PROGRESS IN EROSION AND SEDIMENTATION IN LATIN AMERICA

Hydrosedimentology of nested subtropical watersheds with nativeand eucalyptus forests

Miriam Fernanda Rodrigues & José Miguel Reichert & Jean Paolo Gomes Minella &

Leandro Dalbianco & Rodrigo Luiz Ludwig & Rafael Ramon &

Lilian Alessandra Rodrigues & Norton Borges Júnior

Received: 16 February 2013 /Accepted: 3 March 2014 /Published online: 29 April 2014# Springer-Verlag Berlin Heidelberg 2014

AbstractPurpose Information on the effects of eucalyptus forests onhydrosedimentological processes is scarce, particularly at thecatchment scale. Monitoring and mathematical modeling areefficient scientific tools used to address the lack of informationfor natural resource management and the representation andprediction of those processes. This study evaluates the effectsof eucalyptus cultivation on hydrosedimentological processesin watersheds and to use the Limburg soil erosion model(LISEM) to represent and predict hydrological processes.Material and methods The study was conducted in two for-ested watersheds: the main watershed (94.46 ha) and a nestedsub-watershed (38.86 ha), both cultivated with eucalyptus andresidual riparian native forest, located in southern Brazil.Hydrosedimentalogical monitoring was conducted from 16thFebruary 2011 to 31st December 2012, and LISEM modelcalibrations were performed on the bases of six storms events.Results and discussion The sediment yield for 2011 was 41.6Mg km−2 and 38.5 Mg km−2 for the watershed and sub-watershed, respectively. An extreme event in 2012 providedgreater sediment yield for the sub-watershed (99.8 Mg km−2)than that for the watershed (51.7 Mg km−2). Rainfall eventswith a greater maximum intensity generated rapid dischargeand suspended sediment concentration responses in the sub-watershed due to the smaller drainage area and steeper land-scape. In the mainwatershed, the accumulation of flood waves

occurred for most events, with less steep hydrographs, and alater occurrence of the discharge peak after that of the sub-watershed. The LISEM adequately reproduced the peak dis-charge and runoff for the calibrated events; however, the peaktime and the shape of the hydrograph were not adequatelyrepresented.Conclusions The hydrosedimentological patterns of the wa-tershed and sub-watershed, both cultivated with eucalyptus,was characterized by sedimentographs preceding hydrographsduring rainfall–runoff events where scale effects occur, withmaximum discharge and specific sediment yield greater in thewatershed than that in the sub-watershed. Empirical modelsbased on hydrologic variables may be used for estimating thesuspended sediment concentration and sediment yield.Therefore, LISEM may be used for the prediction of hydro-logical variables in these forested watersheds.

Keywords LISEM . Runoff . Scale effect . Sediment yield

1 Introduction

Studies on the establishment of environmental quality stan-dards and impact assessment that have the watershed as theplanning unit have often been required by private and govern-ment agencies. However, few studies have provided informa-tion on the effects of forests in relation to erosion and sedimentyield at the watershed scale in tropical and subtropical areassuch as Brazil (Vital et al. 1999; Ranzini and Lima 2002;Kobiyama et al. 2004). In addition, there are uncertaintiesabout the effectiveness of forest production in relation toerosion control, either due to the kind of forest cultivated orthe coverage provided by the canopies (Porto et al. 2009).

The forest canopy provides protection for the soil surface,but eucalyptus species provide less soil coverage due to theless dense canopy (Porto et al. 2009). In addition,

Responsible editor: Cristiano Poleto

M. F. Rodrigues (*) : J. M. Reichert : J. P. G. Minella :L. Dalbianco : R. L. Ludwig :R. Ramon : L. A. RodriguesSoils Department, Federal University of Santa Maria, AvenidaRoraima, 1000, Bairro Camobi, Santa Maria, RS 97105-900, Brazile-mail: miriamf_rodrigues@yahoo.com.br

N. Borges JúniorCMPC Celulose Riograndense Company, Rua São Geraldo, 1680,Guaíba, RS 92500-000, Brazil

J Soils Sediments (2014) 14:1311–1324DOI 10.1007/s11368-014-0885-5

management operations, harvesting, construction, and main-tenance of roads increase susceptibility to erosion in planta-tions of such forest species (Schoenholtz et al. 2000; Sheridanet al. 2006; Ferreira et al. 2008; Porto et al. 2009; Oliveira2011). Better knowledge of hydrologic and sedimentologicdynamics in areas of eucalyptus forests is an important aspectwhenmaking decisions regarding the appropriate land use andmanagement of natural resources, which aim to increaseenvironmental productivity and sustainability. Thus, we high-light the relationship between erosion processes on the slopesand sediment yield. Also, the identification of the sources ofsediment and the magnitude of sediment yield during rainfall–runoff events are of great importance.

Little information is available on the relationships betweenthe hydrological behavior of forested watersheds at differentscales. Detailed description and characterization ofhydrosedimentological processes at different scales are fun-damental for using mathematical models, given that modelinghas shown great potential as a tool for describing complexnatural processes, such as those that occur in watersheds.However, the dynamics at which complex processes andsediment transfer occur at different scales is still largely un-known (Duvert et al. 2012). The configuration of the hydro-logic response changes with the spatial scale, with heteroge-neities being greater at larger scales associated with an in-crease in watershed size (Singh and Woolhiser 2002).Therefore, few studies evaluate the scale effect on erosionand sediment yield, particularly in forested watersheds.

