Storm and wastewater in Te Awarua-o- Porirua Whaitua Tim Strang - - PowerPoint PPT Presentation

Storm and wastewater in Te Awarua-o- Porirua Whaitua Tim Strang and Rob Blakemore

During this presentation we…

The water cycle

Three waters in the metro region

Three waters assets

Hutt City Porirua Upper Hutt Wellington GWRC Asset value $505m $323m $279m $1,340m $445m Population 100,300 53,000 39,600 197,600 Connections 38,731 18,220 12,523 69,030 Pipelines (km) 1,878 1,017 650 2,946 183 Pumping stations 74 80 28 98 17 Reservoirs 24 18 16 74 3

What the networks do

Bulk water Stormwater Wastewater Collect Treat Convey Store Treat Discharge

Water supply network

Water supply

Waste and stormwater

Wastewater Network

The question I would like you to consider:

• What containment standard should we be working to ?

Containment Standard Average number of overflows per year 1 monthly 12 3 monthly 4 6 monthly 2 annual 1 2 yearly 1 every two years

Wastewater network

Porirua City’s wastewater network extends from Pukerua Bay to Tawa . The catchment includes the northern Wellington suburbs

• f Tawa, Churton Park,

Grenada and northern Johnsonville.

Wastewater network

Porirua has a large number

• f wastewater pump stations

(45 in total) due to the City’s rolling topography, the spread-out nature of townships, and the location

• f the treatment plant and

discharge facilities.

Wastewater network-What we know

• The network is capable of handling peak

dry weather flows – both now and in the future (for the next 30 years)

• However, during wet weather, certain

points in the network are unable to cope and overflows occur from the wastewater network (pumping stations, manholes and the treatment plant) to streams and the harbour

• Overflows are not ideal, especially close

to recreation or fishing areas where there are public health risks

• Despite this, all cities worldwide have
• verflows during major rain events
• Blockages caused by maintenance issues

and fat build-up can result in dry weather

• verflows. This year blockages have

dropped to 56 per 100km of pipe (was 93 last year).

Manhole overflow

Outcome Monitoring: Respectful for the Environment

• We monitor the performance of the

three-waters assets across the region

• A consistent approach assists with long-

term planning Water quality monitoring

• In December 2014 we began taking

monthly readings from 9 freshwater sites

• In August 2015, this data was assessed in
• rder to identify any network issues. Five
• f the 9 sites exceeded the trigger level

(a reading of 1,000cfu or more – this is a National Standard). Investigations to identify source contamination through targeted monitoring is underway

Green sites have low risk to public health, yellow sites have a moderate risk to public health and red sites have a high risk to public health

Network Monitoring

• Prior to April 2015, an observation system

was in operation, relying on customer complaints, SCADA data and reports of popped manholes

• Since April, we’ve been progressively

installing overflow sensors and alarms in Porirua’s wastewater network. This has allowed us to start to collect data as to how

• ften wastewater overflows occur
• As the overflows occur, a notification is sent

promptly to GWRC

• As we install more overflow sensors

throughout the network, we expect an increase in the number of notifications

• The network overflows are not currently

complying with regulatory requirements Notifications to GWRC

April 2015 Number of notifications

Time

Work is underway to reduce the number of overflows

• Wellington Water and PCC are working hard to identify the causes of the overflows
• A detailed wastewater master plan is currently being developed which will include

plans for reducing the number of overflows

• We will be working with GWRC to determine how the new rules in GWRC’s proposed

Natural Resources Plan will impact on the three-waters activities. A workshop is planned between Wellington Water and GWRC’s consents team which will clarify the consent requirements regarding network overflows

• PCC has allocated $28M for capacity upgrades for the network and the Porirua

Wastewater Treatment Plant in their 2015-25 Long-Term Plan

• During major rain events, overflows are expected in all cities. For example,

Wellington and Christchurch have a 3 monthly containment standard in parts of their cities – this means that around 4 overflows per location per year are expected – while parts of Auckland are on combined sewers that overflow much more

• frequently. We’re still gathering data to ascertain Porirua’s current standard level.

Wastewater Network

Keep thinking about this:

• What containment standard should we be working to ?

Containment Standard Average number of overflows per year 1 monthly 12 3 monthly 4 6 monthly 2 annual 1 2 yearly 1 every two years

Wastewater Treatment Plant

Questions to consider:

• What flow standard should the screens be designed for?
• What flow standard should the oxidation ditch be

designed for?

Element Typical Design Standard Screens 3 to 5 x Average Dry Weather Flow Oxidation Ditch 3 x Average Dry Weather Flow

Porirua WWTP

Current inflow max 1000 L/s 3 screens can take 1050 L/s (with one standby) Oxidation ditch can currently take 630 L/s before overflow 300 L/s overflows Dry weather flow 300 L/s

Porirua WWTP -2015/2016 Works

Re-design of inlet to take 1000 L/s (Compatible with future upgrade To 1500 L/s) New RAS pumping system

Wastewater Treatment Plant

Back to the Questions:

• What flow standard should the screens be designed for?
• What flow standard should the oxidation ditch be

designed for?

Element Typical Design Standard Screens 3 to 5 x Average Dry Weather Flow Oxidation Ditch 3 x Average Dry Weather Flow

Stormwater Network

Questions to consider:

• What do you want to know about stormwater

flooding?

Stormwater network

The Porirua Harbour Catchment has steep hills and gullys, two harbours and numerous streams and tributaries, resulting in a system of fragmented, localised networks. There are many rural catchments with open streams and watercourses, but in the majority of built areas, these streams have been enclosed in piped systems.

14 May Flood Event

Rangituhi Overview

Rangituhi Crescent

CBD Overview

Outlets

Porirua CBD

Thompson Grove Overview

Thompson Gully – Thompson Grove

Stormwater Network

Possible Improvements:

• Debris traps and improved inlets
• Network upgrades
• Overland flow paths
• Storage areas
• Development Controls
• Building modifications and retrofits
• Maintenance of outlets

Some Important Messages

Our current role is:

• to convey what is put into a stormwater network and

discharge it into the environment

• to convey, and treat what is put into the wastewater network

and discharge it into the environment WWL can contribute to better receiving water quality outcomes from management of wastewater and stormwater networks BUT it will never be the sole provider of solutions to problems beyond our control

• People put unwanted contaminants into the systems we manage
• Non point source pollution
• Residual contamination of sea and harbour beds
• Quantity of rain that falls from the sky and other natural

processes eg erosion

Wrap up

Questions Comments What else would you like to know?