It may seem strange, given the cooler temperatures and some recent rain, but the water supply in Nelson is more at risk now than it was in the summer, according to the head of the city’s public works department.
“The discharge [from the creeks that feed the reservoir] on Aug. 26 was the lowest on record,” Colin Innes says, “and the forecast is for 40 per cent less rain over the fall.”
And so the city has imposed water restrictions (see below) effective September 11, that are even more stringent than those in the summer.
At the end of July, the Star reported that 13.6 megalitres of water per day were entering the reservoir and 11.2 was being used by residents.
That, according to Innes at the time, was cutting it very fine because the average year round supply into the reservoir is 73.4 megalitres per day and the average year-round use is about about six megalitres per day.
On Aug. 26, according to Innes, the intake to the reservoir was down to 6.2 megalitres (54 per cent less than in July) and the amount being used by residents was eight megalitres (28 per cent less than July).
So while city residents used less in August than in July, possibly because of the water restrictions imposed during that month, the supply also worsened, and Innes says it will take more than a few days’ rain to fix it.
“It’s not like we have a glacier up there,” he says. “We depend on the amount of water that falls on it. In the immediate runoff from a rain event, it will look like you have a lot, but what comes at you over time is what is important.”
He says in a week or two the gains from recent rain could disappear.
“We need more sustained rain. We need a slow gentle rain so it can soak itself in.
“We are concerned about people hearing about things like lifting the campfire ban and fire hazard going down and forgetting we have a water shortage issue.”
Innes says September and October are always low-flow months, “so you really come up against how much water you have. If we get a lot of rain we will be fortunate.”
In addition to the Level 4 water restrictions that start on September 11 (see below), Innes also wants residents to consider that toilets typically use 27 per cent of household water. Add showers and washing machines, and the percentage rises to more than half.
Nelson’s main water source is Five Mile Creek, located in West Arm Provincial Park, which feeds into the main reservoir on Mountain Station Rd.
The city also gets water from Anderson Creek in Fairview and Selous Creek at Ymir Rd. At each of those places is a diversion dam, screen assembly and electro-mechanical valves. The reservoirs feed into a distribution system that fans out across the city in 87 km of underground pipes.
Asked what would happen if Nelson’s reservoir ran dry, Innes said, “We would be in a state of emergency as we would be unable to provide drinking water or fire suppression.
“Damage would occur with the depressurization of the water distribution system and we would also have upset conditions develop at the sewage treatment plant as there would be no nutrient going for treatment. A really bad situation all round.”
He added that the city is monitoring the situation so closely that it would intervene well before supplies run out.
Level 4 water restrictions, in effect now within the City of Nelson
• No watering of lawns and boulevards;
• No vehicle washing except at commercial car washes;
• No washing of buildings, driveways, exterior windows or parking lots;
• No filling of pools or hot tubs;
• Trees, shrubs, vegetables and flowers may be watered with a hand-held container or a hose with a shut-off nozzle, micro-irrigation or drip line, daily, from 4 to 10 a.m. and from 7 to 10 p.m.