Consideration on Extension of Operating Life of Dams by Removing Sediment

Transcription

1 Consideration on Extension of Operating Life of Dams by Removing Sediment Takayama Dam (1969) Shorenji Dam (1970) Muro Dam (1974) Nunome Dam (1992) Hinachi Dam (1999) 5 Dams in Kizu River System 1

2 N Location of 5 dams in Kizu River System Hiyoshi Dam Lake Biwa Kyoto Pref. Katsura Riv. Shiga Pref. Hitokura Dam Inagawa Riv. Amagase Dam Uji Riv. Setagawa Weir Yodo Riv. Yodogawa Weir Nunome Dam Start of management 1992 Kizu Riv. Start of management 1969 Takayama Dam Mie Pref.. Osaka Bay Osaka Pref. Start of management 1970 Nara Pref. Shourenji Dam Murou Dam Start of management 1999 Uda Riv. Shorenji Riv. Nabari Riv. Hinachi Dam Start of management

3 Position of 5 dams in Kizu River System Kizu River Nunome Dam 1992~ Nunome River Takayama Dam Nabari River 1969~ Shorenji Dam 1999~ Hinachi Dam 1970~ Uda River Muro Dam 1974~ Shorenji River 3

4 Flowchart of consideration Arrangement of consideration conditions 1) Setup of management goal of reservoir function 2) Arrangement for countermeasure items of sediment 3) Setup of evaluation method for economic efficiency Consideration of application to the group of dams in Kizu River System 4) Comprehension of sediment characteristics in the reservoir 5) Case study in Takayama Dam 6) Selection of countermeasure method which is the most economical in each dam 7) Consideration of operating possibility for the group of dams 4

5 Arrangement for countermeasures of sediment options excavation dredging Check dam (+excavation) Flushing Bypass tunnel Dry excavation Description and the cost Removing soil-storing area (more than NWL) in reservoir by machine Initial cost : none Cost : excavation Removing sediment settled under water by dredger Initial cost : none Cost : excavation Construction of check dam and removing sediment in check dam by machine Initial cost : construction of check dam Cost : excavation at check dam Sediment flushing by temporary lowering water level of reservoir Initial cost : Installation for sediment flushing gate Cost : Rehabilitation of facilities Sediment are diverted directly downriver through the bypass tunnel Initial cost : Construction for bypass tunnel Cost : Rehabilitation of tunnel Periodical reservoir reducing water level to excavation and removing sediment Initial cost : none (Installation of a drawdown gate if necessary) Cost : excavation, payment for compensation reduced power energy, loss of storage volume 5

6 Conditions for consideration Evaluation method for economic efficiency Total Cost in T years = T Cost ( 1 r) t= 1 + for thetth year T r=0.04 Initial Cost Evaluation of Running Cost economic efficiency Start of measurement At the time of evaluation (T years after) 6

7 Concept of target sedimentary fraction 100% Sedimentary fraction Operation with margin in case of sudden inflow of sediment Progress of sediment Design sediment capacity Maintain Target sedimentary fraction 80% considered margin Years The largest inflow for one year into 5 dams in Kizu River System: 10~15% 7

8 Annual variation of the amount of sediment in case of Takayama Dam 高山ダム実績堆砂量経年変化図 [*10 3 m 3 ] 各年堆砂量累計堆砂量累計有効容量内堆砂量累計死水容量内堆砂量計画堆砂量 4,000 4,000 Accumulation 3,500 3,500 3,000 In Capacity for Sedimentation (Dead Storage Capacity) 3,000 Design Sedimentation 2,500 2,500 In Effective Capacity 2,000 2,000 1,500 1,500 Maximum: 年堆砂量 (10 3 m 3 ) 累計堆砂量 (10 3 m 3 ) 1,000 1, *10 最大堆砂量 646,000m 3 m 3 /year 3 Sedimentation Volume Average:100*10 3 m 3 /y 平均堆砂量 100,100m 平成 17 年度 平成 16 年度 平成 15 年度 平成 13 年度平成 14 年度 平成 12 年度 平成 11 年度 平成 10 年度 平成 9 年度 平成 7 年度平成 8 年度 平成 6 年度 平成 5 年度 平成 4 年度 平成 3 年度 平成元年度平成 2 年度 昭和 63 年度 昭和 62 年度 昭和 61 年度 昭和 60 年度 昭和 58 年度昭和 59 年度 昭和 57 年度 昭和 56 年度 昭和 55 年度 昭和 53 年度昭和 54 年度 昭和 52 年度 昭和 51 年度 昭和 50 年度 昭和 49 年度 昭和 47 年度昭和 48 年度 昭和 46 年度 昭和 45 年度 8 8 Year 年度

