SEDIMENT YIELD AS A RESULT OF SNOWMELT RUNOFFIN THE PEACE RIVER REGION

D. S. Chanasyk and C. P. Woytowich

Department ofSoil Science, University ofAlberta, Edmonton, Alberta T6G2E3

Received 13 February 1986, accepted 30 June 1986

Chanasyk, D. S. and C. P. Woytowich.Region. Can. Agric. Eng. 29: 1-6.

1987. Sediment yield as a result of snowmelt runoff in the Peace River

Data quantifying sediment yield asa result ofsnowmelt runoff from agricultural land are limited. In 1981 a study todetermine theeffects ofdifferent agricultural management practices onsediment yield andrunoff was initiated inthePeaceRiver region of Alberta. Four erosion plots, three in a canola-barley-fallow rotation and one seeded to fescue, wereestablished inanagricultural field having a 5%slope. Runoff samples, collected at0.5- to 1-h intervals, were analyzed todetermine sediment concentrations in runoff. Twoyears of results for sediment yield are discussed. Sediment yields werehighestfromfallow;lowestfromfescue. A briefmeltfollowed byseveral daysoffreezingtemperatures effectivelyreducedsediment yield. An idealized snowmelt progression is presentedand used to explain temporal variations in sediment load.

Water erosion is a complex processaffected by both soil and non-soil factors.Factors which determine the magnitude ofsoil erosion can be classified into four

groups (Meyer and Monke 1965):1. factors affecting the detachment

capability of the erosive agent;2. factors influencing the detachability

(erodibility) of the soil;3. factors affecting the transport capac

ity of the erosive agent;4. factors determining the transport

ability of the eroded particles.Detachment capability is dependent on

flow depth, velocity and turbulence ofrunoff (Benedict and Christiensen 1972;Foster and Meyer 1972; Bryan 1976).Runofftransport capacity also depends onflow properties. Once a particle has beendetached, the rate of transport depends onparticle transportability, flow depth, turbulence and downstream velocity.

Soildetachability(erodibility)is dependent on several soil physical and chemicalproperties but is usually expressed as ameasure of aggregation or aggregate stability.Commoncultivation practicesbreakdown soil aggregates making them moresusceptible to erosion (Foster et al. 1982).Overwinter "freeze-drying" (Andersonand Bisal 1969) and freeze-thaw cycles(Formanek et al. 1983) can also lead toaggregate breakdown.

Since the transportability of detachedparticles depends primarily on the physical properties of the particles themselves,measures of soil aggregate stability,although useful for comparing relativeerodibility, do not provide much information on sediment transportability for estimating soil movement. Article diameterand specific gravity are the two most

important properties affecting transportability (Yalin 1963).

Erosion will occur at a rate determined

by the factor which is most limiting.Although simple in principle, the approach of Meyer and Monke (1965) iscomplicated by the interactions of manyfactors.

Management practices have a markedeffect on soil erosion. Incorporation ofcrop residues generally increases soilaggregate stability and reduces erosion(Wischmeier and Smith 1978)while tillagebreaks down aggregates increasing soilerosion (Foster et al. 1982). Vegetativecharacteristics must also be considered

as they affect runoff flow properties(Kowobari et al. 1972).

During the springmelt period the soil isusually frozen. Soil erosion potential canbe increased during these periods as aresult of the greater probability of surfacerunoff (Van Vliet and Wall 1981) due toreduced infiltration capacity. Severalresearchers have recognized the importance of soil erosion as a result of snowmelt(Van Vliet et al. 1976; Ketcheson 1977).

The universal soil loss equation hasbeen adapted to predict soil erosion undersnowmelt conditions; however, these estimates are unreliable because of the lack ofknowledge of soil erodibility under frozenconditions. The dynamic nature of soilerodibility during snowmelt further limitsthese predictions. Data quantifying soilerosion during the springmelt are lackingand the few data that are available are fromareas which receive rain on snow.

