Wastewater, stormwater and flood protection

Description

Background and institutional arrangements

Wastewater systems typically incur higher capital and operating costs than drinking water (the Ministry of Health estimates that in some cases, this can be as much as 10:1) as:

• Wastewater pipes are larger and need to be gravity fed (requiring graduated levels for outflow). By comparison, drinking water pipes are smaller and pressurised
• Treatment and disposal processes are more complex, and
• The legislative requirements of the RMA (i.e. minimum standards of compliance for disposal) have meant that wastewater infrastructure is generally much more up to date than that for drinking water.

The total volume of wastewater produced approaches 345 million cubic metres per year for the surveyed territorial authorities. Many large industrial sites also have private discharge arrangements with regional councils, rather than discharging to a reticulated system. The percentage of wastewater can be broken down by source and is shown in the diagram that follows.

Figure 43: Current wastewater volumes by source

Source: PricewaterhouseCoopers Surveys of Territorial Authorities (reproduced from the MED Infrastructure Stocktake 2004)

Assets

The estimated replacement cost of (territorial authority-managed) wastewater-related infrastructure in New Zealand is $12.7 billion.[115] This is greater than the value of drinking water assets.

As with drinking water, metropolitan areas tend to have fewer, larger systems than provincial and rural councils. The table that follows indicates the differences.

Source: Department of Internal Affairs Water network infrastructure report

Total annual operating expenditure on wastewaternetworks (including depreciation) is forecast to be $815 million per annum across all councils. Operating expenditure is forecast to grow by around 4.5% per annum over the next 10 years. Forecast capital expenditure over the next ten years is estimated to be around $5 billion.

Wastewater reticulation capacity can be measured by assessing the number of recorded overflows in wet weather and dry. The Auckland region has the highest proportion of wet weather overflows largely due to stormwater inflow into the wastewater system. The separation of wastewater and stormwater systems to prevent overflows is an ongoing issue for many local authorities.

Estimates of total asset life remaining suggest that, in general, wastewater systems appear to have more life remaining than drinking water assets. Stormwater assets are generally longer-lived than either water or wastewater systems due to the fact they have fewer shorter-life components such as pumps.

The estimated replacement cost of (territorial authority-managed) stormwater-related infrastructure in New Zealand is $8.940 billion.[116] Most of the stormwater infrastructure and expenditure is associated with metropolitan areas and, to a lesser extent, provincial centres.

Total average annual operating expenditure on stormwater networks (including depreciation) is forecast to be $280 million per annum across all councils over the next ten years (increasing at a rate of around 4.5%). Forecast capital expenditure over the next ten years is estimated to be around $2,560 million. More of this expenditure appears programmed for the later part of the 10-year period.

Flood protection (and to a lesser extent drainage) activities are carried out mainly by regional councils and unitary authorities. The estimated value of these is around $1.5 billion.[117]

Analysis

The level of wastewater treatment varies from council to council. In contrast to drinking water quality, which is monitored centrally by the Ministry of Health, resource consents for discharge of wastewater are managed by regional councils (based on guidelines set by the Ministry for the Environment). These consents are valid for a number of years, and decisions to upgrade often coincide with the need for a council to renew its consent (together with public pressure).

Wastewater is treated using a mix of primary, secondary and tertiary treatment. Many systems produce “good” quality outflow. However, around 23% provide only primary treatment. While these will probably meet their current resource consents, increased requirements mean that capital upgrades may be required on expiry. Some small communities may face financial difficulties in meeting these costs, especially if they also have to upgrade their water supplies.

In recent years, local authorities have made significant capital investments in wastewater collection, treatment and disposal infrastructure. Many larger plants have been (or are being) substantially upgraded and a large number of upgrades have been identified in the 2009/10 Long-Term Council Community Plans. This is reflected in the fact that forecast capital expenditure for wastewater is greater than for drinking water for the next 10 years (see the chapter on Planned Investment).