1 to 38.1 m) and the
area converted to grass.
Although water yield
increased slightly, serious erosion was caused by
the mechanical methods used to control sprout
regrowth and summer stream temperatures increased
significantly (Corbett and Spencer 1975).
Water temperature and changes in light intensity in the stream zone can affect the taste, odor,
and color of stream water. Under some conditions,
WATER QUALITY CONSIDERATIONS
Controlling nonpoint-source pollution during
and after forest harvesting is an essential part
4Federal Register 40 (248):59566-59588.Dec.
24, 1975.
188
light and temperature increases stimulate
excessive production of algae degrading raw water
supplies, depleting the oxygen supply for aquatic
organisms, and lowering the esthetic values of
streams.
Water Color And Disease
The importance of organic detritus in aquatic
ecosystems and its relationship to the abundance
and diversity of stream benthos is being increasingly recognized (Slack et al. 1982). However,
natural inputs of organic matter can also impair
the quality of drinking water supplies. Undesirable color, taste, and odor have been linked to
leaf litter in streams and reservoirs. Taylor et
al. (1983) found that significant water quality
problems are likely during extended periods of low
flows and maximum leaf fall. They found increased
chlorine demand and rapid regrowth of coliform
bacteria in alder leaf extracts, which suggest
potential disinfection problems when alder leaf
impacts are significant. The formation of trihalomethanes (suspected carcinogens) in water supplies
from the reaction of chlorine with naturally occurring organic materials during disinfection processes (Rook 1974), is also of concern to municipal
watershed managers.
Beaver activity is a well-known cause of both
true and apparent color in natural waters. Wilen
(1977) reported that controlling the beaver population and increasing streamflow gradients on a forested watershed in Massachusetts were successful
in reducing levels of organic color production in
raw water.
Preventing leaves and other organic debris
from reaching streams is not considered practical
in most forested watersheds.
A measure of leaf
control may be exercised by converting riparian
woody vegetation from deciduous to coniferous
trees (Wilen 1977). However, such a conversion
could result in decreased water yields (Swank and
Douglass 1974).
aquatic invertebrates. If streamside management
zones are to remain a viable buffer for moderating
nutrient leaching they will have to be managed
through selective harvesting.
Old overmature
stands that are not increasing rapidly in vegetative mass or humus depth become less effective in
utilizing available nutrients, particularly nitrogen, and nutrient discharge into the streamwater
is increased (Leak and Martin 1975).
Buffer zones for stream channel and water
quality protection must be capable of long-term
survival if they are to function effectively.
They must be properly designed and managed to prevent failure, and should be evaluated for effectiveness annually. Environmental factors that
affect buffer zone stability and stream shading
have been studied by Steinblums et al. (1984).
They found that the timber volume susceptible to
windthrow tends .to be lost during the first few
years of exposure and that species composition is
important in determining the occurrence and amount
of wind throw.
Buffer zone widths vary with conditions on
different watersheds. The most common widths are
from 40 to 100 feet (12.2 to 30.5 m) on each side
of the stream. A 40-foot (12.2 m) buffer zone may
be adequate to prevent excessive temperature
increases in small streams, but a zone of 66 to
100 feet (20.1 to 30.5 m) is usually needed to
protect the stream ecosystem (Corbett et al. 1978).
A wider streamside management zone may be needed
where slope or soil conditions dictate, or when
windthrow or sunscald may be a problem. Increased
stream discharge as a result of timber harvesting
can cause intermittent streams to become perennial
(Lynch et al. 1985). This would permit the transport of eroded material to the main stream channels and could result in stream temperature
increases, so buffer zones should be maintained
along intermittent streams on municipal watersheds
as well as perennial ones.
DISCUSSION
Another potential problem with beavers on
municipal watersheds is giardiasis. This disease,
caused by a protozoan Giardia lamblia, has
recently emerged as a public health problem where
water supplies are unfiltered. Giardia outbreaks
have occurred in systems that use high- quality
surface water from sparsely populated watersheds.
Beavers have been implicated as one of the potential intermediate hosts of the Giardia cyst that
is transmitted to man (Lippy 1981). Systems using
surface water with disinfection as the only means
of treatment should consider controlling the beaver population on water source lands. Control
measures could include periodic surveys, trapping
programs, and forest management practices to
replace food-source trees along waterways and
around reservoirs with less palatable species.
The impact of any land management practice on
water quality should be analyzed before it is used
on a municipal watershed to see what safeguards
will be needed. Riparian zone management, when
integrated with watershed planning, can produce
economic as well as environmental benefits. Reducing contamination at the source allows more economical water treatment processes to be used. For
instance, direct filtration can treat low turbidity waters of moderate color as effectively as
complete conventional treatment, but at considerably lower capital and operating costs (Castorina
1977). The concept that source protection is the
first line of defense for a water supply is especially important in the Northeast because for many
of its surface water supplies, disinfection is the
sole treatment.
