What is a Drinking Water Supply Catchment?
Everyone knows what a stream or a spring is, but a catchment? Maybe not everyone. A catchment of a particular stream is that area of land that collects the rain falling over the land and drains it into a particular stream. If that stream is used for Drinking Water then by default the Catchment is a Drinking Water Supply Catchment..
Where are the Catchments and how big are they?
The Waiorohi (blue) and Tautau (yellow) Drinking Water Supply Catchments border each other. In terms of day to day management the two catchments are treated as one.
A third catchment, the Waiari (pink), is planned for the future and will supply the Waiari Water Processing Plant. The combined area of the Waiorohi and Tautau Catchments can be described in general terms as “the area bordered on the East by Hereford Road/Oropi Road/Mountain Road, on the West by Joyce Road/Pyes Pa Road, the South by Mangatoi Road and the North by the Oropi intake”.
This area covers approximately 45 km2 (Waiorohi 29 km2 and Tautau 16 km2) of which the Tauranga City Council owns 23 km2. To put this into context the total surface area of land within the Tauranga City Council territorial borders is 135 km2. The Drinking Water Supply Catchments are therefore 33% the size of the entire Tauranga City Territory. The Catchments are situated in their entirety within the Western Bay of Plenty District.
Only authorised people are allowed into the water catchment forests owned by the Council. They are designated for Water Supply Purposes and are not for general recreation.
Waiari Water Processing Plant
||Picture taken above the Tautau Stream looking north. Approximately 50% of the City’s Drinking Water Supply Catchments are dominated by Native Forest. Most of the forest is owned by Tauranga City Council.
Tauranga City Council has a moral as well as a legal obligation to protect, preserve and minimise the risk of contamination to its public drinking water supplies. This starts with the protection of the Drinking Water Supply source waters. The Council is committed to the ongoing management, maintenance and improvement of the Drinking Water Supply Catchments and Stream Water Quality and to maintain a high quality potable water supply to Tauranga residents and Industry, that meets the Drinking Water Standards for New Zealand and the Ministry of Health “Aa” grade requirements.
Looking after the Drinking Water Supply Catchment
As rain water washes over the land in the catchment on the way to the stream, it will collect anything it comes into contact with and this will normally have an adverse impact on the stream water quality. As mentioned approximately half of the catchment is owned by the Tauranga City Council and, thankfully, this land is dominated by native forest. The forests break the impact of heavy rainfall, with the floor absorbing bulk quantities of rain and releasing it slowly over time into the streams. The roots bind the soil preventing erosion and the forests themselves are a barrier to potentially destructive land use.
Land use activities taking place in the Tauranga City Council Drinking Water Supply Catchments, neither of which enhance stream water quality.
As would be expected the stream water quality deteriorates as the catchment moves from being dominated by native bush through to that dominated by agricultural and other human activity.
|The Waiorohi after travelling through 7 km of Native Forest
||The Waiorohi after travelling through 8 km of “altered” land use.
Ever wondered what is staining your glass showers?
The Catchment land can be described as flat to gentle plateaus draining through and down steep valley sides into deeply incised streams. The land is composed of volcanic ash overlaying ignimbrite rock. The rock is a mixture of pumice fragments and fine-grained ash fused together by the intense heat of volcanic activity at the time. Most ignimbrites contain high concentrations of silica, which is found in the water and this precipitates out onto glass and other surfaces and fittings.
Last Reviewed: 22/02/2017