Journal of Coastal Research, Special Issue 56, 2009

Journal of Coastal Research SI 56 1552 - 1556 ICS2009 (Proceedings) Portugal ISSN 0749-0258

Portuguese Northwest Beach Classification Using Aerial Photographs and GIS Tools

J. Pais-Barbosa † F. Veloso-Gomes ‡ and F. Taveira-Pinto ‡ † Centro de Investigação em Ciências Geo-Espaciais,, Faculty of Sciences of Porto University Porto, 4169-007, Portugal jpbarbosa@fc.up.pt

‡Hydraulics and Water Resources Institute, Faculty of Engineering of Porto University Porto, 4200-465, Portugal vgomes@fe.up.pt, fpinto@fe.up.pt

ABSTRACT

Pais-Barbosa, J., Veloso-Gomes, F., and Taveira-Pinto, F., 2009. Portuguese Northwest Beach Classification Using Aerial Photographs and GIS Tools. Journal of Coastal Research, SI 56 (Proceedings of the 10th International Coastal Symposium), 1552 – 1556. Lisbon, Portugal, ISSN 0749-0258.

Coastal features and patterns and its correlation through time are very important to understand coastal evolution, for coastal planning and management proposes. For the Portuguese coast (mesotidal type) the morphological classification is scarce. In this context, the main objective of this paper is to present results of the identification and analysis of the morphodynamic and hydrodynamic features and patterns in the coastal interface zone under study, as well as the beach system morphodynamic classification, using historical data namely aerial photography analyzed with a Geographical Information Systems (GIS). GIS was used to identify features and patterns, to measure its dimensions and comparison analyzes. The results obtained were correlated with wave climate and other sea parameters. In parallel several morphological parameters were calculated and compared with different models presented by several authors. The results show a good approach, leading to a better understanding and classification of the Portuguese northwest coastal morphology. As a result of this study a GIS geodatabase was created, able to be expanded to other geographic and scientific areas, as well as to integrate new datasets. Was also possible to classify morphologically the beaches mostly as intermediate (ridge-runnel or low tide terrace - rhythmic bar and beach), and observe that coastal features and patterns are strictly related with wave climate. A set of morphological parameters that can provide a good approach for beach stage classification of coastal areas especially where Ω is unknown was also selected

ADITIONAL INDEX WORDS: Morphodynamic, Hydrodynamic, Hydroforms, Coastal Zone.

INTRODUCTION Several morphological beach change models and classifications

were presented by different authors (WRIGHT and SHORT, 1984; SUNAMURA, 1988; LIPPMANN and HOLMAN, 1990; SHORT and AAGAARD, 1993; MASSELINK and SHORT, 1993; MASSELINK and HEGGE, 1995; SHORT, 1991, 1999).

These models were mainly established for Australian and American sandy coasts, for microtidal environments. SHORT

(2006) reports a full range of beach morphological classification for Australian coast, based on wave, tidal and sediment parameters. These parameters can be combined producing two dimensionless parameters namely the Gourlay parameter or dimensionless fall velocity (Ω) and the relative tide range (RTR):

Ω / (1)

/ (2)

where Hb is the wave breaking height, T is the wave period, Ws is the sediment fall velocity and TR is the tidal range. Besides these parameters and expressions, these classification models are represented by comprehensive illustrations where several coastal features are represented such as: submerged bar (transverse, crescentic, discontinuous, welded and parallel), troughs, beach cusps, high tide cusps, megacusps, erosion cusps,

runnels, ridges, mini and rip currents, berm crests and erosion berms.

In general, for the Portuguese coastal zone parameters such as Hb, d, and tan β are usually unavailable or simply nonexistent PAIS-BARBOSA (2007) and PAIS-BARBOSA et al., (2007).

An approach based on the presence and dimensions of morphological and hydrodynamic features and patterns was used to classify morphologically the study area located on the Portuguese northwest coast. This approach was presented in several articles, namely PAIS-BARBOSA et al., (2005a, 2005b), PAIS-BARBOSA (2007) and PAIS-BARBOSA et al., (2007).

