The Study on Countermeasures for Sedimentaion Workshop IV, Surakarta, January 18, 2007 in The Wonogiri Multipurpose Dam Reservoir Master Plan on Sustainable Management of Wonogiri Reservoir in The Republic of Indonesia Mitigation Measures of Impacts Present Sediment N Discharge at Babat Basic Policy BENGAWAN SOLO Barrage (Ex.) Operation Rule “To minimize the Q, Turbidity Allowable limit of 22.9 million Impact to the d/s” m3/year concentration & m3/year by careful gate operation duration shall be defined N Combined operation BENGAWANbetween SOLO Wonogiri Dam and Colo Weir Sediment Discharge from Wonogiri Monitoring in Increase of sediment to be 0.8 million downstream reaches m3/year discharge to Solo River Operable period SCALE estuary will be approx. shall be strictly 5%0 15 30 45 60 75 90 km SCALE prohibited in dry 5% 0 15 30 45 60 75 90 km Flushing season Thank You very much for Your Kind Attention ! Japan International Cooperation Agency – JICA Ministry of Public Works The Republic of Indonesia Nippon Koei Co. Ltd. and Yachiyo Engineering Co. Ltd. 䋭㩷㪈㪉㪋㩷䋭 Page / 6 Estimating sediment volume into Brantas River after eruption of Kelud volcano on 1990 Mr. Takeshi Shimizu National Institute for Land and Infrastructure Management 䋭㩷㪈㪉㪌㩷䋭 IEstimating Sediment volume into Brantas River after eruption of Kelud Voncano on 1990 Takeshi SHIMIZU1, Nobutomo OSANAI1 and Hideyuki ITOU1 1National Institute for Land and Infrastructure Management, Ministry of Land, Infrastructure and Transport, Japan The Brantas River that flows through East Java Province, the Republic of Indonesia, is the second largest river. It has 11,800km2 catchment areas and total length of the river approximately 320km. The Brantas River Basin has been developed based on the 1st to 4th master plans since the Second World War. The purpose of master plans was mainly dam constructions in the middle stream and upstream for flood control, water supply for agricultural and industrial use, and electricity generation. The each plan was almost successfully completed. In the Brantas River Basin, several active volcanoes located, originally sediment production is intense. The Brantas River Basin now has two serious water and sediment related problems as followed as bellows. (a) The decrease of reservoir’s effective capacity due to sediment inflow to the reservoirs in the middle stream and upstream. (b) The riverbed degradation due to sand mining in the lower stream. Related to the decrease of reservoir’s effective capacity, a total annual average 3 million m3 of sediment has flowed into reservoirs, and already filled approximately 43% of the reservoirs in 2003. The riverbed degradation has increased the risk of damage such as the flood disasters, lateral erosion, and constructions flow out. The main factor of the riverbed degradation is considered sand mining. More than 4 million m3 of sediment were excavated from the river bed in 2000. Moreover, volcanic materials supply due to the eruption sometimes gives additional effect along the basin. Especially Kelud volcano (elevation: 1,731m) indicates high activity; it might give serious effects to the basin. The aim of this study is to estimating the