A study to determine the effects of different agricultural management practiceson sediment yield and runoff duringspringmelt was initiated in 1981 in the

CANADIAN AGRICULTURAL ENGINEERING, VOL. 29, NO. 1, WINTER, 1987

Peace River region of Alberta. This areawas described as having severe soil erosionproblems as early as 1939 (Albright 1939).

METHODOLOGY

Sediment yields, which occurred as aresult of spring runoff, were measured onfour research plots, each 5 m wide by 75 mlong, near La Glace, Alberta (approximately 500 km northwest of Edmonton).

The plots were established in May 1981.One plot was seeded to fescue; the otherthree were in a fallow-canola-barley rotation. All plots were seeded and cultivatedupslope. Stubble was left standing in thefall. Detailed information on site charac

teristics, soil physical properties, plotdesign and instrumentation have beenreported in Chanasyk and Woytowich(1983). A detailed description of springmelt runoff characteristics can be found inChanasyk and Woytowich (1986).

Flow samples for sediment yield determination were collected at 0.5- to 1-h intervals during springmelt. Each sample wasevaporated and the amount of sedimentweighed to determine sediment load.

To study the effects of soil temperatureon sediment yield, thermistors wereinstalled in late 1982at depths of 0,10 and20 cm at one location within each plot.They were read once or twice daily duringthe 1983 melt period.

The particle size distribution of springmelt sediment samples (collected fromflume bottoms) and summer rainstorm erosion sediments (recovered by evaporatingsamples of summer storm runoff) werecompared to those of the surficial soil forthe La Glace site. Initial comparisons weremade using the standard hydrometer procedure (McKeague 1978). This method

uses calgon todisperse all soil particles sothat the primary particle size distributionfor the sample can be determined. Thereader is referred to Chanasyk andWoytowich (1983) for a more detailed discussion of these data. These results do notreflect thebinding ofprimaryparticles intoaggregates; consequently, the procedurewas repeated using distilled, de-ionizedwaterwithoutcalgon in an attempt to evaluate the sizes of eroded aggregates.

RESULTS AND DISCUSSIONResults for 2 yr of study, 1982and 1983,

are reported here. Mean annual snowfallfor this region is approximately 20 cm(water equivalent), rainfall during snowmelt is unusual and drifting of snow iscommon in open areas. Monthly precipitation at Grande Prairie Airport (approximately 50 km southeast of the study site)was below normal for all months Sep-

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tember to April, inclusive for the 3 yr,1981-1983, except for January 1982 andApril 1983 (Chanasyk and Woytowich1986).

The 1982 springmelt lasted 7 days.Snow meltwater, from upslope, ran on tothe canola plot making data from that plothighly questionable for comparative purposes. Total daily sediment yield fromeach plot is given in Fig. 1A. The fescue,fallow and barley plotseach yielded comparable amounts ofsoiloverthefirst 4 daysof melt but over the last 3 days the fallowplot lost considerably more soil. Totalsediment yields (kg/ha) for the 1982springmelt were 2027, 391 and 260 for fallow, barley and fescue, respectively. Theyield from the canola plot was 2267 kg/ha.

In 1983 snowmelt runoff occurred on 7

days; however, melt was not continuous asair temperatures in the region droppedbelow0°C (for5 days)after 2 daysof melt.

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Asin1982, sediment yields from each plotwere similar over the first 3 days of meltbut the fallow plot lost substantially moresoil over the last 3 days (Figure IB). Totalsediment yields were 247, 114, 77 and57 kg/ha for the fallow, barley, canolaandfescue plots, respectively.

Examination of the runoff and sedimentconcentration graphs for 68 days revealedseveral trends. Runoff rates increased untilthe fourth or fifth day of melt and thendropped off. Sediment loads, althoughrunoff dependent, generally reached peakvalues 1 or 2 days later than did runoffrates. Variation in daily sediment concentration generally increased as melt progressed. Runoff hydrographs during 1982were usually single-peaked while many1983 hydrographs were multi-peaked,causing increased complexity in the timedistribution of sediment concentration.