The case study is located between Esmoriz and Furadouro beach at north of Aveiro Lagoon sand spit (Figure 1) representing a dynamic and fragile physical and biological environment that is constantly changing in response to natural processes as well as human activities.

This stretch is characterized by a mean significant wave height ranging from 2 to 3 m, with mean wave period ranging from 8 to 12 s. In storm conditions the significant wave heights can exceed 8 m, with periods reaching 16 to 18 s. Wave direction exhibits the higher frequencies and intensities in the NW quadrant with 43.8 % of occurrence, WNW with 28.0% and NNW with 21.2% (IHRH, 1993 and VELOSO-GOMES et al., 2006).

The sand sediment size (d50) shows a small dispersion in size ranging between 0.36 mm and 0.81 mm.

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Journal of Coastal Research, Special Issue 56, 2009

Portuguese Northwest Beach Classification Using Aerial Photographs and GIS Tools

From a geomorphologic point of view, this stretch is mostly a low-lying coastal plain with sand dunes and beaches, with a NNE-SSW orientation. Two other relevant aspects are the tidal range, which can reach up to 4.0 m for spring tides (mesotidal), and the littoral drift that acts mainly from north to south.

The methodology developed and the results obtained, using vertical aerial photographs and GIS tools, improved the knowledge on coastal features and patterns identification and typification, at the Portuguese west coast, as well as their relation with the local wave and the tidal regime. This leaded to a better understanding of the coastal erosion phenomena occurring.

METHOD The concept behind the methodology developed consists on the

identification of morphological and hydrodynamic features and patterns to be compared with the illustration of classification models referred, once the parameters data used to establish the type of beach morphology stage are in general inexistent.

For that vertical aerial photographs were needed, especially historical datasets. This category of data has a vital importance since they document the dynamic for a certain moment. Aerial

photographs associated to Geographical Information Technologies (GIT) analysis tools and visualization capabilities are fundamental to understand coastal dynamic evolution.

The methodology included the development of a Geographical Information System (GIS) database and a method of image interpretation and analysis. The method will be described briefly.

More detailed information about the methodology developed is included at PAIS-BARBOSA (2007) and PAIS-BARBOSA et al., (2007).

COastal MOrphoDYnamic GIS (COMODY) To achieve the proposed goals of this study, a Geographical

Information System (GIS) named COMODY was developed. With this geodatabase it is possible to carry out several spatial analyses such as the vegetation line retreat, the urban settlement evolution, the coastal features measurement and evolution, the identification of hydrodynamic and morphodynamic features and patterns and their location through time. The GIS gives the possibility to easily introduce new datasets, overlap and compare data as well as extend to other geographic study areas.

This GIS database stored several vector and raster datasets, as well as alphanumeric information such as: topographic maps obtained from the photographic surveys of 1996 and 2001 at 1:2,000 scale; oblique photographs from 2001 (two surveys) and 2002; tide range; deepwater buoy wave data (with gaps); sediments sizes; beach slopes from 1996, 2001 and 2002; nautical and military charts from 1974/1975 and 1998 (1:25,000). All the data resulting from the image interpretation was also stored in COMODY database.

Photograph Dataset Interpretation Image interpretation consists on a visual identification onscreen

in a GIS environment of eight aerial photographs surveys (Table 1 and Figure 2). The visualization onscreen in a GIS environment methodology allowed the identification and digitalization of coastal features such as beach cusps/high tide cusps/erosion cusps (<100), beach megacusps and megacusps (100<<500), gigacusps (>500), berms, erosion berms, dune cliffs, vegetation lines, submerged bars (parallel, crescentic, transversal), mini and rip currents, rip heads, troughs, channels. The morphological and hydrodynamic features and patterns were measured: length (λ), width (ω) and spacing (ε) of the morphological features (cusps, rip currents, rip head, bar, etc.). Moreover, historical lines were also measured (vegetation line, dune cliff) on an attempt to quantify the shoreline dynamics.

