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International Journal of Advanced Engineering Research and Science (IJAERS) 

httos://dx.doi.ora/10.22161/iiaers.6.5.36 


[VoI-6, Issue-5, May- 2019] 
ISSN: 2349-6495(?) \ 2456-1908(0) 


Identification of the Erosive Processes on the 
Banks of Ribeirao Sao Joao Porto Nacional - TO 

Igor Pereira de Sa Diogo Pedreira Lima 2 

Academic studentofCivil engineering - Institute Tocantinense Presidente Antonio Carlos 
2 Enviromental engineering, Master in Environmental engineering focused on water resources and sanitation -Institute To 

cantinense Presidente Antonio Carlos (Advisor) 


Abstract — The objective of this study was to map the 
erosions that are occurring on the banks of Ribeirao Sao 
Joao in Porto Nacional - TO, these erosive processes 
come from the detachment and transportation of the soil 
particles, which can be deposited in the watercourse of 
the stream, causing the increasing of the load in the 
streambed. Two erosions were the biggest. Soil 
characterization tests were done in each erosion. 
Monitoring its progress was made by pins erosion 
method, which were installed on the banks of those 
erosions. The accomplishment of monitoring made it 
possible to create graphs comparing precipitation and 
erosion. With this study it was achievable to check that 
the precipitation acts directly on the surface, increasing 
the erosive process, verifying that the soil type exerts a 
big influence on the process. 

Keywords — Erosion. Erosion pins. Ribeirao Sao Joao. 

I. INTRODUCTION 

Silva et al. (2007) define that the soil consists 
of organic and minerals particles with different 
dimensions, formed from physical, chemical and 
biological processes. The most common agents for soil 
formation are climate, the place’s topography and the 
biotic community. Soil erosion is understood as a process 
of detachment, transport and deposition of soil particles. 
Erosion at the riverbanks may promote the degradation of 
the watercourse, due to the large accumulation of 
sediments carried by the streams to the riverbed. Among 
the main environmental inpacts problem caused we can 
mention the reduction of the flow, change in the course of 
rivers and in very serious cases can cause the extinction of 
the watercourse (ALVES, 2007). This study delineated 
itself in collecting important information on the erosive 
processes that are occurring on the banks of Ribeirao Sao 
Joao in Porto National - TO. The objective of this study 
was to map erosion along the river, identifying and 
monitoring the development of major erosions. The 
purpose of this study was to obtain a survey of the 


erosions that are occurring on the banks of Ribeirao Sao 
Joao, it was also very relevant monitoring the progress of 
the biggest erosions located in the watershed that supplies 
the city.. 

II. MATERIALS AND METHODS 

2.1 CHARACTERIZATION OF THE STUDIED AREA 

The studied place is located southeast of the city of 
Porto Nacional-TO, in the basin of drainage of Ribeirao 
Sao Joao that has a total area, according to Silva (2010) of 
82km 2 . The basin is located between the meridians 48 ° 
14T6 "and 48 ° 24'51" longitude west and between the 
parallels 10 ° 4 6'43 "and 10 ° 41’20" with South latitude 
as shown in figure 1. Its mouth is located within the urban 
area of Porto Nacional, contributing directly to the 
Tocantins River. According to Tocantins (2012), the are 
present in the region are the Oxisols and a small portion 
of Neosols. The natural vegetation that prevails in the 
region is the cerrado. In Porto Nacional - TO the climate 
is typically tropical. The annual average rainfall is 
1622mm, and the average temperature is about 26.1 ° C. 
The month of September is the hottest month, with an 
average of 27.9 ° C, and the month with the lowest is 
July, averaging 24.9 ° C. The largest part of the 
precipitation is between October and April, which is the 
rainy season, and drought period is between May and 
September (CLIMATE-DATA, 2018). 

