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Increasing Summer Flow in Small Streams
Through Management of Riparian Areas
and Adjacent Vegetation: A Synthesis1
D. Frederic Stabler 2
Abstract.--Construction of small dams, suppression of
woody vegetation in and adjacent to riparian zones, and removal of livestock from streamsides have all led to summer
streamflow increase. Potential may exist to manage small
valley bottoms for summer flow increase, while maintaining
or improving riparian habitat, range and watershed values.
INTRODUCION
Dams
Techniques to increase streamflows through
treatments in phreatophyte (i.e. riparian) zones
depend almost exclusively on reducing evapotranspiration during the growing season (Satterlund
1972). At present, phreatophyte control to improve
water yield has largely been abandoned, as a result
of smaller than expected water savings and poor
benefit/cost ratios stemming in part from potential
loss of high-value riparian habitat (Graf 1980).
Watershed and habitat improvement projects within
riparian zones are, however, occasionally reported
to increase summer streamflows without employing
evapotranspiration control methods (Heede 1977,
Jester and MCKirdy 1966). Are there alternatives
to currently accepted techniques? In an attempt to
answer this question, this paper reports and
interprets the results of a search for information
pertaining to activities in or near riparian areas
that have resulted in summer streamflow
modification.
METHODS
conventional literature search methods were
used. In addition, researchers and field personnel
were contacted to obtain unpublished information.
INFORMATION REVIEW
Information located relates primarily to small
fluctuating streams, orders one through four
(Strahler 1957). Three categories of activity were
identified which can result in modification of
summer streamflows: change in numbers of dams
present, changes in vegetation in and near riparian
zones, and changes in livestock grazing.
Ipaper presented at the North American
Riparian Conference (Tucson, Arizona, April 16-18,
1985) •
2D• Fred Stabler is the District Fisheries
Biologist, Bureau of Land Management, Rawlins,
Wyoming.
206
Beaver Dams
The effects of beaver dams on summer streamflow
were observed on a small stream in Massachusetts
after beaver, their dams and instream woody debris
had been removed (Wilen et ale 1975). In the year
beaver were removed, both experimental and control
streams maintained perennial flow, but the control
stream maintained the higher flow. The following
spring, beaver unexpectedly reoccupied the experimental stream and built dams, while the control
stream remained free of beaver. During the summer
of the same year, the control stream went dry, but
flow continued throughout the year at a station
below the new dams on the experimental stream.
In a beaver study in Utah (Bates 1963),
seepage into the stream in the study area was found
to increase in the summer and decrease during the
winter months. As a result, water budgets could
not be determined with the instrumentation' available. Analysis of streamflow data indicated that
beaver did not, however, significantly affect overall consumptive use of water during the dry season
by building dams and altering adjacent vegetation.
Instead, consumptive use was shifted to earlier in
the growing season in beaver pond areas, as
compared to a stream section without ponds.
Reports of the effects of beaver on
streamflow are rare in the literature, but
where reported tend to support the idea that
beaver ponds augment summer streamflow. Beaver
dams constructed after introduction of beaver on
Ragg Creek in California in 1938 resulted in a
small but steady flow throughout the summer in an
area that normally was almost dry by mid-summer,
and a similar finding was noted on another
California stream (Tappe 1942). Serious economic
losses were reported as the result of the loss of
beaver on several streams in the Ochoco National
Forest in eastern Oregon (Smith 1938, Finley 1937).
Trout streams disappeared and hay crops in beaver
pond areas were reduced by 90 percent, resulting in
a loss at the time of $30,000 per year. Ranchers
were either without recourse or had to drill
wells to water their stock. Downstream, lack of
irrigation water resulted in reversion of cUltivated land to desert. In Missouri, beaver in
headwater streams reportedly restored permanently
flowing water with resultant good fishing (Dalke
1947). Literature reviews by Call (1970) and Bates
(1963) strongly support the idea that beaver dams
help stabilize streamflow regimen and extend flows
into the summer months.
In New Mexico, Jester and McKirdy (1966)
reported that installation of check dams in Taos
Creek resulted in perennial flow within 10 years,
and that trout were subsequently stocked in the
stream. On another stream, Las Huertas Creek,
within three years of installation of 25 gabion
structures, streamflows were extended each spring
by a month or more. The improved stream section
was lightly stocked with trout, and some fishing
was provided.
Reid (1951) stated that enlarged water surfaces created by beaver dams in an Adirondack
spring-fed stream increased evaporation rates and
reduced the volume of streamflow by 50 percent.
