International Journal of Engineering and Science Applications IJEScA ISSN2406-9833

Coastal Erosion Prone Area Assessment in - Coastal Area, .asiite

1,2 1 2 G. L. Simamora ,M. I.Djawad andD. Ware 1Graduate School, Hasanuddin University, 90245, Makassar, Indonesia 2 School of Environment and Science, Griffith University, Brisbane, Australia email: [email protected] (correspondenceauthor)

ABSTRACT

Coastal hazards affect the majority of sandy shores, and are responsible for damage to, and destruction of settlements, infrastructures, public services and sacred places in Bali’s shorelines. However, there is an absence of information regarding the extent of the erosion hazard in Klungkung Regency coastal area. This study aims to assess the suitabilityerosion prone area components and method for assessing them for Klungkung Regency Coastal Area based on available secondary data. Literature review is conducted to evaluate the existingerosion setbacks and previous studies of the location. Then the available information iscorresponded with the erosion components required. For the study location, several erosion setback components that need to be assessed include short-term erosion component, long-term erosion component, sea level rise, dune stability component, and factor safety. Subsequently, shoreline response model is utilized for assessing short-term erosion component, whilst dune scarp migration is conducted to evaluate long-term erosion component. Furthermore, Bruun’s Rule is applied to estimate the sea level rise component. It is expected that for future study, a different approach of erosion prone area assessment will be conducted, so the result from this study can be compared with. Additionally, the result of this study is expected to provide the information about coastal erosion assessment methods and reference about coastal erosion for future study. Keywords: coastal hazards; coastal erosion; erosion prone area; erosion prone area assessment and needs careful handling [6]. Moreover, 1. INTRODUCTION several studies, which have been conducted For Balinese, the coastal area holds important to assess the coastal erosion phenomena in roles. Many economic activities such as rice- Bali, claimed that coastal erosion has farming, fisheries, tourist-hospitality, seaweed occurred in several parts in Bali, including farming, and sand or gravel mining are conducted Jembrana Regency, , in these areas [1-4].Not only providing places to City, , and carry out these activities, the coastal area also is an [7-11]. Thus, settlements, ideal place for settlements. Moreover, the coastal public services, infrastructure and religious area is a sacred place for Balinese. Most sacred sites in these places are threatened by temples where religious services are conducted, are coastal erosion. located in the coastal[5]. Similar to other coastal areas in Bali, However, according to reports, 187 km of Klungkung Regency coastal area has a Bali’s coastline is threatened by coastal erosion variety of land-cover including rice fields,

27 settlements, sacred temples, and traditional ports A.1. Beach Type for fisheries and strait crossings [12]. A study The study area is a flat beach, which conducted to assess coastal dynamics in Gianyar has a low to moderate beach slope (0° to and Klungkung Regency claimed that the area had 10°) [13]. The width of the beach is between been eroded with a rate of approximately 0.88 3 meters to 15 meters, behind the back of the meter per annum [9]. As a result of this problem, beach is a secondary crop field [13]. The the local communities, property owners and local beach material in the study area is composed government are currently considering appropriate of volcanic sand because the fluvial sand is responses. However, there is an absence of supplied from volcanic mountains [13]. information regarding the extent of the erosion Therefore, the sand found there is black and hazard. Consequently, an uncertain risk assessment smooth. might further exacerbate the problem. This study A.2. Water Level aims to assess the suitable erosion prone area Tides in this location are mixed semi- componentsand methods by linkingthe available diurnal types [14]. Based on the analysis data from previous studies and erosion prone area high tide occurred twice in a day as did low setback required for an erosion assessment. tide[14]. The highest high-water level (HHWL) is 3,796 m and mean high water 2. METHODOLOGY level (MHWL) is 2,047 m [14]. Moreover, A. Study area the highest astronomical tide generated from

The location of the research is based in the tidal analysis is 3.9m [14]. Klungkung Regency coastal area of Bali, A.3. Wave Climate Indonesia. The location is situated on the The height of the average wave in Bali northeastern side of Denpasar, Bali. The research reaches approximately 2.0 to 2.5 m on north location coordinates are 115°22'12"E to Bali and 2.5 to 3.0 m on south Bali [15]. 115°28'47"E and 8°34'30"S to 8°33'02"S. The High waves around 2.5 to 3 m are found in length of coastline in the study area is south Bali and to the north of Nusa Penida approximately 11 km. Island where waves come from the southeast [16]. This means that the southern part of Bali, including the Lombok Strait, is directly influenced by the wave energy of the Indian Ocean (from the south). Moreover, the Indian Ocean, which is located south of Java and Bali, has the highest trend of mean significant wave height (SWH) with 5.05 m for January [17].

