Proposed soil and water conservation strategies for Lake Rawa Dano, West Java, Indonesia

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1 248 Water Resources Systems Hydrological Risk, Management and Development (Proceedings of symposium HS02b held during IUGG2003 at Sapporo, July 2003). IAHS Publ. no. 281, Proposed soil and water conservation strategies for Lake Rawa Dano, West Java, Indonesia SENO ADI Agency for the Assessment and Application of Technology (BPP Teknologi), BPPT Building 2, It. 18, fl Thamrin No. 8, Jakarta 10340, Indonesia Abstract Lake Rawa Dano lies within a volcanic caldera in a reserve area of West Java. Locally, Rawa Dano means "swampy lake", reflecting that the lake is mostly covered by the swamp forest and water plantations. The lake acts as a water supply for the Krakatao Industrial Estate as well as for the city of Cilegon. There is significant soil erosion in the lake catchment with sediment production averaging 3.32 t ha" 1 year"'. In addition, lake siltation and water plant blooming has caused a decline of lake water quality. Soil and water conservation strategies are needed urgently to mitigate the sediment and nutrient inputs to the lake. The first step is to adopt a civil engineering approach by constructing control dams, check dams, and gully plug/drops, especially for slopes of >30% where there is a high erosion risk. Subsequently, systems of minimum tillage farming, agroforestry, or farm forestry need to be established. The establishment of a water authority is important to aid reversion to a more natural hydrological status by controlling forest encroachment, encouraging soil and water conservation practice, and regulating community development. The water authority could gain income from local water beneficiaries then reinvest in further soil and water conservation practices. Key words conservation; erosion hazard; Indonesia; institution; strategies INTRODUCTION Lake Rawa Dano is located in the western part of Java island. Administratively, this area is in the districts of Serang and Pandeglang, about 100 km from Jakarta city. The lake and its surrounding area of 2500 ha has been defined as a Natural Reserve Area since It is situated in the Cidanau River catchment ( ha). The ecosystem is unique as a volcanic lake dominated by the swamp ecosystem. The biodiversity is large, and for a number of species of flora and fauna the area is the only remaining habitat in Java island. The main function of Lake Rawa Dano is as the water resources supply for Krakatao Industrial Estate, a coal power plant, as well as for domestic use of Cilegon city. The water requirement from this area was 369, 1101, 1563 and s"' for the years 1984, 1989, 1996 and 2000, respectively. The trend of the increase in water supply, however, is in contrast with the environmental protection in the Cidanau River catchment where this catchment has an important role in the Lake Rawa Dano ecosystem. It is likely that the water quality of the lake is going to decrease due to siltation and water plant blooming. The soil degradation in the upstream part of the Cidanau catchment has been identified as the main problem as the erosion from the surrounding hilly area produces exceedingly large sediment and nutrient inputs into the lake.

2 Proposed soil and water conservation strategies for Lake Rawa Dano, West Java, Indonesia 249 The main environmental degradation issues are the population growth and the economic pressure in this area, which have lead to uncontrollable intensive agricultural development. Therefore, a soil and water conservation strategy is needed urgently to conduct the catchment management in a way such that Lake Rawa Dano will remain intact as a sustainable water supply. In this study, not only the physical aspects of the lake are assessed, but also the social aspects for better implementation of the management programme. ENVIRONMENTAL SETTING Physical aspects Geography The Cidanau catchment is located at latitudes and longitudes of 06 07'30"S-06 18'00"S and '00"E '00"E. The study area of the Cidanau catchment is approximately ha, situated in Serang District of West Java, Indonesia. The Natural Reserve Area is located in the central part of the Cidanau catchment, covering an area of 2500 ha. As shown in Table 1, there are six sub-districts in this area. The sub-district of Padarincang has the largest number of villages (nine villages) as well as the biggest area in the catchment. However, the sub-district of Mancak has only one village in this catchment, even though it is not the smallest area. The sub-district of Padarincang has the largest area, almost 50% of the total area. The second and third largest areas are the sub-districts of Cinangka and Ciomas which cover 16% and 11.8% of the total area, respectively. These are located south of the lake. As shown in Table 1 and Fig. 1, the study area consists of six subcatchments called Cisaat, Cisawarna, Cikalumpang, Cibojong, Cicangkedan and Cikondang. The administrative boundaries of the sub-districts are different from the catchment boundaries. From these subcatchments, there are three subcatchments (Cisaat and Cisawarna, Cikalumpang) where the rivers discharge to the Natural Reserve Area. However there are two subcatchments (Cisaat and Cisawarna) that directly discharge to the Lake of Rawa Dano. These are situated in the eastern part of the Cidanau catchment area. Table 1 Cidanau River catchment distribution. No Name of sub Name of Administrative area: Location in Number of district subcatchment (ha) % catchment villages 1 Cinangka Cicangkedan, Cikondang west 7 2 Mancak Cisawarna north 1 3 Pabuaran Cisaat northeast 4 4 Ciomas Cisaat, Cisawarna southeast 9 5 Padarincang Cikalumpang, south 13 Cisawarna, Cibojong 6 Mandaiawangi Cikalumpang south 4 Total

