NativeAmerican methods for conservation
and restoration of semiarid ephemeral
streams
J.B. Norton, F.Bowannie Jr., P. Peynetsa, W. Quandl!lacy, and S.F.Siebert
ABSTRACT:Combinedeffects of brushencroachmentand channelentrenchmentin the
SouthwesternUnited States threaten ecological, hydrological, and agricultural functions of
ephemeral streams and associated alluvial surfaces. Restoration is difficult because
entrenchmentis widespread,and highly variableflow magnitudesdefy standardizedstructural
approaches.Methodsdevelopedby the Zuni Indiansduring morethan 2,000yearsof farmingon
dynamicalluvial fans combinebrush removalwith ephemeralchannel-erosioncontrol and show
promisefor effectivewatershed-scaleconservationand restoration.Zuni utilize severaltypes of
simplebrushstructuresthat rely on hydrauliccharacteristicsof woodymaterialto modifyerosive
and depositional effects of both small seasonaland irregular storm-flow events. Zuni brush
structuresare inexpensiveand quick to build, require no externalmaterialinputs, and avoidthe
extensivedisturbanceassociatedwith conventionalrigid check-damconstruction.Successive
surveysat three incised-headwaterephemeralchannelson the Zuni Indian Reservationshowed
that Zuni techniquesincreasedthe incidenceof overbankflow during small streamflowevents
(acting as permeablecheck dams) and large floods (movingdownstreamand forming debris
jams) and therebyhelpedreconnectchannelsto alluvial fans.Zuni brush structuresrepresenta
potential alternative to capital- and labor-intensive approaches to semiarid watershed
conservationand restoration.
Keywords: Arroyocutting, conservationfarming, discontinuousephemeralstreams,ecological
restoration, local knowledge, permeable check dams, runoff agriculture, woody debris, woody
speciesencroachment
Arroyo cutting and encroachment by
woody species have been degrading
desert and shrub-steppe grasslands of
the Western United States for more than
100 years (Archer 1994; Bryan 1925).
Although the two processes
are closely related because woody species encroachment
increasesrunoff and erosion (Abrahamset al.
1995; Bull 1997), they are typically treated
separately in rangeland conservation and
restorationefforts.A comprehensiveapproach
that restoresboth plant communitiesand surface hydrology to more desirableconditions
could inlprove the successand cost-effectiveness of ecological restoration efforts. This
paper explorestraditional Zuni methods that
use brush and trees cleared from degraded
rangelandsto control arroyo cutting. It also
presentsan example in which local knowl-
250
jOURNALOFSOILANDWATERCONSERVATION 5102002
edgein dangerof being lost becauseof drastic
declinesin traditional land usecould be valuable in addressinga complex, contemporary
environmentalproblem.
Large-scale gully erosion, which severs
connections between ephemeralstreamflow
and ecologicallyimportant alluvial landforms,
has defied control for decades(Gellis et al.
1995). Conventional approaches,including
rigid impervious check damsmade of earth,
concrete, gabions, or logs (Heede 1976;
Reprinted from dIe Journal of Soil and Woter Conservation
Volume 57, Number 5
Copyright CI 2002 Soil and Water Conservation Society
Seehorn 1992; Zeedyk et al.1995), as well as
soil bioengineering approaches, which use
live plant materials where sufficient moisture
will allow rooting (Gray and Sotir 1996),
address only the erosion part of a persistent
feedback between gIillying and invasion of
rangelands by woody species. Other restoration efforts focus on rangeland brush removal
by cutting, burning, chaining, or other
methods (Connelly et al. 2000) but ignore the
concentration of runoff into gullies that
accompanies the shift &om grass to dominance by woody species.
