Building Global Partnership for Global Challenges April pril 13 th , 2018 CRIT CR ITIC ICAL L INFRAS INFRASTRUC UCTURE IN BEN IN BENGA GAWA WAN N SOL OLO O RIV RIVER RIA ASIH ARYANI SOEMITRO
Research Team Members: Ria Asih Aryani Soemitro Team leader/ Geotechnics Trihanyndio Rendy S. Mahendra Andiek Maulana Dwa Desa Warnana Member/Geotechnics Member/River Hydraulics Co-Team Leader/Geophysics 2
Surabaya - London 3
INDONESIA • >5 million km 2 • >13000 islands • > 1100 tribes • > 700 local languages Indon donesia ia
INDONESIA EQUATOR LINE
Bengawan Solo River • Bengawan U Solo River: Catchment area: 1.70 million ha River length: 600 km Average river width: 150 m River water current: min 0.30 m/sec & max 1.75 m/sec.
BENGAWAN SOLO RIVER OVERVIEW • Main features: – 1.7 millions ha of watershed coverage area. – Water availability for irrigation system and fresh water supply. • Problems: – Critical lands – Sedimentation in the reservoir and the river body – Floods – Failure of river embankment – Stability of bridge foundation – Illegal sand mining – Inhabitants in the flooding area 7
LAND USE CONDITIONS Gajah Mungkur Reservoir • The conservation zones (forests and green zone) are only 24% out of total area → land erosion risk 8
Hydrological condition of Bengawan Solo River 1600 160 Discha… • The maximum 1400 140 flow discharge between 2007 Rainfall height (mm) 1200 120 Discharge (m3/s) – 2013 is 1000 100 1442.509 m 3 /s. 800 80 • The maximum 600 60 annual rainfall: 2951 mm/year. 400 40 200 20 0 0 Apr Agt Mar Jul Nov Mar Jul Nov Mar Jul Nov May Sep Jan May Sep Feb Sep 2007 2008 2009 2010 2011 2012 2013
Bengawan Solo River return period flood Dry season 2500 Discharge (m 3 /s) 1,981.26 2000 1,469.62 1,600.77 1,692.61 1500 1000 Rainy season 500 0 10 15 20 50 Return period flood (year)
Climate changing effect on Bengawan Solo River 2000 • The increment of rainfall height indicates climate Discharge (m 3 /s) 1500 change impact in Bengawan Solo River. R² = 0.6373 • The graphic shows 1000 the correlation between rainfall and discharge on 500 Bengawan Solo River from 2007 to 2014. • 0 It can be seen that the flood is increases as 0 1000 2000 3000 4000 rainfall height Annual rainfall height (mm) incremental during 2007 and 2014.
GEOPHYSICAL INVESTIGATION (river embankment) Soil resistivity at downstream area Soil Down- Unit stream Estuary properties Specific - 2.6 2.45 gravity, G s Plasticity Soil resistivity at estuary area % 10 25 Index, PI Dry density, kN/m 3 12 11 d Undrained Fine grain soil cohesion, C u kN/m 2 7 15 -Downstream area is dominated by silty and sandy soil, whilst estuary area is dominated by clayey soil. -It is due to coarse grain firstly deposits in the down-stream area. -The soil specific gravity and soil plasticity value proves the soil composition at down stream and estuary area. 12
GEOTECHNICAL INVESTIGATION (river embankment) No. Depth Soil description 0.00 m – 4.00 m 1. Clay 4.00 m – 5.50 m 2. Silty and Sandy clay 3. 5.50 m – 7.50 m Clay 4. 7.50 m – 9.50 m Silty and Sandy clay Sub-surface 5. 9.50 m – 28.00 m Clay boring 28.00 m – 30.00 m 6. Silty clay • River embankment soil condition (sub-surface) - Clayey soil stratified at upper sub-surface layer - Silty clay soil stratified at bottom sub-surface layer 13
BATHYMETRY Sedimentation areas Figure. River bathymetry result The riverbed levels are varied along river stream indicating the sediment transport occurred frequently. 14
GEORADAR INVESTIGATION (river embankment) • River bed profile soil condition (from Geo- radar test) - B-2 and B-3 has high impact scouring river profile than B-1 - Meandering area reduced river current, but high pressure of sedimented water led river profile scouring 15
Bengawan Solo Kedung Arum Kec. Kanor - Bojonegoro
Bengawan Solo Kedung Harjo Kec. Widang - Tuban
Bengawan Solo Kedung Harjo Kec. Widang - Tuban
Bengawan Solo Kedung Harjo Kec. Widang - Tuban
Bengawan Solo Kedung Arum Kec. Kanor - Bojonegoro
River bank vegetation and slope failure in Bengawan Solo River Bamboo vegetations Failure river bank
Em Emba bank nkmen ment t failur ailure a e at Bambo t Bamboo o Vegeta getation tion Ar Area ea
Emb Embank ankment ment failur ailure a e at A t Acac cacia ia Vegeta getation tion Ar Area ea
• Uprooted Bamboo and other vegetation were stacked on the tree as flood outcomes in Bengawan Solo River, 2014 • Massive dumped bamboo in the bridge pier, 2016 (Source: Timlo.net)
BENGAWAN SOLO RIVER OVERVIEW Main features: - It stated in the Indonesian National Code (SNI) that river with 2000 – 5000 m 3 /s of periodic flood should have 1.20 m in minimum of free b board otherwise the overtopping flow gives an extra force to the embankment structure. 25
BENGAWAN SOLO RIVER OVERVIEW Main features: - Failure embankment which located in flood plain ± 4 meters Bengawan Solo River was occurred in Banjarejo Village, Bojonegoro remaining 4 m space between river and residence house. - According to the Minister of Public Work and Public Housing Code No. 28/PRT/M/2015 Chapter 6(2) as concerns river and reservoir flood plain border, it is stated for primary river should be 100 meters of right and left sides of river in 26 minimum.