Modeling studies in areas occupied by forests are importantbecause the vast majority of models used to predict erosionand sediment yield were developed for agricultural rather thanforested areas. In this context, the objectives of this study wereto (1) evaluate the effects of eucalyptus cultivation onhydrosedimentological processes in a watershed (main and asub-watershed), (2) modify empirical models based on hydro-logical variables to estimate suspended sediment concentra-tions and sediment yields, and (3) verify the potential of aphysical-based model on the representation of hydrologicalprocesses at the watershed scale.

2 Materials and methods

2.1 Area of study

The study area, known as the Terra Dura Forestry FarmingWatershed, includes of two watersheds—the main “water-shed” (94.46 ha) and the nested “sub-watershed”(38.86 ha)—both under forest cover and located in the JacuíRiver Watershed, located in the physiographic region of thecentral depression of the Rio Grande do Sul state in southernBrazil (Fig. 1). The climate is classified by the Köppen cli-matic classification as Cfa—humid subtropical with hot

summers (Moreno 1961). The average annual rainfall is1,440 mm, with a monthly average of 120 mm, and themonths with the most rainfall, both in rainfall volume andduration and number of rainy days, occurs from June toAugust (Bergamaschi et al. 2003). The average long-termerosivity for the region is 5,813 MJ ha−1 mm−1.

The main soil classes are Ultisols, Inceptisols, andPlanosols (Costa et al. 2009). The texture gradient is greaterin Ultisols and Planosols (Oliveira 2011), where the sandytexture in the surface horizons (A+E) provides rapid waterinfiltration, which decreases in the B horizon due to its lowerpermeability. Locally, subsurface discharge causes the remov-al of particles from the soil, forming channels (i.e., pipes)which move in the opposite direction to the flow of waterand carry smaller particles. The rate of water infiltration intothe soil, in general, decreases from higher to lower elevations,near the drainage network (Table 1). This trend showed thebehavior of watershed in relation to water infiltration andsurface runoff and thus allows the conclusion that runoffgeneration leads to predominant runoff in the watershed andis based on the moisture variation of variable affluence areas.

The predominant land use consists of a forest pro-duction system, with stands of young and old eucalyp-tus trees (planted in 1989, 1990, 2001, 2004, 2005,2007, and 2010), permanent preservation areas (PPA,i.e., riparian native vegetation), and unpaved roads.Soil cover in the young stands is provided by speciesof grasses and legumes that grow between forest rows,that in the old stands is provided by developed under-growth or by a layer of litter, which increases soilsurface protection against the effects of soil erosionagents.

The watershed and sub-watershed are characterized bythird and second order drainage networks (Strahler 1957),respectively. The second and third order channels have de-posits of coarse sediments such as sand and gravel. Themargins of these channels are composed of sandy materialand are highly susceptible to rainfall erosion.

2.2 Hydrosedimentological monitoring

Hydrosedimentalogical monitoring was conducted from 16thFebruary 2011 to 31st December 2012 in automated monitor-ing sections, instrumented with water level (limnigraphs),turbidity (turbidity meters), and rainfall (rain gauges) sensors.These sensors were installed near the triangular weirs installedat the outlet of the watershed. The dataloggers were pro-grammed to record data at fixed 10-min intervals.

The main timeframe of analysis was the entire rainfallevent because the effect of a rainfall event on discharge andsuspended sediment concentration is faster in small water-sheds where hydrographs and sedimentographs, generally, last

1312 J Soils Sediments (2014) 14:1311–1324

only a few hours, and daily information does not represent theprocesses occurring in such watersheds.

2.2.1 Quantification of total solid discharge (suspendedand bed load)

The sampling of the suspended sediment concentration wasperformed manually during rainfall–runoff–sediment trans-port events by using a USDH-48 sampler, to obtain time seriesdata of sediment concentration. Due to the need for continu-ous data acquisition, turbidity measurements were used forestimating the suspended sediment concentration, based on

the relationship between the suspended sediment concentra-tion obtained either during flood events or from sedimentconcentrations prepared in the laboratory, with fine sedimentscollected from the drainage network.

The bed load was monitored by using a BLH-84 sampler.Direct measurements of bottom discharge were conductedacross the width of the section at five equidistant points, inwhich subsamples were collected to form a sample. Aftercollection, samples were taken to the laboratory, where bedload sediment concentration was quantified by drying andweighing. In addition to the direct method using samplers, abathymetric survey was also conducted at the beginning andend of the monitoring period to quantify the volume of sedi-ment retained by the weir. Triangular weir can accumulateflood waves and reduce their ability to transport coarser par-ticles, which are usually deposited upstream of the weir.

2.2.2 Hydrosedimentological behavior of the watershed

The hydrosedimentological behavior of the watershed wasevaluated by analyzing the shape of the hydrographs andsedimentographs and the relationship between discharge andsuspended sediment concentration. The classification andquantification of hysteresis that occur between discharge and

Fig. 1 Location and relief of the Terra Dura forested watershed (1) and sub-watershed (2) in Eldorado do Sul-RS, southern Brazil

Table 1 Steady-state water infiltration rate, determined by using concen-tric rings, for three toposequences (Topo 1, 2, and 3) for the study forestedwatershed in southern Brazil

Position on landscape Water infiltration rate (mm h−1)

Topo 1 Topo 2 Topo 3

Summit 574.9 742.4 46.4

Backslope – 483.0 82.3

Footslope 264.5 170.1 99.6

Toeslope 10.3 70.7 15.5

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suspended sediment concentration (Williams 1989) duringprecipitation events and the analysis of the factors that controlthe hysteresis and hysteresis rates were conducted using themethodology described by Seeger et al. (2004). Quantitativeanalyzes of the hysteresis behavior was evaluated by using theindex of hysteresis (HI), according to the methodology de-scribed by Lawler et al. (2006).