Soils formed in alluvium of headwater
stream systems retain runoff, sediments, and
nutrients to support biological productivity
on-site, protect downstream aquatic resources
(peterson et al. 2001), and support some of
the oldest agricultures, including that of the
Zuni and other Southwestern
Native
Americans (Kintigh 1985; Nabhan 1984;
Sandor 1995), the wadi fam1ers of the Negev
(Evenari et al. 1982), fam1ers of the Nile
Valley Qenny 1962), and others (e.g., Hillel
1991; Hirst and Ibrahim 1996). Overbank
flows are crucial to all these functions because
soil productivity is renewed with inputs of
moisture, sediment, and organic matter &om
upland hillslopes (Norton
et al. 2001).
Channel entrenchment eliminates these alluvial processes (Bull 1997). The Zuni and
other agricultural
Southwestern
Native
Americans have used and protected the natural productivity of soils derived &om alluvium
in annual food crop-based farming systems
for millennia (Hack 1942; Kintigh 1985;
Nabhan 1984; Sandor 1995).
In general, the diverse ways in which traditional farmers approach soil and water
conservation reflect deep-seated practical
knowledge about what works and what does
not work under particular environnlental
conditions (Bocco 1991; Siebert and Belsky
1990). In semiarid environnlents,
local
approaches are often adapted to highly
variable and unpredictable conditions, a
characteristic that is increasingly sought in
modern management systems (Berkes et al.
2000). Traditional agricultural systems in
dry environnlents depend on incremental
methods that emphasize flexibility to take
advantage of pulses of productivity or to
survive drought (Ellis et al. 1993; Niemeijer
1998; Tabor 1995). In the Southwestern
United States, ephemeral stream entrenchment (or arroyo cutting) is a dynamic,
unpredictable landscape process that has been~
managedby mdigenous tarnlers who have a
very rich body of traditional knowledge.
Controlling entrenchment of semiarid
ephemeral streams is difficult because the
extremely variable and dynamic conditions
create stream behavior different from that
where most hydrological principles and erosion control methods were developed (Bull
1997). Small streamflow events that occur
once every two to 10 yearscarry most of the
sedimentthat fills and destroysstructuresbuilt
to storewater and control large floods.Large,
powerful floods can breach,flank, or undercut
check damsdesignedto control erosionduring smallerflows (Gellis et al. 1995).
Though conventional rigid check dams
canmodjfy particular streamreaches(Gelliset
al. 1995), the immense extent of ephemeral
drainagenetworks and relativelyhigh cost of
such structures limit their watershed-scale
effectiveness.
Soil bioengineering approaches
(Grayand Sotir 1996) are alsorelativelymaterial- and labor-intensive for such extensive
application,and soil conditions of semiaridarid ephemeralstreamswhere arroyo cutting
is most prevalent may be too dry to support
fast-growing vegetation. Headwater streams
often make up as much as 85% of the total
channellength in watersheds(petersonet al.
2001) and, in semiarid areas,flow only in
responseto rainfall. Large watershedrestoration efforts must be simple and quick to
implement,require minimal capitaland labor
inputs, and effectively modjfy both small
flows and powerful floods.
Zuni farnlers who still practice traditional
agriculture use simple,low-investment structures that appear to mitigate destructive
arroyo cutting during both small and large
strearnflows.This type of erosion control is
often part of brush- and tree-clearingactivities intended to prepare fields for cultivation
or to improve livestock grazing lands. Our
objective was to describe and evaluatethe
performance of indigenous erosion control
methodsand to evaluatetheir potential application in watershed- and ecosystem-scale
conservationand restoration efforts.
the majority of which often falls during
d1understorms
in July,August,and September.
The combinationof steeperodible sandstone
and shaleslopescoveredby patchy pinyonjuniper (Pinusedulis-juniperns
spp.)and scrubshrub plant conununities wid1 relatively
intense sununer storms contributes to
dynamic,sand-bedfluvial systemsthat move
large amounts of sediment (Lagasseet al.
1990).