Analysis of River Embankment Failure Embankment toe failure after flood 6 m in Bengawan Solo River, 2014 Manmade embankment failure of Bengawan Solo 4 m River in Lamongan District, 2017 5 m (Source: citratv.co.id) 27
Normal River Cross Section Sedimentation Silty clayey sand Silty sand
River Cross Section – Illegal Sand Mining Sedimentation Clay Clay Silty clayey sand Silty sand Clay
LOCATION STUDY Kab.Gresik 2 nd year Kab.Tuban Kab. Lamongan Kab. Bojonegoro 1 st year 30
Bengawan Solo River (1972 – 2015) 31
BENGAWAN SOLO RIVER (1972 - 2015) 32
BED SEDIMENT THICKNESS According to the sediment rate, the bed sediment thickness can be estimated. – Sampling point to estuary range: 100000 m – Average river width: 80 m – Average sediment thickness: (841.866 m 3 /year)/(100000 m x 80 m) = 0.105 m/year 33
RIVER CHANNEL CONDITIONS N • River bed erosion occurred at Kanor side due to high flow velocity. • Sediment deposition exist around inner bend at Rengel side developed by low flow velocity. RENGEL KANOR • Excessive flood is frequently happened in this section. : : 34
EVALUATION - RIVER CHANNEL CAPACITY ANALYSIS • In existing condition, 12 10.41 Full Bank Capacity the over topping 10 flow occurred when 8.31 the flow discharge 8 Water depth (m) reach 1825.55 m 3 /s. 6 • By excavating 2- 3 m of sediment material 4 will increase channel 2 capacity up to 1825.55 2850.77 2850.77 m 3 /s or 56% 0 bigger than existing 0 1000 2000 3000 Flow discharge (m 3 /s) condition. Rating curve of Bengawan Solo River, Kanor section 35
EVALUATION - SEDIMENT MAINTENANCE PROPOSED METHOD 60 50 τ ( kN/m 2 ) 40 30 20 10 0 γ d (kN/m 3 ) 5 10 15 20 Location 1 Location 2 Location 3 Location 4 Location 5 Water injection dredger Ploughing Plain suction dredger Most of the sediment able to be dredged by using grab dredger. 36
EVALUATION - DEPOSITION DEPTH CHANGING AT ESTUARY • Bed elevation in increasing near the shore at estuary area • Sediment deposition was ended in the shore as the final of river path 37
SEDIMENT EFFECTS ON THE ESTUARY • Sediment quantities investigation in Bengawan Solo River-Bojonegoro: – Dry season: 50 mg/L – Rainy season: 1700 mg/L • Sediment rate: 841.866 m 3 /year (1 st year result). • Average longitudinal growth in estuary around 70 m per year (Hoekstra et al, 1989). 38
EVALUATION - SOIL BORE LOG AT SHORE IN ESTUARY • All of the soil below shore is very 0 Mud Brown soft soil with having N SPT 0 • Sediment material at shore is Dark 5 grey dominated by fine grain material • The soil colour describes the function of depth (m) 10 age of sedimentation process 15 Clay Light 20 grey 25 30 -30 m 39 -1 m -15 m -5 m
EVALUATION - DEPOSITION DEPTH CHANGING AT ESTUARY (SUB BOTTOM PROFILE MEASUREMENT) Mud 40
WATER FLUCTUATION EFFECT ON RIVER EMBANKMENT STABILITY • Karang Binangun was 8 Karang the most critical Binangun Safety factor, SF 6 condition (SF < 1.5) due Karang Geneng to water level change 4 Laren • Karang Geneng was 2 Sembayat the stable structure (SF 0 > 1.5) since possessing 0 m 2.5 m 5.0 m 7.5 m 10 m flatter slope water level fluctuation • Considering the unsaturated condition beyond water level, the embankment stability should be re-analyzed. 41
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