2.2.3 Estimation of sediment yield

The total sediment yield was determined from the integratedsolid discharge obtained during the automatic monitoringperiod. Sediment yield at the outlet of a watershed representsa small portion of the total sediment produced in the watershedas a result of all operative erosion processes. The ratio ofsediment yield and gross erosion is defined as the sedimentdelivery ratio (SDR). In this study, although sediment yieldwas monitored, but the information on gross erosion ratesoccurring for each land use in the watershed was obtainedfrom Oliveira (2011); 0.15 Mg ha−1 for eucalypt plantation,0.03 Mg ha−1 for native forest, and 4.48 Mg ha−1 for roads(considered as soil loss values obtained from plots of baresoil).

2.3 Hydrologic modeling

The hydrological processes in the watersheds (main and sub)were modeled by using the Limburg soil erosion model(LISEM) (De Roo and Jetten 1999) (Fig. 2). LISEM is aphysically based and distributed model, which simulates thebreakdown, transport, and deposition of sediment in riverchannels and hillslopes, during and immediately following asingle event, and these simulations are incorporated into ageographic information system (GIS) (De Roo et al. 1996a).

The basic processes incorporated by LISEM are precipita-tion, interception, surface storage in micro-depressions, infil-tration, and water flux into the soil, surficial runoff, channelrunoff, soil detachment by raindrop impact and leaf-waterdroplets, transport ability and soil detachment by surfacerunoff, and sedimentation (Jetten 2002). To simulate in adistributed manner, LISEM divides the area of the studywatershed into a grid of cells. The spatial variability in thewatershed is also represented by the characteristics of eachcell. For each grid cell, rainfall and interception are calculatedafter infiltration, and surface storage are subtracted to obtainthe net runoff. Subsequently, soil erosion and sediment depo-sition are calculate by using the principle of energy flow, andthe fluxes are directed to the stream gauge by using kinematicwave method (Jetten 2002). In the model, the vertical move-ment of water is simulated from choice of different infiltrationmodels that adjust to the soil conditions and climate; surfacewater storage uses the concept of random roughness; detach-ment equations and sediment transport use the concept of

stream power; and surface runoff is simulated by using kine-matic wave routing along with the Manning equation (Jetten2002). LISEM provides, as output data, a summary of themain variables of the simulated event and the hydrograph, thesedimentograph, and the spatial variability of all variables forany time of the event in the form of maps.

This model was used because it is a distributed model,which facilitates its implementation in watersheds with areasbetween 10 ha and 300 ha. Because the model generatesinformation from the hydrograph, the sedimentograph, andthe spatial distribution of the variables involved in the hydro-logical and sedimentological processes, this information canbe used to assess the effects of land use and management onhydrosedimentological processes. Furthermore, the modelwas calibrated and used with satisfactory results in studiesconducted in intensely degraded rural watersheds in southernBrazil (Moro et al. 2008). However information regarding theuse of LISEM in forested watersheds are rare.

LISEM estimates runoff based on the concept of Horton(i.e., infiltration excess) and does not incorporate Dunne-type(i.e. saturation-excess) runoff; this could be a limitation insome conditions. The Green and Ampt infiltration modelwas used for a 100-cm deep soil layer.

The values of maximum discharge, time to peak, andvolume of runoff obtained by monitoring were the variablesthat could be adjusted in the calibration process. BecauseLISEM simulates total runoff rather than total discharge, theconstant slope method was used to separate discharge andrunoff components from the total.

2.3.1 LISEM calibration

The events on 22nd April, 20th June, 14th July, 20th July, 1stAugust, and 7th August 2011 presented greater magnitudeduring the monitoring period and were used for LISEM cali-bration. For these events, the maximum intensity of rainfallwas greater than the saturated hydraulic conductivity thusgenerating runoff (Gomes 2008). The calibration procedurewas performed by manual optimization of the sensitive pa-rameters of the model by comparing the observed and calcu-lated values of the hydrological variables. The parameterscharacterizing the watershed (Table 2) were used for genera-tion of cartographic information with spatial discretization of5×5 m and 20×20 m. The input parameters of LISEM wereobtained from field and laboratory data as well as data fromthe literature. The saturated hydraulic conductivity and totalporosity had higher values as a result of higher gravel andcoarse sand content in the surface soil layer. The tension of thewetting front was estimated by using the equation proposed byRawls et al. (1983), and the initial moisture content wasestimated at 20 % of the total porosity according to the periodwithout rain before the event. Manning’s n coefficient wasobtained according to Haan et al. (1993), which is higher in

1314 J Soils Sediments (2014) 14:1311–1324

humid areas due to surface roughness and the abundance oforganic matter and leaf residues on the soil surface.