3 250 Seno Adi Fig. 1 The Cidanau catchment area. Soil and geology The soils of the Cidanau catchment consists of alluvial, Regosol, Latosol (Oxisol) and Gley Humic soils. The alluvial (Entisol) soils are mostly located in the surroundings of the lake where the soil has potential for paddy field development. Latosol is the dominating soil, covering approximately 58% of the area. Even though it is quite suitable for agricultural development, this soil type is susceptible to erosion, especially in the absence of conservation practices. Geologically, the rock material ranges from volcanic rocks to alluvial deposits. The stratigraphy of the rock from the older formations to the recent formation can be identified as: lava, breccia and tuff of Mt Dano (lower Pleistocene); tuff of Mt Dano (middle to upper Pleistocene); breccia and lava of Mt Tukung (middle to upper Pleistocene); breccia, tuff, and lava of Mt Karang (upper Pleistocene-Holocene); lava and breccia of Mt Parakasak; river sediment; swamp sediment. Physiography The study area ranges from sea level to 800 m a.s.l. (above sea level) in the surrounding mountains. However, the main area is at m a.s.l. The catchment topography is dominated by flat terrain (almost 40%> of the total area), mostly located in the central northern part of the catchment. The steep and very steep terrain (25% of total area) is mostly located in the southern part and some areas in the hilly northern part of the catchment as shown in Table 2 and Fig. 2. Table 2 Slope distribution. No Slope Area (ha) (%) Dominant distribution Central north West and northeast North North 5 > Hilly north and south Total

4 Proposed soil and water conservation strategies for Lake Rawa Dano, West Java, Indonesia 251 Fig. 2 View of Cidanau catchment, the open surface water is the Lake Rawa Dano. Fig. 3 Geomorphology and physiography of Cidanau catchment. As shown in Fig. 3, Lake Rawa Dano is surrounded by swampy area, then a steep crater-like ridge in the north and east. However, in the southern part it is dominated by gently undulating terrain of 4-5 km width and hilly (medium to high relief) terrain about 10 km to the north. The other part of flat terrain is in the west next to the outlet of the river system of the Cidanau catchment to the sea or Sunda Strait. Hydrology The water discharge data available for the Cidanau River indicates that the average discharge is m 3 s" 1 fluctuating from the annual minimum of 1.2 m J s" 1

5 252 Seno Adi in the dry season (August) to an annual maximum of 44.0 m 3 s" 1 in the rainy season (January). There is a decreasing discharge trend in data available for , , and , and a significant fall of the maximum discharge However, it increased and fluctuated after 1986 as shown in Fig. 4. Unfortunately, river discharge data are only available at the outlet of the Cidanau catchment, so the role of the two subcatchments discharging into the lake as well as the three subcatchments discharging into the Natural Reserve Area is not clear. Data for the outlet of Lake Rawa Dano and the outlet of the Natural Reserve Area would be urgently needed to identify the subcatchment response. There are four rainfall stations suirounding the study area. Unfortunately the data is discontinuous, especially from 1991 up to now. There is only one station with rainfall data available for the years The available data (Fig. 5) suggest that Padarincang station showed a significant fluctuation of rainfall during the period However, the other three stations did not show this specific pattern of total rainfall. Land use The land use of the Cidanau catchment is mostly dominated by agriculture development (71%), consisting of mixed farming (36.7%) and rice fields (34.4%>). Forest covers 18.5% and swamp forest covers 8.4% of the catchment, Fig. 6. The map in Fig. 7 shows mixed farming is mostly located in the southern and western parts of the catchment. However, the rice fields are located partly in the northern part and mostly in the central part of this area, next to the swamp forest. The forest mainly occupies the hilly mountain in the northern part and in the southern part of the area. Finally, most of the settlements are clustered along the main road (westeast) and partly in the southern part. 50 -, I 30 Ï 25 I I Year Fig. 4 Water discharge of the Cidanau River , gj 3500 I" 3000 E, 2500 = 2000!E 1500 co Pabuaran " Padarincang -Qornas Fig. 5 Total rainfall per year of rainfall stations in the Cidanau catchment.