sediment volume into Brantas River Basin after Kelud volcano eruption on 1990 using numerical simulation. Keywords: Water and Sediment Management, Brantas river, volcanic eruption 䋭㩷㪈㪉㪎㩷䋭 Investigation Area Surabaya Estimating sediment volume into > Brantas River(basin area : 11,800 km2, river length : 320 km ) is located Brantas River after eruption of on the Island of Java, Indonesia. Kelud volcano on 1990 >There are active volcanoes such as Kelud. Kelud Volcano SHIMIZU Takeshi, OSANAI Nobutomo and KOGA Shozo Kelut Volcano > Development plan of the Brantas river basin have started since 1959. A Erosion and Sediment Control Division, lot of water facilities including Nation Institute for Land and Infrastructure Management reservoirs were constructed in the projects. The 2nd International Workshop on Water and Sediment Management Malang, Indonesia Location map of investigation area 22-23 November, 2007, 2nd 3rd 4th ፸፻፷፷፷፷ ਈϊAgriculture ፸፹፷፷፷፷ 7ϊIndustry Background of this study History of ፸፷፷፷፷፷ ᎎᎋ᎗GDP ᮖ᭿᭍ᯙ ፿፷፷፷፷ ᎀ 1st ፽፷፷፷፷ GDP ፻፷፷፷፷ development in ɢɥ໥ᯘ፸፷ ፹፷፷፷፷ ፷ ፸ᎀ፼፷ ፸ᎀ፽፷ ፸ᎀ፾፷ ፸ᎀ፿፷ ፸ᎀᎀ፷ ፹፷፷፷ Eruption of Kelud volcano is Brantas River Basin ፺፷፷፷ ፻፷፷ ̀ᬡɢɥ୲Paddy production Problem 1 ፹፼፷፷ Żɰ้ƥPaddy field area thought to be one of the biggest Riverbed degradation ፹፷፷፷ ፺፼፷ ᎯᎨᯙ ፺ factors to makeing serious effect There are 4 master plan executed in ፸፼፷፷ caused by sand mining ፸፷፷፷ ፺፷፷ on both problems ̀ᬡɢɥ୲ᯘᎻᯙ the Brantas River Basin Żɰ้ƥᯘ፸፷ ፼፷፷ Paddy field ፷ ፹፼፷ ፸ᎀ፼፷ ፸ᎀ፽፷ ፸ᎀ፾፷ ፸ᎀ፿፷ ፸ᎀᎀ፷ ፹፷፷፷ ፸፿፷፷ > Time going, economic factors ፸፽፷፷ ፸፻፷፷ increasing ፸፹፷፷ > The master plans were effective. ʡɕᯘȱʡᯙ ፸፷፷፷ ፿፷፷ But another problem occurs population ፽፷፷ ፸ᎀ፼፷ ፸ᎀ፽፷ ፸ᎀ፾፷ ፸ᎀ፿፷ ፸ᎀᎀ፷ ፹፷፷፷ ፽፷፷ ࡲŻ୲ ፼፷፷ ØV୲ > For example sedimentation in dam ᯙ ፺ Ꮄ ፽ reservoirs and river bed ፻፷፷ V5ᬊᬡðɯᬡØV୲ Problem 2 ፺፷፷ Dam sedimentation degradation ፹፷፷ ࡲŻ୲ᮦ ØV୲ᯘ፸፷ ፸፷፷ For the water resources management in the Brantas river basin, it is Storage ፷ ፸ᎀ፼፷ ፸ᎀ፽፷ ፸ᎀ፾፷ ፸ᎀ፿፷ ፸ᎀᎀ፷ ፹፷፷፷ important to clarify the effect of volcano-crust for the river. Volcanic Activities of Kelud Volcano The purpose of this study > Kelud volcano ( 1,731m height ) is one of the high level active volcano located in Java Island. > It has 4 eruptions records since 1919. To clarify the effect of Volcanic activities on > Almost all of the scale of eruptions were VEI 3 sediment conditions in Brantas Rivers > In each event, following phenomenon also occurred: 1) Lahar due to Phreatic explosion. 2) Plinian with pylocrastic flow Authors carried out numerical analysis applied to Kelut volcano eruption on 1990. 3) Lahar due to the breach of crater lake Table : scale of eruption of Mt. Kelud since 1919. ᎠᎬᎨᎹ ᎝ᎶᎳᎼᎴᎬ፯፸፷፽፧Ꮄ፺፰ ᎕ᎼᎴᎩᎬᎹ፧ᎶᎭ፧ᎫᎬᎨᎻᎯᎺ ፸ᎀ፸ᎀ ፺፹፺ ፼፸፸፷ ፸ᎀ፼፸ ፸ᎀ፷ ፾ ፸ᎀ፽፽ ᎀ፷ ፹፿፺ ፸ᎀᎀ፷ ፸፹፼ ፺፼ 䋭㩷㪈㪉㪐㩷䋭 1 Numerical simulation carried out in this The latest eruption of active volcano ,Kelud study Considering the types of Kelud volcano eruption, we carried out following simulations to Kelut volcano eruption on 1990. > Lahar due to crater wall collapsed type simulaiton(2-D analysis)፧ > Pyroclastic flow simiulation( 2-D analysis)፧ > Pumice fall distribution calculation(1-D analysis)፧ Jawa Pos , 21st of Nov. 2007 Jawa Pos , 5th of Nov. 