Journal of Coastal Research Charlottesville. Virginia Old and New Observations on Coastal Changes of Jakarta Bay: An Example of Trends in Urban Stress on Coastal Environments Herman Th, Verstappen International Institute for Aerospace Survey and Earth Sciences Post Office Box 6 7500 AA Enschede, The Netherlands ABSTRACT _ VERSTAPPEN, H. Th., 1988. Old and new observations on coastal changes of Jakarta Bay: an ~""" example of trends in urban stress on coastal environments. Journal of Coastal Research, 4(4), •.. , 573-587. Charlottesville (Virginia). ISSN 0749-0208. •• • • Since the author surveyed the coastal environment of Jakarta Bay in the 19508, rapid urban­ ization has affected both the alluvial plain that borders the bay and the cora] reefs in it. The ~ ~ mJ1f urban stress factors are diverse and include baywater pollution, the use of beach sand and coral debris for construction, the implementation of major engineering works (harbour extension, --+ S-- storage lake), intensified fishing and tourism and, within the Jakarta connurbation, ground­ water extraction resulting in land subsidence of as much as 4-5 em/year. Natural stress factors also have occurred and relate to an anomalous behavior of the InterTropical Convergence Zone (ITCZ), resulting in very low precipitation and relatively strong northerly and easterly winds during the 1960s and 1970s. The coastal environment was unable to absorb the combined stress factors and substantial change and deterioration thus resulted. The causative factors are weighed and an outlook for the future is given. ADDITIONAL INDEX WORDS, Coastal development, groundwater withdrawal, land subsi­ dize, erosion, Intertropical Convergence Zone, water pollution. INTRODUCTION delta of the Citarum River (Figure 1) which is quite unaffected by the fan. The alluvial plain bordering Jakarta Bay Coastal accretion and abrasion since the turn started to grow seaward approximately 5,000 of the century was studied by the author in the years ago at the foot of the Pleistocene fluvio­ early 1950s, using aerial photographs and old volcanic Bogor fan. Fluvial deposition, repeated and new topographic maps (VERSTAPPEN, changes in position of river courses, delta for­ 1953). In this context, the turbidity conditions mation, and intermittent build-up of cheniers of the baywater were also recorded using a Sec­ along parts of the coastline occurred simulta­ chi's disc during the dry (NE), wet (SW) and neously with a 5-m sealevel drop. transitional monsoon periods. The coral cays in The present location of the bay can be partly the bay were also subject of study. Their explained from the radial (divergent) drainage changes with time were studied using 1:20,000 pattern on the fan that favoured fluvial depo­ topographic maps dating from 1874/1901, sition to the west and east at the expense of the 1:5,000 maps from 1927 prepared by sedimentation directly north of it. This is where UMBGROVE (1928) and maps at the same scale present-day Jakarta is situated. Much more prepared under supervision of the author in important in this context, however, is the pres­ 1950/51. The changes in the coral cays can be ence of an almost northward stretching struc­ accounted for by recorded climatic fluctuations. tural ridge in the west where Miocene rocks Fluctuations in the average seasonal position of outcrop or occur at shallow depth under the the InterTropical Convergence Zone (ITCZ) Holocene deposits of the Cisadane River. The result in changing relative intensities of the eastern shore of the bay is formed by the large dry and wet monsoons which in turn result in 85003 received 24 September 1985; accepted in revision S September precipitation fluctuations and in frequency and 1986. force changes of the winds from the eight main 574 Verstappen cluster of coral cays in the western side of the bay, black-&-white aerial photographs of some -- \--- ~ Tg K,.w.ng of the islands, selected field observations of the alluvial plain and terrestrial mapping of a number of coral cays in 1983/1985. The results Jakarta Bay are given below. Tg.Pri4t THE URBAN STRESS FACTORS The urban stress factors are diverse. At least eight major and minor factors can be listed and grouped under three headings. Generalized Factors Affecting Large Parts of the Bay or the Hinterland Water pollution in the bay is attributed to the growing Jakarta connurbation and the ship­ ping activities associated with its harbour Tan­ jung Priok. This has been seriously studied by the National Oceanographic Institute (L.O.N.) using measurements carried out by the author in the early 1950s as representing the "clean, pre-pollution" situation (A. SOEGIARTO, 1975, 1976; BIRD and ONGKOSONGO, 1980). The biotope distribution in the bay has been studied by HEHUWAT (1977). The increasing pollution of the baywater, especially near Ja­ Figure 1. Jakarta Bay and surroundings; scale 1:1,000,000. karta and Tg. Priok, has