A geodiversity-based suitability analysis on underground electricity cables on Aruba

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30 May 2021

A geodiversity-based suitability analysis on

underground electricity cables on Aruba

BSc thesis

Author:

Manou Kuik

Student number:

12411329

Supervisor:

Dr. A. C. (Harry) Seijmonsbergen

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Impression of the Aruban landscape: a geodiversity zonation of the coastal area of national park Arikok along the North side of Aruba, showing typical vegetation, like cacti and low thickets, uplifted marine terraces and coastal rock formations.

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Abstract

The growing demand for energy and the negative consequences of fossil fuels have contributed to the rising necessity of renewable energy systems. Islandness makes islands, specifically, vulnerable to these consequences, while also being highly dependent on the import of fossil fuels. This research aims to identify the influence of a characteristic of islandness, geodiversity, on the suitability of underground electricity cables on Aruba. This is done by a three-routine methodology;

pre-processing, analyses and deliverables, where geology, soil, topography, hydrology, geomorphology, geodiversity and suitability maps are processed in ArcGIS Pro 2.7.2. Three different geodiversity indices with different sub-indices have been calculated and statistically compared. The suitability map has five important criteria, based on the multi-criteria decision making process. The criteria for underground electricity cables are 1) the distance from the electricity grid, 2) distance from highways, 3) slope of the terrain, 4) impact on flora and fauna, and 5) the specific geodiversity present.

The most representative geodiversity index for Aruba consists of the topography, materials, geology and hydrology sub-indices. The highest geodiversity values are visible in the central-east and the northern point of Aruba, and the lowest values in low elevated and urban areas. The findings indicate that the lower the geodiversity index value, the higher the suitability for underground electricity cables. Areas with a high slope angle and high elevation levels are classified as unsuitable, which is explained by the inability to perform human activities on these slopes, and the influence of elevation on the hydrology network of Aruba.

Keywords:

Geodiversity index; suitability analysis; MCDM; underground electricity cables; RES; Aruba; Small Island States

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1. Introduction

Energy is a necessity for modern society, and with the evolution of civilizations, the human demand for energy has been rapidly and continuously rising (Asif & Muneer, 2007). Moreover, the growth in global energy demand is expecting to increase by more than 2% per year till 2040 (IEA, 2019). About 80% of this energy demand is continuously sustained by the use of fossil fuels (Armaroli & Balzani, 2011). However, an extensive use of fossil fuels contributes to several unsustainable situations, such as the depletion of sources and global warming (Asif & Muneer, 2007; Höök & Tang, 2013;Atilgan & Azapagic, 2015). Especially islands are challenged with the negative consequences of global warming; sea-level rise and extreme weather events. On the other hand, islands are highly dependent on these fossil fuels (Ioannidis et al., 2019; Meschede, Holzapfel, Kadelbach & Hesselbach, 2016). Fossil fuels are normally not present on islands, which results in high dependency on import, and thus high electricity prices on islands (Ioannidis & Chalvatzis, 2017; Acevedo, 2016). The increasing worldwide energy demand and the consequences of extensive fossil fuels are requiring a contribution of renewable energy systems (RES) to ensure a sustainable living pattern on Earth (Prabhakaran, Kale & Prabakar, 2015; Kale, 2017).

1.1 Islandness, geodiversity and renewable energy systems

Islands’ high vulnerability to global warming is contrary to their dependency on fossil fuels (Ourbak & Magnan, 2018; Petzold & Magnan, 2019). This vulnerability of islands is called islandness, and some characteristics are their small size and the specific bio- and geodiversity. According to Gray (2004), geodiversity is ‘the natural range (diversity) of geological (rocks, minerals, fossils), geomorphological (landform, processes) and soil features. It includes their assemblages,

relationships, properties, interpretations and systems’. Biodiversity entails all species, genetic, and ecosystem diversity in an area (Swingland, 2001). Both geodiversity and biodiversity are sensitive on islands, and in combination with human activities, islands tend to be more vulnerable to disturbances on their diversity (Alahuta et al., 2018; Coulthard et al., 2017).

