Environment Canterbury has temporary measures in place to divert water flowing out of the Ashburton riverbed in the upper reaches of the catchment and off private land.
Many of those temporary fixes on some of the breakouts will need full repairs expected to take months.
ECan rivers manager Leigh Griffiths said water was still flowing out of the riverbed in a couple of places in the upper reaches of the Ashburton catchment early last week but were diverted by the end of the week.
"Many of these diversions should be considered temporary and vulnerable in nature."
She said for full repairs to be done, river engineers were working on understanding the changes that had occurred within the riverbed and surrounding land.
"In some cases, we will need to discuss new stopbank alignments with adjacent landowners," she said.
"There are significant areas of riverbed berm vegetation to be replanted. These serve as a buffer to slow floodwater against stopbanks and terraces.
"Rebuilding stopbanks and other earth structures will require heavy machinery."
In many places water levels needed to drop and ground conditions to dry out before a full rebuild could be undertaken, she said.
The work would include many parties with an interest, such as ECan, adjacent landowners, mana whenua partners, district councils, roading and other infrastructure providers, Fish and Game, and Department of Conservation.
The rainfall which hit the district saw a deluge of water on the foothills; from May 28-31, a massive 545mm of rain was recorded at Mt Somers, the MetService reported. The main centres — Christchurch (110mm), Ashburton (155mm), and Timaru (105mm) — were inundated over that period.
ECan groundwater science manager Carl Hanson said following months of dry conditions the water table across Canterbury had already responded to the rainfall. In late May, many wells were well below average levels for this time of the year, and in areas like West Melton, some were at record lows.
"In some places the water table has risen by less than a metre, and in others, more than 2m," he said.
While much of the rainfall rushed through the river systems out to sea, Mr Hanson expected most of the rain that fell on the plains soaked into dry ground.
One large rainfall event does not make up for months of very dry conditions that much of Canterbury has experienced, he said.
“Groundwater levels have certainly risen in response to this rain, but they’re still not as high as they have been after past wet winters.”