The temporal resolution of simulations was 90 s. Duringthe calibration procedures, changes in saturated hydraulicconductivity, surface roughness, Manning's n coefficient,and antecedent moisture were performed considering the mostsensitive parameters of the model (De Roo et al. 1996a,1996b). For procedure, two modifications were made; we

used the maximum allowable random roughness (10 cm)and multiplied a correction factor (20) to Manning’s n coeffi-cient for each land use, to reduce the propagation velocity ofrunoff. Because Manning’s n coefficient was initially deter-mined for canals and waterways and assumed low valuesrelative to the value observed for rough surfaces, such as forestplantations, with or without soil tillage, a correction factor wasapplied for the entire area of the watershed with the aim to

Fig. 2 Flowchart of the Limburg Soil Erosion Model (LISEM) (adaptedfrom Jetten 2002). Where Ksat is saturated hydraulic conductivity, θ issoil moisture, θi is initial moisture, S is slope, RR is random roughness, nis Manning’s n coefficient, Per is ground cover with vegetation, Perc is

ground cover with stones,H is height of vegetation, LAI is leaf area index,Smax is maximum storage capacity of the canopy, DD is flow direction,As is aggregate stability, Ke is kinetic energy, h is water depth, Φ isparticle size, and Coh is cohesion of soil moisture

Table 2 LISEM model numeric input parameters for different land uses for the study forested watershed in southern Brazil

Use Ksat(mm h−1)

θs(cm3 cm−3)

Ψ(mm)

θi(cm3 cm−3)

RR(cm)

n-

Per(%)

H(m)

LAI(m2 m−2)

Perc(%)

Smax(mm)

Old eucalyptus 1990.16 0.5 15 0.11 4 0.10 1 30 2.9 0 2.3

Young eucalyptus 618.67 0.5 15 0.09 4 0.10 1 2 2.5 0 2.3

Riparian native forest 223.11 0.6 15 0.11 4 0.15 1 25 5.8 0 3.6

Wetlands 223.11 0.6 15 0.11 6 0.20 1 25 5.8 0 3.6

Depressions 223.11 0.6 15 0.11 6 0.20 1 25 5.8 0 3.6

Ksat saturated hydraulic conductivity, θs total porosity, Ψ tension at the wetting front, θi initial moisture, RR random roughness, n Manning’s ncoefficient, Per ground cover with vegetation, H height of vegetation, LAI leaf area index, Perc ground cover with stones, Smax maximum storagecapacity of the canopy

J Soils Sediments (2014) 14:1311–1324 1315

reduce runoff velocity as well as maintain a standard correc-tion of error.

To evaluate the efficiency of the model in estimating run-off, peak discharge, and time to peak, the BIAS statistical test(Error) was calculated, which represents the difference inpercentage between the observed and simulated values. Toanalyze the consistency of results provided by the modelcompared to the format of the hydrographs, the Nash-Sutcliffe coefficient of efficiency (COE) (Nash and Sutcliffe1970) was used in the calibration phase.

3 Results and discussion

3.1 Hydrosedimentological events

Rainfall events increases in discharge and concentration ofsuspended sediments reflect the hydrosedimentological behaviorof forested watersheds, as a response to the rainfall and the soil'sability to allow infiltration and water storage. Thus, of the 102rainfall–runoff–sediment transport events that occured during themonitoring period, 27 were used for hydrosedimentologicalanalysis, 8 were used for hysteresis analysis (Table 3), and 6were used for LISEM calibration (Table 4).

The runoff depth was greater for the sub-watershed thanthat of the watershed, it is directly related to the physiographiccharacteristics and the area of contribution of the watershed.Average, minimum, and maximum runoff depths were 1.03,0.01, and 11.55 mm, respectively, for the events in the water-shed and 1.32, 0.02, and 9.96 mm, respectively, for thoseoccurring in the sub-watershed during the monitoring period.These results may be attributed to the steeper relief and lowerwater infiltration of the sub-watershed in relation to thewatershed.

Runoff depth is largely related to the intensity of the rainand not just to the total volume precipitated and drained. Thisrelationship can be clearly observed for the 14th July 2011event (Table 3), which had the greatest total volume of rainfall,but did not result in high runoff depth for both watersheds, dueto its longer duration associated with a low intensity. Ingeneral, the runoff coefficients of the watershed and sub-watershed increased with the intensity of precipitation, andwatersheds with a greater drainage area generally had thehighest runoff coefficients for most events (see Table 3).

The maximum peak discharge for events in the watershedwas 97.86 l s−1, which was higher than the maximum dis-charge rate of the sub-watershed which was 65.60 l s−1. Theminimum peak discharge had little difference between thewatershed (1.54 l s−1) and sub-watershed (1.13 l s−1). Theseresults indicate that the discharge response to a rainfall event ismore pronounced for events of greater magnitude.

The smaller drainage area and steeper relief of the sub-watershed, associated with the maximum intensity of rainfall,

are factors that generate rapid discharge responses. Thus, whenthere was a temporal variability in rainfall intensity, the differ-ent discharge arrival times at the channel generated compoundhydrographs (Fig. 3d). The range between the flow rates wasless pronounced in events with lower rainfall intensity. Thewatershed hydrographs, in general, had greater dischargepeaks, with smooth increases and decreases and the dischargepeaks occurred between 3 and 6 h after the maximum dis-charge at the sub-watershed, which shows the accumulation ofthe flood wave (Fig. 3b, c, d). This accumulation is attributableto the greater distance traveled by the discharge until reachingthe watershed outlet and to the blockade effect by the weirinstalled on site, which helps to accumulate the discharge flow.

The greatest values of the suspended sediment concentra-tion were recorded in rainfall events of greater intensity andvolume. The results obtained in this study corroborate withthose reported by Porto et al. (2009), who reported that thegreatest concentrations of sediment transported in suspensionoccurred for events of high magnitude. Soler et al. (2008)indicated that suspended sediment concentration is directlyrelated to the intensity of rainfall and the maximum dischargefor the lower watershed in two paired small watersheds(0.56 km2 and 1.32 km2). Such behavior is expected forwatersheds with smaller drainage areas (Williams 1989).