This observation is the only information located
suggesting that the activities of beaver can reduce
summer streamflow.
Streamside Vegetation
Check Dams/Gabions
The conversion of streams to perennial flow
has been reported as a result of check dam and
gabion installation in New Mexico, Oregon, Texas,
and Colorado. The best-documented case was in
Colorado in the Alkali Creek drainage (Heede 1977).
In 1958, the drainage was fenced and cattle were
excluded. In 1963, 132 check dams were installed
in ephemeral gully networks for erosion control,
and disturbed areas were reseeded. In 1967, livestock were reintroduced at a low stocking rate. In
1970, the rehabilitated gullies unexpectedly developed perennial flow. Old beaver dams exposed in
the gully wafls were observed during construction
of the check dams, and since 1977 beaver have
reoccupied a portion of the drainage just below the
study area. 3 Precipitation remained normal during
the term of the study. Increases in ground cover
and new sediment deposits in the gullies were
believed to be responsible for change to perennial
flow. Willow and rushes had become firmly established by 1977, yet perennial flow continued (Heede
1977).
In the Fremont National Forest in Oregon, the
installation of 34 rock check dams on Shoestring
Creek in 1974 resulted in perennial flow below a
mile-long erosion control project (Anon. 1979).
Livestock grazing patterns remained unchanged.
Recovery of bank vegetation and use of the water by
trout and waterfowl where none had existed for
years was reported.
The information reported here has been limited
to situations where streamflows have been measured
at gaging stations, or where flow changes have been
observed in the field, following treatment of valley
bottom vegetation. A large part of the literature
on water yield improvement via suppression of phreatophytes has involved estimation of potential water
savings (Horton and Campbell 1974). Predicted water
savings, however, have often been more than actual
savings, as determined by field measurement. Few
studies meeting the above criteria have been
reported (Sopper 1971). No literature was located
reporting streamflow modification by use of antitranspirants in riparian zones.
In a paired-watershed experiment, Rowe (1963)
reported that removal of 4 acres of riparian and 34
acres of woodland vegetation along Monroe Canyon,
California, resulted in variable but significant
water savings that ranged from 0.4 to 1.2 acre-feet
per acre treated. Perennial flow from the treated
stream section also resulted. The greatest water
savings were attributed to removal of peripheral,
deep-rooted woodland species that were able to tap
the capillary fringe and saturated valley bottom
soils through a layer of aerated overburden. The
smallest savings in water was thought to occur
along the stream channel where free water and wet
soil surfaces, within the capillary fringe, were
subjected to the direct effects of wind and solar
radiation. Evaporation from such areas was estimated to be about the same as evapotranspiration
loss from areas with an undisturbed riparian cover.
Ingebo (1971) reported that removal of
streamside chaparral from Whitespar B watershed in
Arizona resulted in perennial flow from a
previously intermittent stream. Water savings
ranged from 0.35 to 0.55 acre-feet annually per
acre treated.
Brown (1963) reported the results of a water
conservation program undertaken on the Flat Top
Ranch, Texas, in which all major drainages were
converted to perennial flow. Dams were constructed
to accelerate infiltration into sandy banks. Water
storage in banks was also increased by diversion
channels to spread water and promote infiltration
and storage. Development of upland areas into
grasslands, to retard runoff and promote storage,
was also undertaken.
Rich and Thompson (1974) reported that removal
of alder and bigtooth maple adjacent to streams,
springs and seeps in the North Fork of Workman
Creek drainage in Arizona resulted in no significant changes in water yield during the riparian
growing season, and that diurnal fluctuations in
streamflow were not changed. Less than one percent
of the basal area of trees in the 248 acre watershed were removed from riparian areas. Later, the
removal of 80 acres of adjacent nearby moist-site
conifer resulted in a 45 percent increase in annual
water yield.
3Heede, Burchard H. 1983. Personal
communication. USDA Forest Service, Rocky Mountain
Forest and Range Experimental Station, Tempe,
Arizona.
Bowie and Kam (1968) reported that after the
eradication of cottonwood, willow and seepwillow
207
along a 1.5 mile section of Cottonwood Wash,
Arizona, a water savings amounting to 6 percent
over inflow occurred during the growing season.
Riparian vegetation was eradicated on 22 acres of
floodplain and water savings amounted to 1.7 acrefeet per acre treated. Reduced water savings later
in the study were attributed to the reestablishment
of seepwillow. Increased evaporation from exposure
of riparian soils to wind and sun was postulated as
the reason for less than expected savings.
