PAK BENG HYDROPOWER PROJECT

Transcription

1 PAK BENG HYDROPOWER PROJECT Overall Design Report of Sediment Monitoring System September 2015

2 CONTENTS Page 1 OVERVIEW PROJECT OVERVIEW Overview Sediment problems and sediment operation modes in the reservoir Site planning of automatic system of hydrological data acquisition and transmission PURPOSE AND ITEMS OF SEDIMENT MONITORING PURPOSE OF SEDIMENT MONITORING DESIGN PRINCIPLES AND BASIS MONITORING ITEMS SEDIMENT MONITORING PLAN INCOMING AND OUTGOING SEDIMENT MONITORING OF THE RESERVOIR Site layout of sediment monitoring station network Equipment configuration and civil works MONITORING OF WATER SURFACE LINE IN FRONT OF THE DAM AND AT THE TAIL SECTION OF THE RESERVOIR Site layout of monitoring station network Equipment configuration and civil works MONITORING OF SEDIMENT DEPOSITION IN THE RESERVOIR AREA TERRAIN MONITORING OF THE PROJECT AREA (IN FRONT OF THE WATER INTAKES AND APPROACH CHANNELS) TERRAIN MONITORING OF THE DOWNSTREAM RIVER REACH MONITORING OF LANDSLIDE DEFORMATION IN THE RESERVOIR AREA MAIN OBSERVATION RESULTS Incoming and outgoing sediment monitoring of the reservoir Monitoring of pre-dam and reservoir tail water surface lines Terrain monitoring of the reservoir area Terrain monitoring of the project area (Pre-dam and approach channels) Terrain monitoring of the downstream river reach Monitoring of landslide deformation in the reservoir area STAFFING BUDGETARY ESTIMATES i

3 1 OVERVIEW 1.1 PROJECT OVERVIEW Overview The power station is located about 14km in the upper reach in Pak Beng County, and the river reach belongs to the northern mountainous area of Laos, about 96km of the river course in the upstream of the dam site is located in Laos, and the upstream is the Lao-Thai boundary river. The river course in this river reach has a relatively small gradient. The length of the river course between Houayxay and Pak Beng County is about 140 km, with a drop of around 33m, and an average gradient of about Clipped by the mountains, the river reaches about 55km upstream the dam site generally maintains the East-West trend, and then the river course turns to the North-South trend. The Mekong River enters the Lao-Thai boundary river reach in the KengPhaDai region. The right bank of the upstream is Thailand, and the left bank is Laos. The river reach of the Pak Beng reservoir area inside the Laos territory belongs to the mountainous river. Except few of broader river reaches, the river width is generally 100m-200m in the dry season. KengPhaDai is an iconic ground feature of the boundary of Laos and Thailand, about 96km away from the Pak Beng dam site. According to the 1/500 topographical map of the region, the terrains with an elevation of above 340m are mostly regular banks, and at an elevation of above 335m, there are 5 large blocks of rocks, with 3 blocks distributed on the left bank, and 1 in the middle of the river course and 1 on the right bank, respectively. The elevation of the highest point of the rock is m. Under natural conditions, the average water level in the dry season (November to May) is m, and that in the flood season (June to October) is m (339.00m taking into account the adjustment of Xiaowan and Nuozhadu reservoirs). The Laos-Thai boundary river reach maintains the northwest trend in general, with relatively broader river course, especially in the estuary of Nam Ing where the river reach is wide and the water is shallow, the average level in the dry season is about m, and the river width in the dry season is more than 300m - 400m, and that in the flood season is m. In the flood season, the river width can reach up to a few kilometers. In the reservoir area, the larger tributaries are mainly Nam Ing River and Nam Tha river. Wherein, the Nam Ing River is located in the Thailand territory, at the Right Bank of the Laos-Thailand boundary river reach, covering a catchment area of about 9750km 2. The estuary is about 115km apart from the Pak Beng dam site. Affected by the Mekong River flood backwater, the estuary river reach has sediment deposition, forming sandbanks and shoals, where a lot of farmlands are distributed on the Thai side (Especially at an elevation of - 1 -

