Phoenix ASH & Regrowth

For the last several months, I have been hinting at this grand project I have been working on. I have felt it more important thus far to lay the foundation to talk about some of the concepts being implemented onsite. But I think I am in pretty good shape right now in terms of concepts being out there, and before I jump into my next series of posts, I wanted to take a moment to talk about the project I am currently working on.

The site is called Phoenix ASH & Regrowth. It is a half acre site in the Sunnyslope area a little north of downtown Phoenix. The project is an attempt to achieve as high a level of self-sufficiency as possible while simultaneously repairing the ecosystem onsite. The project site will also serve as a demonstration site to help promote these ideas and make significant improvements on a wide variety of fronts including food production, nutrition, flood prevention, urban heat island effect, air pollution, economic resiliency, erosion control, biodiversity, and much more. To achieve this, nearly everything we do onsite is to achieve one of  two goals: 1) Restore soil carbon, and 2) Promote biodiversity. While this may sound a little overly simplistic, these two things, when working in conjunction, cause a cascade of healthy biological functions that achieve everything else.

Let me take a moment to describe how this cascade works. Increasing the amount of carbon in the soil does two things primarily. The first is that it increases absorption of rainwater. This increases biological activity and helps mitigate flooding. The second is that it increases the fertility of the soil. As I have explained previously, carbon in the soil feeds the soil biome and increases the fertility of the soil and the availability of nutrients in the soil. By increasing the available moisture in the soil and fertility of the soil, plant growth is encouraged. Remember, as a gardener, my job is not to take care of the plants. My job is to take care of the soil and the soil takes care of the plants.

Once we have widespread growth of plants, we move to the next level. As I have already mentioned, the driver of ecosystem processes is the cycling of living matter from one organism to the next. This is where diversity comes in. Different organisms make use of different food sources and bring different benefits to the system. Rather than trying to dig through the science of biological systems, most of which doesn’t really exist yet (don’t even get me started on the faults with reductionist thinking employed by modern science), it is best to let the ecosystem find its own healthy equilibrium. We do that by including everything in the whole. There really are no weeds. The only caveat is that they must provide more benefit than they detract. So a pine tree was removed from the site because all it provided was shade. Oleanders were removed because they are highly toxic. And there are a couple of weeds we remove because of toxicity. Otherwise, everything is welcome.

Once the plants are growing, each one is valued for the benefits it brings. Edibles are harvested for human consumption. Grass and forbs are used for forage for the animals. Dead leaves and grass are harvested for compost. Trees are pollarded to provide wood to build more soil. At each level, the plant material runs through its cycle and is returned to the soil, increasing soil carbon and helping plant growth and diversity.

So let me talk for a moment about the various methods we employ onsite to achieve all of this:

Holistic Management

Holistic Management, as taught by the Savory Institute, is more of a guiding principle. Everything we do is viewed through the lens of Holistic Management and its principles. It is through Holistic Management that we can make the best decisions for how to weave the myriad methods together into one cohesive structure. The site also serves as the Arizona Savory Hub (ASH) and the first urban demonstration site for the Savory Institute. We are very excited to demonstrate that Holistic Range Management, which is typically managed on large tracts of land in rural areas, can be applied in an urban setting.

Permaculture

Permaculture is another guiding principle. The permaculture core principles are also core values and guide what we do and how we rebuild a complete ecosystem onsite.

Animal Impact

Animal Impact, as described in Holistic Management is an important part of how nutrients are cycled through plants and back into soil. Right now, we just have chickens and are using them to process forage and create compost. However, long term plans include goats and sheep, and maybe even miniature cows or rabbits. Each animal will have its own impact on the ecosystem, improving diversity and nutrient cycling.

Organic Gardening

Organic gardening, in its ideal form, builds soil carbon, reducing the need for synthetic fertilizers, pesticides, and herbicides. By not using chemistry to manage a biological system, the biological system is allowed to flourish, encouraging diversity and growing topsoil. Everything we do onsite at Phoenix ASH & Regrowth is organic.

Composting

While some of the organic matter is either processed in place (as in animal impact) or allowed to lie where it falls, much of the organic matter produced onsite is processed through the composting facility onsite. This turns decaying organic matter into high quality topsoil more rapidly so it can be spread back out where it is needed most. In addition, we use the chickens (Animal Impact) to process the compost. This allows the chickens to feed off of whatever they deem edible in the compost, including insects that are attracted to the rotting material. It also allows their droppings to be immediately incorporated into the compost. This helps the compost get hot and complete its cycle quickly. And when it is time for the compost to be turned? The chickens help with that, too.

