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SCENARIOS OF SEDIMENT CONTROL SOLUTION FOR MRICA RESERVOIR, BANJARNEGARA, CENTRAL JAVA, INDONESIA CONFERENCE PAPER · AUGUST 2013
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SCENARIOS OF SEDIMENT CONTROL SOLUTION FOR MRICA RESERVOIR, BANJARNEGARA, CENTRAL JAVA, INDONESIA Rr. Vicky Ariyanti, ST, M.Sc, M.Eng1 Ir. Faizal Adicondro, M.E2 Andie Arif Wicaksono, ST, MT3 ABSTRACT Situated in the main catchment area of the Great Serayu River, the reservoir with its 148.29 million m3should last 60 years from 1988. However, due to bad land use condition on its upper stream, it is estimated that its life will only last for another 12 years. Data from 2011 had shown that 59.49 million m3 has covered by sediment, which meant that 60% from of its efective volume is left for the reservoir to function. The reservoir’s electricity plant(PT. Indonesia Power) produced an average of 180,000 MWH per year, which meant that it supplies electricity for the whole Java island. This prospect will threaten to paralizethe economy of Indonesia. Moreover, we are also facing extreme condition caused by climate change.There is the need to seek solution to address this serious sedimentation problem. In this paper, several scenarios are presented. They include technical solutions such as sediment control dams, Sabo System, Garung Scheme, Asahi Scheme, and a nontechnical solution, which isLand Use Planning. Each of the schemes will be elaborately explained and conceptually presented to proof each advantage and disadvantage dealing withsedimentation.Since this is a study of solution scenarios for an important environmental usage and it corresponds directly to human safety, a risk assessment is used as the method to grade each scenario. Using parameters to assess these scenarios based on vulnerability assessment concept by BBC (Bogardi, Birkmann, Cardona)each will be assessed in terms ofsocial, environmental and economical point of view. This study will provide the authorities of Mrica Reservoir and related stakeholdersto control further sedimentation process, and even to alleviate this problem in the future. INTRODUCTION Mrica is a reservoir in the Serayu river basin system. Its total catchment area of is 3,738 km2 and around 30% or 1,022 km2 belongs to Mrica reservoir (INACOLD, 1986). The rivers that run into Mrica reservoir are steep rivers with 10% slope gradient. Dieng Plateau, which is also a complex of active volcanoes, as its upper stream has an elevation of 3,000 – 4,000 m above sea level, while the reservoir’s elevation is around 100m.This contributes to sedimentation potential from alluvial and volcanic debris. The upper stream of Mrica catchment is Dieng Plateau. It consists of marshy plateau as base for 1
Indonesian Minisitry of Public Works, General Directorate of Water Resources, Serayu Opak River Basin Organization, Yogyakarta, Indonesia,
[email protected] 2 Indonesian Minisitry of Public Works, General Directorate of Water Resources, Serayu Opak River Basin Organization, Yogyakarta,
[email protected] 3 Faculty of Science and Technology, Technical University of Yogyakarta, Indonesia,
[email protected].
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Dieng volcano complex, located in Wonosobo Regency, Central Java Province (Van Bergen et.al, 2000). This condition proposed that these rivers are by nature rich with sediment. Map of catchment area:
Serayu Bogowonto River Teritory
Figure 1. Mrica’s Catchment (orange) on Serayu Watershed Source: BBWS SO, 2013 Mrica is an important reservoir in the Java Bali power scheme. Water runs continually into the reservoir even during dry season. This potency is very good for the reservoir’s situation. Initial average inflow of 78.66 m3/sec comes to the reservoir that made the effective volume of 148.29 million m3 ready to be change into the average 180,000 MW. Mrica, which is also known as Panglima Besar Sudirman Reservoir, taken from the name of a great hero in Indonesian revolution war, supports greater economy of the country. The illustration below shows how great the scheme is laid down in the central Java Province.