Maximum suspended sediment concentration, in general,occurs before the maximum water discharge rate and wasgreater for the sub-watershed compared to the watershed.Suspended sediment concentration is not solely dependenton the amount of sediment deposited in the channel andmobilized into the river bed, it is also dependent on thecontribution of water draining close the watercourse or thesubsurface runoff, which is characterized by a very shortresidence time. For the watershed, it is possible to identify adecrease in suspended sediment concentration due to exhaus-tion in the supply of sediments associated with the increase inwater volume provided by a more leveled relief in addition tothe larger number of channels in the drainage network, and, asobserved by Andermann et al. (2012), a larger contribution ofgroundwater. Even if the suspended sediment concentrationwas greater for the sub-watershed than for the watershed, thesediment yield of rainfall–runoff–sediment transport eventswas greater for the watershed (Table 3) due to greater dis-charge rates observed for most of the events; Soler et al.(2008) observed a similar situation.

An example of the importance of initial soil moisture on theformation of runoff depth is given by the 7th August 2011event. A total rain depth of 107.8 mm with a maximumintensity of 16.2 mm h−1 were not the greatest values mea-sured, but was responsible for the largest maximum dischargein the watershed (97.9 l s−1) because the soil rapidly saturateddue to the high initial soil moisture.

The 14th April 2011 rainfall event showed behavior differ-ent from the other events, such that the maximum suspended

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Table 3 Hydrosedimentologic variables and hydrograph components of events during the monitoring period for the forested watershed and sub-watershed in southern Brazil

Date (m/d/y) Qd

(mm)Qp

(L s−1)Precipitation(mm)

IM 1 h(mm h−1)

SSCp

(mg L−1)SY(Mg km−2)

IH Rotation

Watershed

02/23/11 0.01 11.8 9.7 6.7 104.4 0.04 – –

02/24/11 0.12 11.1 7.4 7.4 130.5 0.07 – –

03/10/11 0.04 4.8 18.3 6.9 190.1 0.04 – –

03/27/11 0.05 6.7 34.1 7.9 186.4 0.07 – –

04/14/11 0.28 18.7 66.5 11.7 301.9 0.21 −2.32 CC

04/22/11 0.86 43.2 96.4 39.6 1054.9 2.15 0.2 C

06/07/11 0.02 1.5 28.9 5.9 145.4 0.02 – –

06/20/11 0.75 18.7 67.2 17.9 607.6 0.66 0.34 C

07/14/11 3.48 55.3 139.1 20.0 861.1 4.29 0.2 C

07/17/11 0.31 12.6 25.1 3.8 559.2 1.10 – –

07/20/11 3.27 55.3 66.5 16.5 674.7 5.08 0.08 C

07/28/11 0.51 22.9 54.1 7.9 637.4 2.48 – –

08/01/11 2.53 49.9 65.8 12.1 667.3 4.20 0.13 C

08/07/11 11.55 97.9 107.8 16.2 857.4 12.54 0.38 C

03/14/12 0.27 10.2 58.2 7.2 130.5 0.06 – –

05/29/12 0.28 14.7 36.2 12.7 458.5 0.07 – –

07/28/12 0.67 69.1 60.1 22.6 196.1 0.19 – –

07/31/12 1.32 47.8 53.0 10.7 177.4 0.34 – –

08/13/12 0.05 2.7 20.4 6.4 111.8 0.03 – –

09/09/12 0.16 9.0 49.9 6.2 130.5 0.06 – –

09/16/12 36.68 665.82 266.48 17.1 1096.32 43.28 – –

10/01/12 0.07 4.4 26.1 7.1 130.6 0.05 – –

10/02/12 0.13 10.1 28.5 5.5 156.0 0.09 – –

10/07/12 0.08 6.5 16.9 11.4 134.2 0.03 – –

10/09/12 0.15 8.1 27.1 5.9 193.8 0.12 – –

12/11/12 0.03 2.8 20.2 13.5 89.5 0.01 – –

12/21/12 0.14 6.7 50.6 11.4 115.6 0.05 – –

12/26/12 0.72 23.0 93.3 5.2 152.8 0.41 – –

Sub-watershed

02/23/11 0.02 1.3 9.7 6.7 234.8 0.02 – –

02/24/11 0.03 2.1 7.4 7.4 334.8 0.03 – –

03/10/11 0.03 2.6 18.3 6.9 313.1 0.03 – –

03/27/11 0.11 2.1 34.1 7.9 293.6 0.07 – –

04/14/11 0.15 4.8 66.5 11.7 587.1 0.18 −0.86 CC

04/22/11 1.91 65.6 96.4 39.6 2031.2 3.73 0.16 C

06/07/11 0.04 1.1 28.9 5.9 241.0 0.02 – –

06/20/11 0.99 20.8 67.2 17.9 947.6 1.57 −0.02 C

07/14/11 5.37 49.4 139.1 20.0 1182.5 7.42 0.32 C

07/17/11 0.43 6.3 25.1 3.8 670.6 1.50 – –

07/20/11 3.61 37.8 66.5 16.5 659.2 6.50 – –

07/28/11 1.50 11.8 54.1 7.9 657.2 3.48 – –

08/01/11 3.47 26.4 65.8 12.1 1034.8 2.38 – –

08/07/11 9.96 49.0 107.8 16.2 200.9 2.41 – –

03/14/12 0.16 5.2 58.2 7.2 – – – –

05/29/12 0.17 8.3 36.2 12.7 226.6 0.04 – –

07/28/12 0.49 29.7 60.1 22.6 – – – –

J Soils Sediments (2014) 14:1311–1324 1317

sediment concentration occurred after the maximum discharge(Fig. 3a) for both watersheds. The increase in suspendedsediment concentration occurred more smoothly for the wa-tershed, which after reaching its maximum value remainednearly constant, even with the recession of the hydrograph.For the sub-watershed, suspended sediment concentrationhowed a rapid rise with an increase in discharge and, unlikethe watershed, it had a steep recession.