Typical examples of runoff flow rate andsediment concentration versus time for the

1982 and 1983 springmelts are presented inFig. 2A and B.

Surface soil temperatures remained atapproximately 0°C until 13 or 14 April1983 and then increased. The 10 cm soil

temperatures remained at or below 0°Cuntil 15 or 16 April while the 20 cm soiltemperatures remained below 0°C until18 April for most plots. With the exceptionof the fescue plot, the most dramaticincreases in mean daily sediment loadoccurred shortly after the surface soil temperature rose above 0°C.

Sediment load peaked early in the meltperiod on the fescue plot, untilled fornearly 2 yr and covered by a thick vegetative mat. Once runoff had removed most

of the unconsolidated material on the soil

surface, sediment concentrations dropped.The other plots, in a relatively bare andunconsolidated condition, experiencedpeak sediment loads late in the meltperiod, after the soil surface beganthawing.

A progression was observed in theshapes of the sediment concentrationgraphs for almost all plots and for bothyears. Figures 3A through 3F illustrate thestages in the idealized progression. Earlyin melt, when flow rates were low, soilerosion was controlled by runoff rate. Theshape of the sediment concentration graphroughly approximated that of the hydro-graph (Fig. 3A). As flow rates increased,soil erodibility became a limiting factor.Initially sediment concentration increasedwith increasing flow rate; but, before thepeak flow rates were reached, runoff transport capacity exceeded soil erodibility andthe sediment concentration graph levelledoff (Fig. 3B and 3C).

CANADIAN AGRICULTURAL ENGINEERING, VOL. 29, NO. 1, WINTER, 1987

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As melt progressed and runoff ratesincreased, snow cover became discontinuous and thawing of the soil surfacebegan (Fig. 3D). Early in the day conditions were comparable to those represented by Fig. 3C; however, thaving of thesoil surface during the day increased soil

erodibility. Consequently, sediment concentrations increased (after initially levelling off) until late in the day when flowtransport capacity became the limitingfactor.

Figure 3E represents conditions of lowto moderate flow with significant thawing

CANADIAN AGRICULTURAL ENGINEERING, VOL. 29, NO. 1, WINTER, 1987

of the soil surface as the day progressed.Sediment concentration increased withincreasing flow rate but, as flow rate beganto drop, sediment concentration continuedto increase due to soil thawing. Late in theday flow transport capacity again becamelimiting; as a result sediment concentration

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decreased with decreasing flow rate.On the last days of melt, when the soil

was thawed, low runoff rates limited sediment yield. With runoff transport capacitylimiting, the shape of the sediment concentration graph approximated that of thehydrograph (Fig. 3F).

Although this progression was observedon all plots (except fescue in 1983), not allstages of the progression were observed onall plots. The rapidity of melt initiation,progression and termination determinedwhich stages were observed. For example,Figure 2A lacks stage (A) reflecting aquick onset of melt, while Figure 2B lacksstage (E), indicative of rapid melt termination.

Mean soil surface, spring and summereroded sediment particle size distributionsobtained using the hydrometer methodwith and without calgon were compared(Fig. 4A-C). The spring erosion sedi-

Figure 3. Idealized snowmelt progression.

ments and the surficial material had similar

particle size distributions while the summer storm sediments were significantlyfiner textured. The calgon and water determinations gave similar trends. These datashowed, for all samples, the aggregation ofclay particles into silt-sized aggregates ascompared to the calgon determinations.During springmelt soil particles were notselectively entrained as evidenced byeroded sediment size characteristics, sediment load and soil temperature data.Instead, the mass transport of materialoccurred. Also, as melt progressed, meandaily sediment concentrations increasedeven after runoff volumes began todecrease, indicating that soil erodibilitywas not constant but increased as the soil

surface thawed.

