Peel Estuary and Mandurah - Observations

After periodically visiting our daughter who had lived in Mandurah for nearly 20 years my wife and I moved to Erskine, a Mandurah suburb, in February 2022.

The Peel estuary and the Mandurah area in general is very attractive and popular for visitors and as a place to live. This, of course, leads to challenges in maintaining the environment.

Having a naturally inquiring mind I needed to learn about the local environment. This page sets out some observations, thoughts and provisional conclusions that I have drawn from what I've been able to learn about the area.

As I've noted elsewhere on these pages, there seems little effort made by people to maintain the parks and gardens in their community. The Mandurah area is no different. I've written a page on my efforts to control weeds in and adjacent to the beautiful parks in my area.

This page was started 2022/05/02, last edited 2023/01/02
Contact: David K. Clarke – ©


This is a work
in progress




The Peel-Harvey Estuary

Tidal Movement

I was unable to find any very useful reference on the Internet about the amount of tidal movement that was typical in the Peel estuary so I decided to take my own measurements at a time of Spring Tides, the new Moon of 2022/04/30.

Six readings taken over a period of 22 hours at a period of Spring tides (new Moon, 2022/04/30-05/01) indicated a total range of about 20cm. This seems to be about a third of the tides on the coast.

(Tide levels are available on the Internet for 'Mandurah' but where these levels apply to is not given. If they are in the estuary then they are probably substantially less than on the coast.)




 
This section added
2022/08/11

Water colour change

 
The water in the Peel estuary is usually colourless, sometimes clear, sometimes - if there has been a lot of wind and sediment has been stirred up - cloudy.

On this day we noticed it was clear but strongly coloured brown, probably from tannins that had washed in with the high flows in the Murray and Serpentine Rivers that feed into the estuary.

I also noticed that the water tasted fairly fresh. It is normally about the same as sea water in salinity. It seems unlikely that the salt water in the whole 60 square kilometres of the Peel lagoon could have been replaced with fresh, so more likely that the fresh water had for some reason come over this side.

The data I had from Dr Steve Fisher, Operations Manager, Science and Waterways, Peel-Harvey Catchment Council, showed some very low salinity readings had been collected in the past, so it was quite possible that this water was almost fresh.

Photo iPhone 11 Pro, wide angle lens, 1.54mm, 2022/08/11


 
Two colours in the water
This panorama, which covered about 120 degrees, shows that the water in the Mandurah Quay harbour (on the left) was coloured by the tannins, while the water in the more open estuary (on the right) was colourless.

The water in the harbour was not so strongly coloured as the water that I recorded above, on the previous day. I tasted the water on both sides of this photo. Both were somewhat saline, I couldn't be sure if there was any difference in the salinity between them.

Photo iPhone 11 Pro, 2022/08/12



 
This section added
2022/05/03

Dead trees in the Peel lagoons

Dead trees, egrets and spoonbills
A very few of the thousands of dead trees in the Len Howard Conservation Park (there can be little doubt that the deaths are due to climate change). I think that these particular ones are in what I have called the Spoonbill Rookery near Mandurah Quay.

Anyone walking on the Len Howard Trail (through Len Howard Conservation Park) can't help noticing the number of dead trees in and near the small swamps and lagoons. It seems that the swamps were all once host to healthy Melaleuca trees, but they can no longer support them.

The most obvious possible cause for this would be an increase in the salinity where the trees are. It is not easy to find out if this is definitely the cause.

 

A summary

The text in this section can be summarised as: It seems most likely that the tree deaths are due to increased salinity in the estuary and that the increased salinity is due to decreased runoff which itself is due to climate change.

Salinity record

On 2022/04/13 Dr Steve Fisher, Operations Manager, Science and Waterways, Peel-Harvey Catchment Council - Provided me with data from “the Marine and Freshwater Research Laboratories (MAFRL)  from five  sites in the estuary between the 1970s and mid 2001.

From these data I found that the average of all the top salinity recordings at site #2 (near Dawesville and Falcon) from 1977 to 1994/04 (when the Dawesville Channel was constructed) was 25 parts per thousand (ppt), bottom salinity 27. After that time, up to mid 2001 when the data series ended, the averages were 32 and 35 respectively. From that, for what it is worth, the top salinity (having the greatest relevance for the trees) has increased by 28% since the construction of the Dawesville cut.

