20 November 2016

Dams in the Kaikoura Earthquake

NZSOLD Members have been very active following the Kaikoura Earthquake sequence. Many dam owners have carried out special inspections following the Kaikoura earthquakes that were felt from Auckland down to Dunedin. NZSOLD have not heard of any significant damage to dams. Trevor Matuschka has been involved with assessing the seismic loadings and talking to a number of dam owners in the vicinity and has made the following observations:

Peak ground accelerations recorded were:

  • Ward Fire station (1.27g vert, 1.07g horiz)
  • Seddon Fire Station (0.2g vert, 0.67g)
  • Blenheim -Marlborough Girls college   (0.09g vert, 0.24g horiz)
  • PGA at Ward exceeded SEE for High PIC dam
  • PGA at Seddon close to SEE for Medium PIC dam
  • At the time of the earthquake most dams were full because of the time of the year (late spring).
  • Heavy rain followed not long after the earthquake.
  • No dam failures or uncontrolled releases of water have been reported.
  • No dams have yet been identified as being in imminent risk of failure.
  • No damage has yet been reported for any dams located in the Blenheim/Wairau valley area.
  • Dams at Seddon that are known to have been well constructed generally suffered either no or minimal damage (minor hairline cracking, some minor displacement of riprap and of riprap sliding on top of geotextile). Minor longitudinal and transverse cracks at the abutments were reported at a recently constructed dam.
  • There was more evidence of deformation (longitudinal cracking and transverse cracking at abutment contacts) with dams located near Ward. This is not surprising given the very high intensity of ground shaking.
  • An interesting observation was that some dam owners near Seddon have reported evidence of seiches that in some cases resulted in loss of water via spillways. In one case water had flowed over an auxiliary spillway which was 0.5m above normal water level. In another case water overtopped a saddle dam which was 1.2m above normal water level. It is assumed this is because of the high amplitude of long period ground motion and the long duration of shaking.

Landslide Dams

There were a number of landslide dams formed by the earthquake as you will have read about in the media. One on the Clarence river threatened the safety of groups of rafters and kayakers, and there are others in the Inland Kaikoura range (Ure River) that has been assessed by Civil Defence and Marlborough District Council advisors. At this stage NZSOLD is not aware whether any of the landslide dams have had PIC assessments or dambreak assessments but we are aware that members have offered these services to the various authorities.

University of Canterbury Quake Centre Dams Project

Kayley Crawford-Flett is working part time at the UofC Quake Centre researching: 

“Whole-Life Performance of NZ Earth Dams Research to reduce geotechnical uncertainty and understand the cumulative impact of seismic events on earth dam performance”

She reports that the Centre is keeping in touch with engineers on the ground, and remains tied in to the University reconnaissance efforts. She is reviewing video and photograph footage (+ field reports) as information comes in. If any members have pertinent information that could be of interest to the Quake Centre project please contact kaley.crawford-flett@canterbury.ac.nz

The Quake Centre Project is being driven by their partners and NZSOLD; with the mandate to learn as much as we can, while honouring the sensitive nature of information provided to the project.

Their main focus at present is on the larger engineered/instrumented dams: they are planning to head north to the Wellington/Tasman region in the last 2 weeks of November to retrieve instrument data and likely install a couple of accelerometers in one large dam.

If any NZSOLD members know of instrumented dams in affected areas (outside of Hydropower and Council owners), they would be very interested to learn more. Pore pressure responses are of particular interest.

The Quake Centre Dams project is keen to offer assistance to the wider dam engineering community.