6 Proposed soil and water conservation strategies for Lake Rawa Dano, West Java, Indonesia 253 CD a> 2 c Q) O s <u Fig. 6 The percentage of land use of Cidanau catchment. 5BÏ Fig. 7 Land use distribution of Cidanau catchment. Table 4 Land cover of the Natural Reserve Area, Cidanau catchment. No Type of land cover Area: ha % 1 Swamp forest "Kaso" forest Eichornia crassipes Rice field Open water surface Secondary forest Total Source: Biotrop, 1986 in BPPT-UNEP (1996). Based on aerial photo interpretations of 1981 data, as shown in Table 4, it was identified that the Natural Reserve Area is dominated by forest ecosystems (secondary

7 254 Seno Adi Table 5 Erosion hazard of Cidanau catchment. Source: Bappeda & BRLKT, No Erosion hazard classification Erosion rate (ton/ha/year) % Area Dominant distribution 1 Very light < south 2 Light south 3 Moderate central part 4 Strong 180^ north, northeast, southwest 5 Very strong > north, northeast, southeast forest of 40% and Kaso forest of 25%). Some rice fields cover 29.6% of the reserve area. This intensive agricultural development may cause nutrient enrichment of the lake water due to the use of fertilizers by the faimers. The open water surface of the lake was only 11 ha (0.4%) of the total Natural Reserve Area. The open surface water area has decreased recently due to siltation and water plant blooming. Land degradation Land degradation has occurred in many parts of Indonesia, especially in Java, where upland agriculture is common. The main reason for land degradation is soil erosion due to inappropriate agricultural practices (Suwardjo & Neneng, 1993). These authors noted that degraded land is also found in the forested areas, called critical land with the criteria of vegetation cover less than 25%, slopes of more than 15%, and exhibiting erosion hazard. Water erosion is the most important factor of human induced soil degradation (Oldeman, 1993). Simulations performed for this subcatchment suggested that the forested area is suitable for reducing runoff and the grass area is suitable for reducing erosion rates (Suhartono, 2001). The erosion hazard is classified into five classes, very light, light, moderate, strong and very strong. The erosion hazard has been calculated using the USLE method and GIS facilities to include the spatial information of the Cidanau catchment. The erosion hazard classification and the results are shown in Table 5. Based on this spatial information, the sediment yield for the whole Cidanau catchment has been calculated as t year" 1 or an average of 3.32 ton ha" 1 year" 1. The strong and very strong erosion hazard zones of 12.91%) and 2.6% are mostly located in three areas, in the northern part, southwest part, and along the hilly mountain rim of the northeastern part of the catchment. Social and economic aspects The socio-economic conditions of each village of the sub district will be a significant input to the soil and water conservation strategies. Principally, the more socioeconomic pressure exists in a certain area, the more attention should be given to conservation practices. The data for each village are the basic data to conduct a socioeconomic survey based on the approach of (Bappeda & BRLKT, 2000) detailed below. Population pressure The land for agriculture activities has not extended much recently; in some areas the agricultural area has even decreased as population growth has led to a need for more space for settlements. The population pressure used in this