At the moment digital image processing methodologies are under development using different techniques of image analysis, namely supervised and unsupervised classification and image segmentation.

Figure 1. Study area.

Table 1: Vertical aerial photographs datasets used.

Aerial photographs

Format Coordinate System

Year Scale

Vertical Digital No 1958 1:25,000 black and white

Vertical Digital No 1967 1:15,000 black and white

Orto Digital Yes 1995 1:40,000 colour

Vertical Hardcopy No 1996 1:8,000 colour

Vertical Digital No 1998 1:22,000 colour

Vertical Hardcopy No 2001 1:8,000 colour

Vertical Digital No 2002 - colour

Vertical Digital No 2002 1:8,000 colour

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RESULTS AND ANALYSIS According with wave and tide data series the aerial photographs

datasets correspond to quite different wave and tide conditions. For example in September 29th 1996 the significant wave high (Hs) reaches almost 3 m and in June 13th the Hs is half of this value (Table 2). This fact is mainly related with the time of year that the photograph datasets were acquired (winter or summer).

*Estimated from Cape Silleiro, Spain.

Furthermore, for the aerial survey of 1967 wave records are inexistent.

Tidal level ranges from spring tide (in September 29th 1996 and September 17th 2001) to neap tide (in June 13th 1958 and October 28th 2002) (Table 2). These parameters influence deeply the size and the hydroforms and hydromorphologies existing in each aerial photograph dataset.

PAIS-BARBOSA et al., (2007) show some results of visual analysis in a GIS environment, for four surveys presented in Table 1. Some important conclusions were drawn from the results

achieved. From this analysis several outputs were obtained, such as

morphological maps, vegetation line retreat, beach slope (for surveys of 1996 and 2001), hydroforms and hydromorphologies measurement and beach morphological classification.

Observing Table 3 and Table 4 the vegetation line since 1958 till 2002 shows a mean retreat value (Rt) of 115 m, attesting clearly that this coastal stretch is under an erosion process.

The results are presented in Table 3 and Table 4, are related in particular with hydroforms and hydromorphologies indentified and sizes for each survey analyzed.

In matters of morphology and hydrodynamic features/patterns,

Figure 2. Examples of hydroforms and hydromorphologies identified.

Table 3: Morphological and hydrodynamic features/patterns identified and dimensions at Esmoriz-Furadouro stretch. Survey Date

June 13th, 1958 October 11th, 1967 August 27th, 1995 September 29th, 1996

Morphological and Hydrodynamic Features/Patterns

Ident Rt (m) Ident Rt (m) Ident Rt (m) Ident Rt (m) Vegetation line yes 0 yes 16 yes 86 yes 91

Dune cliff no yes yes yes

Erosion berm yes yes yes yes

Berm yes yes yes yes

Ident No λ ω ε Ident No λ ω ε Ident No λ ω ε Ident No λ ω ε Beach cusps/high

tide cusps yes 64 48 8 yes 214 41 9 yes 64 41 7 yes 60 50 11

Beach Megacusps yes 1 194 23 yes 4 123 12 no no

Megacusps no yes 7 406 17 yes 18 323 27 yes 13 286 28

Gigacusps no yes 10 796 32 yes 4 631 23 yes 9 663 45

Transverse Channel no yes yes yes

Longit. Channel no no no no

Welded bar no no yes 1 8000 165 465 yes 1 11500 235 480

Transverse bar no no no no

Crescentic bar no no no yes

Parallel bar yes 1 87 67 yes 1 318 73 no no

Mini-rip currents yes 56 51 yes 87 41 yes 19 42 no

Weak rip currents no no no yes

Rip currents no yes 11 421 yes 22 370 no 27 432

Rip channels no yes yes yes

Mini-rip heads yes 49 24 yes 25 23 no no

Weak rip heads no no no no

Rip heads no yes 4 98 no yes 27 366

Morphologic Stage Reflective (1) Ridge-Runnel or Low Tide Terrace (2) Transverse Bar and Beach (3) Transverse Bar and Beach (3)

Table 2: Vertical aerial photographs datasets used.