Rainwater Harvesting

At just 9” of rain a year, Phoenix is a desert. But with careful planning and a little infrastructure, the rain can be stretched really far. To do, this, we use two primary strategies at Phoenix ASH & Regrowth. The first is rainwater barrels. There are two rainwater barrels on each of the three buildings onsite. The two smaller buildings have smaller, flattened barrels that sit up against the building. These each hold a little over 500 gallons. On the largest building, there are two larger barrels, each holding about 2600 gallons. The smaller tanks are perhaps a little undersized for the areas they catch, and the larger tanks are a bit oversized. However, with a little planning and some plumbing, we are able to drain the smaller tanks into the larger as they fill up, assuring that no rain is lost. This water is used to water the gardens.

The second type of rainwater harvesting comes from offsite flow, or water that is flowing onto the property. The property has a wash flowing through it. While this was a major problem for previous owners, it is seen as an advantage at Phoenix ASH & Regrowth. With a little regrading, the site was turned into a series of retention basins. As each retention basin fills, it overtops into the basin below it. By doing this, all, or nearly all, of the offsite flow can be captured and stored in the ground. This has the added benefit of reducing downstream flooding. The best part is that the first basins built are already growing lots of vegetation and thus building soil carbon. The change in water infiltration is already visible, with no water standing in these basins a mere 24 hours after a big rain. The newer basins, which haven’t had much of a chance to grow vegetation yet, take 3 or 4 days to drain, even though they get less water.

Nitrogen Producing Trees

In desert ecosystems, and in particular degraded desert ecosystems, there is often a lack of nitrogen in the soil. This can be a limiting factor for the growth of plants and thus the ecosystem as a whole. Nitrogen producing trees, such as palo verde, acacia, and mesquite can make a big difference in this area. Not only do they fix nitrogen from the air and make it into a usable form, but many are well adapted to dry climates with poor soil. They are drought tolerant and fast growing.

Pollarding/Coppicing

As the trees grow, they produce a great amount of biomass. Every two years, the trees at Phoenix ASH & Regrowth are pollarded, and a few select trees are coppiced. The branches and twigs that are cut off are used for a variety of purposes. They are used as feedstock for growing mushrooms, some are used to produce biochar. The bulk are chipped to either produce mulch for various areas around the site or as a bulk carbon source in the compost bins. The biomass produced by pollarding and coppicing becomes a large portion of the biomass we use to feed the soil.

In addition, trees typically have a root structure that mimics the size and extent of the canopy above. When the tree is trimmed back, the tree abandons roots and pulls back, adding as much carbon down in the soil as is harvested from above.

Hugelkultur

Some of the branches that are either trimmed out or are the result of random pruning throughout the year are used to create new garden beds. This use of hugelkultur adds a long-lasting source of carbon to the soil and provides a lasting source of food for the soil biome where it is needed most.

Biochar

Woody debris that is too big for the chipper, unusable for mushroom feedstock, or otherwise scrap material is processed into biochar. The biochar is added to the compost. Once there, it collects nutrients through the processing process. Then it is added to the soil with the rest of the compost where it is used to improve soil quality in perpetuity.

Mycoculture/Mycoremediation

Growing mushrooms is difficult in the desert, but it can be managed. Mushrooms are used in the intermediary process between wood chips and soil creation and provide an additional product. We are also working to find ways to use mushrooms to improve degraded areas of the site. This is a technology that has a lot of potential and we are working on finding a way around the challenges to best make it work.

Aquaponics

Phoenix ASH & Rebirth is located in a very brittle environment and the bulk of the site is being managed with this in mind. However, many of our common vegetables require quite a bit more water, thus necessitating a non-brittle microclimate. In this interest, we are looking for technologies that help use the water resources available onsite to their maximum utility. Aquaponics has some great potential in this respect, being particularly efficient with both water and nutrients. However, as a soil-less technology, it doesn’t fit as well with the goals of the site. We are exploring other options to improve the technology to be more organic.

As you can see, we have a whole lot going on for just a half acre. But combined, these techniques work closely together to make some significant changes in a degraded environment. Please help me in spreading the word. If we can turn a half acre in downtown Phoenix into a productive food forest and organic farm, it can be done anywhere. We just have to have a way to get these concepts out there and teach people to implement them. This world is fixable, and it can be done using the techniques provided to us by nature. Let’s get on this.