4 more than 350m). The Nam Tha River is located on the left bank, in Laos s territory, covering a drainage area of 8990km 2. The estuary is about 90km away from the Pak Beng dam site. There are steep mountains and deep valleys on both sides of the river. Except the No.1 hydropower station of the Nam Tha river, there is no other important affective object. According to the Feasibility study report of No.1 hydropower station of the Nam Tha river, the upper and lower dam sites through comparison and selection are respectively 60 km and 40 km away from the estuary, with the water levels in the dry season respectively of about 380m and 360m, and furthermore, the Pak Beng power station maintains a normal impounded level of is 340m, and hence it will not affect the No.1 station. Under natural conditions, the multi-year average suspended sediment at the dam site is 4524kg/s, and the multi-year average annual suspended sediment load is x10 6 t, wherein, the sediment load in the flood season (June to October) is x10 6 t, accounting for 92.84% of the annual load, and the bed-load sediment load is 4.28x10 6 t. The normal impounded level is 340m, the corresponding reservoir capacity is m 3, and the ratio between reservoir capacity under normal water level and annual sediment volume is about 5. Among the cascade hydropower stations in the middle and lower reaches of the Lancang River, Xiaowan and Nuozhadu hydropower stations have relatively large reservoir capacity and have the multi-year adjustment ability. After their completion, it would have relatively impact on the incoming water and sediment of Pak Beng HPP. Xiaowan and Nuozhadu hydropower stations have started water storage and power generation in 2009 and 2013, respectively. After Manwan, Dachaoshan, Xiaowan, Nuozhadu, Jinghong and other cascade hydropower stations in the upstream of the Lancang River have started water storage and silt detention, the incoming sediment to Pak Beng would be greatly reduced. The multi-year average suspended sediment load at the dam site is t, only 26.6% of the sediment load under natural conditions, the bed-load sediment load is t and the ratio between reservoir capacity under normal water level and annual sediment volume is about Sediment problems and sediment operation modes in the reservoir The sediment problems in Pak Beng HPP mainly include: Sediment deposition in the reservoir area, water intake and sediment prevention for the power station, sediment deposition in the approach channel, riverbank stability and downstream river course scouring. Pakbeng Hydropower Station is a runoff power station. Its reservoir is featured with low - 2 -

5 backwater, large discharge and without sediment retaining effects. After the cascade water storage and silt detention in the Lancang River, small floods occurred not as frequent as before. The inflow sediment load is only 26.6% of that under natural conditions, and the sediment deposition in the reservoir is reduced. In the model of operation, when the incoming flow is more than rated flow 5961 m 3 /s, bottom hole, sediment flushing gate and the flood gate opened gradually, reservoir water level maintains at 340m; when the incoming flow is more than 10000m 3 /s, discharge volume of the flood gate increase gradually, reservoir water level reduce gradually from 340m. In order to ensure navigation the reservoir water level is maintained at 334m if the incoming flow is the P=33.3% flood discharge of 12,900m 3 /s. If the incoming flow is higher than the P=33.3% discharge of 12,900m 3 /s and lower than the P=20% flood discharge of 14,600m 3 /s and inflows are higher than the standard for navigation of ship lock, use of ship locks shall be ceased, the discharging sluices open gradually and reservoir water level reduce gradually from 334m. If incoming flow is higher than the 5-year frequency flood discharge of 14,600m 3 /s, all gate should be opened, the flood passing and sediment discharging are basically approached to the natural channel, the sediment is prevented from depositing in the reservoir, and partial sediment in the reservoir will be carried away at the same time. In order to reduce the coarse sediment into the generating units of the power station, a sand-guide sill with an elevation of 325m to the top is established at the water intake of the power station in the upper reach. The sill stops the bed-load sediment and guides it to the flood-discharging & sand-sluicing gate, and the gate discharges the sediment to the lower reaches. For the sediment passed the sand-guide sill and deposited in front of the water intakes of the power station, one sand-sluicing bottom outlet is set in the middle of every two water intakes of the power station, totaling up to eight sand-sluicing bottom outlets, and the elevation of the bottom outlet is 288.9m. The sediment in front of the water intakes is discharged to the downstream through opening of sand-sluicing bottom outlets. Sediment monitoring in front of the dam should be implemented every year. For the parts with unobvious sand-scouring effect, manual or mechanical dredging measures should be used to remove sediment. In order to solve the problem of sediment deposition in the upper and lower reaches of the approach channels, the 1-hole channel sand-sluicing gate (15m 23m) is arranged on the right side of the ship lock, which adopts the broad crested weir for flow through. The elevation of the weir crest is 317.0m. After the completion of the power station, the sedimentation monitoring on the approach channel should be strengthened. When the flow is relatively small and the water head difference between upper and lower reaches is relatively large, the - 3 -

