Water monitoring

Rivers and Streams

• Our rivers and streams
• What do we measure and where?
• How are rivers measured?

Our rivers and streams

The total length of streams in the Auckland Region is estimated to be 10,000 km. Most are small (less than 2 metres wide) with few tributaries, much like the finger-tips of your hand. The small size of streams is due to the catchments of the Auckland isthmus being small and short. This makes them sensitive to low summer flows and the taking of water.

Streams may be perennial, meaning they flow all year, or ephemeral, which means they dry up in summer. Waterways in the Auckland region are typically soft bottomed due to the underlying clay material on which they are formed.

There are also seven small lakes and a number of dune lakes, especially in the west of the region on the Awhitu and Kaipara peninsulas.

Around half the number of resource consents are associated with surface water sources (dams, takes from dams and takes directly from streams) than there are from groundwater. This gives an indication of the limitations of surface water in the region -Auckland is water short !

Damming water is a popular water supply option, where requirements are small, and flows are inadequate in summer to support a direct take. While there are around 500 authorised dams in the region, there could be as many as 5,000 in total. These range in size from large municipal water supply dams in the Hunua and Waitakere Ranges, to small farm stock watering dams and crossings.

The damming of waterways can have serious environmental consequences, like the prevention of fish passage and reduced flows downstream. For this reason, significant changes are proposed to the policies and rules that apply to damming in chapter 6 of the Proposed Regional Plan: Air, Land and Water (2001).

The ARC has produced a factsheet with information you need to know before you build a dam in the Auckland region. Find out more:

We have also produced a report called 'Dam Safety Guidelines' (technical publication 109) which provides guidelines for the construction, maintenance and monitoring of dams. To make it available from this site it has been broken up into its chapters, which can be accessed by taking the following links:

What do we measure and where?

The ARC automated recorder sites are constantly checking water levels in rivers and streams across the Auckland Region.

For the distribution of sites where water level, flow rate, rainfall and sometimes even water temperature and dissolved oxygen information is available, go to Environmental Data online.

Up to date and historical data is able to be viewed and downloaded.

dam

How are rivers measured?

Measuring river water levels

The most common water level monitoring site consists of a tower with a shed on top. Within the shed the data is collected electronically using a datalogger.

At the bottom of the tower is an intake pipe, which extends out into the river. The intake pipe allows the tower to fill up to the same level as the river.

water level monitoring site

At each monitoring site a calibrated weir is present which enables the water level at a given height to be converted to flow.

The weir is referred to as a water level control, and provides stable river bed conditions for the water level measurements.

weir

Flow river measurements are referred to as gaugings.

A gauging consists of measuring the river area and velocity (river speed) to calculate the "discharge flow".

A most common gauging is a wading gauging.

wading gauging

river cross section

When carrying out a gauging, we measure at least 20 points across the river. At each of these points, referred to as "verticals", we measure river depth, distance from the river edge and the velocity. Current meters are used to measure velocity. Buckets or propellers rotate at a speed in proportion to the water velocity.

From the measurements at each vertical we can determine the area between verticals. Multiplying the area and velocity together produces the discharge flow between each vertical. Adding up the discharge flows between each vertical will give the river discharge for the entire cross-section.

River and stream discharge is measured in units of cubic metres per second. For example if a stream was flowing at 1 m³/s then this relates to a cube of water with sides of 1m flowing down the river every second.