A forecast for more rain in the Upper Waitaki and other alpine river catchments is prompting Environment Canterbury to once again warn people of the dangers of rising levels in the South Canterbury rivers and lakes.
MetService has issued a severe weather warning for rain on the Southern Alps. Predications are for 300mm of heavy rain to fall in the 24 hour period from Tuesday evening (8 January) in the same alpine river catchment areas that were drenched early last week.
"While lake levels have now mostly peaked or are receding after the deluge at New Year's, there is still an excess of water in the lake system and many of the rivers in the Upper Waitaki catchment remain at higher than normal flows," says Chris Fauth, Environment Canterbury's Duty Flood Controller for the Southern Region.
The forecasted rain for Wednesday will mean a longer period of spilling is ahead and lake and river levels in the catchment are likely to increase again from Wednesday onward. The predicted rain is also expected to cause a significant increase in flow in the Rangitata River.
"All campers, fisherman and recreational users of both the Waitaki and Rangitata Catchments need to be aware of the potentially worsening situation and alter the way they camp and use the lake and rivers accordingly.
"Regular holiday makers who leave unoccupied campervans in these catchments need to check they are located appropriately and take action if necessary. Farmers and other landowners near the South Canterbury alpine rivers are also encouraged to watch the forecasts and river flows and monitor their own situations closely."
Chris Fauth also explains that while last week's flood event caused no major river breakouts and little out-of-river damage on the Rangitata, the high flow caused significant damage to in-river flood protection works, including washing vegetation from river berms, erosion of riverbanks and movement and deposition of river gravel.
"The damage to flood protection works has left parts of the river, including the South Branch Rangitata entry point, more vulnerable to further high flows. A considerable amount of rain may also extend into the eastern alpine river catchments and a South Canterbury foothills.
"This rain is expected to cause further significant inflows into the Waitaki, Rangitata and Ahuriri River catchments in particular and may cause lesser increases elsewhere. It is still vitally important that people on the plains also stay alert, even if the weather is fine, as the rivers can still become unsafe as flood waters travels rapidly downstream."
As lake levels rise Meridian energy will continue, and possibly increase, controlled spills from all of the lakes in the upper catchment which will likely keep rivers at higher levels for several days after the rain eases.
Genesis Energy has indicated that the level of Lake Tekapo is likely to continue to rise over this same period, and that they will start spilling water into the Tekapo River as early as the next few days.