Small increases in dry-season streamflow have
been reported after removal of riparian vegetation
from streamsides by Dunford and Fletcher (1947) in
North Carolina, by Nanni (1972) in South Africa,
and by Biswell and Schultz (1958) in California.
Streamflows increased in five small Oregon
drainages where juniper cuttings were performed for
understory release 4• Livestock were excluded
from the treated drainages. Each drainage was
reported to have undergone conversion from a dry,
erosive, juniper-dominated valley to one containing
a true riparian system. Increased release of
groundwater was attributed to the juniper cuttings.
At each site, extension of flows in both time and
distance downstream occurred, and riparian vegetation also developed. Along one of these once intermittent drainages (Skull Hollow, Crooked River
National Grassland, Oregon), perennial flow was
present throughout a mile-long study area and for
0.3 miles downstream four years after treatment.
Livestock Grazing
six years after fencing 7 m(les of Willow
Creek in the Crooked River National Grasslands in
Oregon, flows changed from intermittent to
perennial. 4 While willow Creek for 5 miles above
and below the exclosure remained dry in the summer,
there was perennial flow within the exclosure.
Riparian vegetation recovered, but beaver had not
constructed dams within the exclosure. Fencing of
McMeen Springs and the creek below (a tributary to
Willow Creek) also resulted in development of
perennial flow. 4 A similar finding was reported
on Camp Creek in Crook County, Oregon. 4 By 1974,
4 miles of Camp Creek had been fenced from cattle.
As a result, dramatic increases in wildlife utilization, pronounced buildups of soil within the
stream channel, and sustantial increases in the
amount of riparian vegetation occurred (Winegar
1977). During the droughts of 1977 and 1981, the
West Fork of Camp Creek, which is the main source
of flow in Camp Creek, became dry. Downstream, however, just within the exclosure, flow began and
persisted for four miles and then disappeared just
outside the exclosure. Camp Creek now supports
fish and beaver, although none were present at the
time of fencing. 4
abundant at about the same general time that
perennial flow developed. It is unknown if flow
from springs increased.
DISCUSSION
The research studies that were located generally pre-date the development of modern concepts
of streamflow generation from headwater catchments.
Specifically, the principles of the variable source
area concept (Sattlerlund 1972) have not been used
to help interpret riparian water yield improvement
research, although this research has almost
exclusively been performed in headwater catchments.
Summer flow increases after small dam construction indicates that the potential for water storage
and enhanced summer streamflow within small valleys
is often unrealized. Enough water can be stored,
as a result of a high density of dams, to provide
enough water for increases in consumptive water use
by riparian plants and for change from intermittent
to perennial flow (Heede 1977, Jester and McKirdy
1966, Anon. 1979). By providing materials for
debris jams, dams, and instream obstructions, woody
riparian species may partly mitigate for water
losses through high rates of transpiration during
the growing season. Beaver often construct and
maintain dams in areas where there would otherwise
be few dams, because of the lack of woody debris of
sufficient size and abundance to form instream
obstructions. Wood brought to the stream by beaver
may also later become part of instream obstructions.
Management geared to increase the number of
dams on small, low flow streams may have good
potential for summer flow augmentation, even in
relatively humid areas as demonstrated by findings
in Massachusetts (Wilen et al 1975). Small dams
often have beneficial effects on fish and waterfowl
and can improve watershed values by stabilizing
stream channels and trapping sediment. As an
alternative to removing woody riparian vegecation
to improve water yield during the growing season,
the placement of small dams in the channel is
especially attractive from a fish and wildlife
habitat maintenance standpoint.
Change from intermittent to perennial flow on
three small, spring-fed Texas streams was observed
after elimination of cattle grazing. 5 Big game
species were not removed. Riparian vegetation grew
The means by which small dams can increase
summer streamflow may be postulated. Small dams
may increase the size of the zone saturation, or
the saturated wedge, contained within the valley
bottom. The most striking change in streamflow
reviewed, in which check dams installed in gullies
of the Alkali Creek drainage resulted in changes
from ephemeral flow to perennial flow (Heede 1977),
may have been the result of creating a saturated
zone within the sediment trapped behind check dams
(Heede and DeBano 1984). Small dams may be especially effective in increasing summer flow in
stream channels in which channel downcutting has
occurred and resulted in a greatly reduced
saturated wedge. Peterson (1950) reported that
4Winegar, Harold H. 1982. Personal
communication. Oregon Department of Fish and
Wildlife (retired), Prineville, Oregon.