From the above it does seem that the average salinity in the estuarine system has increased. My impression, again, for what it is worth, is that the increased salinity is likely more to do with deceased rainfalls since the 1970s (itself due to climate change) than due to the construction of the Dawesville Channel.

 
More dead trees
Dead trees
Dead trees adjacent to the Len Howard Trail. Far more can be photographed by a drone.
The fine-stemmed creeper on the left is, I believe, one of the obligately parasitic Cassytha species (that in SA, but apparently not in WA, is called snottygobble).
The tree on the right is commonly called a paperbark, probably either Melaleuca cuticularis, salt water paperbark, or Melaleuca rhaphiophylla, swamp paperbark. Most of the dead trees are probably of the same species.
Photo iPhone 11 Pro, 2022/05/05
Quoting from a Water Corporation publication, Climate change and WA - Climate and Southern WA:

“A 20% drop in rainfall may not sound very dramatic until you understand the impact it has on streamflow – the water that runs off into our dams and other storages. The decline in rainfall throughout Perth and the South West has seen streamflow reduce by an average of over 80%!”

It seems that rainfall and runoff is likely to continue to decline into the future. Quoting Climate projections for Western Australia; Rainfall projections published by WA department for Primary Industries and Regional Development:

“The drying trend in the south-west will continue as greenhouse gas concentrations increase according to the modelling. The projected changes differ a little from the observed changes in recent years. There may be an increase in synoptic systems bringing helpful rainfall to the northern and eastern grainbelt and south coast, but the projected drop in the number of deep low-pressure systems means much less rainfall for the west-coastal regions and far south-west. The overall increase in atmospheric pressure over southern WA will likely drive a shift to a more settled weather regime, with more highs persisting for longer.”
The reference was marked "Page last updated: Thursday, 15 April 2021."




 
This section added
2022/08/11

Len Howard Conservation Park

Weeds in and near the LHCP

 
I've written on another page about the infestations of invasive weeds into the Len Howard CP and nearby area and on my efforts to control several of the most conspicuous and invasive offenders.

The patch of fleabane in the image on the right was in the southern part of the big seasonal paperbark reserve. Note that it is on a slight mound; I suspect that the surrounding area is seasonally flooded and that this kills any fleabane seeds in the soil.

I sprayed this patch on 2023/01/05

Photo iPhone 11 pro, 4.25mm focal length standard lens, 2023/01/05



Lightning blasted and charred tree

 
Lightning blasted tree
The photo on the right is of a lightning blasted Casuarina tree beside the concrete shared-use path adjacent to the Len Howard Conservation Park - on Glendart Court.

Perhaps surprisingly this was not the tallest tree in the area, but it wasn't far off. I wonder why it was hit rather than another tree? Perhaps it was a better electrical conductor?

The splitting of the bigger trunks and the charring of the top part of the tree are shown in more detail in the following photos.

These photos were taken using a Cannon Ixus 190 on 2022/08/11 a few days after the lightning strike.

Most of the tree was killed by the lightning strike, but a small section was still alive at the end of 2022. It had entirely died by early February.

 
Lightning blasted tree trunks
Lightning blasted tree trunks

Note that the largest trunks, on the right and left, have been split. I believe this is caused by the moisture in the tree flashing to steam due to the heating effect of the high electric current.

 
Lightning blasted tree top
The top part of the lightning blasted tree.

To see the top part of the tree and the charring in more detail click on the image.



 
This section added
2022/07/26

The big seasonal paperbark swamp (BSPS) in the Len Howard Conservation Park

Big seasonally paperbark swamp

 

How the swamp came to be a reserve

On 2022/08/08 I was told by an employee of the City of Mandurah that a condition of the development of the Bridgewater Lifestyle Village was that the swamp area had to be kept in its natural state as a reserve. Both areas were owned by the same people,
This swamp, which doesn't seem to have a name (but should have) is either a part of the Len Howard CP or is at least adjacent to it. I have previously called it the 'big ephemeral paperbark swamp' but considering that it contains a significant amount of water for several months from winter onward it seems that 'seasonal' is more appropriate than 'ephemeral'.

In 2022 Erskine had a wet winter, by my records there had been 129mm of rain in May, 148mm in each of June and July and about 70mm in the first third of August. Consequently by this time the swamp was full and overflowing into the main estuary pool. I've written elsewhere on these pages, with photos, on the swamp through the seasons.

