Wulan Delta in Central Java has been experiencd coastal morphodynamics due to interface between Wulan River’s sedimentation and Java sea’s oceanographic process. This paper aims to analyze Wulan Delta’s morphodynamics as well as its impacts on the socio-economic condition of the community. The morphodynamics is interpreted visually and digitally using a maximum livelihood analysis of multiscale and multi-temporal images. The socio-economic impact is defined by field observations and in-depth interviews to the community and stakeholders. Analysis during the period of 1931-2010 showed that Wulan Delta had been changed morphologically from straight with small arc-like (arcuate) to bird-foot (digitate) with a plausible change into rounded (lobate) in the future, which represented dominant sedimentation by oceanographic rather than fluvial processes. Land expansion in Wulan Delta led to landuse change in Wedung, i.e. expansion of settlement area to 167 ha and fish pond area to 1014 ha in 2000-2010. Most settlements in the area, which are built linearly to river levees, own a high vulnerability to both river flood and tidal inundation. Therefore, dissemination about knowledge of the disaster and coastal zone management, as a means of increasing awareness, becomes necessary in integrating the coastal management in Wulan Delta together with improvement in infrastructure and proper regional development. The proper development strategy for the coastal village is aggressive maintenance strategy, including public infrastructure revitalization, quality improvement for human resources, and silvofishery system. Law enforcement on coastal zoning regulations is necessary to achieve an integrated and sustainable coastal zone management.
Indonesia was an archipelago with 99.093 km shoreline length [
Delta, as one of several highly dynamic coastal ecosystems, is a landform where deposition process from the river creates a flat coastal area and, therefore, causes irregular shoreline progradation [
Wulan Delta is located in the northern part of Demak (
The morphodynamic Wulan Delta causes land use conversion from mangroves to fishponds, used as a local livelihood source. Furthermore, the continuously changing extent of Wulan Delta would likely trigger land ownership conflicts. Therefore, an analysis of the morphodynamics of Wulan Delta as well as its physical and social impacts becomes necessary. This paper aims to analyze the morphodynamics of Wulan Delta using multi-temporal remote sensing images and to analyze its impacts on the socio-economic condition of the local community. The results provide a reference on integrated coastal zone management of Wulan Delta, including management of the upper watershed that provides sediment in Wulan Delta.
This research was conducted in the coastal area of Wulan Delta which is located administratively in two villages,
i.e. BerahanWetan and Babalan, Wedung Sub-district, Demak Regency, Indonesia. The research methods include shoreline extractions on Wulan Delta and analyses of oceanographic characteristics, land use changes, and social conditions affected by shoreline and land use change. Shoreline extraction was performed using visual and digital interpretation of geospatial data. Visual interpretation used the 1931 topographic map (1:50,000), the 2001 Indonesian Topographic Map (1:25,000) from the 1999 database, and an Alos satellite image in 2010. Meanwhile, digital interpretation used maximum livelihood analysis on the 1972 Landsat MSS image and the 2002 Landsat 7 image. Maximum livelihood analysis classifies pixel values based on Bayes’ rules. Separability analysis is required in determining the pixel class in order to identify the separability of the classified objects. This analysis used Jeffries-matuista and Transformed Divergence methods with “Compute ROI Separability” option in ENVI 4.5 software. The separability value has a range of 0 to 2, and indicates a good separability whenever the value approaches 2 classified the transformed divergence value into five (5) classes, i.e. <1600 (not separated); 1601 - 1699 (badly separated); 1700 - 1899 (separated); 1900 - 1999 (well separated); and 2 (perfectly separated) [
The oceanographic characteristics were analyzed using Sverdrup Munk Bretschneider (SMB) method on the wind data obtained from the Agency for Meteorology, Climatology and Geophysics (BMKG) Maritime Semarang. SMB method considers the length of the wind path (fetch), which affects both height and speed of wind-induced waves and currents. Wind data was firstly converted into wind speed above the sea surface by considering the different wind stress factors between the land and the sea.
