Water update – rainwater, dam water levels and usage

What a relief to finally receive good rainfall over the past couple of weeks, after the hottest and driest summer on record!

Over the seven months from October 23 to April 24, we only received 40mm of rain at the Ecovillage–this is completely unheard of in our region, which usually has one of the most reliable annual rainfalls in Australia. Over the same seven month period the year before, we received 279mm. The total annual rainfall in 2023 in Witchcliffe was still 917mm, a little under our annual average of around 1000mm, so it was the absence of summer rain that was the anomaly.

Historically, very dry summers are often followed by wetter than average winters, so we have our fingers crossed. Unfortunately, the damage caused by such an unusually dry season to our natural environments has been significant throughout the SW, particularly along the coast where the deep sandy soil holds very little moisture to sustain fragile coastal heath. The forests inland have held up better, due to the underlying clay holding moisture, particularly in areas where there is a decent layer of mulch, but sadly, there has also been many tree losses.

At the Witchcliffe Ecovillage, we are 100% self-sufficient in water. We collect rainwater for households via rooftop catchment and rainwater tanks, and all of our water for our community gardens, street trees, oval and public open space comes from our dams, which are fed from three stormwater catchments across the Ecovillage.

So how did we fare in the hottest and driest seven months on record?

Residential rainwater supply

For the most part, Ecovillage residents who had already moved in with full tanks at the end of winter and who weren’t establishing new landscaping around their homes from their tanks didn’t have any issues getting through the dry summer, although we were all being careful with our water use. For those running short because their tanks hadn’t been installed in time to fill last winter, they were able to buy a truck load of water from the Margaret River town water supply to get them through. We have heard of people across the Shire running out of tank water this summer, so we are very pleased with how our modelling for required tank sizes and roof catchments (per person in each household) is working for our residents. You can find this modelling in our Sustainable Building Design Guidelines (link)

Dam water supply

We keep a very close eye on our dam levels and landscaping water use across the Ecovillage. I have been very fortunate to have the assistance of my good friend, Alex Jolly, who is an Ecovillage resident (1B) and recently retired surveyor.  

The Ecovillage has an extensive network of very large HDPE (blue line) pipes that transport dam water to the eleven residential clusters and fourteen ag lots that are allocated dam water, and also to the public open space (POS) which includes the oval, village square and entrance roads. We meter the water at the dam pumps and each delivery point has a water tank with a digital meter that is read monthly. Alex also has a good quality weather station located in 1B for monitoring daily rainfall and temperature.   

We decided to start surveying the dam levels each month so we can confirm the exact level drop in each dam (see table 1 below). This also enables us to calculate the amount of water used since the dams stopped overflowing in October last year (they don’t usually stop overflowing until November/December). Assuming a 3:1 fall around the surface of the dams (close enough) we can make some reasonably accurate estimates of how much water we have used in total since October. Then, subtracting the total amount of water we have pumped from October 1 to April 30, we get an estimated level lost to evaporation. This is helpful, and by comparing with the evaporation of the middle dam we can compare to the average annual evaporation in our region (BOM).

I’ve provided a breakdown of the dam monitoring data below.

Our central dam, which holds around (50ML) isn’t being used at all, and we don’t intend to take water from it unless necessary. Therefore, we know that this gives us a correct evaporation value from October 1 to April 30 of 1140mm. This sounds right as the

25 year BOM estimate in our region for Oct-Apr is 1055mm, and this summer has been considerably warmer and dryer than average (plus we allow for a small amount of seepage into the clay).

The dams are holding up extremely well, and we can see that the northern dam is actually making water (approx. 240mm over past seven months) from ground seepage. In time, as our irrigated gardens, orchards and ag lots (which are all well mulched) enable water to penetrate into the underlying clay, the amount of water required for trees and deep-rooted vines will decrease and the amount of water seeping into our dams will increase.

Our dams, which are designed to only supply as much water as the increased impervious areas in the Ecovillage creates, are enabling us to slowly but surely improve the Ecovillage’s soil structure, tree cover and the saturation of the underlying clay. This is in contrast to the ongoing impacts of European farming methods, where the clearing of vegetation, loss of topsoil and carbon, and livestock compaction on the South West landscape continues to dry out the soil and underlying clay (which is like a massive sponge that has just been getting dryer each year).