5Mccollum, James M. 1982. Personal
communication. U.S. Fish and Wildlife Service,
Ecological Service Branch, Fort Worth, Texas.
208
gullying on San Simon Creek, Arizona, was
accompanied by change to ephemeral flow, and
channel aggradation has occurred on several
streams where summer streamflow increases have
been reported (Winegar 1977, Anon. 1979). The
possibility that channel downcutting itself may
favor loss of summer flow, without change in
climate, should be seriously considered.
achieved (Bowie and Kam 1968) amounted to 1.7
acre-feet of water saved per acre of the floodplain
treated. This savings, however, represented less
than half the total evaportranspirative water
losses measured before treatment. After treatment,
evaporation and transpiration by untreated
vegetation amounted to over 50 percent of the total
losses of water found prior to treatment.
Substantial increases in evaporation loss were
postulated (Bowie and Kam 1968).
The removal of nonriparian vegetation, such
as chapparal or conifer, from streamsides and
valley slopes near the riparian zone has
resulted in increases in summer streamflow
(Ingebo 1971, Rich and Thompson 1974, Rowe
1963). In several cases, removal of juniper
has apparently resulted in the release of enough
water to provide water for developing riparian
vegetation and change from ephemeral to perennial
flow4. These findings demonstrate that in
some cases the presence of riparian vegetation
is not the most important factor governing summer
streamflow, and that nonriparian vegetation
removal and conversion to grass may be a management alternative to riparian removal for summer
streamflow augmentation in small streams.
Advantages to this approach include increase in
forage production through control of vegetation
not likely to resprout. Disadvantages could
include potential destabilization of valley
slopes and in many cases the need to remove
livestock for a short time after treatment.
Besides shading and maintenance of a moist
microclimate, riparian vegetation provides structural materials for beaver dams and debris jams,
and also the most important foods fqr beaver.
Other suggested water-conserving functions of true
riparian vegetation include building organic soils
better able to retain soil moisture (Marcuson
1977), and stabilizing stream channels and prevention of channel degradation and loss of the water
table. During overbank flows, riparian vegetation
helps slow and spread flows and may encourage better
streambottom aquifer recharge. Although removal of
riparian vegetation may result in small increases
in summer streamflow over the short term, the
elimination of woody riparian vegetation and debris
over the long term may result in eventual loss of
summer streamflow, especially along stream reaches
susceptible to gullying.
Livestock are seldom removed from large,
intermittent stream sections where unexpected flow
increases would be likely to be noticed visually.
This may explain why more reports of streamflow
increase after removal of livestock are not available. Mechanisms by which summer flow increase
might result upon removal of livestock may be
hypothesized. Combined utilization of riparian
vegetation by beaver and livestock can lead to the
virtual elimination of wood, beaver and their dams.
Upon removal of livestock, beaver and woody riparian
vegetation often reestablish. In gully situations,
recovery of riparian vegetation may lead to channel
aggradation, improved channel morphology, and
improved storage capacity. Beaver may in turn help
the situation by colonizing when more water and
structural material becomes available. Removal of
livestock may result in increased ground cover and
reduced compaction in areas contributing to
streamflow, resulting in increased infiltration and
water storage. As the results from Willow creek
indicate, there may be unknown flow maintenance
functions of the riparian zone which may come into
play when livestock are removed.
It is hypothesized here that the downslope
movement of water, or subsurface flow, can be
intercepted and transpired by vegetation on
valley slopes to a greater degree than presently
believed, and that removal of deep-rooted valley
slope vegetation can reduce transmission losses
as water moves toward the saturated zone in
valley bottoms. Diurnal fluctuations in downslope subsurface flow have been measured and are
shown to correspond to diurnal fluctuations in
streamflow (Burt. 1979). During the day, movement of water was toward slope surfaces, and at
night downslope movement of water towards the
vally bottom resumed. Biswell and Shultz (1958)
reported that removal of deep-rooted vegetation
upslope from springs resulted in immediate
increases in spring flow. Although diurnal
fluctuation in streamflow and water tables is
often attributed solely to riparian evaportranspiration, vegetation on valley slopes may also
play a role. Lewis (1961) reports that diurnal
fluctuations in stceamflow have been detected
before the riparian growing season, and suggested,evaporation from riparian zones may play
a more important role in controlling streamflow
than previously supposed. Diurnal fluctuations
in the zone of saturation in response to diurnal
fluctuations in subsurface flow could also
explain this phenomenon, since valley slope
vegetation can begin transpiring earlier in the
year than woody riparian vegetation.
