READY TO PLANT
1 Karaka Trees (grown from urban seed)
2 Karaka Trees (grown from urban seed)
3 Locquet Trees (grown from urban seed)
10 Carex Lessoniana (bought – will divide)
8 Passionfruit plants (grown from stray seedlings)
1000 Pohutakawa seeds (grown from local seeds)
16 Pear Trees (cloned from urban source)
6 Pohutakawa Trees (cloned from urban source)
10 Puriri Trees (Wai O Taki Bay seed)
30 Cabage Trees (urban seed)
10 Nikau Trees (Maungatapere seeds)
10 xxx? Trees (Maungatapere seeds)
12 Karaka Trees (Mt Wellington seed)
We need to extend the retaining walls in the Tamaki Estuary and I don’t want to have to lug a bunch of stone down there so I thought ‘what if we use the mud to make concrete blocks?’ It makes sense right? Use the product from the erosion problem (mud) to fix itself.
I got advice from a chemical engineer who thought ‘as long as I don’t use any rebar I should be ok with the salt water’. He also gave me a mix to try which I adapted to fit the local conditions:
10% Ordinary Portland cement
10% Mc Donalds fine lime
I premixed the cement and lime so I did not have to lug the 25 kg bags on site. I bought a 45 litre bolt box to use as a mould. I put the whole thing in a plastic bag to cure as I am working below the high tide mark (concrete does not need air to cure). Things I learnt:
Mixing takes ages, I was very though but this took an hour!
The first block will not sit on flat ground so you need to add more cement and lime (I did not have any more so I put a large stone in the middle of this block).
I tried to keep the mix as dry as possible for as long as possible. One advantage of this method meant I could pull any crabs out that I accidentally scooped up.
Multi coloured mud helps you monitor your mix. It looks like mine had a lot of clay in it, which makes sense given the eroding banks are clay.
UPDATE: 5 DAYS
UPDATE: 26 DAYS
UPDATE: 3 MONTHS
One thing I quite like about this mix is the lime, which is a much more environmentally friendly product than cement. Tho the engineer has told me ‘If it’s not strong on compressive strength, increase the cement and reduce the lime’.
Let’s see if it turns into a rock or not. I am optimistic because of the clay but I am worried because concrete is usually made of sand. The engineer reckoned it might take a month!
UPDATE: 18HRS: Its solidifying! It feels like brand new plasticine. My 30kg son was able to stand on the block without leaving much of a dent. The bag has worked well and I am confident if it came off now the impact from the sea would be negligible.
UPDATE: 48HRS After Mixing
UPDATE: Third Brick
When I pushed it over it did not break up at all! Even tho the top brick was still very soft at only 5 days old. The bottom bricks are rock hard.
UPDATE: Fourth & Fifth Bock
This is all I need to do for the experiment but I am keen to go one or two blocks higher. I was short on time doing these last blocks so the mix was not that good, I am worried the sea will eat them away leaving me with swiss cheese bricks.
UPDATE: Infill Brick
UPDATE: Another wall
UPDATE: 7 Months later
UPDATE: 8 Months later
UPDATE: 3 Years 5 Months later (August 2016)
The front bit has broken off, probably from people walking on it when the supporting mud it was sitting on got eroded away (I should have built a footing). It has stood up surprisingly well to erosion, the front bit is 390mm and the back 375mm a total of 765mm. So it’s loosing about 0.8mm per month. It’s in the waves for at least two hours per day. Not bad for a first try, and a heck of a lot better than the bank behind it! It’s kind of nice to see algae growing on it, I think I would like to find out if bivalves will grow on it if I moved it (maybe just the broken off bit) further out into the estuary. Bivalves might also help prevent it from eroding. I think this kind of mud sequestration is a great way to deal with legacy sediment, I want to create more prototypes.
UPDATE: 6 Years later (February 2019)
The rate of erosion seems to have slowed down a lot.
While I was watering the dying trees on Omaru Creek (please rain soon) I noticed people were putting out their trash for the local in-organic rubbish collection. So I hauled a bunch of stuff out of the water. Some of it was so rusted it must have been in there for years. The pile was bigger but some of the stuff I found in the bush (bike parts) got picked up by some collectors (sweet!).
UPDATE: Inspired by the recyclers my son and I just pulled out about 60kgs of rusting steel from below the high tide line. I would have photographed my pile of fencing mesh, corrugated iron and shopping trollies but they picked it up so fast!
I decided not to wait for the council to get these out. It looks like a scrap dealer threw them over the cliff at Wai O Taiki Nature Reserve years ago and they have been leaking poison into the estuary ever since.
How I found them, tho most of them were covered in the mud (yes that is a dead dog).
In the other trash at the bottom of the cliff someone left me an old tent which I was able to use as a tarp to keep my car clean.
They did not want them at the local e-waste collection day but they said I could take them down to upcycle.co.nz during the week, this is all of them on a trailer.
Upcycle were so awesome! They were happy to recycle the TVs for me even tho they would normally charge someone $250 for this much waste. And thats if the TVs are in good condition with valuable parts (these have been stripped). They were just as happy as me to see them out of our estuary, what heroes!
I have tried to find out who planted these trees but no one seems to know. Many are completely dead – it has been a very dry summer. I am trying to revive the rest with local creek water (only when the tide is going out) but I am worried about the salt content. I tasted it once and it was a lot less salty than the sea but I will not again, not since I smelt the waste water being pumped into the creek upstream!
UPDATE: It’s officially a drought. I have been giving each tree approx. 4L of creek water once a week. There is no noticeable return of any green leaves. Tho one of the Rewarewa with a tiny amount of green has not lost it. The creek water is getting smellier I am not sure how good it is for the trees. I am bringing my house water down for the only Kauri.
UPDATE: They all died. The drought was bad, but I don’t know why Auckland Council plants trees and does not look after them.
After a very muddy swim, my son (8yrs old) and I have started mapping local erosion areas. It looks like there are lots of obvious places where we can fix tracks, plant trees and build retaining walls. I would like to help get the silt and mud out of the Hauraki Gulf.