Zuni subsistence
agriculture dependedon
corn (Zia mays)grown in nonirrigated fields
in d1esedynamic fluvial settings for more
than 1,500 years(Kintigh 1985). Socio-economic change and assimilation policies
beginning with U.S. occupation of Zuni
landsin d1emid-19dt century causeddrastic
declinesin agriculture (Clevelandet al. 1995).
Major arroyocutting coincided with this shift
away from traditional farming and led to
multiple, U.S.-sponsored erosion-control
effortsthroughout d1e20dtcentury,including
large earthen check darns built by government agenciesand smaller-scaleeffortsby the
Civilian Conservation Corps (CCC) and
od1erprograms(Gellis et al. 1995).
Three actively eroding, low-gradient,
entrenched,meanderingheadwaterephemeral
streams-Rosgen "F-type" channels(Rosgen
1994)-were selected for treatment with
traditionalZuni brush structures(Laate,Lalio,
and Quandelacysites).These streamsare representativeof headwateralluvial systemsand
provide important ecological, hydrological,
and agriculturalfunctions.
The Laatesite is a short ephemeralchannel
that crossesan orchard high on d1eleeward
side of a sandstonemesa.The channel gradient was historically maintained to facilitate
flooding of d1e sandy eolian soils. In 1996,
channelincision threatenedto exclude both
mature and recendy establishedfruit trees
from streamflows.The Quandelacy site is a
continuously incised channel running nom
d1emoud1of a small canyon through rangelandsdominated by big sagebrush(Artemisia
tridentata).Atthe beginning of our study,this
channelranged from a slot-like gully about
1 m deep by 1 m wide to a 6 m deep,VMethods and Materials
Shapedarroyoand had severalsteepheadcuts.
We conducted this study in collaboration The Lalio site is a deeply incised arroyo that
with traditional Zuni farmers on the Zuni
empties onto a traditional, hand-cultivated
Indian Reservation in west-central New cornfield.By 1998,d1earroyo had deepened
Mexico. The Zuni reservation lies on the for a third of the way into the' cornfield,
southeasternpart of the Colorado Plateauat excluding about three-quarters of the field
1,800 to 2,400 m elevation and receivesan from flooding.A continuous rill had formed
averageof 300 mm of precipitation annually, through d1efield.
I 5102002
VOWME 57 NUMBER 51 251 I
A three-part approach for treating and
evaluatingstructure effectivenesswas implemented at eachstudy site:
Treatments.Zuni crewsled by peoplewith
lifdong experiencein traditional agricultural
practices installed erosion-control structures
at the three sitesusing axes,shovels,and posthole diggers.The Laatesite wasfirst treatedin
June 1996,the Lalio site inJune 1998,andthe
Quandelacysite in June 1999. Members of
the crews recorded labor input, wrote
descriptionsof structures,sketchedmapsand
structure designs, and photographed construction.The crew leadersare co-authors of
this report.
Channel morphology.Successive
longitudinal thalweg surveyswere used to document
treatment effects on channel morphology
(Harrelsonet at. 1994).Surveyswere conducted during construction,after flow events,and
at the end of the study.(The relativelyremote
Laatesite was surveyedonly at the beginning
and end of the study period.) Photo points
were establishedalong each channel.Surveys
included devations of thalweg, structures,
banks, and water levels identified by high~
water markson the arroyo banks.
Channell alluvial fan connectivity.Pre~and
post-study channel dimensionswere used to
estimatethe probability of overbankflow at
the Lalio and Quandelacy sites.Manning's
equation was used to estimatethe peak discharge that would be required to overtop
pre- and post-study arroyo banks and then
was applied to two- through 100-yearrecurrenceinterval equations(Thomaset al. 1997)
to estimatethe averagemquency that such
overbankflows would occur.