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Figure 2. Map of Power Scheme in Central Java Province Source: PT. Indonesian Power, 2011 To further illustrate the extreme sedimentation of this reservoir, the table below shows the comparison between Mrica’s original condition and its condition in 2011 with sedimentation calculation byMeyer-Peter and Müller method (Soemarto, 1999) using the following formula. Qb2/3 = (ᵞw (Ks/Kr)3/2 RS-0.047 (ᵞs-ᵞw)d/0.25 (ᵞw/g)1/3) ÷ (1/(ᵞs-ᵞw)) (1/1-e) x L Where: L = length of dam (m) ᵞs = specific weight of sediment (ton/m3) ᵞw = specific weight of water (ton/m3) R = hydraulic radius (m) S = river base slope
d = median diameter ≈ d50-d60 g = gravity (m/s2) Qb = sediment volume (m3/s) e = porus (0.35) Ks/Kr = ripple factor =1
The result of the sedimentation calculation is presented in the following table, which also describes the overall condition of Mrica reservoir: No 1 2 3 4 5 6 7 8
Description Reservoir volume Area of Reservoir +231 m Effective Volume +224.5m (original design) Effective Volume +228 m (actual) Dead Storage Flood Storage Sedimentation Volume Average annual inflow
Unit Million m3 Km2 Million m3
1988 148.29 8.42 46.30
2011 59.49 8.26 28.06
Degradation 60% 2% 39%
Million m3
22.95
17.30
24%
Million m3 Million m3 Million m3 m3/sec
101.99 35.47 0 78.66
23.90 35.41 97.93 68.76
77% 0.2% Total 13%
Table 1. Mrica Reservoir Existing Condition Source: PT. Indonesian Power, 2011 The condition above shows that 60% of Mrica’s volume has been used to accommodate sediment. The Plateau of Mrica’s upper stream is also a rich agricultural area for potatoes, cabbages, tomatoes and other vegetables. This condition combines with Dieng Plateau steep slope are the causes ofthese sedimentation problems. These vegetable farm
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ideaswere directed from the local government in the 1980s about their vision of becoming the best potato supplier in Indonesia (Fransiska, 2011). The farmers, in this sense the people of Dieng, then use this opportunity to exploit the potency and were proven to be successful. Many of them have been economically enhanced through this mean.The following pictures show the farmers activity:
Figure 3. Potato& Vegetable Plantation Source: Taken by Ariyanti, 2011 Nowadays, the local government regretted their recommendation, because most of the plateau is now being developed into vegetable farms (Fransiska, 2011). The costs of this condition are the disappearance of forest, high erosion, landslides during rainy season. In this incident 7 people were killed and many others were injured due to the landslides (Yasa, 2011) and corpses were found in Mrica resevoir, which means that the landslide area correspond directly to the reservoir and it is exposed to debris flow from the landslide potency. SCENARIOS OF SEDIMENT CONTROL Seeing this condition of Mrica,several scenarios were to be proposed i.e. Sediment Control Dams System, Sabo System, Garung Scheme, Asahi Scheme, and Land Use Planning. Each of the scenarios will be explained in general in this part.
Sediment Control Dams This scenario is using low technology and low budget investment (Indonesian Ministry of Forestry, 2007). However, the practice of such scenario requires series of dams in the overall catchment area, which will end up expensive in the end. Since the rivers are steep and controlling effectiveness is based on the overall series, it should be built on each watershed of the tributary that runs into Mrica; Lumajang, Serayu and Merawu. With calculation of allowed sedimentation of 1.42 million m3/year, Mrica reservoir will need 27 more dams (Setyawan, 2011), currently there are only 4 (BBWS SO, 2012). Series of these dams will help to lessen sedimentation, while the materials that collected from the dam construction and from the maintenance of the dams can be sold and used as building materials in the cities. The following image is the proposed typical unit of the dam.