2.2 CREATING THE MAP 

The process of creating the map began with the 
identification of erosions, and later the points were 
collected by a geodetic CPS. The creation of the map was 
through the Google Earth tool, a software that has several 
functions, and among them is the visualization of satellite 
images and the creation of themed maps. The locations 
are given through the geographical coordinates, the 
identification occurred from 10 ° 42'54.92 "S, 48 ° 
2217.93" W to 10 ° 44'21.52 "S, 48 ° 1732.24" in the city 
of Porto Nacional-TO, as it is shown in figure 2. 


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3 km 


International Journal of Advanced Engineering Research and Science (IJAERS) [Vol-6, Issue-5, May- 2019] 

https://dx.doi.ora/10.22161/iiaers.6.5.36 ISSN: 2349-6495(?) \ 2456-1908(0) 


Fig.l - Location map of the studied area 
Source: Silva (2010) 

(Green: Brazil, Orange: Tocantins, Yellow: Porto Nacional, light blue: Ribeirao Sao Joao, Red: UrbanArea, Blue line: 
Hydrography.) 


Fig.2- Location of most erosions 

Source: Prepared by the author (Yellow pin: Right riverbank, Red pin: Left riverbank, Red dot: City of Seisirmaos) 

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70 D 0'0"W 60 C 0’0-W 50WW 40 r 0'(TW 


4o'24vW 

0 TT" 


4B c 40'CrW 48'20 , 0-W 


4820 crw 


0 550 1 ICO 2200 

48 C 24XTW 


40°o , <rw 

3 3CO 4 400 


48 S 20'(TW 


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Tocantins 
Porto Nacional 
RibeirSo S3o JoSo 
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MAPEAMENTO DAS MAIORES EROSOES 



Legenda 

f MARGEM DIREITA 
? MARGEM ESQUUERDA 


• Seis Irmaos 


«f 10°42 , 54.92"S , 48°22 , 17.93 ,, W 


m 


• ^eis/lrjsnaos “ 


10°44’8.74"S , 48°20'10.26"W - ^ 


1p°44;5.3SrS , 48°19 , 42.99"W 


10°44 , 18.84"S 48 o 17'34.20"W 


Google Earth 

mage © 2019 CNES / Airbus 
§•2018 Google 


































International Journal of Advanced Engineering Research and Science (IJAERS) 

httDs://dx.doi.ora/10.22161/iiaers.6.5.36 


[VoI-6, Issue-5, May- 2019] 
ISSN: 2349-6495(?) \ 2456-1908(0) 


2.3 EROSION PINS 

There were selected two erosions to monitor, 
the first one at 10 ° 4418.84 M S, 48 ° 1734.20” W and the 
second at 10 ° 4440.29 "S, 48 ° 18’5.85 ° W. Based on the 
Leal (2008) methodology, the procedure of the study was 
developed by monitoring the edges of the erosion, from 
the installation of rebars with 20cm of size, where they 
were spiked 15cm and 5cm remained out. The number of 
pins varied according to the size of the erosion, in the first 


one were placed eleven points, and the second were 
placed nine points. They were put perpendicular to the 
erosion, two rebar per point, the first at a distance of one 
meter from the edge and the second at two meters. The 
lateral distance between the points was one meter. The 
checks happened fortnightly, with the help of a measuring 
tape. The information was stored and compared with 
rainfall data of the region. 



Fig.3-Distance from the edges to the stakes 
Source: Adapted from Leal (2008) (A stake - lmeter; B stake - 2meters) 


2.4 SOIL CHARACTERIZATION 

The soil was collected near the erosion, and 
prepared according to the NBR 6457 (2016), laboratory 
tests were executed and the characteristics and 
mechanical properties of the soil were determined. The 
tests were done according to the technical standards listed 
below. 

2.4.1 Granulo metric an aly s is 

The methodology for granulometric 
analysis and the execution of the test was made according 
to NBR 7181 (2016), performing a combination of 
sedimentation and sieving. The test was divided into two 
parts, and each case has a different goal. With the 
acquired results, it was possible to make the 
granulometric curve for soil classification. The sieving 
was used to determine the largest fractions as sand and 
gravel, and the sedimentation, which was made with fine 
materials such as clay or silt, measuring the speed that the 
material decant in the water. The determination of was 
based on the Stokes law, where it relates the velocity that 
the particle sediments. The larger the particle, the faster 
it’ll be deposited in the bottom of the test tube. 