To place the eventsand treatment effects
observedin 1999 within the context of longterm Zuni climate, recurrence intervals of
both rainfall and streamfloweventswere estimated. Rainfall volume and intensity were
monitored at a tipping-bucket rain gauge
2 km from the Lalio site (datacourtesyof the
Zuni Conservation Project, Zuni Pueblo,
New Mexico) and rainfall-event recurrence
intervals were determined with intensityduration-mquency curves for Albuquerque,
New Mexico (USWB 1955).The magnitude
of 1999streamfloweventswasdeterminedby
applying Manning's equation to channd
dimensions surveyed after flow events by
using high-water marks to indicate peak
stage.These valueswere compared to peak
dischargesderived from equationsfor twothrough 100-year recurrence interval events
in the two watersheds(Thomaset at. 1997).
252
JOURNAL
OF SOIL ANO WATERCONSERVATIONSIO 2002
Results and Discussion
Traditional Zuni brush treatments effectively reduced ilie erosive power of small
streamfloweventsand largefloodS,iliough by
very different modes of action. They also
effectivelymodified channelmorphology and
restored channel/alluvial fan connectivity.
During small flows, ilie structures acted as
permeable barriers that retained runoff in
temporary pools and accumulatedsediments.
During larger,more powerful floodS,many of
ilie structureswere destroyed,but ilie woody
debris was redeposited in debris jams that
altered channel morphology and drastically
increasedilie likelihood of overbankflow.
TreatmentDesign and LAborRequirements.
The workers installed four general types of
brush structures iliroughout ilie treated
reaches.Construction followed generalprincipalsfrom knowledge about flow eventsbut
variedby worker and by streamflowsituation.
Spacing between ilie structures (Figure 1)
averagedlessthan 20 m for all ilie sites,much
closerilian guidelinescalculatedwiili Heede's
(1976)spacingrule, which is commonly used
for designing erosion-control projects.This
spacingrule is basedon ilie equation:
H
-S =
KGcosa
where S is spacing(m), H is dam height (m),
G is the channelgradient ratio,a is the angle
correspondingto the channel gradient (G =
tan IX),and K is a constant developed through
regression analyses for different channel
gradients (K = 0.3 for G S 0.20).
The exact placement of the brush structures varied depending upon channel characteristics and the types of woody material most
readily available. Simple brush piles were
the most commonly employed technique
throughout the channels, with stronger structures placed in key locations toward distal
ends of the channels and in constricted areas.
Minjrnizing disturbance to channel beds and
banks, using material close at hand, and using
stones only sparingly to compress brush were
concepts common to all four kinds of structures, which are described below:
Brush piles. Limbs of pinyon and juniper
trees and whole, big sagebrush plants were
piled in channels with larger sterns pointing
downstream (Figure 2a). Material
was
stomped down repeatedly and layered sparingly with stones or larger logs where those
were readily available. Large amounts of sagebrush were packed into slot-like channels
over distances of as much as 30 m by stomping down layer after layer. Shallow rills
through the Laate Orchard and the Lalio
cornfield were filled with fine woody material from rubber rabbitbrush (Chyrsothamnus
nauseosus)and broom snakeweed (Gutiemzia
sarothrae).
This was the most rapid method and
had the objective of placing as much debris as
possible into the channel with a minimum of
additional strengthening.
Figure 2
Types of structures installed at study sites: (a) brush pile with fine
branches oriented upstream and stones to compress brush (drawing by
Fred Bowannie Jr.); (b) brush check dam with fine branches woven into
larger limbs piled across channel. (Tape follows thalweg.); (c) pungie
posts immediately upstream from a post-and-wire structure. Posts are
about 8 cm in diameter at the base.
(a)
Arroyo bank
Flow
.
Flow
Arroyo bed
.
Side View
Top View
Checkdams. Simple check damsof interwoven woody material were slightly more
intensive than the brush piles. In this
approach,the largest,longestlimbs were laid
acrossthe channel in a pile about 0.5 to 1 m
high with brushy tops in alternating directions. Smaller limbs werejabbed and woven
into the pile so that branchesand leavespresenteda densemat of fine woody material to
the upstreamdirection (Figure 2b). Some of
these dams were reinforced with posts cut
ttom pinyon or juniper stemsand set immediately downstreamttom the brush structure.
