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Low-cost Treatment of River Bank Erosion Hermono S. Budinetro Researcher in Experimental Stations for River Research Institute for Water Resources Development Ministry of Human Settlement and Infrastructure JL. Solo-Kartosuro, PO Box 159, Surakarta 57101, Indonesia Phone: 001-62-271-719429; Facsimile: 001-62-271-716406 E-mail: [email protected] or [email protected]

ABSTRACT: Bank erosion is the single most common problem in alluvial river. The erosion causes a lot of damage. The bank erosion control structures are usually expensive, massive and not compatible with environment and aesthetic. This structure will bad influence to the vegetation growth and habitat for species which are living around water, it does not match with the spirit of eco-hydraulic. Soft engineering or sometimes-called bio-engineering is a bank erosion control structure which more nature and compatible with environment and also low cost. The structures are porous groins, which are made from bamboos that are filled with packed tree branches. The groins will protect a path riverbank, which is under erosion. They create a pocket of slow-moving water along the banks, which not only halts the erosive action but also throws sediment in the area forming toes needed to support the yielding banks. The newly formed toes gradually develop into berms, which are stabilized latter by ipomea carnia or vetiver grass. Key-words: Soft-engineering, bio-engineering, riverbank erosion control

1. INTRODUCTION River bank erosion is the single most common problem at river which are flow on alluvial plain although the plain usually at lowland area. The erosion causes a lot of damage. That can be seen from existence of meandering symptom at the river. The erosion will result the loss of land, or property and endanger people who are live near the river. The existing bank erosion control structures are usually expensive, massive and not compatible with environment and aesthetic. This structure is made from masonry, stone, iron, etc. Those will bad influence to the vegetation growth and habitat for species that are living around water; it does not match with the spirit of eco-hydraulic. Because those are costly, the erosion control is only conducted to protect important place or populous and costly urban area, which enough worth to be protected with above construction. While, in rural area which is value of land or property is low, cannot be protected by above structure, because that is not feasible if compare the cost of structure. Although, the land is usually owned by impecunious farmer and become the single place drape its life. It is to disturb sense of justice. Because above conditions, World Bank and Directorate Water Resources Management have developed bio engineering since year 1996. Bio engineering is low-cost riverbank protection, easy to construct, using natural and local materials, so that will harmonies with environment. Bio Engineering-1 use vetiver to control of floodplain erosion, have been tested at some location in Jawa. Bio Engineering-2, it is combination bamboo, vetiver and or ipomea carrnia, the construction was design to protect riverbank from current attack.

2. RIVER BANK PROTECTION The function of riverbank protection is to avoid bank erosion, which is caused by current attack. Effect of the erosion is collapsing of riverbank, causing movement of river channel. The movement is vertical and horizontal direction, arise meandering, braiding, or move and changing it river path. Bank protection that commonly use is made from masonry or concrete, this type is expensive and not natural or not environmental friendly; disagree with spirit and soul of eco-hydraulic. Because, riverbank

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“RESUBMIT” stability has an influence on channel form, vegetation growth and habitat for bank-living species, ecohydraulic is solve the river problem with environment and ecology approach. Bank protection measures, which are matching with the spirit and soul of eco-hydraulic, must be: − Using natural materials, which can be found around, that will be low cost. − Labor intensive, lessening unemployment so that as according to condition of our country. − Can provide habitat for water animal and crop. Some low-cost river bank protections method, and natural have been tried by some developed countries can be seen on Figure-1 (adapted from Gordon, McMahon and Finlayson (1992), that are: 1. Stone “rip-rap” or “beaching” Lining the banks with some stone is feasible if local source of rock is available. The pits in stones and the nooks and crannies between them increase the amount of area for colonization by aquatic insects. Plants can take root between the rocks and rocks ledges can be used as resting and roosting sites by waterfowl. Stone is a relatively permanent option if the stones used are sufficiently large that they do not wash away during high flows. More angular stones will interlock and thus more stable. Placing a layer of fine gravel or stone under the larger rip-rap material will help to prevent erosion of finer bank materials from beneath the rocks. To avoid undermining at the toe of the rip-rap, can be used of stone aprons, which extend well out into the riverbed. An extra pile of rocks can be added to the edge of the apron which fall in and continue protecting the bed if it degrades. 2. Dikes, groins or revetments These structures extend out from a stream bank into the flow (Figure-1b). They are used to reduce the speed or change the direction of the stream’s current and thus reduce the erosion force on the banks. They are many designs, to timber planks or logs bolted to posts. With proper design silt will be deposited in the quieter water between the groins. Vegetation can be planted in these silt beds which will eventually form floodplain benches. Normally, a series of groins are used along a bank. 3. Vertical timber posts Wooden posts or pile driven vertically into the streambed can be used to protect they lower part of a bank, for example where a vertical cliff on the outside of a meander bend is to be preserved. That is recommended at least half of the post should be driven into the ground. 4. Woody debris In areas where tree pruning, snag removal and brush cutting must be carried out these materials can be recycled to the stream in the form of bank protection. Debris can also be used to slow the water, trap silt and sediment and permit the growth of river-edge plants. Cut logs and branches can be secured against a bank protection or for filling scour holes. Large trees should be tethered with the trunk end upstream. Stakes driven into the streambed or heavy-gauge wire or cables looped around the debris and attached to firmly embedded stakes on the bank tops may be necessary to hold the materials in place until anchored by siltation and vegetation growth. 5. Wicker spiling and hurdles Smaller material can be woven together for bank protection. Spiling can be used to protect the base of steep banks and to create dikes on smaller stream. Stakes are driven into the ground and braches woven between them. Alternatively, post can be staggered in two rows and brush piled between them. The distance between the posts should be consistent with the length and thickness of the weaving materials. As with timber post (above), the area behind the spiling should be backfilled. If appropriate for the region the use of willow stakes can create a semi-permanent, living form of bank protection.