The direction of wave propagation is Figure 2.1Study Location strongly influenced by the wind direction. Source: ArcGIS Pro, 2019 The effective waves fetch from three 28 dominant courses which are the Flores Sea wave height and storm tide level factors (northeast of Bali), the Lombok Strait (east Bali), interact with the coastline for a length of and the Indian Ocean through the Lombok Strait time (duration). Assessment, of the (southeast Bali) [18]. While the biggest wind fetch horizontal slump of the beach associated is from the Indian Ocean also (southeast Bali) with with storm events, with the techniques a course direction of 135° [18]. available varies from purely empirical procedures to those combinations of A.4. Extreme Wave and Storm Tide practical and theoretical considerations. The maximum distance of inundation in the Several methods to predict beach South Bali coastal area, if storm wave and swell instabilities in response to erosive occur, is 623.5 m, the run-up vertical height is 1.02 phenomena during storm events are m and the depth of maximum inundation in the presented on the Table 2.1. area is 0.46 m[19]. Moreover, extreme waves occur around the Indian Ocean, which is south of Table 2.1Short-term setback model assessment Java and Bali, is caused by the swell from the direction of Western Australia, and are highly Source: Kinsela&Haslow, 2013; Mariani et al, 2012. associated with monsoon cycles, from Asia and No Name Type Data Input Description - beach profile or dune Australia [20, 21]. The positive result of this profile Two-dimensional cross deterministic - nearshore bathymetry 1 SBEACH shore transport based on process - offshore wave parameters cross shore transport sand phenomena is that the wave is colder in this area - water levels sediment properties - beach profile or dune Two-dimensional storm and contains more nutrients [22]. profile impact model of wave deterministic - near shore bathymetry 2 XBeach propagation, long waves process - offshore wave parameters and mean flow, sediment - water levels transport B. Erosion Setback Components and Data - sediment properties

statistical observation data of Probabilistic Analysis and calculation Required statistical - wave climate 3 Coastline of a long set of realistic process - water level Recession erosion and its recovery - periods between storms

Coastal erosion prone area is a composition of - beach profile or dune It has capacity to profile Shoreline simulate short geological deterministic - near shore bathymetry 4 Evolution time scale of shore several coastal hazard seatback assessments [23, process - offshore wave parameters Model evolution and investigate - water levels sea level rise impact - sediment properties 24]. - water level (tide, surge, Combination of both sea level rise) Shoreline longshore, cross-shore statistical - wave input (significant 5 Response sediment transport, and process wave height, period and Model estimation response of direction) the beach to sea level rise - sediment properties Geometric Two-dimensional cross deterministic water level input (including 6 Profile with estimated sand loss process extreme events) Models due to storm events

B.2. Long-term erosion (S2) Underlying recession component is known as long-term erosion component. It happens due to persistent loss of beach and Figure 2.2Erosion setback components dune sediments to onshore, offshore, and

Source: Mariani et al. ,2012 alongshore or sediment sinks [23]. It can be interpreted from the historical trend of B.1. Short-term erosion (S1) shoreline position shifting towards the Short term erosion component is obtained inland. Here are approaches to assess long- from the assessment of the probability of term erosion setbacks. occurrence of storms, which have been recorded statistically [23]. During a storm event, significant 29