Post-anJ-wire methods.In this method,
workerssettwo rows of polesabout 1 m apart
acrossthe arroyo channeland packedbrushy
materialbetween the polesto createa barrier
about 1.5 m high. The tops of the poleswere
then wired together.This method requmd
more effort in sorting and trimming woody
material, setting posts, packing brush, and
wiring braces together. This method was
deliberatelyemployedin relativelywide, lowenergy reaches,at points immediately below
sharpbends,or in seriesof two to three structures. Each of these structureswas built by
one worker and took two to three hours for
structuresup to 7 m long.
Pungie posts. Pungie posts consist of
clusters of pinyon and juniper limbs and
sternsset into the arroyo bed to form comblike structuresthat capturewoody debrisand
create reinforced debris jams during flow
events(Figure 2c).The postswere set at least
60 cm into the ground, angled upstream.
Placementwas downstreamfrom brush-pile
structuresand upstreamfrom other types to
protect and reinforce them. Some of the
pungieswere reinforced with post-and-wire
braces.Part way through the season,the
workers decided to alter this method by
leaving fine brancheson the postsso that, if
posts washed out, they would function as
woody debris.
The crew treated a total of 1.25 km of
ephemeralstream channel during the study
period but had to treat segmentsrepeatedly
after large floods removed structures three
times at the Lalio site and once at the
Quandelacysite.Including the repeatedtreatments, 3.4 km were treated, averaging 93
person-hourskm-1 of channel.The first treatmentsat the Lalio and Quandelacysiteswere
relatively rapid, but the second treatments
required more time to build the reinforced
pungie post and post-and-wire structures.
Treatment Effects. Although
1999 was a
relatively dry year (252 mm, or 80010of normal precipitation), 170 mm of rain fell inJuly
and August, which is 159% of normal precipitation (WRCC 2001). Much of this rain
carne as unusually intense thunderstorms
(Figure 3), including a greater-than-25-year
recurrence interval storm on July 5, at more
than 18 mm in 15 minutes. The thunderstorms generated streamflow events with
widely varying magnitude, including several
five- to 25-year recurrence interval flows and
four that equaled or exceeded 100-year flood
events (one at the Quandelacy site on Aug. '2
and three at the Lalio site on July 5, Aug. 2,
and Aug. 27), according to measurements
conducted by hydrologists of the Zuni
Conservation Project. Because of the remote
nature of the Laate site, channel din1ensions
were surveyed only during treatment installation and at the end of the study, so flow
magnitudes were not estimated for that site.
The structures at the Quandelacy and Lalio
sites all withstood
the less-than-25-year
recurrence interval flows, temporarily retaining water and causing some sedin1ent deposition (Figures 4 and 5). During larger floods,
however, many of the structures washed out.
15102002
VOWME
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5 I 253 I
deposition for more d1an 100m upstream.
Channels upstream from die debris jams
filled widi sediment to within a few centimeters of die bank from pretreatment depilis of
about 1.5 m at die Lalio site (Figure 6) and
1 m at die Quandelacy site.This caused overbank flow for nearly 100 m upstream of die
debris jam at the Lalio site, which deposited
nearly 20 cm of sand on parts of die alluvial
fan. Figure 7 shows die pre- and post-study
channel profiles at die three study sites.The
structures at the Laate site retained sediment
and were mosdy buried during die posttreatment survey, except for die most distal
structure, which had been installed on
bedrock and washed away.
