2007 – Tekapo Canal leakage model used to assess safety

Nigel Connell, Tim Logan and Tim Mills

Leakage from Tekapo Canal, between km 11 and 12, is investigated. A groundwater model is formulated based on construction records, detailed monitored seepage flow and groundwater levels in the canal embankment over the 30 year life of the canal, chemical analysis and flow history. Sieve analysis of embankment materials confirmed embankment fill was sourced from glacial outwash graves excavated from canal cut upstream. Anisotropic permeability of the fill embankment, inferred from the construction method using motor scrapers and vibratory rollers, contributed to explaining inflow to the model primarily from a source up to 500 m from the leakage outflows. Stability of the canal embankment is reassessed considering length of the seepage paths, which are long, hydraulic gradients, which are relatively flat, and resistance of the glacial outwash gravels to piping. The groundwater model that is developed indicated that stability of the canal embankments is not reduced significantly due to the seepage.

Keywords: Tekapo canal, groundwater model, canal leakage.