Jesus Et Al Full Paper 442

8/13/2019 Jesus Et Al Full Paper 442

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thINTERNATIONAL CONFERENCE ON COASTAL AND PORT

ENGINEERING IN DEVELOPING COUNTRIES

COPEDEC 2012, IIT Madras, Chennai, INDIA.

20-24 Feb. 2012

IMPACT OF THE HYDRODYNAMIC IN THE CONCENTRATION OF THE SUPERFICIALSUSPENDES SEDIMENTS INTO THE CHIMBOTE BAY

L. C. Jesus1, G. L. G. Teixeira

2, J. T. A. Chacaltana

3and J. R. Acua

4

Abstract: Chimbote bay is located at the northern coast of Peru and for a long time has been

suffered many impacts from the industry activities, the installation of Fishery Harbor, jetties and the

Lacramarca River. Therefore, our objective in this work is to relate the distribution of the superficial

suspended sediment concentration (SSC) and the hydrodynamics induced by tide and wind. Two

selected images acquired by LANDSAT5/TM, in GeoTiff format, dated January of 2007 and June of

2008 have been used to calculate the SSC. The numerical model MOHID is employed to hindcast the

hydrodynamic into the Chimbote Bay. Numerical results show an anticlockwise recirculation in the

Chimbote bays south portion that may be the associated with the distribution of SSC into the bay.

The presence of a current with magnitude reaching 0.08 m/s, in the Chimbote bays east side might

be the responsible of the highest concentration of sediment plumes, up to 120 g/m in this region.

The main source of SSC is the erosion at the downdrift side of the harbors and the Lacramarca River

into the Ferrol bay and its distribution is related with local hydrodynamics, as seen in the north and

south portion of the Chimbote bay.

Keywords: SSC; LANDSAT5/TM; MOHID; Chimbote bay.

INTRODUCTION

The Chimbote bay is located at the northern Perus littoral and currently pass through many

environmental problems related with the contamination caused mainly by the fishing and steel

industry. Recently the Peruvian government has implemented many efforts to clean and recover the

main bays on the Perus coast, as the Chimbote bay. The Chimbote bay can be divided into the North

BayFerrol and the South baySamanco.

Interdisciplinary studies are carrying out to recovery Chimbote bay. The objective is the knowledge

of the main patterns of the physical-chemical, biological and geological parameters in order to apply

the best methodologies for the environmental management to the interest site. Therefore, the

knowledge of physical processes is an important aspect for the management of coastal and

estuarine waters, since its controls the distribution of salt, pollutants, and sediments among others.

Then, the transport of sediments impact directly the port operations and can carry viruses and

bacteria with it.

1Research Student, Department of Environmental Engineering, Federal University of Esprito Santo, Esprito

Santo, Brazil, e-mail: [email protected]

2Research Student, Department of Environmental Engineering, Federal University of Esprito Santo, Esprito


3DSc. Professor, Department of Environmental Engineering, Federal University of Esprito Santo, Esprito


4 DSc. Professor, Departament of Physics, Universidad Nacional Mayor de San Marcos, Lima, Peru, e-mail:

[email protected]


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Proceedings of COPEDEC 2012, 20-24 February 2012

Impact of the hydrodynamic in the concentration of the superficial suspended sediments into the Chimbote Bay

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Sparse studies have been made to investigate the hydrodynamics of Chimbote bay. Dios and Zorrilla

(2006) investigated the tidal and wind-driven circulation and showed the great importance of the

wind in the generation of currents outside of the Chimbote bay, and low importance inside the bay,

because of the coastline effects. More elaborated studies were made by Quispe et. al (2009) thatanalyzed the oxygen, salinity, temperature and ocean currents fields with site observations and

model results to the year 2003 to 2006.

Thus, this work is an effort of researchers of the Federal University of Esprito Santo (Brazil) and the

Universidad Nacional Mayor de San Marcos (Peru) to understand the sediment dynamics into the

Chimbote bay.

The objective of this article is to correlate the distribution of suspended sediments with the flow

pattern forced by tidal and wind into the Chimbote bay.

