|Environmental Changes on the Coasts of Indonesia (UNU, 1980, 53 pages)|
As the foregoing account has shown, there are major gaps in our basic knowledge of the Indonesian coastal environment. Although highly generalized geological and topographical maps of the Indonesian archipelago are available at scales of 1 :2,000,000 there is only limited coverage at larger scales outside Java. Geological maps covering Java are available on three sheets at the 1: 5,000,000 scale and parts of the north and south coast are mapped on the 1: 100,000 scale. There are also geological maps of Bali, Sumbawa, and Sumba at 1 :250,000, but apart from the Padang area there are no largescale geological maps of the Sumatran coast. Kalimantan is partially covered by 1 :500,000 geological mapping; Sulawes; only on the 1 :1,000,000 scale apart from four sectors at 1 :250,000, while the eastern islands and Irian Jaya are not yet covered by recent maps from the Geological Survey of Indonesia. As geological mapping proceeds it may be possible to include more detailed coverage of coastal regions, showing the extent and nature of beaches, beach ridges, and dunes; of cliffed coasts; and of coral reefs at, above, and below present sea level.
It would be useful to have the equivalents of Verstappen's 1 :2,500,000 geomorphological map of Sumatra for the rest of Indonesia, but for coastal work it is necessary to include details of cliffed and steep coasts, beaches and related features, reefs, and mangrove swamps. Such information should preferably be published on a much larger scale, at least 1 :50,000 (the scale of the engineering geology maps of the Jakarta area), which could then be assembled in the form of an atlas of strip maps, each showing coastal sectors 30 kilometres long and up to 10 kilometres wide. There is little doubt that many important features of the Indonesian coastline have escaped reconnaissance attention and would come to light in the course of assembling such a survey.
Once the nature and pattern of Indonesian coastal land-forms has been fully documented it may be possible to arrive at a more accurate picture of the extent of changes that have occurred in recent decades. Our investigations of this topic have been impeded by the limited availability of detailed surveys and aerial photographs that can be used to establish past configurations for comparison with present outlines, in order to establish linear and areal measurements of the extent of change over specified periods. Evidence has been presented of the extent of such changes in deltaic regions, mainly in Java, but there are many sectors of the Indonesian coastline where the changes that have occurred cannot be gauged from cartographic, photographic, and documentary evidence available at present. In the course of archival searches we found many interesting historical maps and charts, especially those compiled by Dutch surveyors in the nineteenth and early twentieth centuries, but were disappointed to find only a few sectors with coverage sufficiently reliable to establish the extent of subsequent coastal changes. It is possible that additional historical data bearing upon this question will be found as the result of further inquiries.
More satisfactory information on trends of coastal change can be obtained by monitoring shoreline positions in relation to fixed survey locations. Studies of this kind have been initiated by Hehuwat and Hehanussa on the Cimanuk delta and in a number of other locations by the Directorate of Hydraulic Engineering (Bandung). These result in measurements of shoreline changes that are much more accurate than those obtainable from air photographs or cartographical comparisons without such ground control. In Java especially, a comprehensive programme of delta shoreline monitoring-using fixed survey location that can be identified on aerial photographs and used as a basis for field measurements to shoreline positions-would be of particular value in determining rates of change and particularly in providing an early warning of sectors that, having previously prograded, show signs of the onset of active erosion. Given such warning, it should be possible to plan modifications of land use in sectors under threat of erosion or to devise some kinds of anti-erosion procedures, before actual damage is done to brackish-water fishponds, farmland, routeways, or built-up areas. The possibility of managing water and sediment flow to delta shorelines, put forward in the previous chapter, would require detailed survey data of this kind as a basis for designing canals and determining optimal shoreline locations for their outlets.
As has been indicated, Indonesian coastlines are subject to various natural hazards, including the direct and indirect effects of earthquakes and volcanic eruptions, tsunami, and river flooding. Assessments of the risk require detailed mapping of centres of disturbance, such as the location and alignments of fault zones along which earthquake epicentres have been located, and the distribution of active and temporarily quiescent volcanoes. With reference to these it is possible to derive maps showing hazard levels around the more populous parts of the Indonesian coastal zone, for example the heights likely to be attained by tsunami generated from a coastal or submarine disturbance. Such information could be of particular value in planning settlement sites and routeways in coastal regions and devising security procedures such as warning systems and evacuation drills for coastal sectors where the risk is high, for example, on the shores of Sunda Strait where a repetition of the 1883 tsunami (attaining 30 metres above sea level) must be counted a possibility. The extent of river flooding in coastal regions can be established in relation to gauging station levels, and maps could be prepared of the depth of flooding to be expected during predictable floods of specific recurrence interval.
