ORI GIN AL PA PER

Landslide influence on turbidity and total solidsin Cubatao do Norte River, Santa Catarina, Brazil

Masato Kobiyama • Aline de Almeida Mota • Fernando Grison •

Joana Nery Giglio

Received: 11 January 2011 / Accepted: 9 April 2011 / Published online: 1 May 2011� Springer Science+Business Media B.V. 2011

Abstract The rainfall events that occurred in the Cubatao do Norte River watershed,

Santa Catarina State, Brazil, in 2008, were characterized by both high intensities and

amounts and triggered landslides in this watershed. The objective of the present study was

to analyze the influence of landslides on the turbidity and the total solid concentration (TS)

in this river using turbidity, TS, and river discharge data obtained from March 23, 2008, to

June 11, 2010. The comparison between turbidity and discharge patterns implies that the

landslide process was not continuous and increased the turbidity intermittently and

irregularly. The sediment yield during the landslide occurrence was approximately five

times higher than without the landslide, even though the discharges were similar. The

turbidity/discharge relationship during the landslide occurrence was markedly different

from that before and after the occurrence. The correlation coefficients between turbidity

and TS showed that the landslide significantly changed the sediment yield in this water-

shed. The result indicates that sediment yield estimations at the watershed level should be

treated more carefully when landslides occur.

Keywords Landslide � Turbidity � Total solids � Cubatao do Norte River � Brazil

M. Kobiyama (&) � A. de Almeida Mota � F. Grison � J. Nery GiglioDepartamento de Engenharia Sanitaria e Ambiental, Universidade Federal de Santa Catarina, CaixaPostal 476, Florianopolis, SC 88040-900, Brazile-mail: kobiyama@ens.ufsc.br

A. de Almeida Motae-mail: alinemota10@gmail.com

F. Grisone-mail: fernando@ens.ufsc.br

J. Nery Giglioe-mail: joana_n_g@yahoo.com.br

123

Nat Hazards (2011) 59:1077–1086DOI 10.1007/s11069-011-9818-4

1 Introduction

Sediment yield results from erosion processes (detachment, transport, and sedimentation)

that naturally occur in watersheds. Environmental factors such as water and wind dissect

the landscape, and materials are transported and deposited. The floodplains where the

majority of the world’s population lives are formed by such processes over geologic time.

The sediments carry nutrients that fertilize the land and transport microorganisms and

organic matter, which may result in improved fluvial ecology. Hence, it can be said that the

sediments may exercise beneficial effects and that societal development might not happen

without sediment yield.

When an abrupt and high yield of sediment occurs and adversely affects a society, this

phenomenon is called sediment disaster. Excessive suspended sediment concentration (SS)

can degrade water quality. The light and heat interception in the water due to the high SS

reduces photosynthesis, which is essential to the health of water bodies, and modifies the

aquatic ecosystem. Furthermore, bedload and deposited suspended sediment can decrease

water depth, hampering navigation and causing local floods more frequently. Since a

society is embedded in the sediment production ecosystem, the instability of this system

contributes to sediment disasters.

To reduce losses associated with natural disasters, it is important to understand the

mechanisms that cause these phenomena (Kobiyama et al. 2006). One of the typical

sediment disasters is the landslide. Recently, its influence on sediment supply and delivery

has been investigated both in the laboratory and through field observations (Peart et al.

2005; Schwab et al. 2008; Acharya et al. 2009). However, these kinds of investigations are

still rare.

The objective of the present study was to analyze how the landslides changed the

turbidity and the total solid concentration (TS) in the Cubatao do Norte River watershed,

Santa Catarina State, Brazil, which occurred at the end of 2008. The intensity and total

amount of rainfall in this state were extremely high at that time (Kobiyama et al. 2010). It

is important to report the sediment-related behavior in the context of the hydrological

cycle, especially in the hydrograph.

2 Methods

2.1 Study area

The Cubatao do Norte River watershed (total area of 492 km2) encompasses Garuva and

Joinville cities in Santa Catarina state, Brazil; 80% of the watershed is in Joinville. The

main channel of this watershed is 88 km long. Its headwater and mouth are in the Quei-

mada Sierra (at an altitude of 1,100 m) and at the estuary of Babitonga Bay, respectively

(Goncalves et al. 2006). Silveira et al. (2009) analyzed the history of floods in Joinville and

showed that this watershed had frequently suffered from them since its foundation in 1851.