3. BIO ENGINEERING-1 World Bank and Directorate Water Resources Development in Basin Water Resources Managementn Project, since year 1966, have developed Bio- Engineering-1 by using vetiver to control erosion at flood plain and riverbank in some river in Java (Tabel-1, show vetiver cultivation location). Vetiver grass is very easy crop. They can grow at various level and type fertility of land, at wet and dry conditions. The cultivation is easy to do, almost without maintenance. Leaf, blade, root, and also young plan are growing densely. Its root grows vertical downwards more than 3 m, so that is not struggling of with other crop. Vetiver grass is long-lived crop, more than 10 year. The vertiver type for land conservation do not yield seed, and rhizomes or stolons (root which can yield new crop), so that vetiver do not expand

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“RESUBMIT” wild outside from plan area, it will not become to intruder upon another plant. Mouse also does not like to make a nest in vetiver crop area because aroma from its root. The dense of vetiver leave will arrest surface erosion, which is caused by sprinkling of rainwater. The root characteristics are dense, deep, so they will tie soil and building up tight. A line vetiver which tie soil up tight will arrest mud and sediment, and formed a stable and solid terrace, that is core bench.

Balai PSDA Seluna

Balai PSDA CimanukCisanggarung

Table - 1: Location, Area and Cost of Cultivation Vetiver. Locations Area Cost Cultivation by (M2) (Rp.) 76,337,000 Gadjah Mada University, Pecangaan River in Gerdu Village 8.750 Faculty of Agriculture and Welahan Bum River at upstream and down stream rubber dam Wulan River at Mayong River 10.135 184,460,000 Gadjah Mada University, Faculty of Agriculture Cisanggarung River and 6.000 93,967,198 CV. Gratia Loka Bangkaderes River Cijangkelok River Some place at Cirebon area Darma Reservoir Situ Sedong and Situ Patok

5.029 4.500 4.500 3.500

48,202,000 43,527,000 48.275.000 37,682,000

CV. Indra Putra CV. Kali Humus CV. Diky Prima CV. Abimanyu

4. BIO ENGINEERING-2 Bamboo is grass family. This crop grow almost in all area in the world, specially in South-East Asia. According to FAO there is 75 bamboo genus with 250 species. Bamboo reach maximum height after 2 to 4 months, its stalk diameter reach up to 30 cm, with length more than 40 meter. The bamboo is known as villager wood, because the strength and pliancy, the bamboo is used for the building and other construction in the village. In general natural the of bamboo is lower than wood. The durability is depend on condition of environment and climate, with preserving, the bamboo can be used about 3 year, if have interaction with air and soil, but if under water can be longer. Following some bamboo characteristic : – The stalk have shape of pipe, with space between joints. – Having special coat at outside and inside of pipe, the exterior strength is more than twice. – The strength in axial direction, and very limber. Ipomea carnia, some place in Indonesia is named "karangkungan" or " kangkung-kakungan" or " kangkung londo ". That plan is easy grow everywhere, at swampy and dry area. Ipomea carnia is a group of clump, his bar is limber and equal to finger. The bar growing of is not regular, vertical and horizontal. His leaf is thin in form of hart. The flower is like trumpet, with color is pink. The root system is strong, growing is downward. It can be planted by cutting from old bar or from seed. Its cultivation easy to do, seed is easy to find, grow quickly, and without maintenance. From above characteristic, ipomea carnia can be planted on sediment that is formed by deceleration of current. From above characteristics, the bamboo and ipomea carnia, have been developed Bio Engineering-2 which protect river bank from current attack. Bio Engineering-2 is combination between bamboo, vetiver and or ipomea carrnia, they are design to protect bank erosion that is course by current attack. For good result, the water must bring a lot of sediment, and velocity less than 1, 5 m/second. The propose design can be seen at Figure-2 that is design for straight channel and Figure-3 is design for curve channel. According to Figure-2, bamboo bar is driven into the riverbed where its bank experience scouring, vertical and horizontal bar are attached, to be fastened by vertical bar as lashing, between vertical bar are compacted tree stick. Porous groynes are formed to arrest floods current and to trap bed load and suspended load. After sediment formed, as according to Figure-3, vetiver or ipomea carnia can be planted, hereinafter these plant will grow, and its strong bar and grow is irregular, relating each other, will quicken sedimentation process. When bamboo bar have started to destroy to be hit by sun shine, new sediment and plantations at bank foot have enough stabilize, so that can arrest current attack.