Rainwater Harvesting

Last week I had the pleasure of attending a talk by Brad Lancaster, a rainwater harvesting expert. Brad has a background in permaculture, which is the practice of designing human systems to mimic natural systems with the goal of increasing efficiency, with the ultimate goal of making our practices fully sustainable. Brad, who also has a blog, makes the point that we, as a society, are pretty thoroughly water-phobic and do our best to shed water away from our structures and properties as quickly as possible. He encourages us to treat water as a precious resource and harvest it with our landscapes. By doing this himself, he was able to transform his own lot in Tucson, Arizona, USA from a dry, dead landscape with a few of the toughest desert plants to an urban oasis with lush vegetation and abundant fruit, all with little or no additional water. He did this by collecting as much water as he could, mostly by grading the dirt to retain water and by covering the dirt with organic material, which helps the dirt act like a sponge, soaking up rainwater. He also collected rainwater from his roof and the street* in front of his house. All of this means that the runoff from his property is very minimal, as is the water he uses from his tap to water his plants.

As a civil engineer, I think his observation that we are water-phobic is a little extreme, but not too far off base. As engineers, we sometimes get sued over our designs. 90% of the lawsuits against civil engineers are because of drainage or traffic. Water can be very damaging and must be handled carefully. However, our caution of the damage it can do locally has created other, wider problems, opening the door to more damage by water. In a natural system, dirt absorbs water and ground cover, like plants, slow down the flow of water. During rainstorms in natural environment, the water levels in creeks and streams rise slowly to a peak flow and then subside back to normal flow. In urbanized areas, surfaces don’t absorb and are designed to get water out of the way as quickly as possible. That means that for the same amount of rainfall, more water runs off and it runs off more quickly. So the flood stage in the local streams occurs quicker than with a natural system and the water level is higher. Municipalities have begun trying to alleviate this problem with detention and retention basins (detention basins detain water while retention basins retain water). By collecting and slowing the water, we can help to restore the water to a more natural runoff rate. However, I believe that Brad’s way is better yet. By treating water as a resource, he takes extra steps to allow the water to seep into the ground, replenishing aquifers and decreasing our reliance on irrigation. It also increases plant cover, especially for arid climates, which improves our air quality.

So I really agree with Brad, and as an engineer, I think we can do better. But a lot of times we have to convince others. I can help a little with that. When faced with an intractable city engineer, put it in terms they can understand. Tell them that you are exceeding the requirements for retention on your site.

For more information, I highly recommend Brad’s two books: Rainwater Harvesting for Drylands (Vol. 1): Guiding Principles to Welcome Rain into Your Life And Landscape and Rainwater Harvesting for Drylands and Beyond (Vol. 2): Water-Harvesting Earthworks

* As a civil engineer, collecting water from the street makes me a bit nervous, for two reasons. The first is that the curbs and ditches in front of your house usually belong to the city and modifying them can get you in trouble. Secondly, a street is an engineered system. Just cutting holes in the curbs modifies the engineering. It would be like cracking open your computer and soldering on a few more wires. 90% of the time it would be fine, but the other 10% of the time you are potentially opening yourself up for flooding or other problems. Talk to your local city or county engineer before attempting this. Again, use arguments that explain how you will be increasing retention.

The Rational Method

Okay, let’s say that my method for calculating average monthly rainfall in my previous post just isn’t good enough for you. You are too detail-oriented for that little amount of information to be satisfying. You want to know how to calculate how much rain you are getting in a particular storm. Well, this post is for you. For the rest of you who came here looking for some interesting gardening information: may I show you to another lovely post? Just keep it in mind as a reference. At any rate, I’ll have another post up shortly. It is gonna get pretty math-y pretty quickly here.

The Rational Method is an old method that civil engineers use to determine how much water a particular storm even is going to deliver. So, if you are designing a culvert to carry the water from a 100 year storm, this one will do it. As technology and science have improved our accuracy for calculating runoff, the Rational Method hasn’t really gotten left behind. It is still considered pretty accurate up to about 600 acres or so and is often used as a check when more complex methods are used.

The beauty of the Rational Method is its simplicity. Here it is:

Q=CiA

Where:
Q is the runoff in cubic feet per second (cfs)
C is the runoff coefficient
i is the rainfall intensity in inches/hour, and
A is the drainage basin area in acres

Starting with the easier ones, A is pretty easy to calculate. The only tricky part is measuring it. If you have a small area, you might be able to get it with a measuring tape or similar measuring device. If you have a larger drainage area, you might need to go to the USGS and find yourself a topo map of your area. Remember: water always flows perpendicular to the contour lines, so trace perpendicular to the contour lines until you can find the ridgeline. Then measure off and calculate your area. It is easiest for this sort of thing, unless you happen to have a planimeter, to just break it up into simple geometric shapes and calculate the areas individually. Then convert by the scale factor of the drawing and then convert to acres.