2.4.2 Specifics oilmass 

According to the NBR 6508 (1984) standard, 
it has been determined the specific mass of the soil that 
was passed in the 4,8mm sieve through the pycnometer. 
The specific mass was determined by the relationship 
between mass and solid volume. The pycnometer was 
calibrated and the air of the soil water composition taken 
according to the standard and so that air would not 
interfere in the search results. 

2.4.3 Atterbergboundaries 

In accordance with NBR 6459 (2016), the 
liquidity limit (LL) determines the moisture content 
which is the passage from the liquid state to plastic. Lor 
determination of this limit was made test in the 
Casagrande’s equipment that measures the moisture 
content by closing the lower edges of a stem pitting made 
by a standardized chisel that is open in the soil mass, 
requiring 25 strokes for its closure. The result of several 
repetitions changing the moisture of the same soil 
generated a graph showing the flow line that relates the 
number of strokes with moisture. 

According to NBR 7180 (2016), the plasticity 
limit (LP) shows the amount of moisture needed for the 


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International Journal of Advanced Engineering Research and Science (IJAERS) 

httDs://dx.doi.ora/10.22161/iiaers.6.5.36 


soil to be molded. The execution of the procedure 
consisted in the formation of rods of 3mmin diameter and 
10cm to 15cm long on a glass plate. The procedure was 
repeated three times to determine the moisture and was 
calculated the mean to find the plasticity limit. 

III. RESULTSAND DISCUSSIONS 
3.1 EROSION PINS 

Even erosions were considered the larger 
overall, where two of them were selected to perform the 
monitoring from December until April, months with the 
highest level of precipitation during the year. Field 


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analysis provided strong data on erosive processes; it can 
be verified that they evolve faster in the period of the year 
where precipitation reaches a greater volume. It was 
noticed that the active erosive processes are due to the 
action of precipitation water and the predominance of 
material removal is where the flow of the flash flood is 
larger, this predominance was seen in the highest 
graduation of the pins in that flow place. There was the 
development of vegetation which, it was also affected. It 
was also observed that the sedimented materials are being 
carried directly to the streambed. 


Table 1 - Evolutionary data of the first erosion (Distance from cutting to edge oferosion) 


DATAS 

DADOS EVOLUTIVOS DA PRIMEIRA EROSAO (EROSAO DAS BORDAS)- POR ESTAQUEAMENTO 

2018 

2019 

15/dez 

30/dez 

15/Jan 

30/jan 

15/fev 

02/mar 

17/m a r 

01/abr 

15/abr 

POINTOS 

□1ST. EST. 

A BORDA 

DIST. EST. 

A BORDA 

DIST. EST. 

A BORDA 

DIST. EST. 

A BORDA 

DIST. EST. 

A BORDA 

DIST. EST. 

A BORDA 

DIST. EST. 

A BORDA 

DIST. EST. 

A BORDA 

DIST. EST. 

A BORDA 

PI 

196 

194 

192 

186 

183 

182 

178 

177 

177 

P2 

195 

193 

190 

187 

180 

179 

175 

174 

173 

P3 

194 

188 

185 

179 

176 

172 

166 

164 

163 

P4 

195 

187 

184 

176 

173 

169 

164 

162 

160 

P5 

193 

186 

182 

178 

174 

170 

165 

161 

159 

P6 

193 

186 

182 

174 

170 

168 

163 

160 

158 

P7 

194 

185 

181 

175 

171 

167 

162 

159 

158 

PS 

192 

186 

185 

178 

174 

171 

163 

160 

159 

P9 

194 

187 

186 

180 

179 

177 

175 

174 

173 

P10 

196 

191 

190 

188 

188 

186 

179 

178 

178 

Pll 

197 

193 

193 

192 

192 

190 

188 

185 

185 


Source: Prepared by the author.(Evolutional data of the first bank erosion - by staking. From December 15 th to April 15 th , PI 
1 st pin to 11 th and its distance from the banks) 