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“RESUBMIT” Location which have successful apply Bio Engineering-2 is in Cisanggarung River in downstream Rubber Dam Tawangsari. Another location of Bio Engineering can be seen at Tabel-2. Table-2. Another Location Bio Engineering Location Detail Balai PSDA Jratun Babon River, downstream − Flood plain and bank protection, by vetiver Pedurungan Bridge − Length = 60 m, high = 6 meter − Planted in 2 rows. − Bio engineering-1 Balai PSDA Seluna 1. Lusi river bank, Pulongrambe 1. Length ± 200 m, high = 7 m, in 2 rows, Biovillage, Grobogan. Engineering-2 2. Lusi river bank, upstream 2. Length ± 15 m, high 5 m, Bio-Engineering-2 railway bridge Balai PSDA Pemali 1. Gung river 1. Velocity to high 2. Gangsa river Balai PSDA Progo- Code and Winongo river Opak-Oyo Balai PSDA Sermo Galur drainage

2. Not yet been evaluated Not yet been evaluated Not yet been evaluated

5. CONCLUSION AND SUGGESTION 5.1 Conclusion 1. Bank protection that commonly use is made from masonry or concrete, this type is expensive and not natural or not environmental friendly; disagree with spirit and soul of eco-hydraulic. 2. Bio-engineering is a bank erosion control structure which more nature and compatible with environment and also low cost. 3. Directorate of Water resources Development have developed bio engineering since year 1996. Bio Engineering-1 use vetiver to control erosion have been test at some locations in Java. 4. Bio Engineering-2, which is special design to protect bank erosion from current attack, at straight and curve channel. The type is combinations between bamboo with vetiver or ipomea carnia, have been used at some locations. 5.2 Suggestion 1. Meeting, and seminar for dissemination of bio engineering must be conducted. The activities can change the thinking of river engineer that erosion control have not to use massif and expensive structure 2. Directorate Water Resources Development must be continue to use bio-engineering for erosion control and river bank protection, because bio-engineering is low cost and easy to executed by villager. 3. Research Institute for Water Resources Development as scientific backbone of Directorate Water Resources Development must be research the efficiency of bio engineering, and also make another design of Bio Engineering which is more effective to erosion control.

6. REFERENCES Fakultas Teknologi Pertanian UGM, Laporan Akhir Pekerjaan Penanaman Rumput Akar Wangi / Vetiver, Lokasi : Kali Wulan Kabupaten Jepara, Satgas PSDA Jratunseluna, 1998. Fakultas Teknologi Pertanian UGM, Laporan Akhir Pekerjaan Penanaman Vetiver untuk Pemeliharaan Aliran Sungai di Wilayah Pilot Proyek Satgas PSDA Jratunseluna, Satgas PSDA Jratunseluna,1999. Fakultas Teknologi Pertanian UGM, Laporan Akhir, Penanaman Rumput Akar Wangi, Lokasi : Kali Mayong dan Kali Wulan, Kabupaten Jepara, Satgas PSDA Jratunseluna, 2000.

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“RESUBMIT” Gordon, N.D., Stream Hydrology, An Introduction for Ecologists, John Wiley & Sons, 1994. SMEC and Associates, “Basin Water Resources Management Unit Component of Java Irrigation Improvement and Water Resources Management Project: Final Report on River Morphology” , Direktorat PSDA, 1999. SMEC and Associates, Basin Water Resources Management Unit Component of Java Irrigation Improvement and Water Resources Management Project: Vetiver Pilot Program Report, , 1997. Tim Elsppat, Pengawetan Kayu dan Bambu, Puspa Swara, 1997.

a)

eroding bank

b)

rock rip-rap

extra rock

deposited silt apron

c)

permeable fencing

d)

backfill behind posts

top view

front view

Figure-1. Bank-protection measures: (a) stone rip-rap, (b) dikes or groynes, (c) vertical timber posts, and (d) wicker spiling. (Adapted from Gordon, McMahon and Finlayson 1992)

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A

Bamboo Cross Bamboo Brushwood (Packed tree branches)

Flow

Flow A

Plan Cross Bamboo

Bamboo

Eroding Brushwood bank

Stable Bank

Section A – A Figure-2 Bio Engineering-2 for Erosion Control Stage I : Porous Groynes

A

Ipomea Carnia

Flow

A

Stable Bank

Plan Ipomea Carnia New Berm

Section A - A Figure-3 Bio Engineering-2 for Erosion Control STAGE II : PLANTATION OF IPOMEA CARNIA (KARANGKUNGAN) OR VETIVER (AKAR WANGI) ON

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