6 channel sand-sluicing gate is opened to scour the sediment deposited in the entrance area of approach channel. or the parts with poor flushing effect, artificial or mechanical dredging measures shall be taken to clear the deposits Site planning of automatic system of hydrological data acquisition and transmission Because some hydrological stations of sediment monitoring are combined with the automatic system of hydrological data acquisition and transmission, the following briefly describes the planned site layout of Pak Beng automatic system of hydrological data acquisition and transmission. According to requirements for configuration of hydrologic forecast schemes in construction period and operation period, there are 27 telemeter stations and 12 telemeter hydrologic (gauging) stations arranged for automatic hydrologic data acquisition and transmission system of Pak Beng HPP, of which 7 telemeter stations are precipitation station concurrently; and 15 telemeter precipitation stations, of which 6 are in Thailand and 9 in Laos. The station network arrangement of the automatic hydrologic data acquisition and transmission system of Pak Beng HPP is shown in Table 1.1, and station network distribution map is shown in Figure

7 Table 1.1 List of telemeter stations of automatic hydrologic data acquisition and transmission system of Pak Beng HPP No. River Station Country Location Item of hydrologic data 1 Guanlei China Guanlei Hydrological Station H,Q(Constructed) 2 Ban Xieng Kok Lao Ban Xieng Kok Village H,Q (Constructed newly) 3 Ban Tung Lao 4 Hougy Xai Lao 5 6 Main stream Upper cofferdam station (Water gauge A) Lower cofferdam station (Water gauge B) Lao Lao Ban Tung Village (the opposite of Chiang Saen Hydrological Station) Hougy Xai (the opposite of Chiang Khong Hydrological Station) Upper and lower cofferdams of Pak Beng dam site Lower cofferdam of Pak Beng dam site H,Q,P (Constructed newly) H,Q,P (Constructed newly) H,P (Constructed) H,Q (Constructed) 7 KengphaDai Lao Laos - Thailand border H,P (Constructed newly) 8 Water gauge C Lao 9 Pak Beng (Water gauge D) Between county town and the lower cofferdam H,Q (Constructed) Lao Pak Beng County town H,Q (Constructed) 10 Chiang Rai Thailand Chiang Rai Station of Nam Kok H,Q,P (Constructed) 11 Branch es Thoeng Thailand Thoeng Station of Nam Ing H,Q,P (Constructed) 12 NamTha Lao Downstream of Nam Tha 1# H,Q,P (Constructed newly) 13 Nam Ban Nam Ou Lao Ban Nam Ou Village P (Constructed newly) 14 Ngam Namtha Gang Lao Namtha Gang Village P (Constructed newly) 15 River Ban Ta Pha Lao Ban Ta Pha Village P (Constructed newly) 16 Louang Namtha Lao Louang Namtha County P(Constructed newly) Namth a River Ban Nali Ban Hom Lao Lao Ban Nali Village Ban Hom Village P(Constructed newly) P(Constructed newly) 19 Ban Pho Lao Ban Pho Village P(Constructed newly) 20 Mainst Prap Khop Lao Prap Khop Ben Village P (Constructed newly) 21 reams Kong Ban Lao Kong Ban Village P(Constructed newly) 22 Mae Tha Tum Thailand Tha Tum Village P(Constructed newly) 23 Nam Kok Mae Chan Thailand Mae Chan Village P (Constructed newly) 24 River Bang Tau Thailand Bang Tau Village P(Constructed newly) 25 Mae Ban Chien Thailand Ban Chien Village P (Constructed newly) 26 Nam Yam Mangray Thailand Mangray Village P (Constructed newly) 27 River Phayao Thailand Phayao Village P (Constructed newly) - 5 -

8 Figure 1.1 Diagram of station network arrangement for automatic hydrologic data acquisition and transmission system of Pak Beng HPP - 6 -