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Figure 4a. Sediment Control Dams (example made out of wire mesh gabion with stones) Source: Ilustration by Wicaksono, 2013
Sabo System Sabo system is very popular in Japan. It is mostly applied to rivers with characteristic of steep unstable topography with frequent volcanic activities and earthquakes, which resulted on frequent debris flow and numerous disasters, which is why this is suitable for Dieng Plateau condition and Mrica’s situatuon. The original purpose of the Sabo structures was to reduce the excess sediment discharge to prevent river degradation further downstream. More recently the emphasis of Sabo works shifted to the control of debris flows (Japan Ministry of Land, Infrastructure, Transport and Tourism, 2004). In order to succeed, this system should used the right order of dam forms, from the upper stream that stops boulder stones, secondly smaller stones, next are range of even smaller stones or silt, and at the very end, it should stop sand and be equipped with sand trap (BBWS SO, 2011).It will need around 13, scattered at Lumajang (2), Serayu (9), Merawu (2). This will help to control sedimentation at the allowed level of 1.42 million m3 (Setyawan, 2012). The scenario below is implemented at Merapi volcano that has similar debris flow problem as with Dieng:
Figure 5. Sabo Dam System at Merapi Mountain Source: UGM, 2010
Garung Scheme Garung scheme as seen in Figure 6a and 6b is situated at upper stream of Mrica catchment. This scheme is therefore the closest to Mrica condition. Howver, Garung isa special dam for its unique location, which is Menjer Lake, an ancient caldera and its design, which is developed by the
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Nippon Koei in 1975. Its potency was discovered by ANIEM, Netherlands from back in 1929 (INACOLD, 1986).The design has carefully thought about the emergence of Dieng Plateau farming potencies and therefore also included several counter measures towards sedimentation (Ariyanti, 2012). Firstly, the water that runs to its reservoir comes through a horseshoe type channel under the mountain from Klakah to Serayu River. Secondly, at the mouth of Serayu intake, not direct in the stream, water was stopped at a sand trap facility, where sediment can be filtered and dredged at least twice a year. Thirdly, water is channeled again through a horseshoe tunnel into the reservoir. In this respect, water that runs into the reservoir has been filtered 3 times, which made it almost free from any residue of sediments. If Mrica is to implement this scheme, extra construction should be build at reservoir’s upper stream. Below is the picture of Garung Sand Trap and Scheme:
Figure 6.a Garung Sand Trap Source: Ariyanti, 2012
Figure 6.b Garung Scheme &its Watershed Source: INACOLD, 1986
Asahi Scheme This scheme is also known as by pass tunnel. Bypass tunnels, however, have many advantages such as they can be constructed even at existing dams and prevent a loss of stored reservoir water caused by the lowering of the reservoir water level (Sumi, 2004). The subjects of designing sediment bypass tunnels are to secure the safety of sediment transport flow inside tunnels and to take countermeasures for abrasion damages on the channel bed surface. In Asahi Dam, the prolonged turbidity problem has been getting noticeable due to the upstream condition changes by the collapse of mountain slopes and the devastation of forests caused by large-scale runoffs (Kansai, 1999). Since typhoon season also held effect, the mean annual accumulated sediment volume also increased sharply to 85,000m3/year from 1989 to 1995, which is four times than its usual amount in 1978 (Sumi, 2004). This scheme can be implemented at Mrica, however the cost would be expensive. Using a small tributary next to the reservoir, the sediment by pass can be constructed without land resettlement.The following figure shows the schematic diagram of the bypass tunnel at Asahi:
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Figure 7. Asahi Scheme Bypass Tunnel Source: Kansai Electric Power Co.Inc & NEWJEC Inc. 1999
Land Use Planning This scenario actually, can be combined with any technical solution, or even takes place on its own. In this respect local government should highly participate in order to find alternatives for the farmers at Dieng Plateau on other economical means (BBWS SO, 2012). It also means that special law enforcements and mediation methods are needed to provide a strong paradigm shifts on the mindset of the farmers.Most of the farmers in the near future will losethose fertile soils washed by the rain and taken away into landslides. Land use planning should provide the alternatives for farmers to stay cultivating the highlands with certain value of wisdom to stay away from landslides zones and even offer them partnership during the shifts from potato to other hard plantation, for example tea, coffee, or even rubber plant. The following land use map is the product of analysis done to illustrate what the current land use is:
Figure 8. Land Use Plan for Serayu Bogowonto River Territory Source: BBWS Serayu Opak, 2012
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The map shows that Dieng Plateau situated in Wonosobo Regency where most of the regions are occupied by vegetable farms. Therefore, the area should be force to adopt new land use, as recommended to be conservation area or at the very least combination of plantation forestry and farming. This conservation area should be about 46% of the 1,022 km2 of the catchment, in order to succeed sediment control. The government and private sectors role in order to provide livelihood, as the shifts of farms into conservation should also embodies
ANALISIS METHODS Since sedimentation in this context has also created hazardous condition, it is of great importance that each the scenario is objectively reviewed from risk mitigation analysis at least three perspective, e.g. environmental, social and economical.