Photo iPhone 11 Pro, focal length 6mm (telephoto), 2022/07/24.

When is the big seasonal paperbark swamp (BSPS) empty, full, overflowing?

I don't seem to have recorded when the swamp started overflowing, it was probably at least a couple of weeks before I took this photo. Surface flow from the swamp into the estuary stopped on 2022/09/28.)




Wildlife

Bandicoots

 
Southern brown bandicoot
Bandicoot
southern brown bandicoot
Photo Canon Ixus 190, 2022/02/28
There are bandicoots in the more densely scrubby areas along the lagoons of Mandurah. This one was near the Serpentine River in Greenfields.

I have since seen a couple more bandicoots in the Novara Beach Reserve. They seem most likely to be seen at dusk, dawn or night time.



Kangaroos

Kangaroos at a feeding station that someone maintains adjacent to the Len Howard CP
Kangaroos
Photo taken 2022/03/16, Canon Ixus 190

The kangaroos that live in the Len Howard CP are very relaxed around people. Many times we have seen them grazing on someone's front lawn. I've seen one hop through a front gate to do some grazing in mid morning.

 
Injured kangaroo

In the period at least from February 2022 to the end of 2022 there was a mob of 25 or more kangaroos resident in the BSPS. If anything these kangaroos are even more relaxed around people than those that use the feeding station mentioned above. The most relaxed one of them all is possibly the injured kangaroo mentioned elsewhere on this page.

Added comment

Early this morning (2022/05/05), when there was hardly any daylight, I was walking through the little reserve at the western intersection of Silverton Crescent and Wattleglen Avenue on my way to do a fortnightly plasma donation when I saw a kangaroo in front of me. It casually did a couple of hops in the direction I was walking a couple of times then stopped, stood up to its full height - to intimidate me - and stood as I walked past about three metres away. At its full height it was only a little shorter than me (I am about 1.8m tall).

Injured kangaroo - two photos on the right

This kangaroo had a badly injured mouth, but was grazing peacefully when I photographed it. It is one of the big seasonal paperbark swamp (BSPS) mob.

Photo iPhone 11 pro, telephoto lens, focal length 6mm, 2022/05/25

I did not see this kangaroo again in the next two months, at least I did not see a kangaroo that I recognised as this one.

 
Injured kangaroo

I happened across the same kangaroo again on 2022/08/13. This is the best photo I could get at the time.

It looks like the injury has healed quite a bit, but the kangaroo's mouth is never likely to return to anything like its original form.

Click for a more detailed image of the mouth area. Use back-arrow to return.

Photo iPhone 11 Pro, telephoto lens, focal length 6mm.

Update

I came across this kangaroo again on 15th August and 25th September 2022, 2nd of January and 2nd of February 2023. In January she was obviously carrying a large joey in her pouch, so she has done very well. The injury was still conspicuous, but not so much so as it was in the earlier sightings. Oddly she seems tamer than most of the swamp mob, I wonder why. On the February siting there was a young joey near her.



 
This section added
2022/05/04

Lizards

 
Bobtail lizard (Tiliqua rugosa rugosa)
Bobtail lizard
The lizard that I have always previously called the Sleepy is generally called the bobtail in WA. The local variant is Tiliqua rugosa subspecies rugosa, the eastern variant is Tiliqua rugosa subspecies asper.

This was the first lizard that I can recall seeing in the three months that I have so far been in WA. I have not seen any snakes at all. It was between Dampier Avenue and the scrub adjacent to the lagoon.

Lizards of many species were common in SA, tiny skinks particularly so. My son-in-law tells me that there are small skinks around, but I haven't seen them. It is disappointing to see how relatively rare they are in the Mandurah area.



 
This section added
2022/07/26

Bats

 

Update January 2023

I still haven't seen any bats.
While I have watched for bats on my frequent walks in the early morning and occasionally evening, I don't recall ever seeing a bat in the Mandurah area. With so many mosquitoes to provide food for microbats I would have expected bats to be quite common.

I did wonder if the frequent aerial treatment, by helicopters, to reduce mosquito numbers had wiped out the local microbat population. But I read information sheets from the City of Mandurah stating that the mosquitoes numbers are controlled with very specific larvicides (S-methoprene) and Bacillus thuringiensis israelensis.