The discharge and suspended sediment concentrationdynamics during these events generated hydrographs andsedimentographs that were rarely synchronized in time,highlighting the hysteresis effect. Both watersheds showedsimilar hydrosedimentological behavior, with sedimentographpeaks occurring prior to the hydrograph peaks (Fig. 3), indepen-dent of the characteristics of the channel and watershed area.Similarly results were observed by Andermann et al. (2012).

3.2 Hysteresis

The predominant direction of the hysteresis loops was clock-wise (see Fig. 4b, c, d). It has been suggested that the hyster-esis effect and, in particular, its shape are important indicatorsof various discharge processes, location of sediment sources,

and sediment transport conditions (Williams 1989; Seegeret al. 2004; Eder et al. 2010). An important sediment sourcefor small watersheds is sediment deposited into the channel. Inthe event of a subsequent flood wave, this material will affectthe hysteresis loop, or the sediments may come from theerosion of the channel margins. Thus, for small watersheds,rapidly rainfall mobilizes and transports sediment, generatingsedimentographs that precede the hydrographs. In the presentstudy, it was observed that the absence of a large supply ofsediment with the evolution of the flood wave was the maincause for the occurrence of the clockwise hysteresis for smallwatersheds, which confirms the report of Williams (1989).The maximum suspended sediment concentration precedingthe maximum discharge is possibly related to the geomorpho-logical characteristics of the watershed and the spatial config-uration of the landscape and channel, which the latter isconsidered a major potential source of sediments.

The 14th April 2011 event had counterclockwise hysteresisloops in the watershed and sub-watershed (Fig. 4a), with themaximum suspended sediment concentration occurring after themaximum discharge. Similar results were found by Soler et al.(2008), who observed that the hydrological behavior of twosmall watersheds was dependent on antecedent moisture and

Table 3 (continued)

Date (m/d/y) Qd

(mm)Qp

(L s−1)Precipitation(mm)

IM 1 h(mm h−1)

SSCp

(mg L−1)SY(Mg km−2)

IH Rotation

07/31/12 0.52 9.9 53.0 10.7 – – – –

08/13/12 0.04 1.3 20.4 6.4 723.1 0.06 – –

09/09/12 0.09 2.1 49.9 6.2 332.7 0.06 – –

09/16/12 22.20 215.15 266.48 17.1 3389.34 34.93 – –

10/01/12 0.05 1.2 26.1 7.1 – – – –

10/02/12 0.08 2.8 28.5 5.5 – – – –

10/07/12 0.05 2.6 16.9 11.4 592.3 0.06 – –

10/09/12 0.07 1.9 27.1 5.9 973.4 2.34 – –

12/11/12 – – – – – – – –

12/21/12 – – – – – – – –

12/26/12 3.55 15.9 93.3 5.2 350.2 1.76 – –

Qd runoff depth, Qp maximum discharge, Precipitation total precipitation, IM 1 h maximum intensity in an hour, SSCp maximum suspended sedimentconcentration, SY sediment yield, IH hysteresis index, CC counterclockwise, C clockwise

Table 4 Maximum discharge(Qp) and runoff volume for thecalibrated events occurring in theforest watershed in southernBrazil

Date (m/d/y) Qp (L s−1) Runoff volume (m3)

Observed Simulated Error (%) Observed Simulated Error (%)

04/22/11 43.16 43.50 0.78 811.20 881.00 8.60

06/20/11 18.71 18.10 −3.25 705.99 719.60 1.93

07/14/11 55.33 69.40 25.43 3,284.17 3,209.10 −2.2907/20/11 55.33 69.60 25.84 3,088.74 2,942.10 −4.7508/01/11 49.90 57.12 14.48 2,387.71 2,296.40 −3.8208/07/11 97.86 180.78 84.73 10,907.10 10,412.20 −4.54

1318 J Soils Sediments (2014) 14:1311–1324

rainfall characteristics and that suspended sediment concentra-tion acquired several forms, presenting clockwise hysteresis forlarge events (heavy rainfall, high runoff depth, and maximumdischarge) and counterclockwise hysteresis for small events.

The hysteresis loops of the sub-watershed were narrowerthan those of the watershed (Fig. 4). Temporal analysis ofdischarge and suspended sediment concentration shows thatthis behavior is due to the small time interval between themaximum discharge and suspended sediment concentration,indicating that the magnitude of the sedimentographs mayincrease with the evolution of the hydrograph for watershedswith small drainage areas.

Most hysteresis loops were not symmetrical (Fig. 4). Thesymmetry of the loop was observed when the hydrograph andsedimentograph presented a similar opening (same width) andpeaks at about the same height, with the symmetry axisoriented at 45° horizontally. Because most hydrographs andsedimentographs presented lagged peaks and branches andascending and descending branches showed different slopes,the loops had an asymmetrical orientation.

The orientation of the hysteresis loops for the watershedand sub-watershed was predominantly horizontal. The mainfactors controlling the direction of the hysteresis loop in thisstudy were the physiographic characteristics of the watershed,particularly the small drainage area, associated with weirs andsteep channels. Among the constraints, were the contributionof subsurface discharge on the slopes, which generatesexfiltration in areas of lower relief and the presence of sedi-ments deposited in the channel, which are transferred to theriver stream at the beginning of the flood wave in subsequentevents, were noted.