Survey Date Tide Level Deepwater Wave Climate

High (m) Low (m) Height (m) Period (s) Direction (N)

June 13th,1958

2.88 (12.20 h)

1.19 (17.47 h)

1.4<Hs<1.5 11.6<Ts<12.7 260<θ<280

October 11th, 1967

2.73 (09.02 h)

1.29 (15.46 h) Not Available

August 27th, 1995

3.54 (15.31 h)

0.62 (09.14 h)

1.3<Hs<1.9 8<Ts<12.5 294<θ<332

September 29th, 1996

3.68 (16.10 h)

0.4 (09.56 h)

1.9<Hs<2.7 10<Ts<12 300<θ<320

June 12th, 1998

3.40 (16.16 h)

0.81 (09.58 h)

1.3<Hs<2.3 6.4<Ts<8.9 292<θ<316

September 17th, 2001

3.83 (14.40 h)

0.38 (08.23 h)

1.2<Hs<1.8 8.8<Ts<10.1 316<θ<335

August 13th, 2002

3.38 (05.59 h)

0.77 (11.58 h)

1.0<Hs<1.9 7.7<Ts<8.4 318<θ<331

October 28th,

2002*

2.76 (06.46 h)

1.31 (13.10 h)

2.3<Hs<4.1 6.7<T<11.5 -

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Portuguese Northwest Beach Classification Using Aerial Photographs and GIS Tools

some changes of coastal features/patterns and beach morphological stage can be observed between 1958 and 2002. Moreover, it can be only classify the beach morphological stage for the photograph acquisition moment.

The classifications presented by SHORT (2006) are based essentially in two dimensionless parameters: Relative Tide Range (RTR) and fall velocity (Ω). For the coastal stretch under analysis, it is possible to estimate RTR parameter, RTR<3, indicating that is

a wave dominated coast. However, the fall velocity (Ω) parameter quantification needs to be improved.

To overcome this difficulty, a new group of parameters was selected. Table 5 intends to correlate the morphologic stage in the comprehensive illustrations present in classification models (WRIGHT AND SHORT, 1984, SHORT, 1999, 2006) and results obtained by the visual analysis in GIS environment in order to classify morphologically the coastal stretch between Esmoriz-

Table 4: Morphological and hydrodynamic features/patterns identified and dimensions at Esmoriz-Furadouro stretch (cont). Survey Date

June 12th, 1998 September 17th, 2001 August 13th, 2002 Octuber 28th, 2002

Morphological and Hydrodynamic Features/Patterns

Ident Rt (m) Ident Rt (m) Ident Rt (m) Ident Rt (m) Vegetation line yes - yes 108 yes 111 yes 115

Dune cliff yes yes yes yes

Erosion berm yes yes yes yes

Berm no no no no

Ident No λ ω ε Ident No λ ω ε Ident No λ ω ε Ident No λ ω ε Beach cusps/high

tide cusps yes 70 46 8 yes 35 43 8 yes 75 35 6 yes 23 51 11

Beach Megacusps yes 1 103 8 yes 1 128 15 no yes 1 117 20

Megacusps yes 9 430 21 yes 18 300 23 yes 23 321 50 yes 35 262 21

Gigacusps yes 3 706 31 yes 7 559 48 yes 4 678 60 yes 2 593 28

Transverse Channel yes yes yes no

Longit. Channel yes 1 11500

Welded bar yes 1 11500 175 484 no

Transverse bar yes 6 277 yes 13 195 855 no no

Crescentic bar yes 3 391 144 no no yes 1 11500 92

Parallel bar yes 1 1110 140 yes 5 320 100 no yes 1 8000 40

Mini-rip currents yes 74 44 no no yes 9 37

Weak rip currents no no no yes 28 202

Rip currents yes 12 496 yes 28 408 yes 29 389 yes 34 343

Rip channels yes yes yes yes

Mini-rip heads yes 39 31 no no no

Weak rip heads no no no no

Rip heads yes 5 296 yes 27 260 yes 18 213 yes 29 288

Morphologic Stage Transverse Bar and Beach (3) Transverse Bar and Beach (3) Transverse Bar and Beach (3) Rhythmic Bar and Beach (4)