9 2 PURPOSE AND ITEMS OF SEDIMENT MONITORING 2.1 PURPOSE OF SEDIMENT MONITORING To master the inflow and incoming sediment of Pak Beng reservoir, sediment deposition development condition, reservoir capacity, impact of upstream and downstream river courses, and other conditions, to provide accurate and reliable information for power station operation and shipping scheduling, and to improve the management level of the power station, the sediment observation planning is necessary. At the same time in order to accumulate basic data for power station design, sediment testing should be carried out immediately in Pak Beng Hydrological Station. 2.2 DESIGN PRINCIPLES AND BASIS Sediment monitoring design of Pak Beng HPP complies with the following principles: (1) The sediment monitoring network of Pak Beng HPP is designed according to the principles of advanced & reliable, economical & practical, and convenient for construction & maintenance management. (2) The data of original hydrological stations should be fully used, and during layout of station network, the sites should be appropriately added and adjusted according to the requirements of sediment monitoring based on the existing station network. (3) The social forces should be fully used to reduce personnel allocation as far as possible. Design basis of the sediment monitoring station network of Pak Beng HPP: Preliminary DG of LMB Mainstream dams Code for reservoir hydrologic and sediment survey (SL ) River suspended sediment test specification (GB ) Specifications for the Waterway Survey (SL ) Survey Specification for Hydraulic and Hydro-Power Projects (Planning and design phase) (SL197-97) 2.3 MONITORING ITEMS Oriented to the main sediment problems of the reservoir, the main items of the sediment observation are as follows to monitor and analyze the impact of sediment deposition: - 7 -

10 (1) Monitoring water and sediment in/out the reservoir (including: sediment volume, sediment concentration and sediment gradation of the inflow station and outflow station); (2) Monitoring of water surface line in front of the dam and at the tail section of the reservoir; (3) Monitoring of sediment deposition in the reservoir area; (4) Monitoring of sediment deposition in the project area; (5) Monitoring of downstream river course; (6) Monitoring of bank deformation in the reservoir area. 3 SEDIMENT MONITORING PLAN 3.1 INCOMING AND OUTGOING SEDIMENT MONITORING OF THE RESERVOIR The site design principles are: Use the existing sites and the sites of the automatic system of hydrological data acquisition and transmission as many as possible, set up the sites in the places where traffic and living conditions are good, and set up the sites as telemetry stations in order to reduce staffing as far as possible Site layout of sediment monitoring station network (1) Incoming sediment monitoring station (Ban Don station) Construction idea: The LISST suspended sediment particle size distribution probes with real-time automatic acquisition function are configured in the incoming sediment station to achieve real-time monitoring of the incoming sediment. Site selection: The same site as the hydrological station, in the Lao s territory opposite to Chiang Saen Hydrological Station Catchment area of km 2, accounting for 86.7% of the drainage area of Pak Beng dam site, which can act as the incoming sediment monitoring station for Pak Beng. The flow in this station can be measured through tour gauging. To grasp the inflow and incoming sediment of Pak Beng reservoir, sediment monitoring can be added on the basis of flow measurement to monitor water level, flow, sand-bearing content and sediment gradation. Operation mode: The qualified professional institutions are entrusted to use the measurement ship for tour gauging of flow and sediment. In normal times, the equipment is installed in the incoming sediment monitoring station, the LISST-100X - 8 -

11 on-site laser sediment measuring instrument with automatic monitoring function is used together with the data transmission equipment the same as the hydrological equipment to monitor the sediment in real time, and then the GSM module or satellite terminal is used to transmit the data to the center station. (2) Outgoing sediment monitoring station (Pak Beng Station) The same station as the hydrological station, no new station is needed, however, the sediment observation equipment should be added, and the sediment observation items should also be added on the basis of the requirements of the hydrological data. Measuring equipment and operation mode are identical with those of the incoming station Equipment configuration and civil works (1) Incoming sediment monitoring station In order to carry out sediment monitoring, the incoming sediment monitoring station must also have the functions of hydrological station, the monitoring station can use the ADCP configured for the hydrological data acquisition and transmission system for flow tour-gauging to determine the relation between water level and flow, and configure a set of water level automatic measuring and reporting device for water level real-time monitoring, thus realizing the automatic hydrological station function. As the LISST is a precise instrument, in order to achieve continuous acquisition and avoid the LISST probes being impacted by suspended matter when installed in the water, a simple station can be built, and equipped with a water suction pump. The pump and LISST are controlled by the data acquisition processor. The pump pumps water from the Mekong River every 15 minutes, which is then analyzed by the LISST. The data is then sent by the data acquisition controller through the GSM module or satellite terminal to the center station