The points 3,4,5,6,7,8 presented a higher rate 
of evolution, the other points 1, 2, 9, 10, 11 have had less 
degradation, this may be due to several factors, the 
highest rate of erosion may be related to the flow of the 
flash floods, and the points that were less affected may be 
related to the presence of vegetation which is an 
important factor, because it gives protection to the soil 
avoiding the inpacts of raindrops directly hitting the soil, 
reducing the kinetics energy of the drops and reducing the 
possible erosive processes. Points 6 and 7 were the most 
affected in this period, in the month of December, during 
the rainy season, they were found at a distance of 120 cm 
of the border of the erosion, in the month of April they 
found at 158 cm of the edge, meaning 42 cm of evolution 
in these points, associating a direct relation with 
precipitation. 

Through precipitation and the monthly average 
evolution rate, it was possible to monitor and compare the 
relationship between rate of evolution and precipitation. 
To understand the results, it is important to comprehend 
how the rain cycle occurred so they can be compared with 


erosion pins. Monitoring the hydrological cycle was done 
with the data provided by INMET- National Institute of 
Meteorology, from December 2018 to April 2019. These 
data have been transformed into a line graph 
demonstrating monthly rainfall, as shown in Figures 4 and 
5. Cumulative rainfall in this period was 1110.0 mm, the 
months of December and March had higher volume, 
accumulating 56.3% of the total. 

The graph depicted in figure 4 demonstrates 
the comparison between the erosion and the rainfall that 
occurred during that period. It was observed that 
evolution is not directly proportional, in the first month 
the evolution rate and rainfall are almost close, in the 
following months the variables distance themselves, while 
the volume of precipitations in some moments reached 
300 mm monthly and the evolution rate of the erosive 
process was around 4 to 6 cm, as shown in the graph. This 
variation of erosion rate may be related to the amount of 
rain per day. Thus, superficial erosions are related to the 
intensity of rainfall in this place, and the volume of flash 
flood that these rains cause in the region. 


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14,00 

12,00 

10,00 

8,00 

6,00 

4,00 

2,00 

0,00 


TAXA DE EVOLUgAO DOS CANAIS E PRECIPITAgAO 
(MEDIA MENSAL) 


Fev 

-TAXA DE EROSAO 


Mar 

PREClPITA£AO 


400 

350 

300 

250 

200 

150 

100 

50 

0 


Fig.4 - Chart of the rate of evolution of the channels and precipitation (monthly average) 


Source - Prepared by the author. (Rate Evolution of the channel and precipitation, on blue: erosion rate, orange: precipitation, 
monthly average) 

The data of the table 2 presented below refers to the second erosion, demonstrating its attendance. It is at the point 
10 ° 44'40.29 ° S, 48 ° 18.5 ° W. With the monitoring of this erosion a comparison was made between this and the first 
erosion that is located in a place far away. 


Table 2 - Evolutionary data of second erosion (Distance from cutting to the edge oferosion) 



DADOS EVOLUTIVOS DA PRIMEIRA EROSAO {EROSAO DAS BORDAS)- POR ESTAQUEAMENTO 

DATAS 

2018 

2019 


15/dez 

30/dez 

15/jan 

30/jan 

15/fev 

02/mar 

17/mar 

01/a lb r 

15/abir 


DIST. EST. 

DIST. EST. 

DIST. EST. 

DIST. EST. 

DIST. EST. 

DIST. EST. 

DIST. EST. 

DIST. EST. 

DIST. EST. 

