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<Technology Needs for Lake Management in Indonesia - Investigation of Rawa Danau and Rawa Pening, Java> I. Conflicts of Interest Having established certain priorities in regards to the management objectives of Rawa Danau, it is appropriate to consider the consequences of these decisions on the existing problems and conflicts of interest in the caldera. 1. Conflicts of interest over water There are various demands for water from or at Rawa Danau at the present time. The main ones are: Water for swamp and lake conservation Water for lake restoration and swamp rehabilitation and conservation These needs would be met by creation of a dam with the formation of a lake in the caldera. The success of the swamp forest rehabilitation would depend on the implementation of an appropriate, annual, water management regime. Water for people and industries in Cilegon Many of the present needs for water in Cilegon are met by the present supply of water to Cilegon from the Ci Danau river. Future needs might prove to be a problem in a drought year, so it seems likely that a dam with controllable release gates on it could provide additional water from Rawa Danau in such years. This should meet the needs of people and industries at Cilegon into the period of 2010 or beyond. It may be desirable for the Krakatau Steel Group to plan to create additional dams on small rivers such as the Anyer and the Ci Durian to meet any additional requirements for industry after that period. Water for domestic use in Rawa Danau Water is taken from many of the small rivers crossing the caldera for domestic use in kampungs. In some cases the kampungs involved will be flooded seasonally by the waters of the lake and the kampungs will have to be abandoned. In other cases, where kampungs lie above 100 metres in height, the people in the kampungs obtain water for domestic use from streams coming from the adjacent hills. These kampungs will not be affected by the creation of the lake. In a few cases, people in kampungs will find that the water which they normally obtain from small fast flowing streams in the drainage ditches in the caldera have become slow flowing muddy backwaters after creation of the lake. A small number of people will be affected in this way. Water for rice growing in the caldera Water supplies for rice cultivation will, in general, not be affected by the creation of the lake, because the water is taken from streams coming from the hills and led by gravity onto the sawah in shallow canals. The irrigation system for sawah in the caldera is based on a separate system of water canals from the drainage ditches, which are in places over 2 metres below the level of the sawah. Water for fish ponds in the caldera There should be ample supplies of water available for fish ponds. Ideally, these should be created at the edge of the wet season water level of the lake, so that the ponds fill with water at that season, and only lose water gradually as the water level in the lake decreases towards the dry season. The creation of the lake should increase greatly the opportunities for fish culture in the caldera. 2. Conflicts of interest for land in the caldera Demands for land are not always expressed in an explicit form. They may have to be diagnosed from the behaviour of a community. The demand need not be for the land as such but for the resources which can be derived from the land. Land use in the caldera has been detailed previously. Land occupied by swamp forest, allocated for Cagar Alam Land occupied by swamp forest This is obviously part of the Cagar Alam. This is a genetic resource of unknown but potentially huge value, as has been detailed previously in assessment of the conservation value of the forest. Yet the consistent use of the swamp forest by local residents for extraction of wood and for hunting shows that this is a valuable resource to them (Postema, 1994; PHPA, 1993). In the opinion of PHPA these are the same people who are responsible for destruction of that resource. It is likely that the population in the local kampungs cannot survive at present without access to the resources of the swamp forest. If it is to survive, the destruction of the swamp forest must be stopped. This calls for more effective action by staff of PHPA. It also calls for a better understanding of the ecology of the area by PHPA staff and by the local residents. This calls for an educational input. It also calls for the creation of additional sources of income for the local residents. This could, in part, take the form of creation of fish ponds. Land flooded by the creation of a restored lake in the caldera This will, unfortunately, displace several hundreds of local residents because their kampungs will be flooded during the wet season, when the lake will be at its largest. There is no easy solution to this problem. If necessary, it might be suggested that those for whom there is no other solution might become transmigrants. Several thousand former residents of the caldera have already joined in the transmigration program during the last fifteen years. Certainly all those who are seen as being illegal settlers in the Cagar Alam should be removed. Land needed by residents for food production Many of those who at present live in