All three dams have low flow by-pass pipes located in ponds up-stream of each dam, to ensure the creeks downstream get fed consistently from the earliest to the last creek flows of each rainfall season.

Much to my surprise, the by-pass pond for the northern dam has held permanent water through the last two summers, so the reeds that we planted around its edge have established well, and it’s become a wonderful natural environment. It’s now home to a pair of purple swamp hens (mulal) that have nested there and produced two lots of offspring this summer, as well as an abundance of frogs. It’s been wonderful to observe the mulal this season, as they are also managing the reed growth in an extraordinary manner (a future newsletter article)! They say that frogs and swamp hens moving into a wetland are a sign of a very healthy environment, of which I have no doubt.

As the Ecovillage is located at the top of the catchment, our dams are fed by on-site catchments. As such, we are able to completely manage nutrients that flow into the northern and southern dams that we use for irrigation. Therefore, to maintain the health and water quality in each of our magnificent dams, it’s essential that we ensure absolutely minimal nutrient runoff, in particular, nitrogen (N), potassium (P), and phosphorus (K), that can flow from our gardens and EUA’s into the creeks that run through each cluster.

Our horticulturist, Mark Tupman, ran a series of fertiliser trials in the community garden at our old office, which proved that good soil management, using nothing but nitrogen-fixing green manure crops, readily available organic matter, and good compost to drive healthy delivery of nutrition to the vegetables, performed better than those that had been fertilised with manure and organic liquid NPK. We all need to learn how to build healthy life-giving soil that stores available nutrients for plants to use as required, instead of simply adding manures and fertilisers that will leach out of our gardens and into the dams. Otherwise, we’ll end up with dams and cluster swales filled with green algae – like you regularly see on farms and rivers.   

Mark’s annual workshops, including the ones we ran this autumn, are always well attended by existing and future residents – see garden article.

Water budgets

Current Water Use

Our water budgets, set at 136 KL per annum per lot, provide a generous amount of water for the size of our community gardens, if used efficiently. As per our cluster bylaws, all EUA’s and common gardens (except lawn) need to be waterwise, which in our climate means watering via drippers, not sprinklers. Well mulched common garden beds and street trees won’t need to be watered more than once a week between October to December, and twice a week from January to February, then back to once a week from March to April. We will hardly use any water from May to September whilst the dams are filling from rainwater.  

Agricultural lots and Vineyard

We don’t expect all of the Ag lots to use their 3.0 ML allowance and the Ag lots can’t trade water, so I expect an Ag lot surplus here each year. This year we spent considerable funds on re-doing all of the irrigation in the Vineyard, converting the old irrigation pipe to new 19mm poly throughout, with a single 8Lt/Hr dripper on each vine. This has halved the water use at the same time as providing a much more direct water to vine outcome, which enables a deep irrigation to each vine on a fortnightly basis from January to February. While the vineyard is 8Ha, we only water the young vines from December to March, and the old Cabernet vines are only watered a couple of times during January/February.

Public Open Space

The public open space (POS), which was handed over to the Shire in early January is currently using too much water. I have spoken to their manager of POS about this and they are going to start reducing water from next season which will be easy to achieve as the trees and native plantings are now established.

Community Avocado Orchard

The avocado orchard will ultimately only receive recycled water from our wastewater treatment plant. This season around half of the water provided to the avocado orchard has come from recycled wastewater, around 30% from the wastewater dam, and 20% from the Ecovillage dams. This will be the last season that we need to supply Ecovillage dam water to the avocados.

Monitoring of our Ecovillage wide water use forms just a small part of the sustainability monitoring that we hope to conduct and share as we settle into life in the Ecovillage. We developed our annual water budgets with the worst type of season in mind, like the one we’ve just had, and it is so encouraging to see that the Ecovillage is tracking very well, even after the driest consecutive seven months on record! However, we all love swimming in our dams over summer as well, so our monitoring confirms for us that best practice irrigation/efficiency and nutrient management are the name of the game, and more mulch, mulch, mulch!