Changing aspects of a landscape for renewable energy systems will contribute to islandness, since the

available space on islands is limited and energy infrastructures can largely affect the landscape, such as the composition of the soil and the disturbance of biodiversity (Wolsink, 2018; Soini, Pouta, Slamiovirta, Uusitalo & Kivinen, 2011). However, islandness does not only create vulnerability, it also creates opportunities to support the resilience to climate change (Kelman, 2018). The specific characteristics of islands create opportunities for RES; volcanic islands can implement geothermal energy systems and islands with large coastlines wind energy systems (Meschede, Holzapfel, Kadelbach & Hesselbach, 2016). This could result in a decrease in energy import dependence for islands worldwide. However, most islands are unable to take advantage of their opportunities for RES, since their lack of developed electrical grid infrastructure, such as power station locations and

distribution network (Ioannidis, Chalvatzis, Li, Notton & Stephanides, 2019). Moreover, the transition towards a sustainable energy system is possible with ‘forward-looking’ governments, while in

practice most energy governance on Small Island States (SIS) is flawed (Raghoo, et al., 2018).

Consideration of geodiversity is an important step in the development of energy policies concerning both the natural system and (sustainable) human activity (Brilha, Gray, Pereira & Pereira, 2018; Hjort, Gordon, Gray & Hunter Jr, 2015). Moreover, an island’s geodiversity could also be used to determine

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1.2 Aruba as case study for the relation between geodiversity and underground electricity cables Aruba is an example of a SIS that is highly dependent on fossil fuels import, while having ideal climatic circumstances for the implementation of RES. Aruba is located in the tropics of the Southern Caribbean Sea and is approximately 180 km² (Cole & Razak, 2011; DiPietro & Peterson, 2017). Aruba is one of the most densely populated countries in the world, and 44% of this population is located in urban areas (Data Worldbank, 2018; Data Worldbank, 2019). Approximately 18% of the island is designated as a national park, and the elevation of the island ranges from sea level to a height of 165 meters (Mt. Yamanola) (Acevedo, 2016; Schmutz, Potter & Modlin, 2017). The geological centre of the island is composed of Late Cretaceous and Paleogene volcanic and sedimentary rocks. Moreover, Aruba also contains stratified basalt flows, volcano-clastic deposits and intrusions of a large tonalitic batholith (Schmutz, Potter & Modlin, 2017). Throughout the nineteenth century, a gold rush persisted in the landscape of Aruba, which is witnessed by remnants of gold mills and gold mines on the island. Nowadays, agricultural activities are mostly centred on the production of aloe vera (Derix, 2016; Schmutz, Potter & Modlin, 2017).

Figure 1: Climate characteristics ‘windspeed’ and ‘temperature’ of Aruba in 2020.

(Departamento Meteorologico Aruba, 2020).

Aruba is located in the tropics, with an average of 6 sun hours per day, and more than 95% of the time, the wind blows from northeast to southeast direction. As depicted in Figure 1, the average wind speed is 14.1 meter per second (m/s) and blows throughout the year (Acevedo, 2016; Ridderstaat, Oduber, Croes, Nijkamp & Martens, 2014). Aruba’s tropical characteristics give an abundance of opportunities to reach its sustainable energy goals of 100% renewable energy (van Dam, 2018; Energy Transition Initiative, 2015). However, the location of national parks, island elevation, and geological, soil and hydrological characteristics influence the opportunities of RES on Aruba and slow down the road to Aruba’s sustainable energy goals (Acevedo, 2016; Meschede, Holzapfel, Kadelbach & Hesselbach, 2016). It is vital to include the geodiversity to implement RES and its distribution network. The overarching goal of this research is to firstly map the geodiversity of Aruba, and secondly to map the suitability of the energy infrastructure. Therefore, two research questions are formulated as:

1. ‘What is the distribution of the geodiversity index of Aruba?’

2. ‘What are optimal geodiversity-based conditions for locating the underground electricity distribution network on Aruba?’

The first question fills a gap related to the missing geodiversity of Aruba. With a map of the

geodiversity of Aruba, a suitable location for underground electricity cables can be determined. This will support the applicability of renewable energy systems on Aruba, and answer the second research question.

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2. Methodology

The research questions are supported by a range of maps, including a geodiversity and a suitability map for underground electricity cables. These maps require input maps such as the slope or the hydrology of Aruba. Some of these maps are already available, while other maps will need to be processed. The methodology to do so is visualized in a workflow, and consists of three main routines: pre-process, analysis and the deliverables (Figure 2).