9 Sedimentation rate in the group of dams in Kizu River System (up to 2005) Years Design Sedimentation Rate (m 3 /km 2 /year) Actual Average Sedimentation Rate (m 3 /km 2 /year) Sedimentation Fraction* (2005) Takayama Dam < % Shorenji Dam > % Muro Dam < % Nunome Dam < % Hinachi Dam < % * In portion to Design Sedimentation More sediment except Shorenji Dam 9

10 Characteristics of group of dams in Kizu River System So far, sediment problems have not been actualized yet. (The situation is different from one in Chubu Region in Japan) However, we need strategies for extension of operation life of dams now. Kizu River System has a group of 5 dams From the viewpoint of river environment, it is expected that sediment should be provided for downstream of the dams We find direction using as easy method as possible without detailed simulation of sedimentation 10

11 Inflow sediment to each dam classified by grain size Name of dam Average Inflow Sediment (m 3 /year) Portion classified by grain size (%) Wash Load (less than 0.075mm) Sand Sandy Gravel (more than 2.0mm) Takayama 104, Shorenji 41, Muro 45, Nunome 23, Hinachi 56, (Past consideration in Yodo River) 11

12 Example in Takayama Dam Setup of the cost Initial Cost Running Cost Excavation - 2,500yen/m3 Dredging - 20,000yen/m3 Check dam (including excavation) Flushing Bypass for sediment flushing Reducing water level and excavation 5.4 bil. yen (check dam) 10.1bil. yen (gate for sediment flushing) 13.2 bil. yen (bypass for sediment flushing) - 2,500yen/m3 22 mil. yen/year 121 mil. yen/year 2,500yen/m3(excavation) 75 mil.yen/year (compensation for reducing water level) Assuming compensation for reducing water level to compare economically 12

13 Consideration results of combination to maintain function (Compared by annual average) Example in Takayama Dam Check dam (incl. excavation) Removed sediment volume (m 3 /year) Non-removed sediment volume (m 3 /year) Combined Annual Cost (mil. yen) Reducing Dredging water level 69,889 34, Excavating 59,213 45, Bypass for sediment flushing 72,838 31, Flushing 102,350 2, Advantageous 13

14 Sedimentary fraction (%) Variation prediction of sedimentary fraction in Takayama Dam in each countermeasure 0 Check dam (Incl. excavation) Excavation Bypass for sediment flushing Years Years Target sedimentary fraction: 80% Flushing After filled up by sediment, reducing water level and excavation are done. 14

15 Total cost in each countermeasure in Takayama Dam 18,000 Bypass for sediment flushing Total Cost (mil. yen) 16,000 14,000 12,000 10,000 8,000 6,000 4,000 2,000 Flushing Check dam (incl. excavation) Excavation Years Operation by excavation & reducing water level and excavation Most Economical 15

16 Constraint conditions of reducing water level and excavation Is disposal of removed sediment possible? Is compensation for reducing water level possible? Can t the group of dams back up? 16

17 A case of extension of operating life by excavating (returning sediment to the downstream of Takayama Dam) flow Return Excavating Nunome Dam Convey flow Return Convey Muro Dam Takayama Dam Shorenji Dam Convey Hinachi Dam Excavating Excavating Excavating 17

18 Image of collaborative operation of dams (A case of reducing water level in Takayama Dam) For flood control For flood control Takayama Dam For Water Use Available for backup For Water Use Available for backup Reducing Water Level For Water Use Excavation Hinachi Dam For flood control Shorenji Dam For flood control For Water Use For Water Use Available for backup Available for backup Muro Dam Nunome Dam 18

19 Thank you very much for your attention. 5 Dams in Kizu River System Water supports wealthy society 19