The overall effect of die treatments was to
restore flooding to larger portions of die alluvial fans at all three sites.The schematic map
of die Lalio site (Figure 8) shows that, at die
beginning of the study, flows emerged from
the channd near die center of die agricultural field. The apex of die fan, or the point
where flow leaves die channel and spreads
over the alluvial fan, moved upstream after
each flood as the channel filled widi sediment. At the end of die study, small flows
(- two- to five-year recurrence interval)
remained in the channel and flowed to die
agricultural
field, but larger, potentially
destructive floods would overtop die banks
far upstream. Although
die response of
vegetation in the areas cleared for brush was
not measured, increased grass production,
particularly blue g=
(Boutelouagradlis),was
evident compared with adjacent areas.
Repeated surveys at channel cross-sections
at the Lalio and Quandelacy sites confirm
that connectivity between die ephemeral
stream channels and alluvial fans was restored
(Table 1). At the Lalio site, sediment deposition 100 m upstream from die debris jam
reduced the hydraulic radius so that calculated recurrence interval (Thomas 1997) of
overbank flow changed from nearly 50,000
years at the beginning of die study to four
years at the end. Similarly, at die Quandelacy
site, calculated recurrence interval of overbank flow changed from 3,000 years to three
years.
Literature Review and DisCIIssion. Clearing
brush and trees from rangelands and using die
material for erosion control simultaneously
addresses two major ecological degradation
processes.Clearing brush and trees that compete widi grassesis a common approach to
ecological restoration and has been shown to~
~
Figure 5
The lower part of Lalio arroyo shortly after peak discharge on July 18,
1999. Note the stepwise waterlines behind the structures and the
effect of brush clearing along banks.
increase forage production (Archer 1994).
Increased herbaceous ground cover also
increases the hydraulic roughness of soil surfaces, causing more infiltration and lessrunoff
(Bull 1997). The Zuni workers often pruned
lower branches on pinyon and juniper trees
rather than cutting whole trees, explaining
that removing lower branches increased forage production around trees and increased
site distances for livestock herding but maintained the shade and wind protection provided by the trees. Pruning and/or clearing trees
and brush is often the principal purpose; the
materials are disposed of in arroyos to control
erosion.
Our results are supported by a previous
study on the Zuni Indian Reservation in
which Gellis et al. (1995) found that 28 of 47
large, heavy-equipment-built earth and rock
erosion-control structures they evaluated had
breached, and 31 were more than half-filled
with sediment in the 20 to 30 years since
construction. In contrast, only five of 23
brush structures had washed out or were
breached, while the remaining structures
continued to function. The brush structures
were built in the 1970s by a Youth
Conservation Corps team led by an elderly
Zuni farmer. Gellis et al. (1995) attributed
failures of both the large rock and earthen
structures and the Zuni brush structures to
lack of maintenance. Because they require no
heavy earth-moving equipment or offiite
materials, the brush structures would be easier
and less expensive for local people to build
and maintain. Unlike capital- and laborintensive rigid darns, modification of Zuni
brush structures by streamflow events is not
consideredfailure of
the structures but
part of the ongoing
processof conserving
alluvial fan functions.
In thjs traditional
Zuni approach, as
much woody material aspossibleis placed
in channels with
minjmal strengthening. No keys into
bedsor banksand no
reinforcements with
stonesor gabionsare
used.Insteadof relying on rigid check dams,which can cause
scouring of streambedsor banks (Gelliset al.
1995), erosion control is achieved through
hydraulic characteristicsof woody material.
Although there arefew publishedaccountsof
permeable brush structures for controlling
arroyo cutting, woody debris is commonly
used to improve or restoreaquatic habitatin
perennial streams.
There are similarities between the structures built during our study and methods
usedduring the 1930sby CCC crewsat Zuni
and elsewhere(USEPA 1999).However,the
CCC methods all include stone armor and
keying structuresinto beds or banks,while
the Zuni methods purposefully avoid these
techniques.Nevertheless,the similaritiessuggest that some of the techniquescould have
been handed down from Zuni people who
servedon CCC crews.The CCC techniques
may havebeen adaptedby Zuni peopleto fit
local conditions. The workers in our study
explained how, although the approach was
learned from older Zuni people, methods
were constantly modified to fit specific
conditions. The brush structures reflect the
constant experimentation and innovation
characteristicof traditional ecologicalknowledge (Berkeset al. 2000).