Table 2.2 Methods of long-term erosion setbacks Table 2.3Approaches for sea level rise component assessment Source: Kinsela&Haslow, 2013 Source: Mariani et al, 2013 No Technique Data input Potential Limitations reliable quantification of - ground survey longshore sediment budget is No Technique Data input Description 1 Longshore sediment budget - LIDAR survey difficult to attain and often Based on assumption that as sea level is - beach profile require long-term survey raised, the equilibrium profile is moved datasets - water level upward and landward conserving mass the accuracy of magnitude - slope of the beach and original shape - time series aerial and estimation from recent 1 The Bruun rule face The major uncertainty is the definition Dune-scarp migration photographs recession rates are low 2 (photogrammetry) - multi-temporal satellite the confidence of projected - planning years of closure depth images estimation due to map scale The limitation is the lack of any leg time is not rough between sea level change and profile - time series aerial the accuracy of magnitude response photographs and estimation from recent It represents a pragmatic modelling Profile-area-volume analysis - multi-temporal satellite recession rates are low approach based on simple geometric 3 (photogrammetry) images the confidence of projected - beach profile transformation and sediment budget Shore face translation - beach profile estimation due to map scale 2 - planning years principles model - ground survey is not robust the accuracy of the results depends on - time series aerial the accuracy of magnitude the user’s understanding of the physical photographs and estimation from recent Dune-scarp migration and processes affecting a particular site - multi-temporal satellite recession rates are low 4 profile-area-volume analysis - water level the results produced is parallel with images the confidence of projected (photogrammetry) - slope of the short-term erosion component (S1) - ground survey estimation due to map scale 3 Komar geometric model - beach profile is not robust beach face it is not suitable for assessing long-term - planning years profile where the accretion occurs refusion of the Bruun Rule model RD-A model (Davidson - beach profile 4 it has not been compared with field or Arnott) - planning years B.3. Sea level rise (S3) laboratory measurement - water level - slope of the it is similar with the Bruun Rule model, 5 EShorance The sea level rise component is an uncertain beach face but it is for an estuarine environment - planning years - time series of it presents a powerful framework, but element of coastal erosion because it needs future storm waves 6 Process based model without adequate site-specific data a - water level significant uncertainty still remains - beach profile period planning as a consideration for parameter It calculates the equilibrium or maximum response profile to a change - beach profile Shoreline response in wave or water level condition and input. This is due to the time frame planning, 7 - wave data model then incorporates an exponentially - water level lagged response to simulate more which is beyond ahead, and the uncertainty of natural response meteorological parameters included as data input B.4. Beach rotation (S4) to predict the sea level rise [25]. There are several Beach rotation component comprises a methods that have been developed to estimate returning cycle change in the alignment of a coastal response to sea level rise. Basically, these beach's planform due to changes in the wave methods use a basic geometry principle or more course over medium (weeks to months) to complex process-based assessment. Here are long (decades) term time scales [23]. The several methods to estimate sea level rise significance of beach rotation for different component. sections of the coast is likely to vary with latitude, orientation, and length [23, 26]. Moreover, the requirement of differential sediment transport evokes a minimum embayment length, which exists for shoreline variability due to beach rotation [23]. Kinsela and Hanslowin 2013, provided several techniques to assess the beach rotation setback component in New South Wales, as shown on the Table 2.4 [26].

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Table 2.4Techniques to determines beach rotation C. Data analysis setback Literature review from previous Source: Kinsela&Hanslow, 2013 research on the location are performed to No Technique Description Limitations It is utilized for hazard definition Do not reflect the potential for and represents average shoreline generate available data. Cross tabulation coincident medium term erosion 1 Reference beach state planform or future conditions that and episodic storm-induced contribute to enhanced or moderate erosion erosion data are conducted to check the available It is a linear shoreline planform Mean wave direction Future wave climate remains 2 from normal to incident waves for variability uncertain calculating potential rotation data with the required data in each presented It analyses historical records for Frequency of aerial photograph 3 Photogrammetry identifying any erosion or accretion capture remains low confidence records pattern for the isolated beach technique. Suitable method is applied based Do not provide full description It utilizes sampled model wave of the range potential conditions Shoreline evolution climate that considered to be 4 particularly interdecadal wave model representative of the exact on the availability data. climate and storm induced beach condition of the location. rotation.

