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Bathymetric, Topographic and GPR Survey of Glacial Lakes

Funding Agency: Government of Nepal
Client: Department of Hydrology and Meteorology, Nepal
Date: September 2021 – September 2022The 

Department of Hydrology and Meteorology (DHM) conducted a study of Glacial lakes periodically. To give continuity of the study, DHM intends to carry out the study of Tsho Rolpa and Lower Barun Glacial Lake and update the condition of the lake and its surroundings from the GLOF perspectives, proper supervision, monitoring and maintenance of the built structures at Tsho Rolpa Glacial Lakes site.

This study is divided into 2 components

Component 1:

  • Bathymetric, Topographic, and GPR Survey of Tsho Rolpa Glacial Lake.
  • Bathymetric, Topographic, and GPR Survey of Lower Barun Glacial Lake.

Component 2: Study for the Maintenance of the Built Structure of Tsho Rolpa.

Overall Services provided:

The services carried out during the contract period as as follows:

1.       Desk Study

  • Collect previous study reports, reports, maps, drawings, etc.
  • Review and Analyze available information, reports, maps, drawings, etc.
  • Identify data gaps of previous study and recommend additional study/field survey & investigation required
  • Conduct the presentation of the inception report for its approval
  • Incorporate the comments on the Inception Report at DHM
  • Incorporate the comment on the Inception Report for its approval.

 2.       Bathymetric Survey and Mapping of Lakes

The Consultant shall conduct a bathymetric survey of the lakes using a standard eco-sounder and other relevant equipment to measure water depth below the water level in the lake. The survey shall also assess the relation between the elevation area and the storage of the lakes.

 3.       Topographical Survey and Mapping

The Consultant shall conduct a topographical survey of the lake surroundings with a contour line with an interval of 5m. The consultant shall conduct a river longitudinal-section profile and cross-section survey both at the outlet of covering at least 500m downstream at each lake in intervals of at most 50 m depending upon river conditions taking high flood level, minimum water level, existing water levels and bank at least 10 m from bank depending upon the characteristics of the ground.

The topographic survey shall be carried out to 3rd order precision and the admissible error of closure shall not exceed 128kmm. Also, the consultant will prepare a map of the surroundings of the lake on a scale of 1:5000 with a contour interval of 5 m and a drawing of the L-section and X-section of the river in an appropriate scale.

 4.       Hydrological Studies, Sediment studies and Water Quality studies

The consultant shall carry out hydrological investigations including discharge measurement of at least 3 numbers at the outlet of Lower Barun Lake, and prepare an equation for calculation of discharge at different levels of gate operation in a trapezoidal channel from Tsho Rolpa lake.

In addition, the consultant shall collect water samples of different for the study of physical and chemical properties of water including pH, air temperature, water temperature, dissolved oxygen, turbidity, conductivity, BOD, COD, nitrate, iron, sulphate, and total hardness.

 5.       Ground Penetrating Radar Survey

  • Undertake a detailed geophysical GPR Survey of the end moraine areas, at the locations of seepage, cracks etc. on the overall composition of the moraine dam, density, voids, sinks etc. for moraine dam stability
  • Conduct GPR, longitudinal, and transverse profiles at suitable spacing to generate 3D profiles within selected alignments
  • Conduct detailed topographic survey has to be conducted on all GPR Profile
  • Prepare a map with a three-dimensional view of buried ice in the area surveyed
  • Prepare design, drawings, maps, radargrams, database on geophysical – GPR on topographical base maps at appropriate scales
  • Interpretation of radargrams and material type of moraine dam.

 6.       Study for Maintenance of Built Structures of Tsho Rolpa

  • Visual inspection, walkover survey of the site
  • Inspection, photo, and videography of the built structure
  • Inspection of built structure related to 15 Kw micro-hydropower plant
  • Inspection of various structures, measurement of dimensions of damaged parts, and a longitudinal profile survey from the intake to the powerhouse during the field visit.
  • Inspection of the bridges, and operator house. Generator house, equipment store cum workshop, whole part of steel structure gate
  • Preparation of detailed design and drawings, cost estimate, construction planning and scheduling and tender document for the procurement of maintenance of such structures.