Land use analysis included a visual interpretation on satellite images and maps in 2000 and 2010. Furthermore, a correction was also conducted based on field observations and in-depth interviews on land use change. Physical and social conditions were identified from surveys on institution, literature studies, and in-depth interviews to local community. Primary data acquisition was conducted on May 27-29 and June 11-13, 2013.
Coastal management recommendation was determined using analysis of Strengths, Weaknesses, Opportuni-
ties, and Threats (SWOT) which identifies the influencing factors of an object based on internal (strengths and weaknesses) and external (opportunities and threats) factors. Each factor is inventoried and presented in the formulation matrix for management strategy.
Based on the bathymetric map of Java Sea, the mouth of Wulan River and its surrounding area have a depth of 0 - 10 m. The shallow and flat coastal area of Wulan Delta causes waves to break and, then, results in relatively low wave energy. Low wave energy is not able to transport the sediment emptied out by Wulan River. As a result, the sediment is deposited around the mouth of the river.
According to the daily maximum wind data in 2002-2012, obtained from the Maritime Meteorology, Climatology and Geophysic Agency (BMKG Maritime) of Semarang, the wind changes direction in every season. Wulan Delta is influenced by a monsoonal climate that divides a year into four seasons, i.e. West, Transition I, East, and Transition II. During the West season (December-February), wind dominantly blows from the west (32.16%) in a speed of 0 - 10 knots (51.31%). Meanwhile, during the Transition I season (March-May), wind blows from various directions, i.e. from the east (31.36%), north (19.39%), southeast (12.76%), and northwest (18.50%). Furthermore, this wind blows dominantly with a speed of 0 - 10 knots (77.80%), while a more than 27―knot wind speed only occurs for 0.1%. During the East season (June-August), wind dominantly blows from the east (62.55%) with an average wind speed of 9.62 knots. Meanwhile, during the Transition II season (September-November), wind blows dominantly from the east (37.30%) with a dominant speed of 0 - 10 knots (50.0%) and 10 - 15 knots (41.30%).
A wind is considered as a causal factor in the development of Wulan Delta whenever it blows inshore and has a capability of inducing sea waves and currents. Wind speed data shows that such influencing wind blows from the west (12.35%), north (19.39%), and northwest (20.65%). Therefore, an optimum development of Wulan Delta occurs during the seasons of West, Transition I, and Transition II.
Based on sea waves analysis using the Sverdrup Munk Bretschneider (SMB) method on the 2002-2012 wind data, more sea waves are induced by west wind (55%) during the west season, however, their height is relatively low, i.e. 1.5 - 3 m. Meanwhile, both north and northwest wind induced waves with a height of higher than 2 m up to 4 m. Primary measurement on June 11, 2013 up to 11.24 a.m. (High tide) shows that the wave around Wulan Delta was 4.77 m in height and 19.24 m in length. The wave experienced refraction due to a change in depth, causing a wave break on the height of 3.55 m. At the same time, measurement at 03:26 p.m. (low tide) shows that the wave had a height of 2.13 m and a length of 22.53, and broke at a height of 1.92 m.
Seawater around Wulan Delta has a tidal range of less than 2 m; thus, it is categorized as microtidal [
Morphodynamics is a landform geomorphological change due to exogenous factors. Delta is a coastal landform influenced by exogenous factors such as fluvial and marine processes, for instance, Wulan Delta experiences both fluvial processes, originated from Wulan River, and marine processes, induced by the wave and current energy of Java Sea. Wulan Delta has a bird-foot shape (digitate) with a curved shoreline. Its composing material is originated from the upper part of Serang River, which is Muria Volcano in the north and Rembang and Kendeng Hills in the south. Based on Whitten et al., Serang Watershed has an area of 3860 km2 with an average annual rainfall of 2450 mm and a surface discharge of 29 m3∙s−1 [
Landform units in Wulan Delta are composed of mud flats on the delta front and tidal flats on the delta plain. Tidal flat is a marine landform influenced by seawater tides and composed of mud. Mud comes from the overflow during flood events in Wulan River and forms wider tidal flats. Based on the information obtained from local community, there has not been a major flood in the last 10 years, causing less mud supply. Consequently, some parts of Wulan Delta have been experiencing coastal erosion. The nowadays flood occurs in a small overflow which only inundates the nearby floodplains and back swamps of Wulan River.