Studies of woody debris suggestthat the
Zuni methods could be effectivefor increasing sedimentation.Woody debris is responsible for as much as 87% of channel sediment
storagein small woodland streams,with 39%
or more of the individual pieces forming
depositional sites(Fetherstonet al. 1995).As
such,woody debrisis a primary determinant
of channel morphology, forming pools and
regulating transport of sediment, organic
matter, and nutrients.While lack of woody
debrisis often recognizedasa characteristicof
dryland streams,Minckley and Rinne (1985)
suggestthat streamsidevegetationwas abundant before destruction of riparian forests
15/02002
VOLUME
57 NUMBER
51 255 I
vating the water-surfaceprofile and significantly increasingflood travel times (Gippel
1995). In one study,woody debris covered
lessthan 2% of the streambedbut provided
500/0of total flow resistance(Mmga and
Kirchner 2000).After initial treatmentsin our
study,woody material coverednearly 50% of
the channelbed of the treatedreaches.
Implications for WatershedRestoration.
The labor and materialsrequiredto construct
brush piles suggestthat this method could be
implemented rapidly and inexpensivelyover
entire watersheds.
At an averageof93 personhours kIn-! of entrenchedchannel treated,a
20-personcrew could treat more than 1.7 kIn
per eight-hour day. Our work during an
unusuallywet and stormy year required that
we treatthe studyreachesrepeatedlyafter 50to 100-yearrecurrenceevents.These unusually frequentand high magnitudestorm flows
came almost inunediately after structures
were installed,beforesmallereventsbeganto
bury the woody material with sedimentsand
hold them in place.This partly explains the
need to repeatedlytreat the reaches.
Over the long term and across whole
watersheds,treated headwaterchannelsmay
need additional woody material added at
about 20-year intervals, after large floods
remove woody debris or as brush darns fill
with sediment.This observationis supported
by Gellis et al. (1995),who found that five of
28 brush structuresneeded maintenance20
yearsafter installation.More frequent debris
additionsafter flows that causesedimentation
would raise channel-bed elevations and
thereby increasethe likelihood of overbank
flows and depositionin agricultural fields.
These Zuni erosion control practicesare
closely associatedwith traditional rainfed
corn (Zeamays)farming, which provided the
basisof Zuni subsistenceuntil the late 19th
century (Kintigh 1985).Sincethen, changing
socio-economic conditions, devastatingepidemics, and u.S. agricultural development
policies caused drastic declines in rainfed
farming (Oevelandet al. 1995;Fergusonand
Hart 1985).The cessationof traditional farming in ephemeralstream coursescoincided
with the onset of stream-channelincision at
Zuni (Balling and Wells 1990;Bryan 1925).
This suggeststhat the absenceof previously
widespreadtraditional erosion-controlactivities may have contributed to the severity of
channel entrenchment that is now widespreadin the Zuni area.
The Zuni approachto controlling arroyo
256
JOURNAL
OFSOil ANDWATER
CONSERVATION
5102002
Figure 8
cutting may be relevantto large-scalerangeland watershed restoration in the Western
United States.Implementing this approach
could be as simple as using woody material
displacedduring chaining or cutting to build
the simple permeablebrush check dams in
nearby incisedwatercourses.
While this additional work would be relativelyinexpensive,it
could effectivelyreduce erosion and increase
sedimentationover wide areas.
