The boulders, which come from South Canterbury, are in the river as part of a pilot programme that aims to improve diversity in river conditions and to create better habitats for a range of species.
Funding for the operation was provided by Fonterra in order to help improve waterways in Mid and South-Canterbury.
Environment Canterbury (ECan) land management adviser Lachie Ashton says the point of installing boulders is to create different flows of water with a pool, run, riffle effect.
Unlike most man-made drains and canals, natural waterways were not uniform and varied in water flow, speed and depth.
Those variations created different habitats for a greater range of species, he said.
Immediately downstream of the new boulders in the Hinds River, deeper and slower-flowing water forms a pool, which is a perfect habitat for trout.
Towards the north bank, the water flows faster over a shallow channel, known as a riffle. Other sections of river nearby form runs – smooth, steady flowing sections of river.
Although motorists crossing the state highways at Mayfield and Hinds may see the Hinds River running dry, the groundwater does reappear in springs that feed the river’s lower reaches near the coast.
During heavy rains, the lower reaches of the river experience periodic floods. When that happens over the wetter winter months, the full effect of the boulder planting will be seen.
Flooding is all part of the project, Mr Ashton says. "We need to let the river do its natural process and just wait and monitor the effects."
If the pool, run, riffle effect holds over several seasons, the operation will be deemed a success, and it may see more boulders going into the river.