So it seems unlikely that the mosquito treatments would account the the apparent low bat numbers. I've been told that some bat roosting boxes have been placed, so perhaps the low numbers are related to a lack of roosting sites - perhaps that may be connected to the great numbers of dead trees?



 
This section updated
2023/01/03

Dog water

Many people walk their dogs around the Len Howard Conservation Park area. In the summer months there is very little or no fresh water available for dogs to drink in the area. Someone maintains a watering point mainly for kangaroos in the big seasonal paperbark swamp (I wish there as a shorter and generally accepted name for that) from about the end of the year until about May when water starts to become available in the swamp itself. I'm sure that dogs use it too, although it is difficult for small dogs to use because of the high sides of the container.

There is also a tap at the car park near "Nature's Eye".



 
This section added
2022/05/06

Rubbish

Just as around where I used to live in South Australia there is rubbish scattered carelessly around the Mandurah area. I intend to continue cleaning up this rubbish in my new neighbourhood.

Today I picked up a bag full in the little reserve area at the western junction of Silverton Crescent and Wattleglen Avenue.

It is common for people to dump garden waste in the local parks.

I came across a shocking amount of rubbish in the patch of scrub adjacent to the Riverside Primary School on 2022/05/09, apparently left by someone who was sleeping rough. I made no attempt to pick it up.

As discussed on another page on this site, there needs to be a noun for the type of careless, irresponsible, lazy people who do this sort of thing.



 
This section added
2022/06/26

Vandalism

 
Vandalised sign
Senseless vandalism exists in Mandurah as it does in most other parts of the world.

Some hundred or so of the plants I put into Crystal Brook Central Park back in SA were pulled up be one or more vandals. Fortunately, to the time of writing, few of the plants that I've put into a small park near my new home have been damaged by vandals.

Dumping rubbish, discussed above, is a form of vandalism.

Valdalism at the train station car park

I noticed on 2022/07/03 that about a half dozen large recently planted trees adjacent to the new multi-story car park had been broken off. There was only one or two that had been left undamaged. By the 5th they had all been removed.

Vandalism of my tree guards

2022/07/07; see the page on my projects in the Erskine area.


 
This section added
2022/07/29

Weeds

As is the case with most of the public places with which I am familiar there are weeds in Mandurah, adjacent public paths and in parks and gardens. I find the unwillingness of the great majority of the local people to take part in the improvement of their public places puzzling.

 

Reprimanded for digging out weeds

To my amazement on 2022/08/01 a ranger reprimanded me for digging out dune onion weed from one of the parks in Erskine.
I've written on my efforts to remove some of them on my page titled Fleabane. I've speculated on how people look after their private gardens but don't bother with their shared places, and commented on Whatever happened to civic pride? in relation to the unwillingness of the general public to take part in improving their public spaces. And I've written on contribution on another page.

Self or community?

I suspect that selfishness is a factor in people's unwillingness to look after public parks and gardens, as it probably is in the unwillingness of many to donate blood (only some 3% of Australians donate blood or blood products). On the subject of selfishness, there are many private jetties in the Mandurah area, most have signs on them telling other people to keep off. Surely reasonable use by the public would be unlikely to harm the jetties or inconvenience the owners?




Odd comments
Why would anyone want to remove weeds from parks?

I have made a project of working at improving the parks and paths in my local area. It seems to me only natural that I should want to do this. Yet I get the impression that many people find it hard to understand my actions or motivations. I, in turn, find it very hard to understand their lack of understanding; do they not think that we should care for our public places? Or do they just think, "It's not my job. Let somebody else do it."

 

Related work

In addition to the onion weed removal that brought about this section, I've also pulled out fleabane and picked up rubbish. Perhaps the people who can't understand my work at controlling onion weed would find this equally inexplicable?
About mid July 2022 I was hoeing out onion weeds adjacent to one of the paved trails in the big seasonal paperbark swamp east of my home when a man stopped and asked: "Why are you doing that?" as if my purpose was unimaginable to him. Was he unusual or would it be so incomprehensible to many that a person would want to remove weeds from a conservation park?

