Groundwater

Well, well, well by Dan Franklin

It may be raining today, but has it been a good year for rain, what’s the health of our groundwater supplies, how is it trending? Every year the Jandakot Community Consultative Committee meets to discuss the status of the Jandakot Water Mound, including: rainfall, flow into Perth dams, private/public bore abstraction (water term for extraction), specifically groundwater take & recharge by the Water Corporation for all of Perth and the ongoing status of environmental commitments (KPI for specific sites). As a representative of the BRG and interested landholder (living near the Shirley Balla Swamp for over 20yrs) I’ve attended the JCCC meeting for the last 5 years, and was joined this year by BRG committee member, Dave Manning. It’s a big subject, let me know what you want to know more about in the comments. The meeting highlights:

1) Incoming

Rainfall – continues to trend down, Perth is getting drier and drier, less rain means less water in the dams, more pressure on groundwater extraction. Whilst 2018 (844mm), was above average, 2019 (648mm) & 2020 (580mm so far) are well below. Note the long term avg (1975 to 2020) is 811mm and the 10yr avg is 729mm, the downward trend continues with this year and last year even worse.

2) Outgoing

Groundwater allocation – JWM is divided into 3 areas, Jandakot, Cockburn and Perth South. Total issued permits are less than the modelled sustainable limit, except for Cockburn area (16GL), which is trying to meet its reduced limit as of 2017 (14GL). Cockburn is trending down but with permits valid for multiple years it takes time to change direction. Note that Water Corporation extraction (the drinking water bores we’re more familiar with in Jandakot & Banjup) is <5% of the total allocation. The majority of allocation is for private/council use, industry, market gardens, council reticulation of parks/recreation etc.

3) Canaries in the coal mine

Environmental compliance – of the 23 sites identified in Ministerial Statement 688 (https://www.epa.wa.gov.au/.../files/1MINSTAT/000688.pdf), 4 were non-compliant (North Lake, Bibra Lake, Shirley Balla Swamp & Lake Forestdale), either failing water level or ecological condition KPI. The previous year was also 4 non-compliant. Of concern, the Shirley Balla Swamp (between Beenyup and Liddelow, just north of Gibbs Rd) has only met its water level criteria twice in the last 24 years. To assist, Water Corporation extraction from bores local to the swamp has reduced since 2016 (with their allocation increasingly coming from the north/Jandakot where groundwater levels have increased due to the clearing of land for development). Reassuringly, all non-compliant sites get a lot of attention in the JCCC meeting, the criteria are proving tough to meet but help as intended, to keep the system in check.

4) Miscellaneous takeaways:

· Did you know that during the winter, desalinated seawater is processed/fed to designated Perth dams which store/buffer the water for summer use, generally this represents much of the water you see in the dams as stream inflow has significantly reduced over recent years. Yes, some evaporates, yes, it has to be treated again.

· Ground water replenishment (GWR) along with desalination underpin the future of Perth drinking water sustainability given the trending reduction in rainfall and Perth’s growing needs. GWR is where waste water treated to drinking water standards is injected into our aquifers for subsequent extraction (and treatment yet again). I think of it as water laundering for those that find drinking their own treated waste too distasteful. Somewhat inefficient in the scheme of things but better than pumping it all out to sea. Currently occurring in Beenyup (Craigie, north of Whitfords Ave), with talk of a potential future site at Woodman Point being relevant to the JWM. Whatever the Water Corp inject they get to bank/extract at a later date. Interestingly some of that allowance is extracted from the JWM despite it being injected 40km away in Craigie on the basis that there is connectivity!

· Of the 322 private licensing compliance monitoring events, 309 were logged as non-compliant but only 29 related to exceeding annual water entitlements.

· The Banjup Fire of 2014 had a significant effect on vegetation, which is still in fire recovery mode, this resetting of the clock is somewhat obscuring the view that long term reduction in rainfall/groundwater levels is having on local flora.

· Groundwater is the cheapest source of drinking water, GWR is also relatively cheap with desalination considerably the most expensive, hence the financial drive to maximise groundwater extraction.

· The Dept of Water continues to promote “Waterwise” at all levels, be it washing a full load of clothes, leaking taps, better garden reticulation or optimised horticultural practices for bigger users.

· Newly introduced legislation, licensed users of 10,000kL (kL is 1m3 or tonne of water) or more must install a meter by end of 2020, previously it was only required for users greater than 500,000kL (~200 Olympic swimming pools worth!). This should help provide greater clarity of actual consumption levels & better conformance to allocation limits.

5) General background

For those less familiar – Perth has two principal superficial (surface) aquifers/mounds which supply Perth with ~40% of its drinking water, Gnangara to the north, Jandakot to the south. Whilst Jandakot itself is ~18km2, the Jandakot Water Mound stretches from the Swan river in the north, to the Serpentine river in the south, from the beaches in the west to Darling Scarp/Southern River in the east, an area of 760km2. It’s a big area, all named after Jandakot, infamy beyond the airport. The aquifer is essentially a 40m deep sand sponge, rain/streams flow in, rivers flow out, vegetation consumes, evaporation, bores extract. Humans consume water, impact the environment even alter the climate, it’s about trying to find the best compromise. Management of the aquifer falls to the Dept of Water and Environmental Regulation, who personally I think are doing a pretty good job of a complex task in trying to balance the environment and Perth’s need for cost effective & sustainable water needs.

A list of links to performance against local environmental criteria and levels in local water bores follows:

North Lake (staff) - http://kumina.water.wa.gov.au/.../Publish/6142521/gw02a.htm

North Lake (bore) - http://kumina.water.wa.gov.au/.../Publish/61410726/gw02a.htm

Bibra Lake (staff) - http://kumina.water.wa.gov.au/.../Publish/6142520/gw02a.htm

Bibra Lake (bore) - http://kumina.water.wa.gov.au/.../Publish/61410177/gw02a.htm

Lake Kogolup South (bore) - http://kumina.water.wa.gov.au/.../Publish/61410727/gw02a.htm

Lake Thomsons (bore) - http://kumina.water.wa.gov.au/.../Publish/61410367/gw02a.htm

Lake Forrestdale (staff) - http://kumina.water.wa.gov.au/.../Publish/6162557/gw02a.htm

Lake Forrestdale (bore) - http://kumina.water.wa.gov.au/.../Publish/61410714/gw02a.htm

Yangebup Lake (bore) - http://kumina.water.wa.gov.au/.../Publish/61419707/gw02a.htm

Banganup Lake (staff) - https://kumina.water.wa.gov.au/.../Publish/6142516/gw02a.htm

Banganup Lake (bore) - http://kumina.water.wa.gov.au/.../Publish/61419614/gw02a.htm