Table 5: Morphological parameters to Esmoriz-Furadouro stretch. SHORT (2006) – Australian coast (microtidal)

Morphological Stage Dissipative Intermediate Reflective

6 5 4 3 2 1 Parameters RTR <=3 – Wave Dominated Beaches Ω >6 2-5 <1

Portuguese coast (mesotidal): Stretch Esmoriz - Furadouro Morphological Stage 6 5 4 3 2 1 Hs m 2.3-4.1 1.0-2.7 - 1.4-1.5 Hb (Komar and Gaughan, 1972) m - 1.88-3.13 - 2.28 Tidal Range m 4 RTR <=3 – Wave Dominated Beaches Morphological Parameters Breaking zone Number 2 2 1 and/or 2 1 Transformation Zone Width m 200-300 100-300 50-100 0-50 Minirip Currents (space in between)

m 40 Scatter 40-

60 40 50

Weak Rip Currents m 200 Rip Currents (space in between) m 350 350-500 420

Beach Cusp Length (Swash, High Tide, Storm)

Beach Face and Beach Scatter 50 30-50

40 50 Megacusp or Gigacusp Horn m Megacusp or Gigacusp Bay

Megacusp m 300 245-450 Grouped

400

Gigacusps m

600 550-700 Grouped

800

Transverse Bar / Welded Bar x x Longitudinal Bar Small bars Scatter Crescentic Bar x x Tidal Terrace x

Transverse Channel m Small Size x Grouped

800

Longitudinal Channel/Trough x

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Furadouro. The correlation/comparison was based in the presence and/or absence of morphological and hydrodynamic features/patterns such as: submerged bars (transverse, crescentic, welded and parallel), troughs, beach cusps, high tide cusps, megacusps, erosion cusps, runnels, ridges, mini and rip currents, berm crests and erosion berms. Such correlation produces a morphologic beach stage classification for each aerial survey.

As it is possible to observe in Table 3, Table 4 and Table 5 the aerial survey of 1958 was classified as reflective (1), the 1967 as intermediate - ridge-runnel or low tide terrace (2)-, the 1995, 1996, 1998, 2001 and 2002 August as intermediate - transverse bar and beach (3)-, and the 2002 October as intermediate - rhythmic bar and beach (4).

Besides, Table 5 presents a set of morphological parameters that characterize and classify the morphological and hydrodynamic beach stage of Esmoriz-Furadouro stretch. This classification shows the presence of hydroforms and hydromorphologies as well as its size.

Analyzing Table 5 it is observed that increasing the wave high the number of breaking zones increase, as well as the transformation zone width (width in between initial breaking line and the maximum swash line). The hydroforms and hydromorfologies such as beach cusps and minirip currents intend to be scatter and decrease in number.

CONCLUSIONS From the analysis performed, Esmoriz-Furadouro stretch can be

classified as wave dominate and mainly as intermediate - less energetic stages. However, the high energetic intermediate stage and the dissipative stage can also be probably recognized if certain conditions occur.

The aerial photographs datasets analyzed show clearly that this stretch displays different morphologic stages. This stage diversity is strictly related by one hand with the wave climate conditions and by other hand with the tidal range. This analysis also shows an high coastal dynamic, responding and adapting to the wave climate.

The correlation/comparison between coastal features/patterns identified for each aerial survey, and WRIGHT AND SHORT (1984) and SHORT (1999, 2006) comprehensive illustration models can provide a good approach for beach stage classification of coastal areas especially where Ω is unknown.