Even with a similar patterns in the direction of hysteresisloop, the hysteresis index (HI) ranged from −2.32 to 0.38 and−0.86 to 0.32, with a mean value of −0.14 and −0.10 for thewatershed and sub-watershed, respectively. The total rainfallfor the 14th April and 20th June 2011 events were similar,although the intensity of the first event was lower, resulting ina high HI, both for the watershed and sub-watershed.Moreover, the low antecedent soil moisture, measured severaldays without rainfall prior to the events, results in a greater HI,

Fig. 3 Hytographs (i.e., precipitation), hydrographs (Q=discharge), andsedimentographs (SSC=suspended sediment concentration) of someevents that characterize the hydrosedimentological behavior of the

forested watershed and sub-watershed, in southern Brazil (dates areexpressed as m/d/y and time)

J Soils Sediments (2014) 14:1311–1324 1319

which characterizes the condition of a reduced supply ofsediment on the descending branch of the sedimentograph.

3.3 Scale effect

The scale effect for the hydrological variables monitored inthe watershed and sub-watershed were evident for the specificwater discharge rates and were not very pronounced for sed-iment yield. The range between the average and maximumspecific discharge rates for the watershed was greater than thatobserved for the sub-watershed. During the monitoring peri-od, the average and maximum specific discharge rates were4.67 L s−1 km−2 and 704.87 L s−1 km−2, respectively, for thewatershed. In the sub-watershed, the amplitude between thesevariables was lower due to the smaller contributing area; thevalues were 3.69 L s−1 km−2 and 553.69 L s−1 km−2, respec-tively. This behavior is attributed to watershed scale becausethe smaller size relates to a lower buffer and storage ofrainwater capacity. The soil water storage for the sub-watershed is expected to be lower than that for the watersheddue to its smaller area and steeper relief, which provide less

water infiltration into the soil and greater potential for lateraldischarge.

The specific sediment yield was greater in the watershed inless rainy periods than that in the sub-watershed due to greateroutflow. For the sub-watershed, the specific sediment yieldwas greater in rainy periods, primarily due to the rapid re-sponse to the effects of rainfall. The effect of scale in sedimentproduction during the monitored period was negligible butpresent; the specific sediment yield for the watershed and sub-watershed were 41.6 Mg km−2 and 38.5 Mg km−2 in 2011,respectively. Similar to the results obtained in this study, Soleret al. (2008) observed that the sediment yield small water-sheds, was greater for the watershed with an area of 1.32 km2

and lower for the watershed with an area of 0.56 km2. In theyear 2012, given the occurrence of an extreme event, specificsediment production was 51.7 Mg km−2 and 99.8 Mg km−2

for the watershed and sub-watershed, respectively, whichchanged the default sediment yields.

Because the watershed had a greater water dischargeand a larger drainage area relative to the sub-watershed,as expected, the sediment yield was greater than that

Fig. 4 Hysteresis loops betweendischarge (Q) and suspendedsediment concentration (SSC) forevents in the forested watershedand sub-watershed in southernBrazil (dates are expressed asm/d/y)

1320 J Soils Sediments (2014) 14:1311–1324

observed for the watershed, except for extreme events.The greatest sediment yield for the watershed is due tothe contribution of the nested watersheds. Small water-sheds are contributors of sediment yield to larger wa-tersheds with less steep relief because they also controlerosion processes, production, and transfer of sedimentdownstream (Duvert et al. 2012).

3.4 Empirical models for estimating hydrosedimentologicvariables

To expand the knowledge about the dynamics ofsuspended sediments in small watersheds, a major efforthas been directed to developing sediment transportmodels that are based on physical processes (e.g.,Anderton et al. 2002; Duvert et al. 2010). However,these models require the input of large datasets andvalidation for accurate description of erosion and trans-port processes (De Vente et al. 2011). Moreover, theyrequire intensive, accurate, and continuous monitoring.Thus, empirical relationships based on hydrologic vari-ables may be used as a good prediction of the sedimen-tologic variables. The occurrence of a positive statisticalrelationship between the two sets of variables can beused to understand and predict the suspended sedimentconcentration and sediment yield at the watershed scale(Duvert et al. 2010).

The relationship between the average discharge and dailyaverage solid discharge (Fig. 5a) and events (Fig. 5b) indicat-ed a trend of exponential increase in the concentration ofsuspended sediments with an increase in discharge until itreaches a constant value is reached. This behavior may possi-bly due to exhaustion of the supply of sediment to betransported in suspension; thus, after reaching certainsuspended sediment concentration, even if there is an increasein discharge, the concentration of the suspended sedimenttends to be constant. Duvert et al. (2012) observed an expo-nential increase of the suspended sediment concentration withan increase of the hydrological variables, which is similar tothat observed in the present study.

However, the effects of vegetation cover and the processesof fine sediment storage, and sediment remobilization withinthe channel may generate a variation in results of suspendedsediment concentration and sediment yield. Thus, the predic-tion of hydrosedimentologic variables may have better resultswhen using other hydrologic variables for each watershed.Duvert et al. (2012) conducted a study in watersheds locatedin France, Mexico, and Spain and indicated that the concen-tration of suspended sediments had the best correlation withmaximum, average, and total discharge, respectively. Thisbetter correlation occurred because these variables increaseerosion and the amount of suspended sediment transport, bothon the slopes and within channels. In contrast, Andermann

et al. (2012) evaluated the empirical relationships to estimatesuspended sediment concentration and determined that the useof runoff depth provided better results when compared withtotal discharge. Thus, the use of average discharge of events asan alternative for estimating the average concentration ofsediment is promising as long as a longer period and moreevents are analyzed and the correlation is significant.