Figure 2: General workflow of three different routines: pre-processing, analysis and deliverables,

subdivided into individual steps

2.1 Pre-processing

2.1.1 Data acquisition: maps

To conduct research on the geodiversity of Aruba, all background information in the form of literature and thematic maps need to be collected and assessed. The currently available maps included the geology map, a book scan of a soil map, hydrological features, and the STRM 90m Digital Elevation

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Table 1: Metadata of the datasets, based on Seijmonsbergen, Guldenaar & Rijsdijk (2018).

Sub-index Description Data type Coordinate system Scale/cell size Publication date Source Satellite images Satellite imagery of Aruba WGS 1984 UTM Zone 19N 10 m resolution 2021 Sentinel

Geology Geological units Aruba Polygons WGS 1984 UTM Zone 19N 1:20,000 2016 CBS Aruba / DCBD

Hydrology (Non-) perennial streams Lines WGS 1984 UTM Zone 19N 1:20,000 2016 CBS Aruba

Soil Soil units of Aruba Polygons WGS 1984 UTM Zone 19N 1:40,000 1966 DCBD

DEM Surface elevation of Aruba Raster WGS 1984 UTM Zone 19N 90 m 2008 CGIAR CSI

2.1.2 Data preparation

First, the different data is loaded into ArcGIS Pro 2.7.2. Secondly, the maps are compared to available literature or other data which resulted in a few adjustments in the maps (Table 2). All data is retrieved or categorized in vector format. The outline of Aruba is copied from the geological map from CBS Aruba (Table 1) as a basis for the geomorphology, geodiversity and suitability map. The soil map has a different island boundary. Therefore, small differences occur along the coastline of Aruba.

Table 2: Original source and the adjustments made of the four maps of the pre-processing routine, with the correct tools

and/or remarks

Map Original source Adjustments Tools Remarks

Geology

Beets, Metten &

Hoogendoorn (1996) Derix (2016) Literature & geology map from Derix (2016)

Hydrology Derix (2016) OPM: openstreetmap.org Hydrology toolbox (Spatial Analyst) Points from OPM, stream feature from toolbox

Soil Grontmy (1966) Material map No soil types, but soil elements & material types

Topography SRTM DEM (90m) Contour, Curvature, Hillshade, Slope & Aspect CGIAR CSI (2021)

2.1.3 Determining grid cell size

The calculation by Hengl (2006) is used for an appropriate grid cell size:

P = SN * 0.0025, where P is the grid resolution and SN is the scale number.

Giving that the scale of the maps will be 1:120,000, the suitable grid resolution is 300 x 300m. This cell size will be used as input for a fishnet grid, which is used to calculate the geodiversity index scores. The fishnet grid is being clipped according to the outlines of Aruba, which is a vector file.

2.1.4 Geomorphology mapping

The newly developed geomorphological map its legend is based on three hierarchical tiers (Table 3). Tier 1 entails the geomorphological environments, Tier 2 entails the geomorphic process groups, and lastly, Tier 3 entails the morphogenic domains, that were recently suggested for digital

geomorphological maps by De Jong, Sterk, Shinneman & Seijmonsbergen (2021). The legend categories of the three tiers are combinations of elements derived from topography, geology, material and hydrology maps, in combination with the satellite image-based information and recent literature.

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Table 3: Three tiered geomorphological map legend for Aruba, as newly developed for input into a geodiversity index map. Geomorphology

Tier 1: Environments Tier 2: Process Groups Tier 3: Morphogenic Domains

Fluvial (1000) Fluvial - Accumulation (1100) Alluvial fan (1111)

Salinja (1112)

Isolated (medium) high hills (2111)

Low hills (2112)

Mass movement (2000) Mass movement - Degradation (2100) Medium high hills (2113)

High hills (2114)

Very high hills in ridges (2115)

Mass movement - Accumulation (2200) Colluvial fans (2211)

Volcanism (3000) Volcanic - Accumulation (3100) Aruba Lava Formation (3111)

Aruba Batholith (3112)

Aeolian (4000) Aeolian (4100) Active duneland (4111)

Sandy beach (5111)

Marine - Accumulation (5100) Coral shingle / rocky beach (5112)

Fossil dunes (5113)

Marine (5000) Lower terrace (5211)

Marine (limestone) terrace (5200) Middle terrace (5212)

