Christchurch is lucky to have some of the best drinking water in
the world. All of our drinking water is obtained from the ground,
and it provides for what must be close to 400,000 citizens now.
Most other communities have their water treated with chemicals
before it is potable.
Our water is an extremely valuable resource that needs
monitoring, conservation and protection to ensure that we manage
our aquifers in a sustainable manner.
One of the aquifers that is nearest the surface is the Riccarton
aquafer, and this is where this earthcache brings you. This aquafer
as well as being fed from the mountains, also receives water from
the Waimakariri River.
Peverel Street in Riccarton was one of the first in a series of
'Living Streets' in Christchurch. The concept of living streets was
to create streets designed with a priority on living and community,
rather than an emphasis on vehicles.
The Living Streets vision is to create a living city
where a variety of road environments support and encourage a better
quality of life and a greater range of community and street
activity.
CCC
Page on Living Streets
A lot of our waterways are fed by springs from the aquifers. As
we are drawing more water from the aquifers, the water level of the
aquifer drops, and some of the springs can no longer be fed from
the aquifer. Over time, this causes our waterways to dry up because
the springs have disappeared - these are the dry waterways you see
in some of our parks, and now they only carry water when it rains.
This has an impact on many plants, insects, birds and animals that
live in the waterways.
Most of the water originates in the Southern Alps and foothills
from rain, ice and snow. Much of the water is quite old as it has
been in the aquifer for a long time. The groundwater flows
underground eastwards towards the sea through layers of gravels
called aquifers. The aquifers are permeable, meaning that water is
able to flow through spaces between the gravel. Aquifers are
bounded by impermeable layers of fine sands, silts and clays that
don't allow the water to pass - meaning that the water is trapped
in the aquifers as it cannot move up or down through these layers.
This creates a series of alternating layers that contain multiple
aquifers layered on top of each other and separated by impermeable
layers.
Near the mountains, the gravel aquifer is believed to be up to
350m thick. Around Christchurch, the layers introduced above are
understood to have been created by alternating periods of high and
low sea levels. During high sea levels, marine deposits were laid
on the land - consisting of silts and fine sediments. When the
ocean receded however, the rivers deposited gravel on top of the
ocean sediments. As seas levels were raised and fell over long
periods in time, the alternating layers of aquifers and impermeable
deposits were created.
As more water is drawn from the aquifers in Christchurch, this
reduces the pressure of the aquifer, and near the shore, sea water
can actually intrude into the aquifer system. As the fresh water is
drawn off the top, salt water intrudes into the aquifer underneath
the fresh water. Over time, the salt water can intrude further
inland and higher up into the aquifer, until wells tapping the
aquifer pump salt water. A critical component of aquifer management
is managing the drawing off of fresh water from the aquifer to
ensure that further salt water does not intrude into the
aquifer.
There are a few tasks I would like you to complete, and you can
do them in any order. You need to send me the answers to prove that
you have learnt something about our aquifers. Don't post these to
your log, rather PM me using the link above to answer the
questions.
You have to answer all 4 questions to be able to log
this earthcache. This is non-negotiable. You would be surprised how
many libraries have this book.
Part 1
Go to the listed co-ordinates.
1. From how many metres deep is the aquifer that is feeding this
spring?
2. What are the minimum and maximum flow rates of the spring in
litres per minute?
Part 2
Time for some research. The map for Q3 should be made available
for online access and download later this year. Currently this
resource is only available in some libraries. There are a few
copies in the public libraries; and the University has some, but
they are on restricted loan - unless you're staff or student at
Uni, I'd recommend going to the public libraries instead.
Brown, L.J.; Weeber, J.H. 1992. Geology of the Christchurch
urban area. Institute of Geological and Nuclear Sciences.
3. Locate the spring on the geological map (should be inside
back cover). Look up the geology of the spring location in the map
legend. What are the three letters in the coloured box representing
the geology at the location of the spring?
Now return to the book.
4. On pages 33-34 is a summary of the Riccarton Gravel contained
in this aquifer. What is the age range of the Gravel? (you need to
supply both lower and upper ages to define the age)
Don't answer these questions in the logs, they will just be
deleted. Remember to send them to me via a private message.