12 Table 3.1 Equipment configuration and civil engineering content of the incoming sediment monitoring station Item Number Unit Remarks LISST-100X 1 Set Pump type water level gauge 1 Set Instrument box 1 Piece Equipment configuration Data acquisition processor 1 Piece Beidou Satellite terminal and antenna 1 Set GSM module 1 Set Solar panel and support 1 Set 40W Accumulator battery 2 Pcs. 100AH Civil engineering content Number keyboard 1 Piece Lightning protection grounding system 1 Set Instrument chamber 1 Set Commercial power access 1 Set Manual water gauge 1 Set Pumping system 1 Set Ground resistance less than 10 ohm 2 station rooms, covering a total area of 8m 2 Elevation translocation by water gauge at zero point Installation of pump and pumping pipe LISST is an instrument used for on-site underwater measurement in the water environment to obtain the settling velocity distribution of suspended particles in the field. In addition to measuring particle size distribution, particle settling velocity, it can also measure the water pressure and temperature. LISST-ST is a precisely designed and reliable conductivity-temperature-depth (CTD) instrument, with low energy consumption, and able to carry out accurate measurement in the long-term deep water. LISST-100 technical indicators are as follows: Technology: Small angle forward scattering; Laser: Solid state diode (670 nm); Optical path: 5.0cm (Standard), 2.5cm (Optional), 20.0cm (Optional) Parameter: Particle size distribution Light scattering function (VSF) Light penetration Water depth (0 to 300 m)

13 Water temperature (-5 to 50 ) Implementation method: Underwater, laboratory, field, towing, anchorage, platform, profile Operating range: Concentration (Approximate range of the particles with an average size of 30m): 5.0 cm light pool 10 to 750 mg/l 2.5 cm light pool 20 to 1500 mg/l 20 cm light pool 2.5 to 175 mg/l (The range shows linear variation with the particle size) Particle size range: m (Type B) m (Type C) Light penetration: 0-100% Accuracy: Concentration: 20% (Full range) Light penetration: 0.1% Resolution: Concentration: 0.5 l/l sampling Particle size distribution: 32 size grades, interval Measurement rate: Programmable, up to 4Hz (Measured 4 times per second) Data programming acquisition unit: Internal memory and / or external data output, RS-232C Data capacity: 16MB Interface: RS-232 C, WINDOWS 95/98/NT software Energy: Internal power-common alkaline battery External power- REG +15 & Ma max Actual dimension: 32inch long 5 inch diameter (81 cm long 13 cm diameter) Weight: 25 pounds (11.25KG) in the air; 8 pounds (3.6 KG) in the water Rated working depth: 300m (For special requirements, depth can be upgraded) According to the sediment conditions of the Mekong River, LISST-100 can be used to monitor the sediment. (2) Outgoing sediment monitoring station

14 Equipment configuration and civil engineering content are the same as those in the incoming sediment monitoring station. 3.2 MONITORING OF WATER SURFACE LINE IN FRONT OF THE DAM AND AT THE TAIL SECTION OF THE RESERVOIR Site layout of monitoring station network (1) Pre-dam gauging station The pre-dam gauging station has been already set up in the hydrological data acquisition and transmission system, and no such station is needed. (2) Reservoir tail gauging station Because of the sparse population and inconvenient traffic, the gauging stations should be built in the places where living and traffic conditions are relatively good as far as possible. In order to avoid duplicate construction, the acquisition and receiving equipment of telemetering water level data should be compatible with the hydrological system as far as possible, and its data can be stored in the hydrological database. The reservoir tail water level observation of the Mekong River mainstream mainly ranges along the Lao-Thai boundary river reach, where five self-meter gauging stations are built, located in the estuary of Nam Tha, KengPhaDai, estuary of Nam Ngao, estuary of Nam Ing, and Chiang Khong (Houayxay). Wherein, the gauging stations at the estuaries are located in the downstream of the estuaries, and the gauging stations in the boundary river reach is built on the Laos side (Left bank) Equipment configuration and civil works (1) Pre-dam gauging station The pre-dam gauging station of the hydrological data acquisition and transmission system is used directly, without additional establishment. (2) Reservoir tail gauging station The reservoir tail water level observation of the Mekong River mainstream mainly ranges along the Lao-Thai boundary river reach, where five self-meter gauging stations are built, located in the estuary of Nam Tha, KengPhaDai, estuary of Nam Ngao, estuary of Nam Ing, and Chiang Khong (Houayxay)

