Cover Image
close this bookConducting Environmental Impact Assessment in Developing Countries (United Nations University, 1999, 375 p.)
close this folder10. Case studies to illustrate environmental impact assessment studies
View the documentCase study 10.1 Tongonan Geothermal Power Plant, Leyte, Philippines
View the documentCase study 10.2 Accelerated Mahaweli Development Programme
View the documentCase study 10.3 Tin Smelter Project in Thailand
View the documentCase study 10.4 Thai National Fertilizer Corporation Project
View the documentCase study 10.5 Map Ta Phut Port Project
View the documentCase study 10.6 EIA at Work: A Hydroelectric Project in Indonesia
View the documentCase study 10.7 The Greater Cairo Wastewater Project

Case study 10.6 EIA at Work: A Hydroelectric Project in Indonesia

Philip Paridine, Canadian International Development Agency

The proposed Lake Sentani hydroelectric development is located in the province of Irian Jaya in the extreme northeast of Indonesia. The site is near Jayapura, some 20 km from the border with Papua New Guinea. Sentani is a natural lake with an outflow through the Jafuri River eventually reaching the Pacific Ocean. By closing off the Jafuri outlet and diverting the flow through a series of channels and tunnels to Yautefa Bay, it is possible to generate hydroelectricity.

The main environmental features of the project are therefore a reduction of the Jafuri flow, manipulation of the lake water levels, input of extra fresh water into the marine system of Yautefa Bay, and terrain disturbances along the flow diversion corridor.

Sentani Lake is surrounded by 22 small villages whose residents live a traditional lifestyle. In the Yautefa Bay area fishing is practised while the diversion corridor is currently designated for high intensity development. The Sentani culture is very old and is traditionally orientated towards the lake with houses constructed on stilts in the water. This factor became a key aspect of the impact assessment.

When the Canadian-based consultant firm Acres International became involved in the Sentani Lake project in 1982, several studies had already been completed. In 1977 Tata consultants did a feasibility study which developed the flows through channels. The Tata study proposed a 10 MW plant and would have raised the lake level by 2 m, requiring relocation of the Sentani people. Subsequently, a 1975 feasibility study was performed by NEDESCO and SMEC. That consortium, also funded by the Asian Development Bank, examined the Sentani proposal and redefined it to increase the installed capacity. As in the previous study, no environmental assessment was included in the terms of reference.

Form of the assessment

In 1982 when the Canadian International Development Agency (CIDA) became involved in the project, Acres was asked to re-examine the situation. A proposal for a feasibility study and environmental reconnaissance was funded and work subsequently progressed to the design phase, during which a full EIA was conducted. An interdisciplinary environmental team worked with the designers to develop alternative scheme and integrate mitigation measures directly into the project proposal. The local population was directly consulted and the lifestyle of the lake-dwellers will continue to be possible after project development. The proposal submitted to decision makers involved a 12 MW project and decisions are now pending on construction.

Content of the assessment

There has been a growing awareness of the necessity to increase energy in this part of Indonesia. National policy is to promote development of some of the less populated areas of the country, thus creating the need for energy to supply the projected growth. The projected population increase and associated industrial activity within the Japur region over the next four years requires an increase in the generation capacity of the existing electrical system. The most economically attractive alternative involves use of the outflows from Lake Sentani as a potential hydroelectric supply. This would substitute for expensive diesel-generated electricity and permit supply to the provincial capital and surrounding region.

Scoping of studies of the existing environment

The environmental reconnaissance level study involved the fielding of a team which was on-site for six to eight weeks. The team consisted of a civil engineer, a hydrologist, a scientist, an economist, and an energy systems planner. The team operated interdependently through daily meetings. Based on an understanding of hydroelectric projects in general, and a limited database from previous studies, a generic list of impacts was established. The reconnaissance was intended to verify the database and scope issues for further studies.

The team's first priority was to establish contacts with local government, residents, the university, and anyone else who could provide baseline information and help identify the issues of importance for the local population.

During the environmental reconnaissance, the project concept became very important as it was obvious that the original 2 m water level increase would entail major impacts. The effect of alternative lake operating levels was determined as a critical area for further study and subsequent environmental information gathering was scoped accordingly.

Food availability for the Sentani people is directly related to the lake levels. Not only is the lake used for fishing, but the nearby marshes are harvested for sago. In addition, the shoreline behind the houses is used for the planting of vegetable gardens, so that lowering of lake levels during the farming season would be beneficial.

