Hvammsvirkjun Ground Investigation Report

The Hvammur Hydroelectric Power Project (“HEP”) is located at the Þjórsá river in southern Iceland, 120 km East of the capital of Reykjavik. Mannvit took care of ground investigation research at Hvammur HEP. Four main geological investigation actions have been carried out especially as part of the Núpur HEP and Hvammur HEP design. The investigation period was between the years 2001-2017.

Components of the Ground Investigation work

- Geological mapping

- Tectonic and Seismicity

- Geological hazards (volcanic eruption, earthquakes, flooding)

- Site Investigation

- Laboratory testing


Hvammur HEP is the uppermost of three planned hydropower plants in the lower region of the river. Mannvit is a lead engineer in the design on behalf of Landsvirkjun. Mannvit has been the main engineering consultant, doing research, engineering, tender documents, HSE planning and cost estimates in cooperation with Verkis. Mannvit also did 3D graphic and managed the setup of an online EIA report for Hvammsvirkjun Hydropower Plant. The report includes information on the effects on tourism and effects on the landscape and visual changes in the area.

Hvammur technical info:

Installed capacity: 93 MW
Turbines: 2 Kaplan units, vertical shaft
Gross head: 32 m
Harnessed discharge: 352 m3/s
Annual energy production: 720 GWh
Dam: Total length main dam 900 m
Water reservoir: Hagalón reservoir 116 m.a.s.l, storage capacity of 13,2 Gl.
Headrace canal: Width/height: 6,6/7 m; length 140 m
Penstocks: 2 penstocks, ø6,8 m; length 191 m
Tailrace canal: 2000 m

Hvammsvirkjun jarðgrunnsrannsókn

Details of the site investigation and lab tasks performed:

  • Site Investigation
    • Test pits
    • Excavated trenches
    • Cored boreholes
    • Percussion boreholes
    • Penetration boreholes
    • Permeability and pumping tests in boreholes
    • Groundwater level measurements
    • Water temperature and conductivity measurement
    • Standard penetration tests (SPT)
  • Laboratory testing
    • Tests on cores
      • Triaxial compressive strength
      • Uniaxial compression strength (UCS)
      • Split tensile tests (Brazilian tests)
      • Point load tests (PLI)
      • Porosity, density and absorption
    • Tests on soil
      • Moisture content
      • Density
      • Specific gravity
      • Grain size analyses
      • Standard/modified proctor
      • Permeability test
      • Consolidation test (oedometer test)
      • Static triaxial (CIU) test
      • Dynamic triaxial test
    • Concrete aggregate test
      • Particle size distribution
      • Moisture
      • Humus content
      • Water absorption
      • Particle density
      • Particle shape
      • Resistance to freezing and thawing
      • Chloride content
      • Petrographic analyses
      • Assessment of fines
      • Alkali-silica reactivity


Ground investigation tasks:

  • Geological mapping
  • Tectonic and Seismicity
  • Geological hazards 
  • Site Investigation
  • Laboratory testing

Other tasks:

  • Hydraulic design
  • Civil design
  • Design memorandum
  • Tender design and tender documents
  • Final design (remaining)
352 m3/s 
Harnessed discharge
720 GWh 
Power production
93 MW 
Installed power

Hvammsvirkjun - Hydropower plant