At the middle of this watershed, it was installed an infrastructure for water capture and

treatment by the Water Company of Joinville (CAJ), which is responsible for the drinking

water supply in this city. The Cubatao Drinking Water Treatment (DWT) plant normally

provides 10 L/s to Araquari city and 1,200 L/s to Joinville city, which currently accounts

for 70% of the total water consumption in the latter. At the convenience of the present

study, the DWT plant location is considered the outlet of the Cubatao do Norte River

watershed (CNRW). At this point, the CNRW has an area of 375 km2, the main river is

1078 Nat Hazards (2011) 59:1077–1086

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56 km long, and its minimum, mean and maximum altitudes are 40, 750, and 1,500 m,

respectively (Fig. 1).

The CNRW is in the Santa Catarina Granulite Complex, in a metamorphic embasement

from the Archean/Proterozoic composed mainly of granulitic gneisses, magmatic gneisses,

and quartzites, with iron formations and dykes of metabasic rock. Furthermore, there are

alkaline granite batholiths from the Proterozoic/Paleozoic, and in the Serra do Mar region

occur the Campo Alegre and Corupa volcano-sedimentary basins, with diabase dykes and

quaternary sediments (Goncalves and Kaul 2003).

The CNRW is inserted in the Atlantic Tropical Forest domain, which features a high

biodiversity. The Atlantic Tropical Forest is one of the most threatened forests in the

world, recognized by the UNESCO as a biosphere reserve (Trein 2003; UNESCO 2010).

The CNRW relief is characterized by the Sao Bento do Sul Plateau (landscape with a

dense drainage network), the Serra do Mar (an arrangement of crests, peaks, ridges,

mountains, and scarps), and the Serras Cristalinas Litoraneas (mountainous terrain and

scarps) (Rosa 2003). The native forests in the Serra do Mar and in the Sao Bento do Sul

Plateau are extensively transformed to pine reforestation. However, the native forests are

well preserved in the Serras Cristalinas Litoraneas (Trein 2003).

The climate in the region is subtropical humid, characterized by two seasons: winter and

summer. The mean annual precipitation amount is 1,900 mm. During summer, the pre-

cipitation events are predominantly intense convective rainfall storms. Furthermore, there

is an important orographic effect due to Serra do Mar. During winter, there is a decrease in

the precipitation (Veado et al. 2003).

2.2 Hydrologic and water quality monitoring system

At the DWT plant, the CAJ automatically measures various water quality parameters for

both raw and treated water, including the turbidity at 30-min intervals. Moreover, the total

solid concentration (TS) of raw water is monitored monthly. TS and turbidity were ana-

lyzed by the methods outlined in the Standard Methods for the Examination of water and

Wastewater (2540B–total solids dried, and 2130B–turbidity) (APHA et al. 1998). At the

same location, the Hydrology Laboratory (LabHidro) of Federal University of Santa

Fig. 1 Location of the Cubatao do Norte River watershed, Santa Catarina State, Brazil

Nat Hazards (2011) 59:1077–1086 1079

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Catarina (UFSC) installed a river and rain gauge station that automatically measures river

water level and rainfall every 10 min (Fig. 2).

The present study used the rainfall, river water level, turbidity, and TS data obtained

from March 23, 2008, to June 11, 2010.

2.3 Field survey

Since surface access to their localities by land was extremely difficult, the landslides that

initiated the mass movements in late November 2008 were first observed by helicopter

(Fig. 3). Thereafter, the extent of the largest landslide was surveyed with a GPS. It was a

Cubatã

o doNor

teRiv

er

49°11'45"W

26°00'30"S

48°56'00"W

23°13'45"S0 10 km

DWT plant

Landslide

N

River

do Norte

Cubatã

o

Fig. 2 Location of the Drinking Water Treatment (DWT) plant and the landslide

Fig. 3 Aerial photographs. a Landslide near the Cubatao River. b Confluence of Quiriri River to Cubataodo Norte River

1080 Nat Hazards (2011) 59:1077–1086

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rotational landslide followed by a debris flow that transported the sediment to the Cubatao

do Norte River. The dimensions of the landslide are approximately 35 m (width) by 3 m

(depth) by 750 m (debris flow travel distance). The mass movements were evaluated by

comparing hydrographs, turbidity, and TS. Figure 3b clearly shows the influence of

landslides on the river turbidity.

2.4 Data analysis

In this study, the rainfall data of the gauge located at the DWT plant were used as mean

rainfall over the whole CNRW. Based on the data presented by Grison et al. (2008), the

stage–discharge curve was established as follows:

Q ¼ 10:945 � H2:9 ð1Þ

where Q is the discharge (m3/s), and H is the water level (m).