According to the methodology presented the morphological stage was the following: aerial survey of 1958, reflective (1); aerial survey of 1967, intermediate - ridge-runnel or low tide terrace (2); aerial survey of 1995, 1996, 1998, 2001 and 2002 August as intermediate - transverse bar and beach (3); and aerial survey of 2002 October as intermediate - rhythmic bar and beach (4).

A set of characteristics/parameters of classification to help on futures morphologic analysis on Portuguese coast as well as on mesotidal environments was presented.

The results presented, are being confirmed with other aerial photographic datasets analysis, field work and new classification methodologies such as image classification and image segmentation.

LITERATURE CITED IHRH, 1993. Plano de aproveitamento da zona entre o molhe sul

e a ponte-cais No. 3, Vol. I. Estudos da Agitação Marítima no Porto de Leixões. IHRH Report (in Portuguese).

LIPPMANN, T. C. and HOLMAN, R. A., 1990. The spatial and temporal variability of sand bar morphology. Journal Geophysic Research, 95 (C1), 11575-11590.

PAIS-BARBOSA, J.; VELOSO-GOMES, F., and TAVEIRA-PINTO, F., 2005a. GIS tool for coastal morphodynamics analysis. Proceedings of the CoastGIS 2005 (Aberdeen, Scotland), CD.

PAIS-BARBOSA, J.; VELOSO-GOMES, F., and TAVEIRA-PINTO, F., 2005b. Analysis of the Portuguese west coast morphology and morphodynamics, based on aerial images and GIS tools. Proceedings of the 2nd EARSel Workshop - Remote Sensing of the Coastal Zone (Porto, Portugal), pp 809-818.

PAIS-BARBOSA, J.; VELOSO-GOMES, F., and TAVEIRA-PINTO, F., 2007. Coastal features in the energetic and mesotidal west coast of Portugal, Journal of Coastal Research, Special Issue No. 50, pp 459-463.

PAIS-BARBOSA, J., 2007. Hidroformas e Hidromorfologias costeiras locais (in Portuguese). Faculty of Engineering of Porto University, PhD Thesis, 2 Vol.

MASSELINK, G. and SHORT, A. D., 1993. The effect of tide range on beach morphodynamics and morphology: A conceptual beach model. Journal of Coastal Research, 9, 785-800.

MASSELINK, G. and HEGGE, B., 1995. Morphodynamics of meso and macrotidal beaches: Examples from central Queensland, Australia. Marine Geology, 129, 1-23.

SHORT, A. D., 1991. Macro-meso tidal beach morphodynamics - An overview. Journal of Coastal Research, 7(2), 417-436.

SHORT, A. D. and AAGAARD, T., 1993. Single and Multi-bar beach change models. Journal of Coastal Research, Special Issue No 15, 141-157.

SHORT, A. D. (ed.), 1999. Beach and Shoreface Morphodynamics. Chichester, United Kingdom: John Wiley and Sons, 379p.

SHORT, A. D., 2006. Australian beach systems – nature and distribution. Journal of Coastal Research, 22(1), 11-27.

SUNAMURA, T., 1988. Baech morphologies and their change. In: Horikawa, K. (ed.), Nearshore Dynamics and Coastal Processes. University of Tokoyo Press, pp. 136-166.

VELOSO-GOMES, F.; TAVEIRA-PINTO, F.; DAS NEVES, L., and PAIS-BARBOSA, J., 2006. EUrosion - A European Initiative for Sustainable Coastal Erosion. Pilot Site of River Douro - Cape Mondego and Case Studies of Estela, Aveiro, Caparica, Vale do Lobo and Azores, Porto, Portugal, 317 p.

WRIGHT, L. D. and SHORT, A. D., 1984. Morphodynamic variability of surf zones and beaches: a synthesis. Marine Geology, 56, 93-118.

ACKNOWLEDGEMENTS Portuguese Geographic Institute (IGP); Water Institute (INAG); POCI 2010 - FCT

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