Wulan Delta was initially formed due to the scenario to direct the sediment flow of Serang River to the southern shore of Jepara through Wulan Canal in 1892 [
The 2000 satellite image indicates that the left side of Wulan Delta has been developing westward due to the westward tributary formation of Wulan River. This tributary has been developing together with a larger river channel. In addition, Wulan River has several small tributaries formed both naturally and artificially for irrigation purposes. The nowadays shape of Wulan Delta is bird-foot with a curved shoreline. The large amount of sediment supply as well as the constructive oceanographic characteristic of Java Sea becomes the key causes of Wulan Delta development. Sunarto stated that Wulan Delta will continue to develop northwestward until a point where the main channel of Wulan River reaches the ocean trench [
Despite the progradation tendency of Wulan Delta, some parts of this delta experience coastal erosion (see the red-circled area in
The left map in
The sea waves around the Wulan Delta transport sediments from the river and deposit them around the delta forming sand barrier (
opposite applies during low tides. In addition, beach moring glory plant (Ipomoea pes-caprae) or locally known as tapakkambing (
The formation of sand barrier indicates that sea currents and waves proceed dominantly among the other influencing processes in a delta development [
The morphodynamic Wulan Delta triggers land use changes, with a prominent change experienced by fishponds, settlements, and mangroves. Wulan River has been transporting sediments from Serang Watershed to its mouth gradually since 1892 [
The in-depth interviews to community leaders, fishponds farmers, and fishermen conclude that nowadays river floods no longer occur in Wulan Delta. This is deemed the result of successful Serang Watershed management including the land use management and dam development, conducted by Watershed Management Authority (BPDAS) of Jratunseluna as parts of strategies in managing soil erosion in the upper part of watershed and in fulfilling the water demand in Serang Watershed. Due to the lack of significant amount of sediment supply, the area of fishponds is not extendible. In some locations, fishponds have experienced damages due to the eroding currents and sea waves (
Damages on the fishponds result in economic losses since aquaculture is the leading economic sector in the coastal villages in Wulan Delta. These ponds are used to breed milkfish, shrimp, and crab. In dry season, some fishponds are used as salt ponds. Normally, fish farmers earn IDR 3-5 million per month, while tenant fish farmers earn IDR 1.5 million per month. Nevertheless, coastal erosion causes fishpond damage that drastically decreases the income of the local households.
Besides causing damages to fishponds, currents and sea waves also create damages to mangroves. Mangrove is an ecosystem found muddy coast with low wave energy, estuaries, lagoons, and deltas [
The extent of mangroves decreased by 92.81 ha in 2000-2010 due to current and wave energy as well as landuse conversion into fishponds. The dominant mangrove found in this area is Rhizophora sp., whose stilt roots decrease the sea wave energy; therefore, this species survives in the outer side of delta. Other mangrove species growing in this area are Avicenniaalba, Sonneratia sp. and Bruguiera sp.
Settlement area in Berahan Wetan village increased 167 hectares in 2000-2010. Meanwhile, the settlement area has been developing in the last 20 years especially around the upper part of the delta, whose soil materials are more resistant. Menco, the closest settlement area to the coast (
posed to river flood and tidal inundation hazard. The local community built concrete levees along the Wulan River. However, most settlement is still inundated during the high tides. In order to adapt with this hazard, the local community builds their houses with higher foundation in order to prevent the inundation from flowing into the house.
The development of coastal villages cannot be separated from coastal management, especially on both problems and potentials of the area. Therefore, it is necessary to establish a development strategy to develop a sustainable coastal area based on ecology and community. The problems and potentials of a coastal area are inventoried based on their strengths, weaknesses, opportunities, and threats.