Farming was also potentially affected along the proposed corridor where rice and vegetable plots could be subject to disturbance by the construction of channels. Another aspect of the food availability issue concerned the tribes along Yautefa Bay, where traditional fishing lifestyles are followed. Possible disturbance by the sudden overflow of lake water into the marine environment was of concern.

An anticipated issue concerning lake water levels that was identified during the reconnaissance phase was that of public health. As the Sentani people use the lake as a latrine, too low a water level could spread disease, while too high a level would contaminate the shore.

Along the corridor, local planning objectives had to be considered. Ridges and swamps alternate continuously along the route. Areas that are dry and suitable for housing are limited, and estrangement of prime potential housing lots was to be avoided. Lack of land registration was of concern and projected urban growth had to be taken into consideration. National planning objectives were also of importance, since a proposed transmigration area exists south of Sentani Lake and along the Jafuri. The impacts this project would have on the water supplies and land uses for the transmigrants had to be considered.

On the basis of issues identified in the field, a scope of work was prepared for the environmental assessment and alternatives proposed for operational lake levels.

Study of alternatives

During the preparation of the environmental assessment, local people were extremely important in providing site-specific information. Although the team spent four months working on the Sentani Lake, statistically significant information could not be collected in such a short time. Where necessary, the collective memory of the Sentani people was used in lieu. Information on historical lake levels, resource utilization, and fishery in particular, was gained from the local population. Cultural information was an integral part of the data collection.

The major alternative examined during the environmental assessment was the lake level rate curve, which is the constraint governing manipulation of the water level during operation. A computer model of Sentani Lake was prepared to try various operating scenarios. The lowest constraint was dictated by sanitation levels while inundation of floorboards was the upper constraint.

For fishing, it is preferable to raise the lake level during the spring to allow the fish to spawn in their natural areas, with the water being kept high long enough for the fry to hatch and move down into the lake (thereafter drawing the lake down as fast as possible to allow people to plant their gardens).

Often a computer model is used to optimize the energy production without integrating environmental impacts. However, in this case, it was possible to achieve the same amount of energy while staying within all the environmental parameters.

As for the corridor alignment, values were placed on all of the relevant structures, so that every time a change was made, it was possible to recalculate how many houses, people, or hectares of crops would be impacted. Through land-use planning, it was possible to avoid cemeteries or schools and avoid cutting transportation paths. Hence, the corridor alignment was, in the end, quite different from that which had originally been proposed. In fact, the corridor was actually diverted considerably, to avoid land that was slated for future housing. It was also essential for the design to include safety considerations with regard to the canals.

As described above, real alternatives were considered in project design using information obtained during the environmental assessment. This resulted in some improvements being predicted for the project area including: improved fishing areas on Lake Sentani for people of Yoka near the approach channel; more recreation areas or islands in the lake from generally lower lake levels throughout the year; improved sago stands and access to swamps around Lake Sentani from generally drier conditions resulting from lower lake levels; and improved conditions in Yautefa Bay for milkfish and other estuarine species.

Environmental impacts

Despite these improvements, a number of anticipated impacts remained. Potential mitigation measures and proposed compensation were therefore summarized in the environmental assessment as follows. Construction of the hydro corridor and powerhouse will affect between 448 and 593 people, 67 to 97 structures, 30 to 45 ha of land (purchased or leased), and 25 to 145 ha of crops, depending upon the alternative chosen. The village of Puay will be the most seriously affected community on Lake Sentani as a result of weir construction on the Jafuri River. Fish resources of the upper Jafuri River will be lost and a decline in fish catches on Lake Sentani near Puay is likely. The latter is expected due to anticipated water quality degradation in this end of the lake when the natural outflow to the Jafuri River is blocked by the weir. The drying up of the upper reaches of the Jafuri River will also adversely affect Puay's accessibility to agricultural lands and wildlife (and, hence, hunting) along the river. The people of Lake Sentani will be inconvenienced by having to adapt their fish cages to a greater annual range in lake-level fluctuations. The people dependent on Yautefa Bay fisheries are likely to be adversely affected in the short term by a reduction in fish harvests until marine resources in the bay adapt to an estuarine environment. The virtual termination of lake flows to the Jafuri River will reduce mean annual flows in the Sunggrum River, although these are estimated still to be adequate for irrigation requirements currently forecast.