Summer streamflow can be influenced by a large
number of interacting factors within the areas
contributing to streamflow in small valleys.
Information reviewed suggests that riparian vegetation may not be as detrimental to summer streamflow maintenance as is generally supposed, and that
there may well be, depending on the situation,
management alternatives that would allow for both
increasing summer flows and for maintaining or
improving riparian zones and other values.
Studies involving removal of woody riparian
vegetation have shown that summer streamflow can
be increased as a result of removal of this
vegetation alone, but that savings have been at
most moderate. The best water savings after
eradication of woody riparian vegetation yet
Without including ephemeral channels, small
streams (orders 1-4) comprise over 85 percent of
the stream mileage on a worldwide average (Windell
1980). Information reviewed, however, suggests
209
vegetation for maximum multiple use
values. Res. Paper RM-117, u.s. Forest
Serv., Fort Collins, Colo. 23pp.
that the complexities of streamflow generation
and maintenance in these streams during the dry
season are not fully understood. Particularly
where dry-season water is at a premimum,
improved knowledge of summer streamflow
generation could be beneficial in many ways.
Ingebo, P. A. 1971. Suppression of channelside chapparal cover increases streamflow.
J. Soil and Water Cons. 26:79-81.
Jester, D. B., and J. H. McKirdy. 1966. Evaluation of trout stream improvement in New
Mexico. Ann. Conf. West. Assoc. State Game
and Fish comm. 26:79-81
Lewis, D. D. 1961. Effects of controlling riparian
vegetation. Arizona Watershed Symp. Proc.
5: 27-32.
Marcuson, P. E. 1977. The effect of cattle grazing
on brown trout in Rock creek, Montana. Mont.
Dept. of Fish and Game, Spec. Rpt. Proj. No.
F-20-R-21, II-a. 26pp.
Nanni, u. w. 1972. Water-use by riparian vegetation at Cathedral Peak. s. Afr. For. J.
80:1-10.
Peterson, H. v. 1950. The problem of gullying in
western valleys. In: Applied Sedimentation,
John Wiley and Sons, New York pp. 407-434.
Reid, K. A. 1951. Planning for wildlife on a
managed forest. J. Am. For. 49(6):436-439.
Rich, L. R., and J. R. Thompson. 1974. Watershed
management in Arizona's mixed conifer
forests: the status of our knowledge. USDA
For. Ser. Res. Pap. RM-130, Rocky Mtn. For.
and Range Exp. Stat., Fort Collins, Colo.
15pp.
Rowe, P. B. 1963. Streamflow increases after
removing riparian vegetation from a southern
California watershed. J. Forestry 61:365-370.
Satterlund, Donald, R. 1972. Wildland Watershed
Management. The Ronald Press co., New York.
Smith, L. H. 1938. Beaver and its possibilities in
water regulation. Univ. Idaho Bull.
33(22):85-88.
Sapper, William E. 1971. Water supply augmentation by watershed management in wildland
areas. Nat. water Comm. Rpt. NWL 71-008:
65-90.
Strahler, A. N. 1957. Quantitative analysis of
watershed geomorphology. Trans. Am. Geophys.
Union 38:913-920.
Tappe, D. T. 1942. The status of beavers in
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Wilen, B. 0., Bill P. MacConnell, and Donald L.
Mader. 1975. The effects of beaver activity
on water quality and water quantity. Proc.
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Windell, John T. 1980. Colorado Water Resource-Status 1980. Proc. Colo.-Wyo. Chap. Am. Fish
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response. Rangeman's Jour. 4(2):10-12.
LITERATURE CITED
Anonymous. 1979. Proceedings of fish habitat
improvement workshop. Ochoco Ranger
Station, Sept. 26-29, 1978. Oregon Dept.
Fish and Wildl. 19pp.
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streamflow. Job Camp. Rpt. Fed. Aid Proj.
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Biswell, H. N., and A. M. Shultiz. 1958.
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flow. Calif. Dept. Fish and Game
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62pp.
Brown, J. B. 1963. The role of geology in a
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Ranch, Basque County, Texas. Baylor Geol.
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29pp.
Burt, T. P. 1979. Diurnal variations in stream
discharge and through flow during a period
of low flow. J. Hydrol. 41:291-301.
Call, M. w. 1970. Beaver pond ecology and
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Wyoming. Ph.D. thesis, Univ. Wyoming,
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Dalke, P. D. 1947. The beaver in Missouri. Mo.
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Dunford, Earl G., and P. w. Fletcher. 1947.
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Management of phreatophyte and riparian
210