Figure 9.BBCVulnerability Assessment Concept Source: Bogardi & Birkmann, 2004
Using vulnerability assessment from BBC (Bogardi, Birkmann & Cardona), each of the risk aspects is break downed into several parameters. For example on economy, writers will see the projected investment, economic values, and support to local economy. On environmental aspects, several parameters are used to assess effect on river condition, land use plan, promote conservation, and effectiveness on sediment control. Meanwhile on social aspects, parameters used are social support, social values, and communal sense of belonging. These parameters are used to simplify the effect of each scenario and characterize them into rankings. After each of the parameters is assessed, range of grades and rakings are given. The result will be used to give recommendation on sedimentation control for Mrica. RESULTS Each of the scenarios positive impacts is graded in the column and at the end of the assessment. The greatest grade, which means good rank will be recommended as the best solution in terms of environmental, economical, and social aspects. Environmental Aspect Type of Scenario Sediment Control Dams
Effect On River Condition Small size, may interfere stream
Land Use Positive impact in land use
Promote Conservation Water & stream conservation
Effectiveness on Sediment Control Slight effectiveness (1.42 mio m3/year)
Grades ++
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Sabo System
Garung Scheme Asahi Scheme
Land Use Planning
Big size infrastructures on river, definitely interfere stream system Water diversion on rivers
Positive impact in land use plan for watershed
Water conservation and stream recondition
Very effective (20 million m3/year)
+++
Positive impact in land use plan
Very effective (unlimited)
+++
Interfere river bed sedimentation, but does not interfere its system Stops potatoes farming and lessen sedimentation on rivers
Positive impact in land use plan for watershed
Promote water conservation with the scheme Conserve water and improve river condition
Very effective (unlimited)
+++
Better conservation on land and water
Effective only when 46% of land is forest, actual 11% (unlimited)
+++
Positive impact in land use plan for watershed
Table 2. Environmental Aspect Analysis Source: Analysis, 2012
Social Aspect Type of Scenario Sediment Control Dams Sabo System Garung Scheme Asahi Scheme Land Use Planning
Social Support
Social Values
No conflict arises
Gotong royong(communal work) in maintenance of the infrastructure
Conflict from land resettlement and/or nature conservation NGOs Does not incur any conflict
Sand trap with economic favor will win social values
Bypass tunnel does not need land resettlement When mediated in proper way and combine with public participation would win community support
Sand trap with economic favor will win social values May not include public participation Great social values with public participation
Communal Sense of Belonging Need to be introduced properly to the responsibility of belonging Only when properly introduced and mediated Also need a way of mediation No sense of belonging Only when mediated properly
Grades ++
+ ++ + +++
Table 3. Economical Aspect Analysis Source: Analysis, 2012
Economical Aspect Type of Scenario Sediment Control Dams Sabo System Garung Scheme Asahi Scheme Land Use Planning
Investment
Economic Values
@IDR 100,000,000 (needs 27) = IDR 2,700,000,000 @IDR 2,000,000,000 (needs 13) = IDR 26,000,000.000 IDR 20,000,000,000 (whole system)
Weak economic values (small amount of sand to be mined, scattered) Strong economic values (sand mining, at several points/sabo dams) Average economic values (much sand, only from 1 point/sand trap) Strong economic values (much sand downstream) Strong economic values (from forest agriculture)
IDR 600,000,000,000 (whole system) 46% x 1,022 km2 x IDR 4,166,000,000/km2 = IDR 1,958,800,000,000
Table 4. Economical Aspect Analysis Source: Analysis, 2012
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Support Local Economy Sand trap can be used as income generator
Grades
Sand trap can be used as income generator
++
Sand trap can be used as income generator
++
No connection
+
Generate other income as alternative of potato
++
++
CONCLUSIONS & RECOMMENDATIONS As the final results of the overall aspects, the conclusion is as follows: Type of Scenario Sediment Control Dams Sabo System Garung Scheme Asahi Scheme Land Use Planning
Environmental Aspect
Social Aspect
Economical Aspect
Total Grades 5
++
++
++
(good land use & conservation)
(no conflict, gotong royong)
(low investment, income generator)
+++
+
++
(good land use, conservation, effective)
(sand trap will win social values)
(much sand, income generator)
6
+++
++
++
(water diversion, good land use, conservation)
(no conflict, sand trap wins social values)
(much sand, income generator)
+++
+ (no land resettlement)
+ (much sand)
5
+++
+++
