As many of you know, I am a PDC instructor. For the past two weeks, we've been discussing water - our greatest limited resource here in the desert - and one of three major things we have to design for very carefully (extreme heat and high evaporation are the others).
Last week I took the students through an exercise to develop a site water budget. I used my own homesite for the water budget exercise because it is a well-known permaculture site and it uses a lot of rainwater and greywater harvesting techniques already.
So what is a 'water budget'?
Water Budget = A site's rainfall + runon (from upstream) - runoff. Notice this is only "rainfall".
In the desert, we often include greywater in our water budget as well, even though the original source of the water might be municipal water. Greywater is water that is "gently used" and comes from sinks (other than kitchen sink), shower, tub and washing machine. Because it's becoming legal in AZ, I also included my kitchen sink water (dark grey water due to organic matter) in my calculations.
Once you figure out what your water budget is, you can match your vegetation to the type and amount of harvested water.
So how did I do here at Dolce Verde? Good question - I've laid it all out for you below.
Background info: Dolce Verde is my 1/6 acre property in the Central Phoenix Historic District. It has one human occupant, 2 cats and 3 hens.
Water Budget Income:
--Rainwater: (18,912 gallons of rainwater are collected on my site + 1,661 gallons from my neighbor's carport) - NO runoff = 20,572 gallons of harvested rainwater per year (all in infiltration basins).
--Greywater and Dark Grey Water: 2,080 gallons of washing machine water + 5,475 gallons shower water + 5,475 gallons kitchen sink water = 13,030 gallons of harvested greywater per year (all goes to mulched infiltration basins)
Total Income: 20,572 + 13,030 = 33,602 gallons of harvested water.
Water Budget Withdrawals for landscape use:
To calculate water usage, I've used water use numbers developed by Brad Lancaster and Watershed Management group. These numbers are calculated for 5 categories of plants:
--Very high (veggie gardens*) = 65" of water per square foot per year
*The style of veggie garden used is the most water conserving: MULCHED and SUNKEN. If you do not mulch or have raised beds, this number could be 10+ times greater!
--High = 43" of water per square foot per year
--Moderate = 30" of water per square foot per year
--Low = 16" of water per square foot per year
--Very Low = 7" of water per square foot per year (note: these are the only plants that will survive on our annual rainfall of 7.4" per year without supplemental water after their establishment phase).
--Very High Water Use = 8,914 gallons per year (and yes, I use sunken, mulched veggie beds)
--High Water Use = 9,510 gallons per year (citrus trees)
--Moderate Water Use = 36,992 gallons per year (deciduous fruit trees, Chinese elms, Vitex). I should note that the deciduous fruit trees will need less water when dormant in the winter and a much greater amount of water in the growing season
--Low Water Use = 11,290 gallons per year (Screwbean Mesquite, Pomegranates)
--Very Low Water Use = 7,364 gallons per year (Velvet Mesquite, Palo Verde, Willow Acacia)
Total Withdrawals: 8,914 + 9,510 + 36,992 + 11,290 + 7,364 = 74,070 gallons per year (!!!)
At this point, I'm thinking HOLY CR*P - I don't want to see the final numbers. But, we persevere...
Total Income: 33,602 gallons per year
Total Withdrawals: 74,070 gallons per year
Annual DEFICIT = 40,468 gallons per year!
I meet only 45% of my water needs by harvesting every drop of rainwater and greywater I can on my site. This is NOT sustainable.
Well - I set myself as an example because I wanted to illustrate to my students how important it is to have a water budget figured out BEFORE you start to plant. I didn't have one and we can all see where that got me.
I set myself as an example to illustrate some other points as well:
--Work with your greatest limiting factors first (water, heat, evaporation)
--Your limiting factors will indicate the kinds of solutions that are appropriate for your climate (sunken beds over raised beds, mulch and other anti-evaporation methods, etc.)
--Understand that in our climate, there is a particular PATTERN IN TIME - as we know, permaculture is all about patterns. This is a succession pattern and it looks like this:
Step 1: Understand clearly what the carrying capacity of your land is right now, in whatever state it's in. Could be that you lack shade, or mulch, or your are totally dependent upon flood irrigation/drip irrigation to water your land, or you have very compacted soil that doesn't absorb water, or you have mounds/raised beds instead of sunken beds.... Whatever you have right now, will determine what you do next.
Step 2: Water = Life. Permaculture is a design science based on Living Systems. Make a plan to harvest as much rain and greywater as you can on your site so you can support as many living systems as possible. Use the best technology you can to make that water stick around as long as possible. Sunken beds retain water longer. Mulch, tree canopy coverage, cover crops, dense plantings of low water use natives, all protect against evaporation. Phoenix gets 7.4 inches of rain a year. But our evaporation rate is so high, we have the capability of losing 94.5 inches of rain per year! The simple definition of a dryland is an evaporation rate that is higher than precipitation rate. For Phoenix, our evaporation rate is 8 times higher than our precipitation rate.