Higher terrace (5213)

Terrace remnants (5214)

Inland waterbody (6111)

Water (6000) Water (6100) Lagune (6112)

Intermittent river (6113) Urban area (7111) Settlements (7100) Building (7112) Antropogenic (7000) Mines (7113) Road (7211) Infrastructure (7200) Airport (7212)

Vader Piet wind farm (7213)

2.1.5 Data acquisition: cables

The existing distribution networks need to be evaluated for their suitability in relation to spatial geodiversity. The access to the current electricity distribution network was denied, and thus the water distribution network of W.E.B. Aruba is used as a guideline for suitable locations (Figure 3). It visualizes that the northern and eastern coastlines, and the central-east area are excluded from the water distribution network. Taking into account the water distribution network of Aruba, it is expected that the western and southern areas of Aruba are the most suitable for the application of electricity distribution network.

The location of fresh groundwater could be a vital aspect in the suitable locations of electricity cables. However, research has shown that Aruba does not have fresh groundwater, but W.E.B. Aruba is desalinating seawater for drinking water purposes (Besseling & Schoneveld, 2012). Therefore, groundwater is excluded from the criteria of the suitability analysis.

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Figure 3: Water distribution network of Aruba (W.E.B. Aruba, n.d.)

2.2 Analyses

2.2.1 Geodiversity analysis

To calculate the geodiversity index (GDI) a standard calculation is the basis: GDI = Gi + Pdi = Hdi + Tdi. However, missing information or too much overlap in some indices has led to three types of the geodiversity index: 1) GDI = Gi + Mi + Twi + Tdi, 2) GDI = Gi + Gmi + Twi + Tdi, and 3) GDI = Gmi + Mi + Twi + Tdi. All calculations are made with the Raster Calculator tool and the results of the maps are shown in Figure 6, 7 and 8. The five classes are based on the Jenks classification, ranging 1) very low, 2) low, 3) moderate, 4) high, and 5) very high.

The geology, geomorphology, slope and material map are rasterized and reclassified according to the natural breaks (Jenks) to create sub-indices: a geology sub-index (Gi), a material sub-index (Mi), a topographical sub-index (Tdi) and a geomorphology sub-index (Gmi). The hydrology index is calculated by means of the topographic wetness index (Twi), which is based on the upslope area and the slope to quantify the hydrological processes (Sörensen, Zinko & Seibert, 2006). Similar to the previous maps, this Twi has been reclassified following the natural breaks (Jenks) into five categories.

2.2.2 Suitability analysis

The suitability analysis is based on a multi-criteria decision making (MCDM) process, which assesses the comparative importance of several variables to use as input criteria for complex decisions (Baseer, Rehman, Meyer & Alam, 2017). The five most important criteria to implement a new or expanded electricity distribution network on an island are 1) the distance from the electricity grid, 2) distance from highways, 3) slope of the terrain, 4) specific geodiversity present and 5) impact on flora and fauna (e.g. birds’ or natural park locations).

The distance from the energy grid is important for the costs related to cabling and electricity losses with long transmission lines (Baseer, Rehman, Meyer & Alam, 2017). However, the criteria for long transmission lines is 1000 km, and considering the length of Aruba is only 30km, the electricity losses are negligible (Humpert, 2012).

Secondly, the distance from highways should be minimal 0.5 meters to minimize the construction and maintenance costs (Municipality Texel, 2014). Furthermore, a buffer is recommended, and thus a distance of 1.0 meters from the highways is used.

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Thirdly, the slope of a terrain is of great influence for finding suitable locations, considering the impact a high slope angle has on the operation costs and the performance and quality of the cables (Picchio, et al., 2019; Turner, Keane, Mullins & Phipps, 2010). Therefore, a threshold value of 20% is used for the slope of the terrain. This percentage is estimated following literature statements of a threshold range from 10% to 30% (Baseer, Rehman, Meyer & Alam, 2017; Tegou, Polatidis & Haralambopoulos, 2010). The threshold value of 20% corresponds with 10-12.5 degrees, using the following formula:

Degree of the slope = X tan X = rise/run

Percent of the slope = rise/run * 100

The next criterium is the impact on flora and fauna. The national park Arikok and some specific bird habitats are very unsuitable for the implementation of electricity cables, considering the biodiversity of the island. Therefore, they are specifically mentioned in the suitability analysis.