By using 28 contemporaneous data of turbidity and TS, which were obtained before and

after the landslide occurrence, it was verified that the probability distributions of both the

variables were not normal. Therefore, its normality could be gained by applying the Box–

Cox transformations (Box and Cox 1964). Based on the maximum log likelihood, the best

value for the parameter k was determined (Table 1). After confirming that its normality

was guaranteed, the correlation coefficients, Pearson’s r and Spearman’s R, were calcu-

lated between these two variables.

3 Results and discussion

Figure 4 shows the 10-min hydrograph and hyetograph for the period November 1, 2008,

to December 31, 2008. During this period, landslides occurred and caused a sudden

increase in turbidity. It should be noted that rainfall values were very high, reaching up to

60 mm/h.

Before and after the landslide occurrences, both discharge and turbidity were well

correlated (Fig. 5a, c). On the other hand, this correlation can be disrupted by some

external factors. For example, when landslides occur, turbidity values sometimes markedly

increase, while discharge displays a little or no change. Figure 5b illustrates how the

turbidity sharply increased on two days: November 30, 2008, and December 3, 2008. The

turbidity pattern implies that mass movement process was not continuous. In other words, a

landslide can trigger an increase in sediment concentration intermittently and irregularly.

The linear correlation between turbidity and discharge can be observed under different

conditions (with and without landslides) (Fig. 6). With landslides, the correlation is not

significant at 95% confidence interval. Without landslides, the correlations are consider-

ably high at the same confidence interval.

Lewis (1996), Pavanelli and Bigi (2005), and Wass and Leeks (1999) found a statis-

tically significant relationship between turbidity and suspended sediment concentration

Table 1 Variables and their kvalues for the Box–Coxtransformation

Variable k

Turbidity -0.5

TS 0.0

Nat Hazards (2011) 59:1077–1086 1081

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(SS). The present study compared turbidity with TS, considering that there were no SS data

available and TS value can include SS information. The turbidity and TS behaviors during

the whole period are shown in Fig. 7. Though the period before the landslide occurrence is

shorter than that after its occurrence, it can be observed that the behavior of the variables

before the occurrence is rather different from that after its occurrence.

Table 2 shows the correlation coefficients between turbidity and TS. The linear cor-

relation (Pearson’s r) is a little higher than the nonparametric statistics (Spearman’s R). By

considering the whole period, it is affirmed that both the variables do not have any kind of

correlation. Then, the data were divided into two phases: before and after the landslide

occurrence. A statistically significant correlation between turbidity and TS before the

occurrence can be found at 90% confidence interval. On the other hand, after the occur-

rence, this correlation does not exist anymore. Thus, the landslide represents a kind of

rupture at the sediment yield process in this watershed.

The TS mean value during the landslide occurrence period was much higher than that

without the landside (Table 3). The sediment yield during the occurrence was

0

2

4

6

8

10

12

14

16

18

Rai

nfa

ll (m

m/1

0 m

in)

1-Nov 7-Nov 13-Nov 19-Nov 25-Nov 1-Dec 7-Dec 13-Dec 19-Dec 25-Dec 31-Dec

Time (10 min)

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Dis

char

ge

(mm

/10

min

)

Fig. 4 Ten-minute hyetograph and hydrograph in the Cubatao do Norte River watershed during the periodNovember 1, 2008, to 31 December 31, 2008

1082 Nat Hazards (2011) 59:1077–1086

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approximately five times higher than without the landslide, although the discharges are

similar among the compared days.

This landslide raised serious problems at the DWT plant. Part of raw water is normally

used to clean the DWT plant filters by the backwash process. However, the landslide

affected the raw water quality, which caused the necessity to use the treated water for

cleaning the filters during the disaster period. Then, the drinking water supply was inter-

rupted on December 3, 2008, and was reduced about 20–25% for a few hours. Figure 8

shows the water with extremely high turbidity upstream of the DWT plant.