Beautiful scenery of Wulan Delta can be developed as a tourist area. Mangrove ecosystem and bird sanctuary increase the pulling factor of eco-based tourism. The potential of aquaculture practices need a more sustainable management in order to decrease the destructive impacts of coastal erosion on fishponds and mangroves, as well as to increase the economic condition in Wulan Delta. Moreover, the poor sanitation on the settlement area needs a further environmental management involving the government and the local community. In order to increase the adaptive capacity of the local community in Berahan Wetan, the central government and NGOs need to provide assistance to fish farmer and fishermen community and support in the form of ship loans. Unfortunately, parts of the community have not implemented the regulations issued by the government and suggested by NGOs. This area is exposed to the threats of river and tidal flood. Such exposure causes damages to the ponds and settlements and also inflicts economic and social losses.
SWOT analysis described above results in a formulation of several strategies in coastal management for the physical and social environment. Analysis of Internal Factor Analysis Summary and External Factor Analysis Summary (IFAS-EFAS) on the quadrant matrix of strategy shows that the coastal village of Berahan Wetan is suitably developed using an aggressive maintenance strategy, i.e. an active and aggressive management in solving the problems and increasing the potentials of the coastal village. The government has issued the zoning regulation for coastal area, however, the enforcement is low. The regional and local government should provide assistance to the community regarding the zoning regulations set by the government. Revision on the zoning regulations should include the participation of the community in order to obtain acceptable results for all parties. The quality of coastal ecosystem needs improvements in order to support the sustainability of fisheries and aquaculture practices. Silvofishery system is suitably applied on Wulan Delta, i.e. by planting mangroves around the fishponds; thus, the ponds become relatively safer from the coastal erosion. The outer side of the delta is a protected and a buffer zone. Therefore, an area with a width of 100 m from the shoreline is classified as coastal buffer zone based on Decree of the Ministry of Environment No. 201 in 2004. The protected area should be functioned as a green belt by planting mangrove as an ecological-based breakwater.
The development of coastal village as a tourist destination needs to consider public infrastructure. The procurement and revitalization of public facilities need water treatment, drainage channel management, and also waste management. Road network and public transport need an improvement considering the very limited infrastructures. Community empowerment through socialization on the importance of health and environmental sustainability is also important due its role as the key to improving the quality of human and environmental resources in coastal villages as well as the ability to develop their potential.
Wulan Delta had experienced morphological changes from straight then arcuate, into bird-foot (digitate) in 1931-2010. Nowadays, Wulan Delta has formed sand barrier in front of the delta which indicates the dominance of oceanographic processes rather than fluvial processes. This condition shows that Wulan Delta has a tendency to transform into a round delta (lobate) in the future. The progradation of Wulan Delta leads to land use changes in Wedung Sub-district. The settlement area had increased by 167 ha, while the fish ponds had increased by 1014 ha within a period of 2000-2010. The ponds are increased due to the conversion of mangroves into fishponds, as the main livelihood source of the local community. Besides experiencing land conversion, mangroves also experience damages due to coastal erosion. Coastal erosion occurs lately because there is a change in the pattern of sea currents and waves due to the obstruction created by the delta. Coastal erosion has also damaged 30 - 40 ha of fish ponds since 2005. Most settlements are built linearly along the river levees. Therefore, the settlement in this region has a high vulnerability to river floods and tidal inundation. The suitable development strategies for the coastal villages of Berahan Wetan is an aggressive maintenance strategy, with an improvement in public infrastructure, human resources quality, and the implementation of silvofishery system in the fish ponds management. The implementation of law enforcement on the zoning regulation as well as its socialization to the local community, become necessary in applying an integrated and sustainable coastal zone management.
This research is supported by Research Grant of International Corporation and Publication, Directorate General of Higher Education Indonesia 2015.
Muh ArisMarfai,Desy WahyuningTyas,IdhamNugraha,AyuFitriatul’Ulya,WidianaRiasasi, (2016) The Morphodynamics of Wulan Delta and Its Impacts on the Coastal Community in Wedung Subdistrict, Demak Regency, Indonesia. Journal of Environmental Protection,07,60-71. doi: 10.4236/jep.2016.71006