An array of ecological changes is known to accompany natural and artificial modifications of the coastal margin: progradation often leads to the seaward advance of mangroves and successional migration of mangrove communities, whereas erosion leads not only to loss of vegetation but also increased landward penetration of marine influences, especially salt water, leading to the replacement of freshwater and vegetation by halophytic communities and to the die-back of trees and shrubs that cannot tolerate high levels of groundwater salinity or occasional inundation by floodwaters that have become brackish. Few maps have been made of coastal vegetation and, although mangrove species have been listed at a number of sites, information on their distribution through Indonesia remains scanty and quite inadequate for assessing the extent to which they occur and can be conserved within coastal reserves declared for this purpose. Systematic listing and mapping of mangrove species, and of other coastal vegetation such as salt marsh and beach/dune woodland, is necessary as a basis for botanical conservation on the coasts of Indonesia.
There are similar limitations in available data on Indonesian coastal zoology. While some information is available on species of economic value, especially fish and crustaceans, in the coastal waters of Java and Sumatra and to a lesser extent elsewhere in Indonesia, there is only scattered and fragmentary data on the rest of the fauna, even the bird life having received little attention. There is considerable scope for surveys of animal ecology in the coastal zone, especially on the smaller islands, and in the swampy environments of Irian Jaya.
The distribution of coral reefs in the Indonesian region has been indicated on hydrographic charts and we have reviewed some of their features, as described and discussed by Davis (1928), Molengraaf (1929), Kuenen (1933), Umbgrove (1947), and others. While much detailed observation has been carried out, and the biota of Indonesian coral reefs widely investigated, the richness, variety, and profusion of coralline features in this region are so great that an immense amount of research is still necessary on the evolution, ecology, and dynamics of these reef structures. One field of study concerns the initiation of reefs and their rates of growth, a topic that may repay investigation on the volcanic shores of Sunda Strait, where reefs that began to form after the Krakatau explosion show nearly a century of growth. Another is the response of reef corals to the effects of sedimentation, especially the accumulation of silt and clay discharged into the sea by rivers, and of pollution. These topics can conveniently be studied on the reefs in Jakarta Bay.
In Chapter 2 reference was made to the numerous raised reefs, found at a variety of levels, especially in eastern Indonesia. Many of these have been dissected by rivers, and on such islands as Atauro, off Timor, it is possible to study sections showing the internal structure of fringing reefs attached to volcanic slopes, now uplifted out of the sea. Chappell and Veeh (1978), who have illustrated these sections, have also applied uranium-thorium dating to establish the ages of reefs. Particular attention is given to reefs about 120,000 years old, which are thought to have formed when the sea stood between 5 and 8 metres above its present level. The altitude of such reefs above or below the 5- to 8-metre level is thus an indication of the extent of subsequent uplift or depression of the land margin. Mapping of the present level of the 120,000-year-old reef formation will generate a picture of the late Quaternary tectonic history of the Indonesian region and help to resolve some geophysical questions concerning the movements of bordering plates.
In the course of such research, some coastal sites will prove to be of particular scientific importance, either because they show clearly features and relationships that are typical of a wider area or because of their uniqueness. This applies not only to geological and geomorphological features but also to sites that show characteristic or rare botanical, zoological, and archaeological features. The location, delimitation, documentation, and management of such sites is essential for their maintenance for further scientific research and for educational purposes. Inventories of such sites have been compiled in a number of countries in Europe and the Americas, as well as in parts of Australia and New Zealand, and it is necessary now to document them in Indonesia. It is obvious that such sites as Krakatau in Sunda Strait, the dunes of Parangtritis, and the uplifted coral reef terrace stairway on Atauro Island are of international significance, for they are already established in scientific literature, but many other coastal sites are of scientific importance and their mapping and documentation should be carried out systematically, preferably within a framework of data collection organized by LIPI.