Lastly, a hypothesis is that the geodiversity present in the area largely dictates the suitability of electricity cables. The geodiversity is based on a large range of diversities, and the higher the

individual diversities, the more complex the geodiversity of the area is (Nijdam, 2019; Serrano, Ruiz-Flaño & Arroyo, 2009). The expectation is thus that the higher the geodiversity index, the less suitable the area for electricity cables. The importance of the geodiversity map results in a weight change for the suitability map, and unlike the other criteria, the weight of the geodiversity has been set at 1.25.

2.3 Deliverables and results

Eight maps are created, including the diversity maps of geology, hydrology, materials, slope,

geomorphology, the geodiversity and suitability map. Correlation matrices of GDI1, GDI2 and GDI3 have been made to select the most representative geodiversity map. These matrices can be found in the results for the geodiversity map (Table 4; Table 5; Table 6).

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3. Results

3.1 Pre-processed maps

The deliverables of the maps in the pre-processing routine are presented in Figure 4. These maps contributed to the creation of the geomorphology map, and the sub-indices for the geodiversity map. The results of all figures in this chapter are also presented in Appendix I (pre-processing) and Appendix II (analyses), where the size is bigger and the classifications are better visualized.

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3.2 Geomorphology map

The landscape is primarily dominated by Aruba Batholith, with low to medium high hills. Moreover, near the coastlines, marine terraces dominate the landscape. The lowest terrace occurs on the northeast coast, while the middle terraces encircle the whole island. The terraces consist of hard coral limestone, or soft, limy marl (Alexander, 1961; Derix, 2016).One area is classified as ‘fossil dunes’, following the probability of uplifted limestone formations, aeolian activities to create dunes and was uplifted over time on top of the marine terraces (Figure 5; Appendix I). The materials of the ‘terrace remnants’ are originally alluvial detritus from land and remains of marine organisms. This deposition was nearly destroyed by aerial erosion and left the alluvial marine terraces to remnants (Alexander, 1961). Furthermore, the presence of the urban area on the geomorphology map is remarkably high compared to the soil map from 1966 it was partly based on. Literature indicates that the population in 1960-1970 was almost half of what it is now (Cole & Razak, 2009). In addition, current satellite imagery showed a larger urban area than in 1966. The urban area in the material map consists of 14,584.4 kilometres, while the urban area in the geomorphology map consists of 38,603.5 kilometres, which is an increase of 164.7 percent.

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3.3 Geodiversity index

3.3.1 Geodiversity map

The results of the geodiversity indices are visualized in Figure 6, 7 and 8.

Figure 6: Geodiversity index 1 Figure 7: Geodiversity index 2 Figure 8: Geodiversity index 3

In general, the higher geodiversity values are mostly visible in the middle part and the northern point of the island, which are the areas with the highest slope angles variations, the most varying hydrology system and diverse materials (Figure 4). As visualized in GDI1 and GDI2, the lowest geodiversity is found where low slope angles and urban areas are located, however, GDI3 shows medium to high geodiversity values in these southern areas. Compared to GDI1 and GDI3, the GDI2 shows more extreme values in the geodiversity index; Very Low Geodiversity and Very High Geodiversity.

The differences in geodiversity indices are because of the usage of sub-indices, as visible in the calculations in Figure 6, 7 and 8. The geomorphology (Gmi), however, is based partly on the material map (Mi) and the geology map (Gi), and thus there might be an overlap in those sub-indices.

3.3.2 Statistics

To determine the least data overlap in geodiversity indices, the Band Collection Statistics tool is used to calculate the correlation matrices of the geodiversity indices (GDIs).

