Under the rocks and stones there is water underground

Living in Christchurch, I am grateful for many things, especially the quality of the tap water.  In Christchurch we are very lucky because our tap water is of such purity that it doesn’t need to be treated with chlorine like many cities have to, which means it tastes so good [never fear – the Council closely monitors quality]. Christchurch’s water is so pure because it comes not from river, stream, or desalination plant, but is sourced from natural underground reservoirs called aquifers – water saturated geological substrata that lie at great depth beneath the city. The story of Christchurch water is an interesting one and lately in the office we’ve been talking a lot about the subject, especially after the recent discoveries of some fascinating old wells in the central city. So, grab a glass of two parts hydrogen and one part oxygen and stick around for a taste of what we have learnt about water supply in 19th century Christchurch from archaeology.

The first brick well of 2017. Well, can you feel the excitement? Image: Angel Trendafilov.

Christchurch was quite unusual compared to most other cities as the local council built a sewerage system (this was completed in late 1882) long before it laid on a high pressure piped water supply (works began on this in 1909). Historically it’s usually the other way round – first comes water then comes the sewers, if both of these weren’t constructed at the same time. Part of the reason for this was the fact that Christchurch was built on a swamp next to a river, so finding water was not a particularly difficult task for early settlers.

As things typically are on a swamp, you don’t have to dig very deep to hit the water table, so shallow wells were reasonably commonplace in the first few decades of the settlement. We have found a good number of these shallow wells – mostly of a circular shape, with an average diameter of 900 mm and lined with bricks. The depth of those has varied somewhat. The shallowest we have found was only 1.6 m deep, and the deepest went down more than 3 m. Often however we don’t get to excavate them in their entirety, either because of safety considerations, or because the depth of the excavation means that the bottoms of these features can stay in situ.

This brick lined well took the top prize for best well of 2016, SCIRT found it when they were laying a new sewer mains in Richmond. The bricks that lined the upper part of the well were missing – salvaged for reuse we reckon. Image: Hamish Williams.

On a Lichfield Street site we found a well that was lined not with bricks but with two wooden barrels stacked atop each other. At the bottom of this barrel well was a large block of porous limestone – we reckon this functioned as a water filter. We can only guess how effective this was.

The barrel lined well – the timber staves were very well preserved. At left is the outside of both barrels, and at right after we sectioned it, showing the fill inside. Unlike a lot of infilled wells, this one didn’t contain very many artefacts. Both image: Hamish Williams.

The bottom of the barrel well was filled with fine grey silt not dissimilar to liquefaction silt- was this well abandoned because it silted up as a result of a 19th century earthquake event? Hamish still ponders this – but he will probably never ever know for certain because Underground Overground Archaeology’s flux capacitor is broken. Image: Hamish Williams.

The problem with shallow wells was that they got easily contaminated – many people got crook and some even died from drinking sewage contaminated water. To some extent this problem was overcome by the council banning long drops/privys and their subsurface cesspits, and later with the construction of a proper sewer system, but mostly it was the geological discovery of the artesian aquifer system below the city. Because these artesian aquifers were located super deep, there was a much lesser risk of their becoming contaminated.

When the groundwater in an aquifer is under pressure greater than the pressure that exists at ground level, these waters are called artesians. If the geology is just right, these waters rise up naturally through cracks in the ground to surface as springs. In fact, the source of the Ōtākaro/Avon River and its tributary streams are artesian springs. In addition to fracturing many underground water pipes, the earthquakes also fractured the ground in many places, which allowed new artesian springs to rise to the surface. A well drilling frenzy to tap these artesian aquifers struck the city in the 1860s. By January 1872 a total of 654 artesian wells in the city had been sunk – both on private property and in the street by the council for public use (Weeber 2000: 11). By the late 1870s the water level in the uppermost aquifer, into which most of these earlier wells were sunk, was starting to decline (Lyttelton Times 17/10/1879:6). Once gushers, many of these artesian wells (often also called  ‘tube wells’) were fast becoming tricklers, necessitating the increased adoption of pumps, or the drilling of new wells to tap deeper and more reliable aquifers.

Old artesian wells are reasonably common finds on archaeological sites about the city and typically take the form of small diameter iron pipes sticking out the ground. The tops of these are often surrounded by larger diameter glazed earthenware pipes, which served as well casings or reservoir chambers to which hand pumps or taps would have sometimes been fitted. Often it’s hard to tell conclusively whether artesian wells of this form are 19th century or not. There is often very little difference in form between 19th and 20th century artesians, and, because water mains were only laid on incrementally throughout the city in the early 20th century, the sinking of artesian wells in people’s backyards continued in some places well into the 1950s. I will always remember the first artesian I found on a site. Disturbance from the digger brought forth a small trickle of tepid water (I remember it was a bloody freezing winters day and the artesian waters that came up out the ground were steaming). Left unchecked over the weekend, this artesian trickle transformed the excavation into a small lake, much to the delight of the local ducks.

A ‘dead’ artesian uncovered on a central city site. Image: Hamish Williams.

An old ‘live’ artesian well – left unchecked and unattended, this one flooded the excavation over the weekend. By the time this photo was taken, half the water has been pumped out. Can you spot the high tide mark? Image: Hamish Williams.

Not long ago we found a brick well on a site that had an artesian pipe sticking out the middle of it, and close by, another artesian pipe sticking out of an adjacent rubbish pit. We interpreted these two artesian pipes as possible evidence of the 19th century decline of the uppermost aquifer that most of the early artesians tapped. The brick well was early – maybe 1860s (we could tell this from the bricks) so we are pretty confident that the brick well came first. Whether because the water in this well dried up or the water got fouled, it at some stage thereafter was filled in, before an artesian well was sunk down through the middle of it. Later on we suspect that the water from the artesian started to decline, so a second artesian was sunk next to it, probably to a deeper level in order to tap a more reliable aquifer. What do you think about our interpretation?

At left, rubbish pit, and at right, brick lined well. Image: Hamish Williams.

The rubbish pit and well after being sectioned, exposing the artesian pipes that had been sunk through both these features at a later date. Image: Hamish Williams.

I suppose that the story of how the people of early Christchurch got their water, and how this changed over time is a bit like life. In the beginning things are often easy, you don’t have to work too hard to get what you are looking for – you can find what sustains you just by scratching away at the surface a little. Sometimes however things inevitably change, (often as a result of external factors) so you have to adapt, give up on the old way of doing things and adopt new methods. Start afresh by digging a bit deeper – it can be hard going at first, but the rewards are worth it. When things change again, you just got to dig a little deeper once more, but second time around its always a little easier. Because, like a Zen master, we have learnt from previous experience that by going deeper within, while at the same time being grateful for what nature provides, you can always find a way.

Hamish Williams

 

References

Lyttelton Times [online]. Available at <http://paperspast.natlib.govt.nz/>

Weeber, J. 2000. Watering Christchurch: The story of well drilling and water suppy in Christchurch. Christchurch NZ: Environment Canterbury.

One thought on “Under the rocks and stones there is water underground

  1. This is a good one: :Hercus A I 1948 A City Built on a Swamp. The story of the Chch Drainage Bd 1850-1903.

    Your idea that a tube well might have succeeded a sunk well tapping into a deeper aquifer looks perfectly rational.

    One consequence of having artesian water was that Chch got used to having a low pressure water reticulation. This was revealed as dangerous by the Ballantynes fire, after which Chch had to raise the pressure in its reticulation.

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