0

50

100

150

200

250

0.00

0.02

0.04

0.06

0.08

0.10

0.12

0.14

0.16

29-Oct-08 30-Oct-08 31-Oct-08 1-Nov-08 2-Nov-08 3-Nov-08 4-Nov-08 5-Nov-08 6-Nov-08

Tu

rbid

ity

(NT

U)

Dis

char

ge

(mm

/ 30

min

) Discharge

Turbidity

(a)

0

200

400

600

800

1000

1200

1400

0.08

0.10

0.12

0.14

0.16

0.18

0.20

0.22

0.24

0.26

0.28

27-Nov-08 28-Nov-08 29-Nov-08 30-Nov-08 1-Dec-08 2-Dec-08 3-Dec-08 4-Dec-08 5-Dec-08

Tu

rbid

ity

(NT

U)

Dis

char

ge

(mm

/ 30

min

) Discharge

Turbidity

(b)

0

50

100

150

200

250

300

0.00

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

21-Oct-09 22-Oct-09 23-Oct-09 24-Oct-09 25-Oct-09 26-Oct-09 27-Oct-09 28-Oct-09 29-Oct-09

Tu

rbid

ity

(NT

U)

Dis

char

ge

(mm

/ 30

min

) Discharge

Turbidity

(c)

Fig. 5 Discharge and turbidity: a October 29, 2008, to November 5, 2008 (before the landslide occurrence);b November 27, 2008, to December 4, 2008 (during the landslide); c October 21–28, 2009 (after thelandslide occurrence)

Nat Hazards (2011) 59:1077–1086 1083

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0 20 40 60 80 100 120 140 160 180 200 220

Turbidity (NTU)

0.06

0.08

0.10

0.12

0.14

0.16

Dis

char

ge

(mm

/ 10

min

)

R2 = 0.749CI = 95%n = 384

(a)

0 200 400 600 800 1000 1200 1400

Turbidity (NTU)

0.09

0.12

0.15

0.18

0.21

0.24

0.27

Dis

char

ge

(mm

/ 10

min

)

R2 = 0.001CI = 95%n = 384

(b)

0 20 40 60 80 100 120 140 160 180

Turbidity (NTU)

0.01

0.02

0.03

0.04

0.05

0.06

0.07

0.08

0.09

0.10

Dis

char

ge

(mm

/ 10

min

)

R2 = 0.791CI = 95%n = 384

(c)

Fig. 6 Correlation between discharge and turbidity. a October 21–28, 2008 (before the landslideoccurrence); b November 27, 2008, to December 4, 2008 (during the landslide); c October 21–28, 2009(after the landslide occurrence)

0

20

40

60

80

100

120

0

20

40

60

80T

S (

mg

/L)

Tu

rbid

ity

(NT

U)

Turbidity

TS 03-Dec-08:landslide occurrence

Fig. 7 Turbidity and TS concentration

Table 2 Correlation coefficients between turbidity and TS for the considered periods

Period n Pearson’s r p-level Spearman’s R p-level CI

Whole 28 0.17 0.40 0.16 0.42 0.1

Before 8 0.79 0.02 0.66 0.08 0.1

After 20 0.14 0.56 0.16 0.49 0.1

1084 Nat Hazards (2011) 59:1077–1086

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3.1 Final considerations

The landslide occurrence in the Cubatao do Norte River watershed and its influence on

water turbidity and total solid concentration were reported and discussed. The landslide

yields sediments in rivers. Hence, it can be considered a kind of erosion process. It was

found that the sediment yield by the landslides was intermittent and irregular. Thus, the

mechanism of sediment yield by the landslide is very different from that of surface erosion

such as sheet and rill erosion. It implies that models that consider only these types of

erosion cannot properly simulate the sediment yield in watersheds where landslide

occurrences yield substantial quantities of sediment (Bathurst et al. 2007; Acharya et al.

2009).

Furthermore, it was found that TS and turbidity were correlated before the landslide

occurrence, but not anymore after the occurrence. Therefore, landslides can represent a

kind of rupture in the sediment yield processes.

Table 3 Mean daily dischargeand TS concentration during dif-ferent periods

Period Day Qmean (m3/s) TSmean (mg/L)

Without landslide 6/Nov/2008 70 133

24/Nov/2008 104 77

17/Dec/2008 83 87

Mean 86 99

With landslide 28/Nov/2008 111 487

30/Nov/2008 83 429

03/Dec/2008 71 552

Mean 88 497

Fig. 8 High turbidity at the DWT plant: a flocculants and decanters, b water capture point, and c Parshallflume

Nat Hazards (2011) 59:1077–1086 1085

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Although this is only a preliminary study, it is sufficient to draw the attention of

watershed sediment yield modelers in terms of the importance of studying the influence of

landslides on the sediment yield.

Acknowledgments The present work was supported in part by the National Research Council of Brazil(CNPq) through the Grant No. 555421/2006-6. The authors are thankful to the Water Company of Joinvilleand the members of the LabHidro-UFSC for advice and support.

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