a strong negative effect on coral growth and thus on the evolution directions. The changing wind regime is impor­ of the bay's coral reefs and cays. Pollution is in tant in explaining the changes of the coral cays part related to oil spilled by ships and in part since they govern the wave and current pat­ to urban waste. The recent coral debris ridges terns around them (VERSTAPPEN, 1954). around the cays show a high proportion of float­ The research undertaken in the early 1980s ing plastics. aimed at assessing how the environment has Land subsidence is caused by the extraction responded to the heavy stress of rapid urbani­ of groundwater. The rapid growth of the Jak­ zation and industrialization during the last arta connurbation has resulted in a sharp rise three decades, when the population increased in both domestic and industrial water require­ from approximately 1 million to 6 million. This ments. Most of this water is derived from the urbanization has resulted in excavation of four major aquifers of the Jakarta artesian building materials (mainly beach sand and basin. They occur at less than 60 m, 6-150 m, coral debris), pollution of the baywater, land 150-225 m and more than 225 m depth respec­ subsidence caused by groundwater extraction, tively, and plunge northward (SOEKARDI & etc. The human factors were unprecedented, HADIWIDJOJO, 1979). The pumping of large but the climatic factors were rather extreme as quantities of groundwater has resulted in land well. The period includes the years of the ill­ subsidence, the magnitude and spatial distri­ famed Sahelian drought which, in the humid bution of which is still largely unknown. An tropical realm, are also characterized by a cli­ indication of the importance of this phenome­ matic fluctuation of rather unusual amplitude. non is the 50 ern subsidence of the ground sur­ The data on which this study was based con­ rounding the Sarinah Department Store in sist of meteorological data, 1982 false colour Jalan Thamrin during a 12-year period, or aerial photographs of the coastal zone and a approximately 4 ern/yr. Study of the spatial dis- Journal of Coastal Research, Vol. 4, No.4, 1988 Coastal Changes of Jakarta Bay, Indonesia 575 (1) The excavation of sand for construction from beaches and nearby beach ridges border­ ing the bay. Excavation is concentrated in the Cilincing area to the east of Tg. Priok. Strong abrasion, first mentioned by PARDJAMAN (1977), and saline water intrusion have taken place and will be discussed below. Excavation of beach sand may also have contributed to the coastal abrasion of the coast at the NW of the bay. Sand is also excavated from inland beach ridges, but this has only limited direct adverse effects. These ridges are of the chenier type and form shallow sandy lenses in the otherwise clayey material of the plain. Excavation thus does not affect the salinization of aquifers. Only the shallow groundwater in the cheniers will ,.6.;1<' disappear, but the small quantities of water concerned, though important in a rural context, would hardly be of importance in a densely pop­ Figure 2. Fluctuations in annual precipitation (dashed line) ulated, urbanized area. The excavated areas and number of rainy days (full line) in Jakarta since about 1880 (ll-years running averages). become more susceptible to flooding. (2) The excavation of coral sand and shingle for construction from the reefs and cays. Mining tribution is hampered by the absence of of coral boulders and the extrication of the shin­ repeated precise levelling. Observations can be gle accumulated in ridges at the windward side made only at buildings with deep pile founda­ of the reefs obviously have an adverse impact tions and at artesian wells that gradually on the islands. Mining the boulders destroys the "rise" above the sinking ground. Houses with­ Ii ving reef. Lowering the reef flat, by mining out deep foundations subside at the same rates the coral, results in increased wave activity and as the ground surface and become more suscep­ consequently in abrasion of the islands. Where tible to inundation, without visible traces of the the shingle ridges have disappeared, the waves amount of subsidence. Since especially the are dissipated on the primary shores of the northern part of Jakarta that borders the bay is cays. The excavation of coral sand from the cays only a few metres above mean sea level, it is adds to the abrasion, even ifthe mined material obvious that abrasion of the coast and invasion comes from accumulations on the relatively by the sea are realistic dangers. The extracted protected leeward side of the coral cays. If the groundwater is, at least in the northern parts climatic conditions were constant, which of the town, in part replaced by saline water obviously they are not, this sand would have and the subsidence is thus reduced to some reached its ultimate position and could not con­ extent.