Table 4: correlation matrix of GDI 1

GDI1 Tdi Mi Gi Twi

Geodiversity index 1 - GDI1 1

Topographical sub-index - Tdi 0.335 1

Material sub-index - Mi 0.408 -0.227 1

Geology sub-index - Gi 0.635 0.272 0.179 1

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GDI2 Tdi Gmi Gi Twi

Geomorphology sub-index - Gmi 0.625 -0.096 1

Geology sub-index - Gi 0.693 0.272 0.442 1

Topographic wetness sub-index - Twi 0.396 -0.364 0.087 -0.107 1

GDI3 Tdi Gmi Mi Twi

Geomorphology sub-index - Gmi 0.624 -0.128 1

Material sub-index - Mi 0.59 -0.227 0.45 1

Topographical wetness sub-index - Twi 0.499 -0.364 0.074 0.094 1

It is suggested that the GDI1 is the most representative geodiversity index for Aruba, considering the low correlation between the Gi and the Mi (0.179). The GDI2 and the GDI3 show much stronger correlations between the Gi and Gmi, and the Mi and Gmi respectively. The matrices show that the sub-indices geomorphology and geology, as well as the sub-indices geomorphology and material, are similar and therefore contribute equally to the GDI. Furthermore, the Gmi (0.625) and the Gi (0.693) have a quite strong dependence on the GDI2, and the Gmi (0.624) and the Mi (0.59) have a quite strong dependence on the GDI3. The dependence of the sub-indices on the GDI1 is more equally distributed. This is why GDI1 will be used in further analysis.

On Aruba, the low to very low GDI classes dominate 70.6 percent of the total island area (Table 7). The geology sub-index has the highest correlation with the geodiversity on the island, and the materials, topography and hydrology contribute to the GDI1 to a lower extent (Table 4). Possible explanations are the largely similar materials on the island, a high slope angle on only a small area of land on Aruba, and the hydrology on Aruba is not very complex, considering all rivers are intermittent and largely depend on rainfall.

Table 7: Area count in meters and percentages per geodiversity class of the GDI1

3.4 Suitability map

Figure 9 composes the final result of the geodiversity-based suitability map. The map presents suitable locations for underground electricity cables on Aruba, and is divided into five suitability

Value (GDI1) AREA (m) AREA (%) Very Low GDI 43,919,865 25.3

Low GDI 78,670,495 45.3

Medium GDI 38,363,531 22.1

High GDI 10,470,564 6.1

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Figure 9: Suitability map for the location of underground electricity cables on Aruba, based on the distance from highways,

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4. Discussion

4.1 Interpretation of methodology

All the maps have been reclassified for the geodiversity indices according to the ‘Jenks’ method, to create five predefined classes (North, 2009). This method has been chosen because the most common values will be in the middle class, and the ‘outliers’ closer to the lower and upper classes (Nijdam, 2019). Other methods use different classification intervals or calculations, where the number of groups can be statistically defined for the Jenks classification. Choosing different classification methodologies results in different geodiversity indices due to a difference in class boundaries.

The topographic wetness index (Twi) is used as hydrology sub-index for the geodiversity index. The Twi is computed from the digital elevation model (DEM) and is a model where topography aspects estimate the tendency of an area with elevation differences to accumulate water (Hojati & Mokarram, 2016; Sörensen, Zinko & Seibert, 2006). However, research has shown that there are numerous factors capable of influencing the Twi, which are not included in this thesis (Raduła, Szymura & Szymura, 2018). For example, ‘micro-relief’ is essential in very low elevated parts or specific soil humidity of the study area, which can be obtained by a DEM resolution of 0.25 meters (Alexander, Deák & Heilmeier, 2016).

4.2 Interpretation of the results

The distribution of the geodiversity index on Aruba is influenced by its several sub-indices. The importance of the geology sub-index on the geodiversity of Aruba is relatively high (Table 4), which can likely be addressed to the complex tectonic and geological history of the Caribbean (Derix, 2016). Due to different processes, such as magmatic intrusions and uplifting of limestone deposits, the geology of Aruba is broadly stretched over the island. Overall, the geological components of the landscape exert a strong influence on the geodiversity (Hjort & Luoto, 2010; Melelli, Vergari, Liucci & Del Monte, 2017;Necheş, 2016). The importance of the topographical sub-index is the least (Table 4), which is contrary to the results of a low geodiversity index with a lower elevation level. However, the low to zero existence of a slope in lower elevated areas does not only influence the topographical sub-index, but it also largely influences the hydrology sub-index which is based on the DEM

(Sörensen, Zinko & Seibert, 2006). Furthermore, the Aruban rooistelsel (dry-river system) is essential for the discharge of rainfall water towards the sea, and the drainage system is mainly influenced by the types of geology and elevation present (Besseling & Schoneveld, 2012; Beijering, 1950). The northern side of Aruba is becoming more eroded by the influence of elevation on the hydrology network (Derix, 2016). This results in differences in the intra-island hydrology network, which is shown in research by Stavi, Rachmilevitch & Yizhaq (2018) and Seijmonsbergen, Guldenaar & Rijsdijk (2018). The influence of the slope is thus broader than the topographical sub-index, and the elevation of an area is directly influencing the geodiversity.

