The project has been downsized from original plans to minimise effects on the environment. The original plan included up to five large water storage sites and three to four new power stations along a 40km stretch of the Wairau river, leaving a residual flow in the river of 6m³/sec. The new plan would see the canals moved slightly closer to the river and five power stations built at intervals between Birch Hill and Marchburn.

Instead of a flat residual flow of 6m³/sec, the minimum flow in the remainder of the Wairau river has been increased to 10m³/sec and could vary up to 20m³/sec according to the season.