The sediment yield was directly related to water dischargeand to the product of water discharge and peak discharge inboth watersheds, for events that occurred during the monitor-ing period, in both (Fig. 5c, d). The high coefficient of deter-mination indicates that the largest sediment transfer occuredduring flood events in the channels. Thus, these variables maybe used to estimate the sediment yield in a small forestedwatershed, as long as most events are analyzed and the corre-lation is significant, which corroborates with Duvert et al.(2012). The empirical models developed by these authors toestimate sediment yield showed better fit when maximumdischarge was used, which differs with the results of empiricalmodels obtained in the present study.

3.5 Hydrologic modeling

The saturated hydraulic conductivity (Ksat) was the only cal-ibration variable that showed smaller values in relation tobaseline values. The change was greater than 99 % of theinitial value. The determination of this parameter was per-formed in a laboratory and does not characterize, with fidelity,the hydraulic conductivity of a given area due to spatialvariability. Thus, generally, the laboratory results are notconsistent with the processes occurring in the field, as evi-denced by the results of the soil water infiltration rate.

The initial moisture and random surface roughnessrepresenting micro-reliefs had the largest variations in themodel calibration. The variation in initial soil moisture wasfrom 127 % to 445 %. The random surface roughness rangedfrom 67 % to 150 %, and a high alteration was necessary toassist in the representation of runoff speed and propagation inaddition to soil water infiltration capacity, according to thespecific watershed.

From LISEM calibration, the peak discharge and totalsurface runoff were simulated satisfactorily, with a low per-centage of resulting errors (Table 4). The peak discharge was,in general, overestimated for the evaluated events, with small-er percentage errors between the observed and simulated peakdischarge for the 22nd April and 20th June 2011 events. Therunoff was generally underestimated for the evaluated events.The percentage errors may be attributed to the effect of floodwave attenuation by the triangular weir situated in the moni-toring section and by the graphical method used for determin-ing the runoff volume. The smaller errors for this variable inrelation to peak discharge are mainly due to the intensity ofrainfall events, where runoff is governed by the characteristics

J Soils Sediments (2014) 14:1311–1324 1321

of the event with less interference from antecedent moistureand saturated hydraulic conductivity (Gomes 2008).

The simulation of hydrographs resulted in anticipation ofpeak time only for the 08/07/11, which provides translation tothe left of the simulated hydrograph in relation to observedone (Fig. 6). The delay peak time observed for other eventsprovided a translation to the right of the simulated hydrographin relation to observed. The peak time observed in monitoringwas lower when compared to the simulated, mainly due to theamortization effect of the flood wave provided by the weir.

The translation of the simulated hydrographs when com-pared to observation a low LISEM performance, when mea-sured by the Nash-Sutcliffe COE, mainly resulting in negativevalues. The average COE value was −1.22, ranging from−0.43 to −2.30; however, for the representation of thehydrograph format to be acceptable, the COE value shouldbe at least equal to 0.36.

Even with the low efficiency of the model inrepresenting the shape of the hydrograph, and hence thesedimentograph, empirical models based on the results

obtained during monitoring showed the potential forpredicting suspended sediment concentration and sedi-ment yields due to correlation coefficients >80 % forevents and >55 % for means of the variables.

4 Conclusions

The hydrosedimentological patterns of watershed and sub-watershed, which are planted with eucalyptus species, is char-acterized by sedimentographs preceding hydrographs duringmost rainfall–runoff–sediment transport event. The maximumdischarge and specific sediment yield were greater for thewatershed relative to the sub-watershed. However, the differ-ence in sediment yield between the watersheds was not sig-nificant, because they are small. In addition, interception bythe canopy of eucalyptus plantations decreased the instanta-neous effect of rainfall, which provided fewer differences insediment yield. The range between the maximum and mini-mum discharges was greater in the sub-watershed. The rapid

Fig. 5 Relationship between (a)the average daily water discharge(Qa) and the daily average soliddischarge (Qssa), (b) the averagedischarge (Qa) and averagesuspended sedimentconcentration per event (SSCa),(c) the sediment yield (SY) withthe runoff (Qd), and (d) thesediment yield (SY) with theproduct of runoff and peakdischarge (Qd versus Qp) perevent, for the forested watershedand sub-watershed in southernBrazil

1322 J Soils Sediments (2014) 14:1311–1324

hydrological response of the sub-watershed to rainfall eventsresulted from its smaller area and steeper relief.

The proposed empirical models based on the results ob-tained during monitoring showed promising results for esti-mating the suspended sediment concentration and sedimentyield of watersheds under eucalyptus plantations with a highcoefficients of determination. Using a physically based model(LISEM) for the calibration of six monitored events enabled

adequate representation of peak discharge and total runoffvolume. This result is important because these variables areof great interest for the management of natural resources, butstill require a further step in validating the calibrated param-eters by using different events from those used for calibration.However, the shape of the hydrograph was not reproducedsatisfactorily, which consequently hindered sedimentologicalsimulation.

Fig. 6 Simulated and observed hydrographs using LISEM model (dates are expressed as m/d/y and time)

J Soils Sediments (2014) 14:1311–1324 1323

Acknowledgments We thank the Coordination of Improvement ofHigher Education Personnel (CAPES), the National Council for Scien-tific and Technological Development (CNPq), and the Foundation forResearch Support of the State of Rio Grande do Sul (FAPERGS) for thefinancial support in the stipend and fellowship study, and CeluloseRiograndense Company (CMPC), for the area of study and financialsupport.

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