15 Table 3.2 Equipment configuration and civil engineering content of reservoir gauging station Item Number Unit Remarks Pump type water level gauge 5 Set Instrument box 5 Piece Equipment configuration Data acquisition processor 5 Piece Beidou Satellite terminal and antenna Marine satellite terminal and antenna 5 Set 5 Set Solar panel and support 5 Set Accumulator battery 5 Pcs. 100AH Number keyboard 5 Piece Civil engineering content Instrument chamber 5 Piece Building area: 4m 2 Lightning protection grounding system 5 Set Manual water gauge 5 Set Ground resistance less than 10 ohm Elevation translocation by water gauge at zero point 3.3 MONITORING OF SEDIMENT DEPOSITION IN THE RESERVOIR AREA Sediment monitoring in the reservoir area mainly adopts the way of transverse section monitoring. (1) Transverse section monitoring of the reservoir area In the Lao's territory of Pak Beng reservoir area, a total of 60 cross sections were arranged during design of the power station, and a total of 30 cross sections were arranged in the downstream of Chiang Khong (Houayxay) in the Lao-Thai boundary river reach, totaling to 90 cross sections. After the operation of the power station, the monitoring sections should be overlapped with the above sections as far as possible, and intensified as necessary. The end pegs should be built on both banks of each section, and the fourth order leveling wire mesh is set in the reservoir. One warning board above the ground should be built on one bank at least, and the fourth order leveling wire mesh is set in the reservoir. The gauging station and the warning board should be set on the same bank of the reservoir uniformly to the best. The embedment of the fixed section signs should comply with the following provisions: a The fixed section signs should be embedded in the steady places above the highest design water level of the reservoir, and overlapped with the endpoints of the layout

16 sections in the preliminary design stage as far as possible. If the positions of the endpoints vary, the end peg embedment unit should give out the new coordinates, and mark the positions of the endpoints in the river schematic map. b c Because the section signs are arranged above the reservoir inundation zone, and land compensation may occur, therefore, the mark layout should avoid farmlands, cottages, etc. as far as possible. If land expropriation compensation occurs, the relevant provisions of the compensation for reservoir inundation shall apply. The fixed section signs generally adopt the embedded stone markers, and use the warning boards. The stone markers should be poured with concrete or chiseled with stone, the specifications should be not less than m 1.2m, and the buried depth during sign embedment should be not less than 0.8m. On every stone marker, the section No. and the left or right bank sign should also be simply specified. For example, bb5-r represents that the point is the right bank mark point of the bb5 section. In addition to warning information on each warning board, the section No. and the coordinates of the point and other information should also be specified. d The measurement scale of the fixed section of the reservoir is 1:1000. The error in the point position should be no more than ±0.8mm in the map, and the error of the elevation should be no more than ±1m. The maximum underwater distance between the measuring points of the reservoir fixed sections is not more than 10m. The underwater data acquisition uses the digital navigation fathometer, the land data acquisition uses the total station instrument, and the positioning uses the GPS. In additions, the professional acquisition software, calculation software, graphics integration software should be configured. The equipment to be used is listed in Table 3.4. Because of the large amount of measurement work in the reservoir area, it is suggested that the owner should entrust the qualification agencies for measurement, and the equipment used by the agencies shall prevail. According to the Preliminary design guidelines of the proposed mainstream dam in the Lower Mekong basin, the section measurement for the whole reservoir area should be carried out once in the early storage period of the reservoir, which should be taken as the initial data of the reservoir fixed section, and then the section observation of the reservoir area should be implemented once every year after the operation of the reservoir. (2) Reservoir shoreline monitoring