Mitigation measures

A number of proposals for mitigation were presented to alleviate impacts. The people currently occupying or owning lands along the hydro corridor and at the Jafuri River weir site should be compensated for buildings, lands, and crops lost or damaged as a result of the project. The people of Puay and Sekanto should receive sufficient compensation to enable them to continue their lifestyle with adequate fish resources and without the need to relocate their village. Families with fish cages around Lake Sentani prior to operation of the hydro project should be provided with screening materials to eliminate potential problems associated with a greater annual range in lake-level fluctuations. Families who regularly fish Yautefa Bay as their primary resource base should be provided with additional gill nets to off-set a possible reduction in fish harvests following construction and operation of the hydro project. Footbridges with railings across the tailrace channels in the vicinity of the fishponds and at the tailrace outlet to Yautefa Bay should be constructed to allow people continued access to both sides of the channel in these areas. Efforts should be made to restore the environment as far as possible following completion of the project, through grading, contouring, and planting.

Results of the assessment

While the project has not yet been completed, the substantial changes in design without power loss already indicate the value of the environmental assessment. Detailed actions have also been suggested for appropriate government agencies to take before construction of the project. Ensure no further development occurs on the corridor easement, including a 30 m buffer zone on either side. Provide careful inspection when staking out the easement in detail as discrepancies between technical drawings and site conditions can easily occur. Organize preparation of compensation payments for building, land, and crops, and ensure consistent and equitable treatment of individuals (including compensation for lands temporarily disrupted during construction). Planning for relocation of people and structures should begin well ahead of construction, and the affected populace should be included in the process. A reasonable schedule for relocation should be determined, and the people affected should be notified well in advance. Keep local residents well informed of project activities so they may adjust their own activities accordingly. Appoint a responsible individual to manage compensation awards for the people living around Lake Sentani, the Jafuri River, and Yautefa Bay who are expected to be impacted by the disruption to fishery resources.

During construction, it is important that a safety and environmental inspector be employed as part of the construction management contract to ensure that all necessary safety precautions are in place and that environmental recommendations contained in this report pertaining to construction activities are followed. This should include supervision of daily reporting of fish catches in the villages of Puay and Sekanto and in villages around Yautefa Bay, since these data are vital to any subsequent monitoring programme following project implementation.

Monitoring following construction

Approximately three months following project operation, a survey of Puay, Sekanto, and Yautefa Bay fisheries should be undertaken to determine impacts and assess whether further mitigation is warranted. This should be undertaken by the safety and environmental inspector. Approximately one to two years following commencement of hydro operations, it is strongly recommended that a comprehensive environmental evaluation be carried out to compare post-project conditions with impact predictions. The need for further mitigation based on the above assessment should be documented as part of the monitoring programme. Further environmental monitoring is recommended five years after hydro operation using a similar programme to that outlined above.


While some government authorities in Jakarta were initially skeptical about the environmental assessment, attitudes changed as the results started to be known. It became evident that the project design and operation could change without affecting the cost-benefit ratio of the project. Government agencies, locally and in Jayapura, provided the study group with information requested, although constraints on horizontal coordination limited the ability of the team to discuss the project with various ministries.

Unfortunately, the university and environmental studies centre could not provide the group with technically skilled personnel. Although keen to assist in any way, the resources were not available to offer. Ultimately, however, a useful baseline study was completed. Fortunately, local people were always willing to give information about their lives and priorities and this compensated somewhat for the lack of technical knowledge.

One specific constraint was a requirement that local people not be told about the proposed hydroelectric project. Therefore, questions had to be formulated in an odd manner, which tended to make them suspicious.

To sum up, the Sentani project demonstrates the value of incorporating environmental factors early in the planning process, such as during reconnaissance. Because of this, key decisions were made early to allow changes to the project before designs were set. The value of scoping a list of issues to consider was also demonstrated. It allowed focusing on the right questions and eliminated costly and delaying studies.

Integration of the environmental team with the overall project team allowed a major impact, potentially involving the relocation of 60,000 people, to be avoided. It also permitted optimization of resource utilization in the proposed project operations.

Because of effective communication with local people, the study was able to obtain information that was not available as published baseline data. This made a critical difference to project design. The involvement and cooperation of local agencies was also essential.

Finally, the importance of monitoring must be emphasized. It is impossible to quantify everything, especially with so little reference material on which to base some key predictions. Thus monitoring is absolutely necessary to make sure that the study and design are correctly verified and implemented, and that the mitigation measures that were proposed actually work.