Step 3: Plant according to your water budget. Determine how much of your water budget you want to dedicate to high water use veggies and fruit trees. At this stage, you're probably looking at about 10-15% of your yard in veggies and high water fruit trees.
Stack functions so that you get the most bang for your water buck. I've challenged my students to find at least 3 functions for element on their site. If they can't find at least 3 functions, they need to look for a different option as one-and-done elements are not sustainable.
So, some stacking functions for harvesting rainwater in a sunken earthworks basin would be: Planting native trees in a way that they shade your house from the morning or evening sun. Mulching to conserve that water up to 10 times longer - decreasing your water bill. The mulch will provide organic matter which will encourage and protect soil life. Soil life will break down the mulch and turn it into high grade, organic matter rich, compost. For every 1% increase in organic matter, you increase your soil's ability to hold water - up to 5 gallons per square yard!
Step 4: Once you've designed in the most water harvesting features you can, once you've built in anti-evaporation strategies, once you've built the water-holding capacity of your soil, you can start adding more high water use plants. This is the succession that you can keep rolling with. Geoff Lawton demonstrates this when he builds his food forests. At first he digs swales and plants a lot of natives and mulches very heavily. Once the soil has been improved and has greater carrying capacity, he adds more fruit trees, etc.
It's a pattern over time.
And that's what I originally failed to understand.
So now I'm part of the problem. I don't like being part of the problem because that problem affects our very ability to live in Phoenix. No water = no Phoenix.
So now I'm undergoing a retrofit. I'm taking out many of my veggie gardens and any fruit trees that don't make it are not getting replaced. The west side of my house (hottest side) will be all low water or very low water natives. They will be planted in such a way that they provide passive cooling and heating. They will also build soil and attract native pollinators and be part of decreasing the Urban Heat Island effect. They'll clean the air and soil of pollution. Some of them will provide edibles.
I have to admit that this was a hard (and expensive!) lesson for me to learn. But I can't continue to deplete our water resources. I can't continue to feel good about living that far out of balance with my water budget.
And so, I redesign. For the betterment of my own property, my city and my region. Because one day, enough of us will be doing this that we will rebuild what has been degraded. The air will cool and the rivers will run and the soils will be more and more fertile. I want what used to be, to be our future.
Once upon a time, the Salt River flowed through southern Phoenix. Open canals lined with shady cottonwood trees carried water to farms. Families picnicked on the riverbank, caught fish and swam in the refreshing water. Historians believe this picture shows residents of Gold Alley picnicking near the banks of the Salt River. Gold Alley was once a middle-class Mexican American neighborhood that existed near where Phoenix's Chase Field ballpark is today. Photo cir. 1915, courtesy of Frank Barrios.
Why are you aiming for zero? I'm not sure I agree with that although I'm willing to be swayed. I'd think that water into the ground doens't disappear into an abyss. We get items from that water (fruit, shade, etc.). Now I think things that get water that have purpose are okay to have a net negative impact. For example - Citrus yeilds a lot of fruit. While that water went into the tree it came back out in the form of my families enjoyment of the fruit. There is no transportation cost lowering the total yield of water my family consumes compared to buying oranges at the store. yadda yadda yadda
Also, where do you keep graywater? Does it just spill onto the ground? That is: sink on to wash a dish and water goes into the rose bed? I simply cannot concieve how gray water would work at my house.
Brian - these are awesome questions. I wrestled with these same questions myself. This has been a long learning adventure for me.
To answer your question, I am, indeed, aiming for zero. To be clear - I don't want to exceed my rainwater + greywater budget (grey water was once municipal water). Will I get there? Probably not. But I aim to come as close as I can. It's an experiment. Like Brad Lancaster's place is an experiment in Tucson. Brad is no longer hooked to city water, sewer or electricity. And when I did a tour of his place a month ago, he comes right out an says he does not consider himself sustainable. WOW. And it has taken him 15 years and a ton of experiments to get where he is today. He showed us a ton of mistakes that he, himself made. I think I learned more from those than from what he did right.
Why am I aiming for zero? Short answer - I am probably a little nutty about water. Long answer: Because anything above zero comes from someplace else. Places like our rivers (dried up now), our ground water (decreasing at an alarming rate - average well depth in Phoenix is now something like 800 ft - parts of the desert are collapsing because of this), or even further afield like the Colorado river (now stops flowing long before it reaches the Bay of California). Phoenix is now buying the water rights of our farmers and ranchers so that we can ship that water into our cities. That doesn't bode well for our food supply or our long term sustainability.
And while water flowing into the ground doesn't flow into an abyss, in our climate, it often evaporates before it can move to a soil depth that benefits plants. That's why it's so important to water deeply and less frequently.
Like you said - growing things in your yard does come with yields and permaculture is all about getting a yield. It's way, way better than growing a lawn with the never ending mowing, overseeding, possible pesticide/fertilizer use, etc. However, permaculture is also about sustainability. I know that people don't often think of it, but just as there is a transportation cost to get food to this area, there is also a transportation cost to get water to this area - and this cost is not going to go down. In fact, Phoenix is now looking to partner with Mexico to put desalinization plants in Mexico and ship water to southern Arizona. That's going to be some REALLY expensive water.