17 The high resolution satellite imagery of Pak Beng reservoir area should be purchased every year, and then the reservoir topographical map can be generated using the 3S image analysis technique. Accordingly, the changes in river courses, shorelines and terraces over the years can be grasped and analyzed. Every year before and after the flood season, patrol inspection should be carried out to the river course in the reservoir area to monitor the side slopes on both banks of the river course in the reservoir area, emphatically monitor the parts with possibilities of deformation. 3.4 TERRAIN MONITORING OF THE PROJECT AREA (IN FRONT OF THE WATER INTAKES AND APPROACH CHANNELS) In order to grasp the sediment deposition development in the power station project area and the sediment deposition in the approach channels, after water storage of the power station, the terrain monitoring of the project area should be carried out every year, focusing on sand-guide sills, water intakes, in front of flood-discharging gates, and upstream and downstream approach channels. The monitoring uses the topographic survey method and the main equipment to be invested are shown in Table 3.4. The underwater data acquisition uses the digital navigation fathometer, the land data acquisition uses the total station instrument, and the positioning uses the GPS. In additions, the professional acquisition software, calculation software, graphics integration software should be configured. The quantity of equipment is determined comprehensively according to the measurement workload and scheduling requirements. The topographic survey requirements are as follows: (1) Range: 1km upstream of the dam site to 2km downstream of the dam site; (2) The scale is not less than 1:500. The measurement scale and mappable unit had better not be changed after selection; (3) The whole monitoring range should be observed once every year before and after the flood season; The approach channels should be observed more often than the above observations, but not on a regular basis

18 No. Main equipment name 1 Trimble GPS Trimble R Total station instrument Multi beam sounding system Single beam sounding system Vehicles, working boats Table 3.4 Equipment to be used Overall Design Report of Sediment Monitoring System Model Manufacturer Remarks Trimble Navigation, US GPS RTK TCR802 Leica Land data acquisition R2SONIC2024 Hi Target US R2SONIC Hi Target Underwater data acquisition Underwater data acquisition Transportation, underwater data acquisition 6 Computer Data processing 7 Mapping software Cass9.0 South Digital Data processing 8 Acquisition software PDS Calculation software TBC2.8 Trimble Navigation, US Multi-beam data acquisition GPS control network calculation 3.5 TERRAIN MONITORING OF THE DOWNSTREAM RIVER REACH The high resolution satellite imagery of 50km downstream of the Pak Beng dam site should be purchased every year, and then the reservoir topographical map can be generated using the 3S image analysis technique. Accordingly, the changes in river courses, shorelines and terraces over the years can be grasped and analyzed. Every year before and after the flood season, patrol inspection should be carried out to the river course in the downstream of the dam site to monitor the side slopes on both banks of the river course in the reservoir area, emphatically monitor the parts with possibilities of deformation. In order to reduce duplicate investment, it is recommended to combine the downstream river course monitoring of Pak Beng with the reservoir monitoring of Luang Prabang Hydropower Station. 3.6 MONITORING OF LANDSLIDE DEFORMATION IN THE RESERVOIR AREA Research results of the geological conditions in Pak Beng reservoir area at this stage: Within the reservoir area, the slopes are gentle, vegetation is well developed, rock strata have steep dip angle, and there are no large landslides, collapses, or rock mass toppling; only some small collapse accumulations are distributed in the steep limestone cliffs, at the elevation of over 375m, which is higher than the normal impounded level. The reservoir sections are mostly longitudinal valleys or in sequent valleys; the slopes of both sides are generally 20-35, gentler than the dip angle of rock strata, belonging to stable reservoir banks and basically stable reservoir banks; the slopes on both sides show overall good stability. Before the impoundment of the power station, it is required to investigate the stability of the

19 reservoir banks in the reservoir area, identify the potential positions of landslide deformation bodies, sizes and other parameters, and arrange the monitoring equipment based on the characteristics to monitor the landslide deformation. The owner should entrust the professional institutions with the relevant qualifications for landslide deformation monitoring. Prior to the implementation of the monitoring, a detailed report on monitoring design should be prepared, and necessary measures should be taken to deal with the landslide bodies according to the monitoring results. 3.7 MAIN OBSERVATION RESULTS After completion of all the monitoring items every time, the data should be compiled and analyzed accordingly. The incoming and outgoing hydrological sediment measurement data of the reservoir should be compiled according to the current codes of China and the guidelines of the Mekong River Commission (MRC) Incoming and outgoing sediment monitoring of the reservoir (1) Daily average water level, discharge, sediment concentration, sediment gradation of the incoming station. (2) Daily average water level, discharge, sediment concentration, sediment gradation of the outgoing station. In the sand flushing process, it is necessary to monitor water level, discharge and sediment concentration in real time Monitoring of pre-dam and reservoir tail water surface lines Daily average water level observation results of the pre-dam and reservoir gauging stations, and river course water surface line results at different flows Terrain monitoring of the reservoir area (1) The vertical section and transverse section measurement results of the river course over the years are used to draw the vertical section and transverse section plans of the river course in the reservoir area over the years and analyze the distribution of sediment deposition in the reservoir area. (2) Based on the topographic survey results in the reservoir area, the total reservoir capacity, reservoir capacity under normal impounded level, dead reservoir capacity, and regulating storage capacity over the years are calculated; the reservoir capacity loss over the years is also added up; the multi-year reservoir capacity curve is drawn, and the changes in the reservoir capacity over the years are compared and analyzed