POINTOS 

A BORDA 

A BORDA 

A BORDA 

A BORDA 

A BORDA 

A BORDA 

A BORDA 

A BORDA 

A BORDA 


(CM) 

(CM) 

(CM) 

{CM} 

(CM) 

(CM) 

(CM) 

{CM} 

(CM) 

PI 

198 

196 

195 

194 

191 

189 

186 

186 

185 

P2 

196 

194 

193 

191 

189 

186 

184 

183 

181 

P3 

196 

192 

191 

189 

185 

183 

180 

178 

177 

P4 

195 

191 

189 

188 

186 

180 

179 

177 

175 

P5 

197 

188 

187 

186 

185 

182 

177 

175 

173 

P6 

196 

189 

188 

187 

185 

181 

178 

175 

172 

P7 

194 

190 

189 

189 

187 

186 

186 

183 

180 

PS 

196 

189 

189 

189 

185 

184 

181 

180 

178 

P9 

197 

196 

196 

196 

194 

193 

193 

192 

191 


Source: Prepared by the author.(Evolutional data of the second bank erosion - by staking. FromDecember 15 th to April 15 th , 
PI 1 st pin to 9 th and its distance from the banks) 


In comparison with the first erosion monitored 
with erosion pins , this onet behaves in a similar way, 
presenting similar characteristics, as it can be seen in 
points 3,4,5,6, which had a higher scale, showing that the 
superficial water flow from intense rainfall and lack of 
vegetation can be considered the one of the biggest 
reasons of these erosions. Leal (2008) reports a similar 
behavior in a study which was observed that the evolution 


of erosion occurs basically from one side of the gull, 
demonstrating that the flow of the rainfall has influence 
on erosion. 

The graph presented in figure 5 represents the 
comparison between the precipitation and erosion rate. In 
comparison with the first one, the graph shows 
similarities, with lower erosion rates. The development of 
this erosion, as in the first, for instance, the erosion rate 


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followed the precipitation volume, but in the following 
months there was a variation between the precipitation 
line and the erosion rate, showing that the evolution is not 
proportional to the precipitation volume. Those results are 
similar to those observed by de Casado et al (2002), in 


[VoI-6, Issue-5, May- 2019] 
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which it was verified that the evolution is not continual 
and it is related to climatic events, such as the intensity of 
the hydrological events, the winds and the speed of the 
flow. 



Fig.5- Chart of the rate of evolution of the channels and precipitation (monthly average ) 

Source- Elaborated by the author.(Rate Evolution of the channel and precipitation, on blue: erosion rate, orange 
precipitation, monthly average) 


3.2 SOIL CHARACTERIZATION 

The plasticity index is the ability of the soil to 
remain in a plastic form without passing to the liquid 
state, therefore the lower the plasticity index the more 
common will be the erosion to happen due to the breaking 
of soil particles, and the higher the index, the more soil 
will resist the erosion. The plasticity index found in both 
soils are different. The soil of the first erosion has a 


plasticity index equal to 7.5 and the second had a 
plasticity index of 10.7 analyzing the data, the first one 
had a greater evolution when compared to the second. 
According to the theory proposed by Jenkins, the soil 
having 7 <IP <15 is considered as medium plastic 
(CAPUTO, 1988). In this way, plasticity of both soils are 
in this parameter (Table 3). However, the second one 
showed greater resistance against erosion. 


Table 3-Atterberg Boundaries 



LL 

LP 

IP 

PONTO 1 

30,6 

23,1 

7,5 

PONTO 2 

36 

25,3 

10,7 

LL-Limite de 

; Liquidez | 

LP- Limite de 

Plasticidade | 

| IP- Indice de Plasticidade | 

1 


Source: Prepared by the author. Ponto 1: 1st point, Ponto 2: 
index) 

The Granulometric analysis performed showed 
the most stable features as the percentages of the particles 
that constitute the soil. With data referring to the first 
erosion, it was possible to classify as a sandy-loam soil, 
as it can be observed in Figure 6. The soil has 28% fine 
sand, 20% sand coarse, 10% fine sand, 22% clay and 19% 
silt. According to Bertoni and Lombardi Neto (2014), 
when the soil has a large amount of sandy material, it 


2 nd point, LL: liquidity limit: LP: plasticity limit, IP: plasticity 

makes it more susceptible to erosion. Comparing the 
monitoring of the erosion pins we can notice that there 
was a bigger variaton in the first monitored erosion. 
According to Casado et al (2002), the presence of sandy 
material contributes significantly to the increase in 
erosion rates due to its lack of cohesion, the soil becomes 
more susceptible to erosion. 