The estimation of soil erodibility ismade even more difficult during thespringmelt period because soil moisture

TIME

conditions must also be considered. Pre-

melt soil moisture was higher for 1982 thanfor 1983 (Chanasyk and Woytowich 1986).As a result, 1983 mean daily sedimentconcentrations during the first 2 days ofmelt were higher than those observed fromsimilar crops during the first 2 days of meltin 1982. Meltwater, from the first 2 days ofmelt in 1983, infiltrated and then frozewhen temperatures dropped. The resultingfrozen soil mass had a low erodibility.Mean daily sediment concentrations overthe remainder of the 1983 melt period weremuch lower than those observed during1982. Total 1983 spring sediment yieldfrom each plot were 12-29% of thoseobserved from comparable vegetativecovers in 1982.

Previous researchers (Zingg 1940;Meyer and Monke 1965) found that sediment yield was dependent on slope length.The following equation, modified from

CANADIAN AGRICULTURAL ENGINEERING, VOL. 29, NO. 1, WINTER, 1987

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Figure 4. Top, particle sizedistribution: surface soil. Middle, particle sizedistribution: springerosion sediments. Bottom, particle size distribution: summer erosion sediments.

CANADIAN AGRICULTURAL ENGINEERING, VOL. 29, NO. 1, WINTER, 1987

Wischmeier and Smith (1978), was used toestimate sediment yields from differentslope lengths:

sl = ml- ?v<m + » (l)

where SL = the estimated yield fromslope (length K),ML = the measured sediment yield from slope (length L),N = thenumber of length intervals (K/L),m = theslope exponent of the universal soil lossequation (m = 0.5 for the study site havinga 5% slope (Wischmeier and Smith 1978)).

The research plots were 75 m in length;however, slope lengths up to 400 m aretypical and lengths of 1.5 km not uncommon in the Peace River region of Alberta.Table I contains extrapolations of the 1982and 1983 measured sediment yields to different slope lengths. The 22.1-m slopelength corresponds to the standardWischmeier erosion plot. As the projections in Table I indicate, significantamounts of soil may be translocated fromthese moderate to long slope lengths.

CONCLUSIONS

Sediment yields were highest from thefallow plot and lowest from the fescue plotin both study years. Sediment yields weremuch lower in 1983 than in 1982. This

resulted from 2 days of melt followed by afreezing of the wetted soil surface in 1983.

The amounts of sediment eroded

annually are small compared to generallyaccepted tolerable soil losses. However,several factors must be considered before

one concludes that sediment yield duringspringmelt in the Peace River region wasnegligible. Existing tolerable soil lossguidelines have been established on thebasis of research undertaken in the United

States. The shallow surface horizons and

long periods of time required for soildevelopment in the Peace River regionwould indicate that U.S. guidelines probably do not apply. Tolerable soil lossesmust be established for this region.

The validity of extrapolation of resultsreported here is always difficult to assess.Attempts were made to select a site representative of a large area; however, differences in the timing of melt within theregion were observed in both years.

Problems extrapolating data from theresearch plots to larger fields were believedto be minimal because of the large plot sizeused and plot placement within an agricultural field. The plots were not replicatedand thus no statistical significance wasattached to the results; however, the relative ranking of plots with respect to sediment yield and runoff is believed to bevalid.

TABLE I. SPRINGMELT SEDIMENT YIELDS (t/ha) EXTRAPOLATED TODIFFERENT SLOPE LENGTHS

Slope length (m)

Crop 22.1 75t 525 750 1500

1982

1983

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BarleyFescue

Fallow

BarleyCanola

Fescue

0.32

0.06

0.04

0.04

0.02

0.01

0.01

2.03

0.39

0.26

0.25

0.11

0.08

0.06

37.54

7.24

4.82

4.58

2.11

1.43

1.06

64.10

12.37

8.22

7.81

3.61

2.44

1.80

181.30

34.97

23.26

22.09

10.20

6.89

5.10

tSediment yields measured from soil erosionresearch plots.