The Zuni methods could be useful in
other semiarid regions where incised
ephemeralstreamchannelshavesandor finer
beds,flow eventsmove large amounts of bed
load and suspendedsediments,and there is
abundant fine woody material near eroding
channels.An important characteristicof the
Zuni approachis that farmersmodify erosion
control methods to fit particular situations
(i.e.,channelgeometry or the typesof woody
material available)or objectives(i.e., control,
prevention, or restoration of connectivity
between channels and surrounding alluvial
surfaces).As such, the Zuni methods would
probably be most applicable if built upon
local environmental knowledge and traditions. Traditional, low-input erosion-control
practices are widely used throughout the
world (e.g., Mexico, Bocco 1991; and
Indonesia, Siebert and Belsky 1990) and
typically displayadaptationsto local environmental and cultural conditions,aswell asbasic
principles of potential use elsewhere.
Summary and Conclusion
Traditional Zuni erosion-control mediods
effectively modify channel morphology of
entrenched headwater ephemeral streams
after small flows and powerful floods in ways
that increase die occurrence of overbank
Sketch map showing chronology of flood events and reaction of treatments at the Lalio site.
Drawing by Fred Bowannie Jr. See discussion in text.
Debris
jams
+
,
I
flows and die areaof alluvial fans flooded by
recurrenceinterval flows of lessthan or equal
to five years.Frequent,low-intensity floods
are important to renewal of desirablesoil
properties.Thesemethodsarerapid and inexpensiveto implement and thus may be useful
in watershed-scalerestorationefforts.While
most conventional erosion-control methods
rely on rigid check damsof concrete,stones,
gabions,and/or logs keyed into streambeds
and banks,the Zuni brush structuresrely on
hydraulic characteristicsof woody debris to
modify erosive flows. Rather than investing
time in strengtheningstructures,Zuni farmers and livestock herdersfocus on placing as
much woody material as possibleover long
channelreachesin an attempt to reduceflood
power, move fan apexes upstream, and
increasedle ttequency and areaof overbank
flows. The Zuni medlods combine clearing
brush and trees widl erosion control in an
efficient, comprehensiveapproachto watershedrestoration.
The approachdescribedherein is basedon
long-term understanding of dle range of
variability in dle dynamic fluvial environ-
Table 1.. Estimated discharge for overbank flow (discharge required to reach top of channel banks calculated using Manning's equation with
channel dimensions at the beginning and end of the study period. See discussion in text.
Parameter
Units
Lalio
overbank,
pretreatment
Lalio
overbank,
post-treatment
Quandelacy
overbank,
pretreatment
Quandelacy
overbank,
post-treatment
ha
m
36
320
36
320
0.006
1.08
0.20
0.026
1.10
4
17
130
0.035
1.94
0.44
0.026
8.07
never
17
130
0.01
0.58
0.15
0.026
0.63
3
Watershed area
Station'
Slope
Cross-sectional area
Hydraulic radius
Manning's n"
Peak discharge
m3s2
Recurrence interval'"
years
*
**
**
0.02
4.5
m2
m
0.58
0.026
never
Meters from lower end of longitudinal
Based on roughness coefficients
Estimated
using regression
17.02
profile.
for sand bed channels (Jarrett
equations
.1.985).
of Thomas (.1.997).
ISIO2002,
VOWME
57 NUMBER
5 I 257 I
ment of the SouthwesternUnited States.It
incorporatessome methodsbrought to Zuni
during nearly 100 yearsof U.S.governmentsponsorederosioncontrol but adaptsthem to
fit local conservationobjectivesand traditional environmentalknowledge.TraditionalZuni
soil conservation measures allow local
residentsto effectively conserveand restore
natural resourceswithout expensiveequipment. These methods may also representa
comprehensive,cost-effective approach to
large-scalewatershed restoration applicable
to other semiarid environments around
the world, particularly when combined
with local knowledge of runoff and erosion
characteristics.
Acknowledgement
This work
was funded
by National
Science
Foundation grant DEB-9S284S8 and is dedicated
H.Laahty,who lead this
to the memory of Andrew
research effort as director of the Zuni Sustainable
Agriculture Project. We thank the Zuni Tribe and
Zuni Conservation
Program for supporting
this
research. Craig Goodwin's review contributed
to
the accuracy of our report.
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