B.5. Dune stability (S5) 3. RESULTAND DISCUSSION Dune stability factor encompasses a setback component relating to the geotechnical stability of A. Short-term erosion component (S1) dunes [23]. According to Ramsay et al. in 2012, The available data generated from the generic formula to determine dune stability previous studies are presented on the table factor is applying thirty degrees slopes in the below calculation[25].However, in a tropical area with a Data Available Source Required for humid climate, a dune is rarely found. Beach Beach Profiles Not available - 1,2,4 Dune profile Not available - profile commonly found in tropical climate area near shore bathymetry Not available - 1,2,4 consists of sandy beach with low beach ridge and Offshore wave Not available - 1,2,4 parameters little transgressive dune development [27]. The Indonesia Geospatial Water level / tidal level Available 1,2,3,4,5, lack of dunes development in humid tropical area Information Agency (Parawangsa, Arthana, & is due to the high intensity of precipitation on the Sediment properties Available Ekawaty, 2018; San-Nami 2,4,5 et al., 2013) Wave climate statistical area, meager sediment sorting in the beach and Not available - 3 data nearshore zone and low wind energy at the Periods between storm Not available - 3 Wave input (significant (Bachtiar & Novico, wave height, period, and available 5,6 shoreline due to the nature of the coastal 2012) direction) Extreme events available (Ningsih et al., 2012) 6 orientation [27, 28].

B.6. Factor safety (FS) Based on the table above, the available Factor safety (FS) is the calculation procedure data assessed for this component are tidal adopted for erosion prone area width level, sediment properties, wave input data, determinations and are consistent with current and extreme events data. Hence, the engineering practice in this field but are subject to component is assessed using shoreline uncertainties and limitations. Typically, it is response model. associated with the calculation of short-term B. Long-term erosion component (S2) erosion, ongoing recession component, and sea While for the long-term erosion level rise[23]. However, in NSW, the calculation component, the existing data are shown on procedures of factor safety are used for short term the table erosion, continuous recession component, and sea level rise and dune stability component[26].

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Data Available Source Required forF. Factor safety (FS) Ground survey not available - 1,3 LIDAR survey not available - 1,4 Google earth (2003, 2005, Multi-temporal satellite images available 2,3,4 2013, 2015, and 2019) No particular data is required to assess Indonesia Geospatial Aerial photographs available Information Agency 2,3,4 this component because the calculation is (1994) Beach profile not available - 1,3,4 subjected to the calculation of other setback

Multi-temporal satellite images are utilized to components such as short-term erosion evaluate this component. Aerial photograph is not setback (S1), long-term erosion setback employed for calculating due to unmatched scale (S2), and sea lever rise setback (S3). Hence and image distortions. Dune scarp migration this component is an uncertainty factor of technique is performed to analyze this component. prior setbacks calculation. Therefore, this component is included into computation. C. Sea level rise component (S3)

The available data toevaluate sea level rise 4. CONCLUSIONS component is presented on the table below A coastal prone area component for Data Availability Source Required for Klungkung Regency is generated from four Indonesia Geospatial water level available 1,3,5,6,7 Information Agency seatback components and uncertainty factor, slope of the beach face available (San-Nami et al., 2013) 2,3,5 generic set for 2050 and planning years available 1,2,3,4,5 including short-term erosion component, 2100 beach profile not available 2,4,5,7 long-term erosion component, sea level rise wave data not available 7 component, dune stability component, and

Water level data, slope of the beach face and factor safety. Subsequently, shoreline planning year are obtained to predict this response model is applied to assess the component. Bruun’s Rule is selected to estimate short-term erosion component, while dune the future sea level rise on the study location. scarp migration is utilized to evaluate the D. Beach rotation component (S4) long-term erosion component. Moreover, the Bruun’s rule is employed to estimate the sea No available data is presented for this level rise component. The setback component and it can be seen on the table below components are established on the Data Availability Source Required For high resolution aerial availability of secondary data, whilst the not available - photography recording videos of the presented methods are based on previous location in a period not available - time studies. Hopefully, the result of coastal beach profile not available -

erosion prone area assessment using these No data available to calculate this component, setback components can be applied as therefore this component is disregarded. information source about coastal erosion E. Dune stability component (S5) study for future research.

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