METHODOLOGY

Remote Sensing

The images used in this work was collected by Landsat5/TM and processed by the Level 1 Product

Generation System (LGPS). These images have a GeoTiff format, dated 21/01/2007 and 16/06/2008.

All digital image pre-processing is realized in IDL programming language. First, the data pre-

processing is a calibration of the proper radiance, its involves rescaling the raw digital number of

image (Q) to sensor spectral radiance (L) using the Eq. 1 (CHANDER et al., 2009).

where,

= Spectral radiance at the sensors aperture *W/m2sr m]

= Quantized calibrated pixel value [DN]

= Minimum quantized calibrated pixel value corresponding to LMIN [DN]

= Minimum quantized calibrated pixel value corresponding to LMAX [DN]

LMIN = Spectral at sensor radiance that is scaled to [W/m2sr m]

LMAX = Spectral at sensor radiance that is scaled to [W/m2sr m]

The values of LMAX e LMIN were taken from Chander et al.(2007).

So the radiance data is compensated for atmospheric effects and the radiance values of images is

converted into reflectance values. For research interested in quantitative analysis of surfacereflectance it is necessary remove the influence of the atmosphere. Therefore, an absolute method

is used in order to remove the atmospheric effects, as diffusion and dispersion, with Fast Line-of-

sight Atmospheric Analysis of Spectral Hypercubes (FLAASH) calibration tools. The standard equation

of the FLAASH for spectral radiance at sensor pixel is, as follows:

where,

= Spectral radiance at a sensor pixel [W/m2sr m]

= Radiance back scattered by the atmosphere [W/m2sr m]


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= Pixel surface reflectance

= Average surface reflectance for the pixel and surrounding region

S = Spherical albedo of the atmosphereA and B is the coefficients that depend on atmospheric and geometric condition but not on the

surface

The A, B, S, L coefficients is determined from MODTRAN4 calculations and strongly depend of the

water vapor column amount (Matthew et al., 2000). Also, in the compute of these variables is

considered proprieties such as elevation and aerosol distribution. The result is a reflectance matrix

free of atmospherics interferences and ready to apply the SSC algorithm. A suitable algorithm

proposed by Tassan (1987) is used for the determination of SSC, Eq 3.

Its a log model based on the empirical algorithms presented by Gordon and Morel (1983). We used

the algorithm to the band 2 reflectance ( 0.569) of the TM sensor. Itshas a better correlation, r =

0.92, in contrast with the algorithm to the band 3, r=0.89 (TASSAN, 1987).

The images were registered and geo-referenced to a standard datum (UTM/ WGS1984) and

projection. Finally a color palette was created to a representative presentation of the distribution of

CSS into a bay.

Hydrodynamic model

The numerical model MOHID was used to hindcast the hydrodynamic forced by astronomical tide

and wind. In this work the MOHID hydrodynamic module is used, that basically solves the

momentum equations in three dimensional reference (Eq. 4, 5, 6), which considers the Boussinesq,

Reynolds and hydrostatic equilibrium approximations.

where t, represents the time; u, v, w the velocity components; f is the Coriolis parameter; p the

pressure, rthe density of the water; acceleration due to the gravity and, AHe AV the cinematicand turbulent viscosity, horizontal e vertical, respectively.

However, the model runs vertically integrated for this work. The nesting technique is used to take

the global boundary conditions to the finer resolution gridthe Chimbote bay.

For the bathymetry is used the ETOPO and GEBCO data base and for the Chimbote bay is made by

digitalization and interpolation of nautical chart provided by Perus navy through the Direccin de

Hidrografia y Navegacin (DHN). The Chimbote bay domain, with spatial resolution about 90 meters,

is shown in the Fig. 1.

For the open boundary conditions is used the tidal harmonics calculated by the FES2004 tide model,

with the 15 major harmonics. The wind is considered constant, with intensity of 5,17 m/s from the


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south quadrant, that are the typical winds in Chimbote, as shown by Dios e Zorrilla (2006). The

Peruvian current is not taken into account.