Also, don't misunderstand me. You can certainly have a citrus tree, a veggie garden and the like. What I'm suggesting is that we think more about the following:
--limit your higher water use trees to what you can reasonably support with your water budget.
--use sunken, mulched veggie beds instead of raised beds for all the reasons above.
In other words - let us take into consideration the climate and resources we have and make the best decisions possible.
While growing food is definitely part of permaculture - it is just one element of a whole. The end game is to restore intact ecosystems that provide for the needs of a growing population. This takes time and care along the way. We can't bring about intact ecosystems by overusing our natural resources. A water budget is one way of looking at what resources are available and how much.
One of the things that you do when you figure out your water budget is to match the type of water to a use for which it is best suited. Greywater is an excellent water source for fruit trees (or any woody plant) and ornamentals. It is not appropriate for use on vegetable gardens.
Greywater is vented directly out to the landscape - never stored - it gets stinky really quickly if it's stored. It is usually vented to a mulched infiltration basin (earthworks).
I've done a couple of blogs about my water harvesting efforts here (and need to do more - pics and videos speak volumes!)
A video of my "Laundry to Landscape" installation posted on Geoff Lawton's site: http://permaculturenews.org/2014/01/14/laundry-to-landscape-urban-g...
A blog on my multi-purpose shade house which houses my outdoor shower (Brad Lancaster designed the outdoor shower and infiltration basins): http://abundantdesert.com/2013/11/13/dolce-verde-the-multi-purpose-...
Thank you for asking those questions. I don't know if I've made things more muddled or clearer. Part of why I posted here was so that I could hear people's concerns and formulate answers that could be helpful. In my experience, it's an iterative process =)
An awesome video by Brad Lancaster talking about rainwater harvesting - fun and easy to visualize! The sound is a little wonky for the first 30 seconds or so.
Jennifer, thank you for an excellent mental exercise and thought provoker. I wonder about storing the roof-rainwater in huge tanks as opposed to filtration basins and using as needed? I do understand about the concept of basis and french drains etc. but having watched our bermed yard dealing with the rain water, I am leaning towards tanks instead of just capturing on-ground. Except for our driveways every drop of rain which falls on our property stays on it. I'm just not sure that is the best use of roof run off. When I did the math for Deane on roof capture he was very surprised at just how much it was. Our primary delimma is where to put the tanks (I'm thinking 250-500+ sizes).
Thanks for the comment, Catherine. And thanks for berming your property - I love that no water flows off of it!
Tanks are great for a veggie garden that needs water on a regular schedule - this is how most of us would use tanks, I'm thinking. Obviously you can water other things with the stored water but if you have extensive veggie gardens - this is a great use for stored rainwater because annuals have high water needs.
250 to 500 gallon tanks are not all that large - they could probably fit in any number of places depending upon the layout of your property.
If you don't have a place near your roof to capture water from gutters overhead (a "dry" cistern install), you can do a "wet" cistern install farther away from your roof (the pipes to the cistern go underground and up inside the cistern).
If you want to provide for all the water for your veggie garden, size your cistern(s) to meet the needs of your garden for the longest dry period we experience. For Phoenix, the longest dry period was 160 days. How much water you can collect depends on the size of your catchment area (your roof).
So say you have 100 square ft of veggie gardens.
You will need 4052 gallons of water per year to water it. See calculation below for how I got that number.
--Veggie garden water use: _______ ft 2 x (65in/12in) x 7.48 gal/ft3 = _______ gal/yr
However, we really need to store only the amount that will get us through our longest dry period - 160 days.
--So 160 days/365 days = .44
--4052 gallons x .44 = 1783 gallons of storage.
There are a few more considerations but this is the gist of cisterns.
You could possibly get away with one 6 ft wide by 8.5 ft tall cistern (depending on the height of your roof)
Or there are other configurations such as two 4 ft wide by 8 ft tall cisterns. Other options include going wider and shorter too.
Thanks for the thoughts Jennifer. An underground cistern is not feasible. I've seen the 500 gal tanks at the gardenpool property, that's what I have visually in mind. Anyway, I will keep your ideas in mind.
And just for clarification, the "wet" install cisterns are not underground - just the piping conveying the water is underground.
Ah, obviously there are a couple of cistern options :-)
Have you been over to Dennis's place recently? The Garden Pool has been collecting additional water through condensation as long as the dew point is high enough overnight. He's got a clean roof for collection (not asphalt) and he says he gets a steady supply all winter. I have been meaning to get out there for a tour to see the improvements as it's been a while since I've seen the place and he's been busy! :) Want to come with sometime?
Here is a link for more info on what he's doing:
I've never seen Dennis's place and would love to see dew harvesting at work. I've often wondered if it would work here! Let's "dew" it! (that was so bad).