Comparing the suitability map to the geodiversity map, certain trends can be observed. First, the northern tip of Aruba consists of medium to very high geodiversity index values, and this area is marked as unsuitable. In general, the higher the geodiversity index, the less suitable the area is for underground electricity cables. Second, the angle of the slope contributes to the human activities on an area (Serrano, Ruiz-Flaño & Arroyo, 2009), considering the actual inability to perform some activities with a steep slope (>30º). Thus, an area that can be marked suitable should be of lower

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resistance against erosion of the hornblende tonalite (Finkel & Finkel, 1975). This results in either softer shallow sandy soils, or fertile loamy soils, which are suitable soil mechanical properties for the positioning of cables (Derix, 2016; Taserlaar, 2018).

4.3 Limitations

At first, it is important to note that the quality of the geomorphology map, as well as the geodiversity and the suitability maps, are dependent on the quality of the input data. While some data, such as the DEM, the topographic wetness index and the geology map, have recently been updated or calculated, other data like the soil map of Grontmy (1966) contains old data and lacks the classifications as wanted in a soil map. Therefore, the choice of calling it a material map has been made, however, this does not change the probability of outdated data. Moreover, the Sentinel satellite imagery had 10 meter resolution and was thus not ideal for details of the landscape. For instance, coastal areas could not be classified based on the imagery, and thus the dependency of the input data was high. Field research could have been done to evaluate the current landscape and soil elements on Aruba. The geomorphology map would then be based on field knowledge, supported by satellite imagery, the DEM, and literature, instead of only science-based and expert-based research. Due to the COVID-19 pandemic, it was not possible to analyse the current landscape trends in the form of field research.

4.3 Further research

The outcome of this research can be relevant for multiple organizations and stakeholders, including the energy company Utilities Aruba and its partners WEB N.V. and N.V. Elmar. Research institutions or the government of Aruba might benefit from the outcomes as well, considering the different maps created and the suitability for energy infrastructure.

The geodiversity patterns on Aruba turn out to have a great influence on the suitability areas of the energy distribution network, in this thesis researched as underground electricity cables. This research questioned where the most suitable locations were based on the geodiversity and did not include specific characteristics of the cables. For the actual implementation of the electricity network, it is nonetheless important to include these characteristics, its costs, and policies.

This research gives a general overview of the suitable locations of underground electricity cables on Aruba. However, it does not provide recommendations on specific locations, which could have been done with a suitability map that visualized the most optimal locations for cables with pathways or lines. Further research could use the suitability map in this research for a more detailed route from power stations to cities.

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5. Conclusion

Aruba’s landscape is vulnerable to changes, and thus diverse landscape aspects should be taken into account for the implementation of renewable energy systems and their distribution network.

Especially the geodiversity of an area can play a large role in decision making, considering its role in islandness, landscape planning and the relation to ecosystem services. The answer to the research question: ’What are the optimal geodiversity-based factors for a suitable location of the underground electricity distribution network on Aruba?’ is visualised in the specific maps that resulted from this thesis. Nevertheless, the most important optimal geodiversity-based factors are 1) a low elevated area, 2) a shallow loamy, clayey or sandy soil, 3) low rates of hydrology network, and 4) Aruba Lava Formation; hornblende tonalite. These areas are mainly in the west and central parts of Aruba, where the lowest geodiversity values are present.

The geodiversity index in this thesis is been calculated with the geology, materials, hydrology, and topography. The geodiversity is quite diverse on Aruba, with the north and north-eastern parts of the island containing the highest geodiversity index values. Geology contributes most to the geodiversity index and topography the least.

The suitability map shows that the highest suitability is found on the southern coast, and slightly west from the centre of the island, mainly due to low geodiversity values and the presence of low elevated areas.

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6. References

Acevedo, D. (August 2016). Sustainable Energy for Small Islands: Aruba’s road to 100%. Sustainable Energy

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7. Appendices

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A geodiversity-based suitability analysis on underground electricity cables on Aruba