kampungs on the floor of the caldera cultivate adjacent padi fields. Residents of kampungs such as Tambakan and Kajaroan will find that they have to abandon their homes during the wet season. They will also find that they are unable to cultivate their padi fields as these may be under water in the new lake. They will be unable to meet their needs for food. The possibility of cultivation of the interseasonal mud of the lake exists, but is not recommended. It is likely that these people will have to leave permanently if they cannot obtain an adequate income from fish ponds. Land formerly sawah, now reallocated as Cagar Alam These areas of abandoned sawah should be flooded seasonally by the construction of a dam at the exit from the lake. This should encourage regeneration of the swamp forest. One might hope that the swamp forest would spread under such conditions, along the edge of the new lake, towards the exit from the caldera. This area of unused land is a source of potential conflict at present, as it is seen as fertile land which is deliberately not being used by the Government, but which is not occupied by swamp forest or any other useful vegetation. Land available for the creation of fish ponds Considerable areas of existing sawah in the caldera may have to be taken over by the Government, from their legal owners, and converted to fish ponds. The cash flow per hectare from a fish pond should be several times that from an equivalent area of sawah. The fish ponds will become viable in the caldera following the creation of the lake, because of the seasonal availability of abundant water on the surface of the soil. The fish ponds may have to be constructed by Government along the edge of the lake in the wet season, by mechanical excavators or by paid human labour. It will be difficult to predict for the first four or five years exactly where the edge of the lake during the wet season will be as this depends on the height of the water retained in the caldera. This in turn depends on the regeneration of trees in the swamp forest. A number of species of fish are known to occur in Rawa Danau. These are mostly indigenous fish, and none are believed to be endemic. The commonest species are Trichogaster trichogaster (sepat siam), Monopterus sp (swamp eel), and Clarias batrachus (catfish or lele). It is probable that other species of Indonesian and exotic fish have been introduced deliberately and accidentally in the course of the last 50 years. If the proposal to create a lake with a depth of two metres or over is accepted, then there will be increased pressure from anglers for the introduction of more fish species better able to benefit from a lake environment. Because of the continuity of the lake with the conservation area of the swamp forest this proposal should be rejected. However, experience in other countries such as Australia shows that anglers feel they know better than scientists, and inappropriate species are frequently introduced into lakes and dams irrespective of restrictive legislation. It would be very desirable to introduce into Rawa Danau the species Ctenopharyngodon idella, the grass carp. This species feeds on the roots of aquatic plants such as the floating water plants Eichornia crassipes (water hyacinth), and Pistia stratiotes, as well as on submerged water plants such as Hydrolla verticilata, Ceratophyllum demersum, Najas indica, which are its preferred food. Ctenopharyngodon idella would not be likely to compete with the existing species of fish in the lakes and rivers, but it would assist in the control of water hyacinth which covers large areas of the surface water in the existing river system. This species of fish should be introduced whether or not the proposal for construction of a dam is adopted. Crass carp are not predators and are unlikely to affect the invertebrate fauna of the caldera. It is doubtful if grass carp could breed naturally in the waters of Rawa Danau, and it might be necessary to establish breeding ponds on the shore specifically for the supply of quantities of young Ctenopraryngodon. This would supply additional work opportunities for local villagers. Although Rawa Danau is a well developed lake and river system which has been in existence for many hundreds of years, it would be feasible to increase fish production in the caldera. This would involve both the creation of fish ponds on the shore of the lake and the introduction of new species of fish to the lake. Possibly some of these are already present in the river system. One of the species most appropriate for introduction is Orcochromis nilotica (the Red Nile). This is a species of shallow water fish which could feed and breed in the water of the lake with minimal interference with the existing fish populations in the caldera as far as is known. It would be very desirable to assess the suitability of this species in advance of its introduction. Other exotic species such as Oreochromis mossambica (Ikan mujahir) should not be introduced without careful assessment, well in advance, of the risks of the impact of the new species on the aquatic fauna and ecosystems of the Cagar Alam. O. mossambica is a species which is likely to grow very well in fish ponds in this sort of environment.
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