2022/07/24, another man stopped and said: "I've got to ask, why are you doing that?" I said something like "I'm digging out weeds; they have no place in a public park." Several other possible answers came to mind after I had thought about it for a while:

  • Would you dig a weed out of your garden? Why then not out of a public park?
  • Do you not care about weeds in your public places?
  • I dig weeds out of my garden, why should I care less about a public park?
  • If I am unwilling to try to improve our public places, why should anyone else?
  • If no one cares for our parks what will become of them?
  • If you have to ask you will probably not understand my answer.
  • This is a beautiful park which the people of Mandurah are very lucky to have. Removing the most conspicuous, unsightly and invasive weeds can only improve it.
Is caring for our shared environment such an uncommon thing to do? My page on contribution covers the point in depth. My notes on self or all and the rights and needs of future generations are also relevant.




Primewest, Erskine shopping centre: a lost opportunity to reduce greenhouse emissions and increase profitability at the same time?

 
Prime West shopping centre, Erskine, WA
Shaded car park
A great opportunity lost.
And a careless waste of electricity.
In August 2022 car park shades were installed in the Prime West Erskine, WA shopping centre car park. The shades were plastic mesh, not solar PV panels, a lost opportunity.

Had solar panel shades been installed rather than simple shade sails most of the power consumption of the shopping centre could have been offset and a huge amount of greenhouse emissions avoided (most of Western Australia's power is generated by coal-fired power stations). I estimated that the area covered by the shade sails was 1,320m2, twice that of the Woolworths, Clare, shades, so had solar PV panels been used rather than shade sails the installed capacity would be around 280kW. Such a solar PV installation would generate about 490 megawatt-hours of electricity each year and that could reduce WA's greenhouse CO2 emissions by something like 400 tonnes each year.

I've written a page on solar PV shade in car parks and other places elsewhere on this site.

In 2022 solar PV panels typically pay for themselves in about five years. In this case where the cost of installing the shade cloth sails would have been avoided, the payback time would be shorter. PV panels also have the advantage of casting denser shade than shade cloth, so the cars beneath the panels would be cooler in summer.

A waste of electricity for needless lighting too

Note in the photo too that the lights beneath the shades are on, as are the two tall floodlights that can be seen in this photo. There were about 40 of each types of lights in the shopping centre. So far as I have been able to tell all were left on 24 hours a day. The shopping centre is open only from 8am to 6pm most days (Sundays 10am to 5pm, plus to 9pm on Thursdays) so outdoor lighting would only be necessary Thursday evenings and evenings in winter. On 2022/09/18 I emailed Prime West telling them about the lights being on all the time; I had not received a response by the 12th October.

A letter to the editor and a result

On 2022/09/30 I wrote a letter to the local newspaper on both the above points. It was published in at least one (Mandurah Coastal Times) a few days later. On 2022/10/12 I noticed that the car park lights were off..

One can hint and push but it is a rare thing to get a definite result such as this one. Having the car park lights on only when needed (if that is what happens in future) will reduce greenhouse gas emissions by something like 30 tonnes each year.

Other shopping centre owners are far more progressive

In Western Australia for example Northam Boulevard (article in The West Australian), belonging to Perdaman Group, 2,211 panels in total, 900 of these shading the carpark, and Dunsborough Centrepoint shopping centre (article in The West Australian).

In my home state, SA, there are big solar shaded carpark installations at Vicinity Centres (claimed to be the biggest in Australia at the time of construction, 1,400 panels on the car park alone) and Castle Plaza (430 solar shaded parking spaces).

Also see my page on solar car park shades.






Related pages

On this site...

Bowman Park, Crystal Brook, South Australia

Cleaning up roadside rubbish

Climate change, the world's great threat and challenge

Contributing to our communities
  Blood donation

Crystal Brook's Central Park, SA

Destruction of roadside vegetation by a body that should be protecting it

Gleeson wetlands, Clare, South Australia

The remainder of my life

Why I support the local wind farm

Specific to WA

Fleabane in the Len Howard Conservation Park

WA Images; from a visitor
  WA Images; from a resident




Names and abbreviations I've used

Big seasonal paperbark swamp, BSPS
The large reserve area west of Bridgewater Lifestyle Village and south of Oakleigh Drive. See Google Earth image.

Reserve at the western junction of Wattleglen and Silverton roads, W/S Reserve.
See Google Earth image.

Car park on the lagoon in Len Howard Conservation Park, LHCP
The car parking area near the western end of the Len Howard Conservation Park, Left of centre at the bottom of the Google Earth image.