++
8
(lessen sedimentation, good land use, conservation)
(community support & participation, sense of belonging)
(forest agriculture, income generator)
(no interference on river, good land use, conservation)
7
Table 5. Conclusion Source: Analysis, 2012 From the above table, the most recommended scenario would be land use planning, followed by Garung Scheme, Sabo System, Asahi Scheme and Sediment Control Dams. This scenario can also be put into combination, for example Land Use Planning with Sabo System, which will heighten the probability of success. It is of course of great importance in order to successfully adapt the scenario to include community participation and for that mediation attempts about the scenarios should be implemented from the very beginning of planning process. As the solutions prepared here are mostly technical to semi-technical, several other recommendations in relation with the scenarios should be added, which are: Public Private Partnership As the solutions may result in infrastructures or change in land use planning, there is a great necessities to put forward partnership framework. This idea should include investments, between PT. Indonesian Power, Serayu Opak River Basin Organization (BBWS SO), BPDAS Serayu Opak Progo, foreign investors, Local Government of Banjarnegara and Wonosobo Regency, Dieng Plateau farmers, to work together. Either in the form of role sharing or investment sharing, the partnership would benefit all sectors. For collaborative actions, the spirit of Gotong Royong should take place where great responsibility such this calls for a great action. Alternative Income Generator When the changing of land use plan is or going to be implemented, several alternatives for the farmer’s livelihood should be secured. There is the need to educate the community about other ways of life than depending on potatoes or other vegetable farming. In this sense, the role of community pioneers would be very important. Conservation concept needs to be popularized and
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farmers as nature guardianidea will make them realized their important role especially for the fate of others downstream. Private sectors cooperation in the land use change also needs to be intensified. Local and the central government will need to give incentives as attraction for those private investors in helping the community to shifts their vegetation. Operation and Maintenance Whatever the solution is, operation and maintenance of the infrastructures or the land use planning should be priority. In order to succeed, from the beginning, budget plans should be ready for the future and the role sharing for each of the scenario. Maintenance holds strong point in every infrastructure life cycle and it needs to get alternative share cost in order to reduce costs.
REFERENCES Ariyanti, Vicky, et al (2011): “Garung Dam on Menjer Lake, Planned to Last 650 Years” in Proceeding of ICOLD 2011, June 1 -5, Kyoto, Japan BBWS SO (2011): Draft Rancangan Rencana WS Progo Opak Serang, Yogyakarta, Indonesia BBWS SO (2012): Draft Rancangan Rencana WS Serayu Bogowonto 2, Yogyakarta, Indonesia BBWS SO & UGM (2004): Pola Pengendalian Lahar Gunung Merapi, Yogyakarta, Indonesia Bogardi, J. and J. Birkmann (2004): “Vulnerability Assessment: The First Step Towards Sustainable Risk Reduction” in Malzahn, D. and T. P lapp, eds,Disaster and Society – From Hazard Assessment to Risk Reduction, Berlin: Logos Verlag, Berlin, pp. 75 – 82. Fransiska, Lucky (2011): Kaldera Gunung Api yang Menghidupi, Kompas, Selasa, 27 Desember 2011 INACOLD (1986): Dams in Indonesia, INACOLD, Jakarta, Indonesia Indonesian Ministry of Forestry (2007): Pedoman TeknisGerakan Nasional Rehabilitasi Hutan Dan Lahan (Gn-Rhl/Gerhan)Peraturan Menteri Kehutanan No. P. 22/Menhut-V/2007, Jakarta, Indonesia Japan Ministry of Land, Infrastructure, Transport and Tourism (2004): What is a Debris Flow? http://www.mlit.go.jp/river/sabo/panf/j_sabo/english/14-15.pdf Kansai Electric Power Co.Inc & NEWJEC Inc. (1999): Reservoir Sedimentation Management at the Asahi Dam, Japan Sinaro, Radhi, et al, (2007): Menyimak Bendungan di Indonesia (1910-2006), Bentara Adhi Cipta, Jakarta, Indonesia Sumi, Tetsuya (2004): “Reservoir Sedimentation Management With Bypass Tunnels In Japan” in Proceedings of the Ninth International Symposium on River Sedimentation, October 18 – 21, 2004, Yichang, China Setyawan, Chandra (2012): Kajian Pengendalian Sedimentasi di Waduk PB Soedirman dengan Bangunan Pengendali Sedimen dan Pengaturan Tata Guna Lahan, Gadjah Mada University, Yogyakarta, Indonesia Soemarto, C.D (1999): Hidrologi Teknik, Erlangga, Jakarta, Indonesia Van Bergen, Manfred J, et.al. (2000): Crater Lakes of Java, Dieng, Kelud and Ijen Yasa, P Raditya Mahendra (2011): Tanah Longsor dan Banjir Bandang di Tieng, Kompas, Selasa, 20 Desember 2011
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