8 Proposed soil and water conservation strategies for Lake Rawa Dano, West Java, Indonesia 255 study is a function of the minimum agricultural area for subsistence, number of fanners, total population, all compared with the total agricultural area. It is then assigned low, medium, and high pressure values. Agricultural pressure The leading sector in the villages up to now has been the agricultural sector. By knowing how far people depend on agriculture activities, the role of the agriculture sector could be evaluated. It is a function of the number of people working in the agricultural sector compared with the total work force in all other sectors. The agricultural pressure is measured by low, moderate and high values. Economic pressure The economic status of the people is represented by their income. The income of an inhabitant would affect the land resources protection because the conservation practice usually needs some extra cost that leads to a smaller economic benefit. The income is defined by calculating the agricultural produce and other products in cash value, compared with the standard minimum living cost. The economic pressure is measured by low, moderate and high incomes of the inhabitants. The socio-economic condition is the combined result of population pressure, agricultural pressure and economic pressure. The summary of the social economic aspects, as shown in Table 6, indicates that the sub-district of Mancak (in the Natural Reserve Area) and sub-district of Pabuaran (in the eastern part of the Cidanau catchment) exhibit the most favourable socio-economic conditions. The second in rank is the sub-district of Cinangka, which is located in the western part close to the outlet of the Cidanau River. The poorest socio-economic conditions are found in the subdistricts of Ciomas and Mandalawangi. Low to moderate socio economic conditions occur in the subcatchment of Padarincang where the number of villages is largest. Table 6 Summary of the social economic condition distribution of sub-districts. No Name of sub Social economic aspect Socio-economic district Population Agriculture Economic condition pressure pressure pressure 1 Cinangka high high high high 2 Mancak high high high high 3 Pabuaran high high high high 4 Ciomas low low-moderate low low 5 Padarincang low-moderate low-moderate low low-moderate 6 Mandalawangi low low low low Source: summarized and analysed from Bappeda & BRLKT (2000). CONSERVATION STRATEGIES AND DEVELOPMENT Based on the characteristics of the environmental setting and the current land degradation, a sustainable development of land and water conservation in this area can be carried out by priority development. The erosion hazard in this region urgently requires proper soil protection by conservation practices. The impact of erosion is not only local losses by decreasing soil productivity, but also in losses as a result of decreasing water quality and siltation in the lake. A study done by Margareth reported that the impact of erosion in Java cost US$ million year" 1 (Supirin, 2001).

9 256 Seno Adi Soil and water conservation The significant erosion hazard and the high ratio of minimum discharge in the dry season and maximum discharge in the rainy season, indicate that the catchment needs much attention for soil and water conservation. As discussed previously, the use of agricultural strategies and engineering structures are suitable for maintaining soil productivity and water sustainability. The conservation practice then could simply be defined as follows: Agronomic method This method consists of protecting the soil from the raindrop energy by covering the soil with vegetation such as grass, residue management, cover cropping, alley cropping, multiple cropping, strip cropping, and agroforestry. The use of alley cropping in West Java was reported to reduce runoff by 51-85% (Partowijoto et al, 2001). Engineering or mechanical methods This is physical treatment of the land surface to increase its ability to reduce runoff as well as to increase soil infiltration. The structures are contour bunds and terraces (diversion, retention, bench). An experiment with terrace benches in West Java on slopes of 15-22% showed a reduction of runoff by up to 32% (Partowijoto et al, 2001). Other structures are check dams, control dams, gully packs, and enhancements of river bank stability. Priority development The whole catchment area needs an appropriate strategy for the implementation of soil and water conservation. A priority scale is important for implementing an effective scheme. First of all, there is an urgent need for soil and water conservation in the subcatchments draining to Lake Raw Dano. These are in the district of Padarincang and Ciomas (in the southern part), Mancak (northern part), and Pabuaran (northeastern part). These areas are associated with strong and very strong erosion hazards, high pressure socio-economic conditions and seasonal crop, perennial crop, and forest land utilization. The following priority developments are therefore proposed for different land uses: (a) The first priority development is strong and very strong erosion hazard zones with high socio-economic pressure, under seasonal crops where the farmers manage the land for agricultural development on a seasonal basis by a multi-cropping approach. The seasonal crop has economic benefits and is very important for supporting the food supply. The areas of these conditions, however, occur only in a small part of Padarincang district in this region. (b) The second priority development is strong and very strong erosion hazard zones with high socio-economic pressure in forested areas which have an important role controlling the hydrology of the system and hence are of key importance in sustaining the water supply for Lake Rawa Dano. Next, agroforestry with a minimum tillage approach is recommended in these areas. These areas are widely distributed in all districts in the vicinity of Lake Rawa Dano, mostly in the districts of Padarincang, Pabuaran, Mancak, and Ciomas.