The model was run for two cases, a summer month (January/2007) and a winter month (June/2008),

as made for the concentration of the suspended sediments.

Fig. 1Bathymetry of the study site, the region of the district of Chimbote. The bathymetry was

interpolated from the nautical chart provided by the DNH.

RESULTS AND DISCUSSION

Atmospheric correction

After the atmospheric correction of images, the water, cloud, vegetation and water with sediment

spectra were extracted from six absolute reflectance datasets of Landsat 5 ETM images, as shown in

Fig. 2.

Ferrol Bay

Samanco Bay


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(a) (b)

(c) (d)

Fig. 2The cloud, vegetation, ocean water and plume spectra extracted six reflectance dataset of

Landsat 5/TM. These patterns are present for all processed images.

The water spectra, Fig.2(c), extracted from absolute reflectance datasets of Landsat 5 TM image

shows the absorption near of Band 2 (0.569 m) and Band 4 (0.840 m), however in the presence of

sediment (Fig. 2(b)) we can see a peak at the band 2 that is related with the increasing of the back

scatter of this wavelengths. In addition of water was extracted the vegetation and cloud spectra. The

clouds have high reflectance in the band 2 and 3 (0.569 e 0.660 m) and near the infrared (band 4)

where the major absorption was at the end of spectra (band 1 and 5), while the vegetation spectra

has a high absorption at the visible spectra and a high reflectance at the near infrared. Kayadibi

(2011) compared the atmospheric corrections methodologies and get that the absolute correction

methods have better spectral results. This author obtained a shape for the water and vegetation

spectral curves in agreement with that calculated in this work (for the absorption and reflection

bands). Owojori and Xie (2005) in their work classified the vegetation and obtained spectra with highreflectance peak at the near infrared too.

The spectral curves calculated in this work for the main targets (water, vegetation, cloud and water

with sediments) are in good agreement with those calculated for other authors and can be used to

calculate the proprieties from the reflectance.

Chimbotes Bay Hydrodynamics

In this section the main features for the ebb and flood tides are shown. The velocities for the ebb

and flood tide are shown in the Fig. 3 as the representative pattern of the main flow of the Ferrol

and Samanco bay.

Band 2

Band 4High

reflectance

High

reflectanceBand 1

Band 5


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Fig. 3Velocity (in m/s) field for an instant of flood tide (a) and for the ebb tide (b), the red

arrows show the main path of the flow.

The flood tide (Fig. 3 (a)) on the study site has a different pattern in the Ferrol bay and Samanco bay,

in the first, the main flow is driven to the south after the entrance of the bay and it tends to drift to

the south due to the effect of the friction with the Ferrol peninsula and its islands, being driven to

the north near coast due to the effect of northward wind.

(a)

(b)


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The island (Isla Blanca) in the north of the bay has an important feature in the distribution of the

currents. It makes a barrier to the flow outside the bay creating a shadow zone, as we can see in the

north of the Ferrol bay where the lowest velocities inside the Ferrol bay are.

In Samanco bay the main flow has two different paths; both are located near the coastline. This

pattern is result of the orientation of the entrance of the bay and the direction of the main flow

outside the bay. The main flow outside the bay comes from south and the entrance of the Samanco

bay is aligned to the southwest resulting in a flow that follows the coastline contour due to the drift

effects caused by the friction. In the north of the bay the opposite flow that comes of the north and

south of the bay create low velocity area in bay.

For the ebb, the currents in Ferrol bay are driven to the north with the major intensities behind the

Isla Blanca and its contours, as we can see in the Fig. 3 (b). The influence of the wind makes the

magnitude of the flow increase northward being, together with the Chimbote peninsula and little

islands, the responsible of a low velocity area (marked with a black circle in the Fig. 3(b)) due to the

interference in the direction of the main flow and friction with the coastline.

The Samanco bay there is two main flows that go to the entrance of the bay. The friction with the

Ferrol and Samanco peninsula causes a recirculation system with the lowest velocities on the bay as

seen in the Fig. 3 (b).