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Fig.6 - Granulometric analysis of the first erosion 

Source: Prepared by the author (ABNT’s sieve, Vertical: percentage that goes through the sieve(%), horizontal: grains’ size 
(mm) ) 



Fig.7 - Granulometric analysis of the second erosion. 


Source- Prepared by the author.(ABNT’s sieve, Vertical: percentage that goes through the sieve(%), horizontal: grains’ size 
(mm) ) 


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[VoI-6, Issue-5, May- 2019] 
ISSN: 2349-6495(?) \ 2456-1908(0) 


The granulometric analysis of the second 
erosion is shown in figure 7. The present soil had a silt 
percentage of 38%, followed by 32% of clay, classifying 
this soil in silt-clayey, having more ability to keep the 
connections and in consequence, presenting greater 
cohesion. O sum of the percentages of fine, medium and 
coarse sand were around 29% of the total. In comparison 
with the methodology of erosion pins, it can be confirmed 
that the erosion which has a soil with greater cohesion, is 
less susceptible of appearing and developing erosions. 
The second monitored erosion had less progress than the 
first one, being able to notice that the type of soil also has 
a great influence in the development of erosions. 

IV. CONCLUSION 

At the end of this study it was possible to 
notice that the methodologies applied were effective. The 
results allowed us to understand how the precipitation 
factor influences the acceleration of erosive processes, 
acting directly on the surface, causing the erosion process 
to increase, generating a big loss of sediments, which are 
released by the kinetic energy of the water drop and the 
power of the flash flood. The incline of the land is also a 
contributing factor, since it affects the speed flow of the 
water. The higher the incline the faster will be the flow 
and consequently will have more power transporting the 
particles. The first erosion had sandy material and 
plasticity index smaller than the second one, 
consequently, a smaller cohesion, which explains a higher 
erosion rate over that time. The technique used in this 
study is considered cheap and easy to keep up with, and it 
may be used by the competent bodies to monitor other 
erosions that may offer some environmental or social risk. 
It was possible to understand how important the works 
that contribute to this type of objective are. Having access 
to a mapping with the identificated erosions and their 
monitoring would facilitate and help to locate them, and 
for a future monitoring, giving the right containment 
treatment so these erosions will not keep growing.. 

V. RECOGNITION 

I thank God first for blessing my life and the 
lives of my family always giving us health, peace, joy and 
also giving me forces to move on. For the support and 
affection, I thank my parents Joshua Moreira and Ines 
Pereira, I thank my brothers Jo sines Pereira and Fabrfcio 
Pereira and also my niece Ana Clara Gonsalves. Last but 
not least important, I thank my counselor Me. 
DiogoPedreira for his guidance, support and trust. Thank 
you all, without you it would not be possible to achieve 
this dream 


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erosivos e da dinamica hidrologica e de sedimento 
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[2] ASSOCIAgAO BRAS ILE IRA DE NORMAS 

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[3] ASSOCIAgAO BRASILEIRA DE NORMAS 

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[4] ASSOCIAgAO BRAS ILE IRA DE NORMAS 

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[7] BERTONI, J.; LOMBARDI NETO, F. Conservagao 
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[8] CASADO A.P.B., et al. Evolugao do processo erosivo 
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[9] CAPUTO, H.P. Mecanicados solos e suas aplicagoes. 
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[10] CLIMATE-DATA, https://pt.climate-data.org. Dados 

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[11] LEAL, C. B. Uso e comparagao do metodo de 
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[12] SILVA, A. M.; SCHULZ, E.; CAMARGO,.Erosao e 
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