How much rain is too much?

Excessive rain has soaked the land this year and increases the risks around swimming and fishing in our river because of elevated levels of animals and bird faeces or cyanobacteria.

This farmland behind Uxbridge Terrace has a new lake.

Maybe you’ve had it up to here with the rain? You wouldn’t be the only one. Puddles and mud seem to be the most characteristic feature of Waikawa Beach at the moment. And long grass as we get rain then sun, then rain then sun so the lawns keep growing but it’s too wet to mow.

This farmland behind Uxbridge Terrace has a new lake.
This farmland behind Uxbridge Terrace has a new lake.

Round on the Strathnaver side new lakes have formed and lower lying parts of properties are underwater.

So it was interesting to see some data from the Horowhenua District Council, in an article about the Foxton Cemetery Horowhenua District Council says:

Over the past few months Horowhenua has experienced unprecedented rainfall, which has saturated the grounds meaning water cannot dissipate as it usually does, but rather pools.

Figures from our rain gauge show that Horowhenua has had 50% more rainfall over the past few months, compared to the same period last year and 141% more than in 2015 over the same time. …

The issue is that the soil is close to 100% saturation which means it cannot store any more water and the water table following the preparatory [cemetery] works at Foxton cemetery is only 50mm below the existing soil level.  

Soil contains air gaps which fill with water when it rains. When the soil reaches 100% saturation it cannot take any more water, this is why we are seeing surface flooding and ponding water. When it rains consistently the way it has done in Horowhenua over the past few months, the ground gets saturated and those pockets fill up with water.

As we look at plants standing in water where they belong on dry land we have to ask what the toll will be on our vegetation.

Another difficult consequence of the excessive rain is its effect on our river, and what how we might enjoy the river now and over summer. Wet summer makes rivers unswimmable says:

Wet weather was to blame for unswimmable waterways around Manawatū last summer as almost all rivers in the region were deemed unsafe at some point.

After a damp spring, people will need to have a careful look at the weather before swimming in rivers this summer, too.

Horizons science and innovation manager Abby Mathews said if it was another wet summer people should wait to swim when it was clean and clear.

If it’s three days after rain and the water is not dirty or fast-flowing, it should be safe to swim.

Health risks could include the presence of faeces or cyanobacteria.

When entering cyanobacteria-contaminated water, people are at risk of getting diarrhoea, nausea or gastroenteritis, which can lead to liver damage or even death in some cases, a council report says. …

Horizons natural resources and partnerships manager Jon Roygard said last summer was wetter than usual. More rain meant river beds were stirred up and more sediment ended up in waterways, he said. …

The council will continue monitoring the 80 swim spots this summer at an estimated cost of about $40,000.

We already know that Waikawa River at the Footbridge was unsafe for swimming on quite a few occasions last summer: The river runs red. We need to keep an eye on the weather this summer too. Check the monitoring results (often delayed by a few days) at the Land, Air, Water Aotearoa website. Note that our long term risk status based on 3 years of data is Caution — At times this site can be high risk (5% or greater risk of illness). Remember: it may not be safe to eat fish from the river either.

Overall Waikawa River risk status is Caution.
Overall Waikawa River risk status is Caution.

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