20 (3) Based on the high precision satellite image, the topographic map of the reservoir area is generated by using the 3S image analytic technique, and then the changes in river courses and shorelines over the years should be compared and analyzed Terrain monitoring of the project area (Pre-dam and approach channels) Sediment deposition conditions in the range from 1km upstream of the dam site to 2 km downstream of the project area, especially the sedimentation distribution of sand-guide sills, in front of the water intakes of the power station, and upstream and downstream approach channels, including sediment distribution, sediment thickness, sediment development trend, etc Terrain monitoring of the downstream river reach Based on the high precision satellite image, the topographic map is generated by using the 3S image analytic technique, and then the changes in river courses and shorelines under the dam over the years should be compared and analyzed Monitoring of landslide deformation in the reservoir area Before the impoundment of the power station, it is required to investigate the stability of the reservoir banks in the reservoir area, identify the potential positions of landslide deformation bodies, sizes and other parameters, and arrange the monitoring equipment based on the characteristics to monitor the landslide deformation. The monitoring results of landslide bodies include: Displacement, displacement velocity, acceleration, displacement vector map, etc. The deformation data should be added up and analyzed. 4 STAFFING In order to save management costs, the reservoir sediment monitoring system of Pak Beng HPP should make full use of professional social forces and professional bodies for operation as far as possible. It is unnecessary to increase staffing, and the sediment monitoring project can be managed by the Department of Hydrological Project. The measurement of the reservoir area & the project area and the monitoring of the landslide deformation bodies can be entrusted to the professional institutions with the relevant qualifications. The sediment deposition conditions of the reservoir, reservoir capacity loss and the sediment deposition conditions of the project area can also be entrusted to the professional institutions for calculation and analysis

21 5 BUDGETARY ESTIMATES The total expense for sediment observation will be $523,511. To be specific, the cost of sediment observation equipment and installation for the hydrological station will be $129,032, and the survey cost will be $260,332 one time (With the exception of the coast of Traverse Network of Bench Mark $102,500). Based on the water regimen reporting system, the estimated sediment observation cost may be referred to Table

22 Table 5.1 Estimated Construction Cost of Sediment Monitoring Station Network No. Items Unit Quantity Unit Price (USD) Total (USD) (1) Construction Engineering 76, New Stage Gauging station before the dam Stage Gauging Station at the Reservoir Head Nr. 1 3 Central Station Nr. 1 4 Nr. 5 9,836 49,180 Note The costs are included in the flood regimen reporting budget The costs are included in the flood regimen reporting budget Endpoint Stake Notice board Nr. Nr ,705 7,377 Including precasting, transportation, construction embedded costs and the construction cost after impoundment of reservoir. Administrative expense % 10 2,508 (2) Equipment and Installation Works 129,032 5 Sediment Observation and Analytical Instruments and Installation, etc. Nr. 2 64, ,032 (3) Survey 260, Traverse Network of Bench Mark Cross Section Measurement in the Reservoir Area For the Inlet and Outlet Station km ,500 Class IV Times 1 65,574 65,574 8 Survey of Hub area Times 1 32,258 32,258 9 Purchase and Analysis of satellite imagery km ,000 (4) Miscellaneous Expenses 57, Investigation/Survey and Design Cost Technical Consultation and Personnel Training 24,590 16, Contingency cost 8, Information Cost of Chiang Saen Station Total 523,511 It is to measure the entire reservoir once before impounding the reservoir. It is to measure Water inlet and ship channel include satellite imagery purchase and analysis 8,197 Estimated