The main flow outside the bay is driven to the north/northwest affected by the wind and its friction

with the coastline. There is a increasing in the velocities in front of the Ferrol bay that can be by the

orientation of the coastline and the bathymetry that increase the velocity in this region getting

values greater than 0.2 m/s.

Distribution of Suspended Sediment Concentration Field

(a)


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(b)

Fig. 4Spatial distribution of SSC for 21/01/2007, (a), and 16/06/2008, (b).

Fig. 4 are shown the SSC fields calculated from the band 2 of the TM sensor that presents distinct

distributions related with the concentration and spatial distribution.The Fig. 4(a) shows the spatial distribution of SSC inside both bay Ferrol and Samanco; Samanco

have a more homogeneous distribution of SCC. The SSC field inside the Ferrol bay is characterized by

a high concentration core next to the harbor in this bay (black square), with high values reaching 132

g/m3. The distribution of the SSC in this region is a northward driven plume. Opposite to Ferrol bay,

the homogeneity is the main feature of the distribution of the SSC in the Samanco bay, with the

majors values reaching 16 g/m3in shallow areas as seen in the red square inside the Samanco bay

and the Ferrol peninsula.

The presence of the SSC core in the Ferrol bay may be related with the presence of a river that

contributes both discharge and sediment percolation that generates susceptibility to the transport

of the beach sediments. The advection of the sediment plume can be explained by the local

hydrodynamics, Fig. 5. This is a snapshot taken for the same instant of time that was calculated the

SSC, this was an ebb moment with an anticlockwise recirculation system with the increasing of the

hydrodynamics around the recirculation, reaching velocities near to 0.08 m/s driven northward

inside the bay. The Samanco bay has two recirculation systems next to the coast a flows outside the

bay by the central part of bays entrance that may be responsible of the homogeneity of the

distribution of the SSC as seen in the Fig 4. (a).


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Fig. 5Instantaneous velocity in m/s for 21/01/2007, 15:00 GMT. The red arrows show the mainpath oh the flow in both bays.

The Fig. 4(b) shows the SSC field that has a well defined distribution of the SSC where we can see

mainly the plume pattern in the Ferrol bay.

The Fig. 4(b) shows the SSC field that has a well defined distribution of the SSC where we can see

mainly the plume pattern in the Ferrol bay and the distribution in the Ferrol peninsula (red square),

with concentrations reaching 25 g/m3.

It is observed a plume in the Ferrol bay with concentrations reaching concentrations near to 130

g/m3 in the plumes core (the Black square) in the harbor region in the Fig. 4(b). These high values of

SSC may be related with the industrial wastes and port activities and the presence of the piers thatcan generate erosion at the downdrift side of the pier (Torres, 2009). The SSC in Samanco bay (Fig.

4(b)) has a low concentration distribution, near to 2 g/m3 and high concentrations patches in the

south part of the bay, reaching concentration near to 25 g/m3.

In the Fig. 6 we can see an anticlockwise flow in both bays with the major velocities near the

coastline. The increase in the hydrodynamic in the Ferrol bay may be the responsible of the a more

evident plume, as seen in Fig. 3 (b). Thus we can see the increase in velocity that can be spatially

related with the highest values of SSC, as seen in the Fig. 6 in the black circles at the Ferrol peninsula

and inside the Samanco bay.


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Fig. 6Instantaneous velocity in m/s for 16/06/2008, 15:00 GMT. The red arrows show the mainpath of the flow.

CONCLUSIONS

This work demonstrated the potential of Landsat5/TM images in integrated study of distribution of

SSC in the Chimbotes Bay due a good relation between hydrodynamic and field of sediment showed

on the third topic of results. The main source of sediments is the Lacramarca River and the groins

region for Ferrol bay, while Samanco bay its occurs by resuspension. The coastal geometry has an

important role on the circulation into Chimbote bay.

We suggest the measurement of the SSC and hydrodynamics into Chimbote bay to validate and

improve the calculations these parameters with more accurate and reliable results.REFERENCES

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AVIRIS. Rem. Sens. Envirion, v. 65, pp. 367-375

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Jesus Et Al Full Paper 442