Returning from the consideration of such broad scientific problems to more specific and applicable research in the coastal zone, we regard the practical problems of brackishwater fishpond construction and management as being of paramount importance in Indonesia. The origin of fishpond cultures of this kind is uncertain: there have certainly been brackish-water fishponds on parts of the north coast of Java for several centuries. In the past few decades these have spread along much of the deltaic shoreline on this island and to a few scattered sites elsewhere in Indonesia. Since they produce a valuable source of animal protein, chiefly in the form of milkfish and shrimps, their design and management are of great practical importance. Some aspects of landwater interactions relevant to the management of brackishwater fishponds are being investigated by the United Nations University's Natural Resources Programme, in association with LIPI and the Bogor Agricultural University (IPB), but there is really a need for a comprehensive research programme involving coastal geomorphology, engineering, hydrology, ecology, and climatology, as well as the socioeconomic aspects of tambak cuIture in Indonesia.
Existing brackish-water fishponds become hypersaline, or even dry out in the dry season and are subject to inflow of hinterland water that is commonly eutrophic, polluted, or bearing toxic chemicals, notably pesticides, used on the ricefields. These effects seriously limit the productivity of the fishpond ecosystem. Provision of a sea-water supply is largely based on gravitational inflow by means of channels that are apt to become silted or sealed off by wave-deposited sand at their mouths during the dry season, when northeasterly wave action is relatively strong. The design of the fishponds and their sea-water supply could be rationalized in relation to inflow sources that can be maintained, particularly if simple pumping devices can be utilized.
Reference has also been made to problems of stability of areas converted to fishponds where the mangrove fringes have been cleared away and wave erosion facilitated. In addition to the necessity of conserving the mangrove vegetation, it may be possible to use mangroves in and around the fishponds to improve shelter, shade, and nutrient supply, benefiting the fishery at the same time as maintaining mangroves for timber and firewood production.
Our hope is that existing studies can be amplified and extended to the point where practical contributions can be made to the design and management of brackish-water fishponds. In socioeconomic terms we see this as the most important single problem in the changing environment of the Indonesian coastal zone.
The impetus for this study derived initially from the work of the International Geographical Union's Working Group on the Dynamics of Shoreline Erosion. Between 1972 and 1976 this Working Group sought world-wide data on the extent of advance or recession of shorelines over the past century. Published information on the world scale was inevitably patchy, some sectors having been repeatedly mapped, air photographed, and studied in great detail, while others were known only at a reconnaissance level, with limited data. Apart from the work of Verstappen, Hollerwoger, and Tjia, mainly in Java and eastern Sumatra, Indonesia fell into the second category, and the Working Group had to be content with a relatively brief statement (Bird 1976a)..
In 1976 the Working Group was expanded into a broader Commission on the Coastal Environment and charged with the task of world-wide reporting on five topics: changes in progress on mangrove and salt marsh coasts, the effects of artificial structures on shorelines, the dynamics of coastal dune systems, and the requirements for delimiting coastal sites of scientific interest, in addition to further work on sandy shoreline changes. In practice, the Commission has been led to consider a wide range of problems of coastal management arising from the environmental changes that it has been documenting.
The present study has sought to document and review existing knowledge of environmental changes in the Indonesian coastal zone, and to examine some of the management problems and research needs that arise from awareness of these changes. Reference has also been made to such features as changing mangrove systems, the effects of land reclamation, the problems of the mobile dunes in south-central Java, and the need to locate and document coastal sites of scientific interest, especially in the less-known eastern Indonesian region. The study has thus developed an Indonesian contribution to the world-wide projects of the IGU Commission on the Coastal Environment.
It is acknowledged that there are many gaps in our information on the coastal features of Indonesia and the environmental changes that are, or have recently been, taking place. This reflects the great length and complexity of the archipelago coastline; the fact that access to many sectors remains difficult; and the relatively early stage in development of Indonesian scientific resources in this field. The United Nations University, through its coastal resources management project, is endeavouring to stimulate further surveys and research work at the same time as training and giving experience to young Indonesian scientists embarking on various kinds of coastal research. The initial project (1979 to 1980) was based in Jakarta with emphasis on the deltaic coast eastward to Cirebon and field studies on the Cimanuk delta. In succeeding years, similar projects are to be conducted elsewhere in Indonesia. In each case coastal data are assembled for an introductory programmatic workshop (Bird and Soegiarto 1980) and refined and supplemented in the course of the year's work. One difficulty has been the lack of background material for use by Indonesian scientists. Our hope is that the present study will provide a framework for this research and for further coastal-data collection during the next few Years.