2007 Simulation model for lahar Input of Hydrograph This calculation assumes that crater wall collapse triggering lahars. We calculate the hydrograph according to the volume of crater lake on 1990 eruption. ፧ Total discharge of Water is about 4,000,000 m3 Discharge(m3/s) Sediment supplied by M.P.M Time(s)፧ Red relief map around crater of Kelut volcano formula Relationship between time and discharge Results of lahar calculation ȸƂȡƏɻąK1 ȡȵƸശŬǃ ፯Ꮄ፰ minutes፯ą፰ ፸፷፵፷ᰮ ፷ᰮ፸ ፼፵፷ᰮ፸፷፵፷ ፸ᰮ፼ ፺፵፷ᰮ፼፵፷ ፼ᰮ፸፷ ፸፵፷ᰮ፺፵፷ ፷፵፼ᰮ፸፵፷ ፸፷ᰮ፸፿ ፷ᰮ፷፵፼ ፸፿ᰮ፻፿ ፻፿ᰮ፾፿ •․…‣ •․…‣ Kilometers Kilometers Arrival time distribution of Lahar Distribution of depth of the flow 䋭㩷㪈㪊㪇㩷䋭 2 This figure shows sediment volume inflows into Brantas River within about 3 hours. ȸ΋OVØƥɻ ፯Ꮄ፰ ፸፷፵፷ᰮ ፼፵፷ᰮ፸፷፵፷ So the more time going, ፺፵፷ᰮ፼፵፷ the more volume flows ፸፵፷ᰮ፺፵፷ ፷፵፼ᰮ፸፵፷ into Brantas River. ፷ᰮ፷፵፼ According to these figures, almost all of water and sediment from crater lake flows into Brantas River Basin. •․…‣ Total volume of water is about 4 million m3 in this case. Kilometers So, Lahar has serious effect on the conditions of Brantas Distribution of sediment depth after lahar flow down River. Simulation model for pyroclastic flow Result of calculation of pyroclastic flow ȸ΋OVØƥɻ ȡȵƸശŬǃhours ፯Ꮄ፰ ፯Ƹശ፰ ፸፷፵፷ᰮ ፷ᰮ፹ ፼፵፷ᰮ፸፷፵፷ Pyroclastic flow divided to two ፺፵፷ᰮ፼፵፷ ፹ᰮ፸፷ ፸፵፷ᰮ፺፵፷ layers; Surge and main body. ፸፷ᰮ፹፷ ፷፵፼ᰮ፸፵፷ ፹፷ᰮ፻፷ ፷ᰮ፷፵፼ Main body is dragged to surge. ፻፷ᰮ፽፷ ፽፷ᰮ፿፷ So, it is important to know the behavior of main body. We followed Yamashita & Miyamoto(1991)’s model in •․…‣ which the main body behavior Kilometers is treated as the dry particle Distribution of arrival time of Distribution of pyroclastic thickness flow. Schematic model of a pyroclastic flow pyroclastic flow of deposition፧ Numerical analysis model of pumice fall distribution It is difficult to model behavior of pumice fall precisely, because pumice fall has complex factors to simulate. This results show Pyroclastic flow doesn't have serious effect on Brantas River in short term. We use the geometrical model following Miyamoto(1993). But pyroclastic flow supplies hillside area with a lot of unstable sediments. So, In the long term, it becomes high potential to make debris flow or lahar generate as the secondary disasters. Distribution of pumice fall is calculated Schematic model of volcanic plume by hight of plumes and wind direction. 䋭㩷㪈㪊㪈㩷䋭 3 Result of calculation of pumice fall distribution A lot of pumice fall does not directly fall in the Brantas River. But After the heavy 10 cm rainfall, pumice fall is possible to flow down, changing forms to concentrated flow. 5 cm Because gradient of hillside over a wide range on Kelud volcano Distribution of pumice fall is determined by wind direction. is greater than 2 degree. In Brantas River Basin, everywhere is possible to damage by Distribution of gradient more than 2 degree pumice fall. about Kelud volcano Summary and conclusion Summary and conclusion Lahar reach the main river course. Lahar is possible to make severe impact on the We can recognize the impact of eruptions on the sediment conditions in Brantas river basin. river is not so big in short term. Pyroclastic flow does not reach