10 Proposed soil and water conservation strategies for Lake Rawa Dano, West Java, Indonesia 257 (c) The third priority development is the strong and very strong erosion hazard zones with high socio-economic pressure under perennial crops. These areas occur in many parts of Padarincang district and in some parts in Ciomas district. Institutional development The objectives of catchment management are to maintain the soil productivity and water availability in a sustainable way. This means that soil and water conservation practices are the core of catchment management. It is understood that the work of a soil and water conservation programme is an intersector and even interdepartmental programme. The participation of all stakeholders such as government institutions, NGOs, farmer communities and scientists is needed to achieve the objectives mentioned above. Governmental institutions are the Department of Agriculture (Soil and Water Conservation Division), the Department of Forestry (Centre for Land Rehabilitation and Soil Conservation), the Department of Public Works (Water Resources Services), the Regional Development Planning Board, and Research and Development Institutes. The policies of the soil and water conservation programme at the district level are under the coordination of a Regional Development Planning Board. This is to keep close contacts with other sector programmes related to the regional development such as civil infrastructure, tourism, agriculture, etc. However, the implementation project of soil and water conservation and land rehabilitation is done by the Centre for Land Rehabilitation and Soil Conservation (Department of Forestry). The field implementation is also done by this institute or Regional Forest Services. In the forested area it is called the Re-boisation programme and in the non forested area it is called the Re-greening programme. The other stakeholders of nongovernmental institutions such as community groups and water supply companies are, however, often neither included (at least not informed well) in the policy nor in the implementation project. Therefore, a lack of coordination between the government institutions and nongovernmental institutions may cause the soil and water conservation programme not to work efficiently in the field implementation. In addition, soil and water conservation should not only be an intersector programme, but also an inter-regional programme as the catchment boundary usually does not match the administrative boundary. To address this issue, an authority should be established to facilitate coordination so that all stakeholders can meet in one institution. Therefore an institution such as a water authority could be considered as the authority responsible for river basin management. The concept of one river, one plan and one management strategy should be established first in this authority from the planning to the implementation level. The function of this institution would be to prepare a master plan, controlling forest encroachment, encouraging soil and water conservation practices, and promoting community participation in the programme. The financial support of these activities should come from the water beneficiaries such as water supply companies and industries who benefit from the Cidanau River water. In principle, the income from water or agriculture products should be reinvested for soil and water conservation practices to maintain soil productivity and water continuity in a sustainable way.

11 258 Seno Adi CONCLUSIONS Conservation strategies for Lake Rawa Dano have been defined based on the physical aspects and socio-economic aspects under conditions of moderate to very strong erosion hazard in agricultural and forested areas. The combined result of these factors provides a ranking of priority development for soil and water conservation, from seasonal crop areas, to forested areas, and perennial crops. The current lack of coordination among the stakeholders of the soil and water conservation programme, especially between the governmental and nongovernmental institutions, may cause the conservation practices not to work efficiently. A coordinating body such as a water or lake authority should be established to overcome this situation where the concept of one catchment, one plan, one management strategy has to be defined first. The financial support for soil and water conservation should, in principle, come from the water beneficiaries such as water supply companies and industries. These contributions should be re-invested for soil and water conservation practices. REFERENCES Bappeda tk. II Serang & BRLKT Citarum Ciliwung (2000) Field Technique Planning on Land Rehabilitation and Soil Conservation of Cidanau Catchment, Book 1 (Main Book), Book 2 (Data Book), Book 3 (Map), Bogor (in Indonesian). BPP Teknologi & UNEP (1996) Proceeding on Lake Management in Indonesia, Case Study: Lake Rawa Danau. Jakarta, Indonesia. Partowijoto, A., Sitompul, A. T. M. & Faridz, A. E. (2001) The implementation and effectiveness of land and water conservation engineering: case study in Java Island. In: Water Resources Management in the Era of Regional Oihonomy (Proc., Malang, East Java) (in Indonesian). Suhartanto, E. & Hardjoamidjojo, S. (2001) The optimisation of catchment management in the subcatchment of Cidanau River, Serang district by using ANSWERS hydrological model. In: Water Resources Management in the Era of Regional Oihonomy (Proc., Malang, East Java) (in Indonesian). Supirin (2001) Soil and Water Reources Conservation. Yogyakarta (in Indonesian). Suwardjo & Neneng, L. N (1994) Land degradation in Indonesia: data collection and analysis. In: The Collection and Analysis of Land Degradation Data. Report of the Expert Consultation of the Asian Network on Problem Soils, Regional Office for Asia and Pacific, FAO-UN, Bangkok, Thailand.