The short length of the study is alsorecognized. A longer study period isrequired before the representativeness ofthe results reported here can be determined.Nonetheless,thisstudysupplie1ter-mined. Nonetheless, this study suppliedmuch needed preliminary data.

ACKNOWLEDGMENTSThe authorsgratefully acknowledgefunding

received from Farming for the Future.

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watererosion in the Peace. Sci. Agr. XIX(5):241-248.

ANDERSON, C. H. and F. BISAL. 1969.Snow cover effect on the erodible soil frac

tion. Can. J. Soil Sci. 49: 287-297.

BENEDICT, B. A. and B. A. CHRISTIENSEN.1972. Hydrodynamic lift on a stream bed.Pages 5-1 to 5-17 in H. W. Shen, ed, Sedi

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BRYAN, R. B. 1976. Consideration on soilerodibility indices and sheetwash. Catena 3:99-111.

CHANASYK, D. S. and C. P. WOYTOWICH.1983. Soil erosion in the Peace River

Region of Alberta. PNR 83-201. Presentedat 1983PNR-ASAE Annual Meeting. 17pp.

CHANASYK, D. S. and C. P. WOYTOWICH.1986. Snowmelt runoff from agriculturalland in the Peace River region. Can. Agric.Eng. 28:7-13.

FORMANEK, G. E., D. K. McCOOL, andR. I. PAPENDICK. 1983. Effect of freeze-

thaw cycles on erosion in the Palouse. ASAEPaper 83-2069. Presented at 1983 SummerMeeting. Montana State University,Bozeman. Montana.

FOSTER, G. R. and L. D. MEYER. 1972.Transport ofparticles by shallow flow. Trans.ASAE (Am. Soc. Agric. Eng.) 15:99-102.

FOSTER, G. R., W. R. OSTERKAMP, L. J.

LANE, and D. W. HUNT. 1982. Effect ofdischarge rate on rill erosion. ASAE Paper82-2572. Presented at 1982Winter Meeting.Chicago. 111.

KETCHESON, J. W. 1977. Conservationtillage in eastern Canada. J. Soil Water Con-serv. 32: 57-60.

KOWOBARI, T. S., C. E. RICE, and J. E.GARTON. 1972. Effect of roughness elements on hydraulic roughness for overlandflow. Trans. ASAE (Am. Soc. Agric. Eng.)15: 979-984.

McKEAGUE, J. A. 1978. Manual on soilsampling and methods of analysis. 2nd ed.Can. Soc. Soil Sci. Subcommittee of Soil

Survey Committee on Methods of Analysis.212pp.

MEYER, L. D. and E. J. MONKE. 1965.Mechanics of erosion by rainfall and overland flow. Trans. ASAE (Am Soc. Agric.Eng.) 8: 572-577.

VAN VLIET, L. J. P., G. J. WALL, and W. T.DICKINSON. 1976. Effects of agricultural land use on potential sheet erosionlosses in southern Ontario. Can. J. Soil Sci.

56: 443-451.

VAN VLIET, L. J. P. and G. J. WALL. 1981.Soil erosion losses from winter runoff in

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451-454.

WISCHMEIER, W. H. and D. D. SMITH.1978. Predicting rainfall erosion losses — Aguide to conservation planning. USDAAgric. Handbook No. 537. pp. 12-15.

YALIN, M. S. 1963. An expression for bed-load transport. Proc. ASCE (HY3) 89:221-250.

ZINGG, R.W. 1940. Degree and length ofland slope as it affects soil loss in runoff.Agric. Eng. 21: 59-64.

CANADIAN AGRICULTURAL ENGINEERING, VOL. 29, NO. 1, WINTER, 1987