Buffer Zones
Buffer zones can protect streams from excessive temperature increases and from accumulations
of slash and debris. They moderate siltation and
nutrient leaching and provide food for many
189
The riparian zone is generally the most sensitive part of the watershed. The impacts of management are often integrated in the channel area and
in the quality and timing of streamflow. Learning
to read early signs of stress here will aid in
evaluating how much "management" a watershed can
take.
Aubertin, G.M. and J.H. Patric. 1974. Water quality after c1earcutting a small watershed in
West Virginia. J. Environ. Qual. 3:243-249.
Wat er Res ources Bulletin.
USDA
For. Servo Res. Note
Lippy, E.C. 1981. Waterborne disease: Occurrence is on the upswing. J. Am. Water Works
Assoc. 73:57-62.
LITERATURE CITED
AWRA. 1983.
419.
Hampshire.
NE-211, 5 p.
19: 351-
Castorina, A.R. 1977. Surveillance and monitoring program for Connecticut public water supply watersheds. In: Drinking Water Quality
Enhancement Through Source Protection. R.B.
Pojasek (ed.). Ann Arbor Science Pub. Inc.,
Ann Arbor, MI, p. 137-149.
Corbett, E.S. 1970. The management of forested
watersheds for domestic water supplies. In:
Proc. Conference on Multiple Use of Southern
Forests, Nov. 5-6, 1969, Pine Mountain, GA,
Georgia Forest Research Council, p. 35-38.
Corbett, E.S., and J.H. Heilman. 1975. Effects
of management practices on water quality and
quantity - Newark, New Jersey, Municipal
Watersheds. In: Municipal Watershed Management Symposium Proc. USDA For. Servo
Gen. Tech. Rep. NE-13, p. 47-57.
Lull, H.W. and K.G. Reinhart. 1967. Increasing
water yield in the Northeast by management of
forested watersheds. USDA For. Servo Res.
Pap. NE-66, 45 p.
Lynch, J.A., E.S. Corbett, and K. Mussallem. 1985.
Best management practices for controlling
nonpoint-source pollution on forested watersheds. J. Soil & Water Conserve 40:164-167.
Odum, E.P. 1979. Ecological importance of the
riparian zone. In: Strategies for Protection and Management of Floodplain Wetlands
and Other Riparian Ecosystems.
USDA For.
Servo Gen. Tech. Rep. WO-12, p. 2-4.
Ponce, S. L., and J. R. Meiman. 1983. Water yield
augmentation through forest and range management - Issues for the future. Water Resour.
Bull. 19:415-419.
Ring, C.A. 1977. The water supply industry and
source protection. In: Drinking Water Quality Enhancement Through Source Protection.
R.B. Pojasek (ed.). Ann Arbor Science Pub.
Inc., Ann Arbor, MI, p. 63-70.
Corbett, E.S., and W. Spencer. 1975. Effects of
management practices on water quality and
quantity - Baltimore, Maryland, Municipal
Watersheds. In: Municipal Watershed Management Symposium Proc. USDA For. Servo Gen.
Tech. Rep. NE-13, p. 25-31.
Rook, J.J.
1974. Formation of haloforms during
chlorination of natural waters. Water Treat.
and Exam. 23:234-243.
Corbett, E.S., W.E. Sopper, and J.A. Lynch. 1975.
Municipal watershed management: What are the
opportunities? In: Forestry Issues in Urban
America. Soc. Am. For. National Convention
Proc., Sept. 22-26,1974, New York, NY., p.
50-57.
Corbett, E.S., J.A. Lynch, and W.E. Sopper. 1978.
Timber harvesting practices and water quality
in the Eastern United States.
J. For.
76(8):484-488.
Slack, K.V., L.J. Tilley, and S.S. Hahn. 1982.
Detritus abundance and benthic invertebrate
catch in artificial substrate samples from
mountain streams.
Water Resour. Bull.
18:687-698.
Steinblums, I.J., H.A. Froehlich, and J.K. Lyons.
1984. Designing stable buffer strips for
stream protection. J. For. 82:49-52.
Swank, W.T., and J.E. Douglass. 1974. Streamflow
greatly reduced by converting deciduous hardwood stands to pine. Science 185:857-859.
Douglass, J.E. 1983. The potential for water
augmentation from forest management in the
Eastern United States. Water Resour. Bull.
19: 351-358.
Hibbert, A.R. 1967. Forest treatment effects on
water yield. In: Proc. International Symposium on Forest Hydrology, W.E. Sopper and
H.W. Lull (ed.) Pergamon Press, New York, p.
527-543.
Leak, W.B., and C.W. Martin. 1975. Relationship
of stand age to streamwater nitrate in New
190
Taylor, R.L., P.W. Adams, P.O. Nelson, and R.J.
Seidler. 1983. Effects of hardwood leaf
litter on water quality and treatment in a
Western Oregon Municipal Watershed. Water
Res our. Res. I nst. Pub. WRRI-82, Oregon State
University, Corvallis, OR, 56 p.
Wilen, B. O. 1977. Options for controlling nat ural organics. In: Drinking Water Quality
Enhancement Through Source Protection. R.B.
Pojasek (ed.). Ann Arbor Science Pub. Inc.,
Ann Arbor, MI, p. 375-392.