Your value for C is going to be based on observation. Take a look at the area that you are draining from. C gives you the percentage of water that is actually draining off. So impervious surfaces will give you a higher C value than a soft, fluffy forest floor. Here are some sample C values:

Paved areas, roof areas, impermeable areas: 0.95
Bare ground: 0.25
Lawn area: 0.20
Suburban areas: 0.35
Steep terrain: 0.70

The value for i is the tricky one. Basically, shorter storms tend to be more intense. However, when a drop of rain falls on the farthest reaches of your drainage basin, it takes a certain amount of time to reach your concentration point. If it takes 30 minutes for your raindrop to reach your concentration point and you calculate for the 10 minute storm, the storm will be over before the entire area is contributing to the runoff at the same time. However, for most areas that a homeowner would be dealing with, i.e. under a few acres, 10 minutes is a reasonable assumption, so use the 10 minute storm. To actually get the values for your area (in the United States), go to the NOAA site and get an intensity-duration-frequency chart for your area and use the column for a 10 minute storm. Just make sure that the final number you plug into the Rational Method is in inches/hour. If not, be sure to convert it beforehand.

Then you just plug the numbers in and calculate your flow. You can use that to tell you how quickly your basin will fill up in a particular storm, or multiply by the length of your storm to figure how much rain you will get.

I will offer one caution, though. A lot of what is involved in accurately determining the numbers to plug into the formula relies on expertise. If you don’t have the expertise, it is called guessing. If you really need this calculated accurately, which you will if you have flooding issues, or you are building it near your or anyone else’s building, or if you have a large drainage area near your house, to name a few, you should really have this calculation done professionally by a civil engineer.

To say it another way: The calculation above is for entertainment purposes only and should not be attempted by non-professionals for any purpose other than idle curiosity.

Collecting Rainwater Through Grading

Grading is the process of moving and shaping dirt. It is usually done for aesthetics, but it can certainly be used to catch rainwater. The concept is actually pretty simple: You shape the earth so that runoff is captured and held in place by a berm long enough that it will soak in. This method works particularly well on a hillside. You can create a system of berms in a sort of fish scale pattern down the hill. Each area collects a certain amount of water and then spills over to the next basin below.

The methodology is actually pretty simple. The first and most important step is to observe your particular situation. Walk around and look at the grades. If you are on the top of a hill, this won't work as there is nowhere for water to come from. If you are in the middle of a large drainageway, it probably won't work as well because the large volume of water will wash away your berms or flood your plantings. It is particularly helpful to walk around during a rain. Sometimes visually inspecting slopes can be tricky, but flowing water never lies. Look for places where water collects, how far it comes from, and what sort of surface is picking up water. If you have a large area draining to your basin, it may affect how big you make it. Also beware of picking up water off of parking lots or other possible sources of pollution.

The next step is to build a berm (which is a mound of earth) in a line on the downhill side of your basin. This will hold the water in. Remember that water will always find its level, so the top of the berm needs to be level all the way around. If you mound it up on the downhill side and leave it low on the sides, the water will just flow around your berm.

There are also a few construction methods to use when building your berm. First of all, be sure to leave a low spot in your berm where you want the excess water to overflow and make sure that you protect that with some rock. You might be surprised how fast moving water can remove dirt. Secondly, you will want some degree of compaction in your dirt. Walking on the berm as you build it up works pretty well. Mechanical compactors work better. The compaction does several things for your berm. It reduces pores and keeps the water from flowing through your berm, it protects your berm from erosion and failure, and it ensures that as your berm compacts naturally over time, it maintains the elevation you built it at.

Now for the big question: how do you determine how tall to build your berm? Well, first we'll state the obvious. Your berm can't be taller than the spot where water is entering your basin, or the water will never get in. Other than that, the trick is to balance two factors: how much water you are getting, and how fast it will soak in. If you provide too little storage, it won't soak in before it runs off. If you provide too much storage, it will drown your plants.

To determine how much water you are getting, you will need to do a quick calculation. The hard part will be determining how big of an area is draining to your bed. Again, this comes down to observation. Do your best to determine the square footage of the area (A) draining to your basin. Rough numbers will do as this is far from an exact calculation, though better numbers are, well, better. Measuring is better than eyeballing. Next, look up your local monthly rainfall averages (R). The weather channel is a good place to look for this information. You will probably going to want to do this for each month as it will help you fill out your water budget. The last number you need is the runoff coefficient (C). This number explains how much of the water that fell from the sky actually ran off as opposed to what soaked in. Here are a couple of sample numbers:

Paved areas, roof areas, impermeable areas: 0.95

Bare ground: 0.25

Lawn area: 0.20

Suburban areas: 0.35

Steep terrain: 0.70

Obviously there are a lot more numbers to this table, but I don't want to overwhelm you. For more information, look up C values for use in the Rational Method.

Next you will calculate how much water (W) you are getting. To determine how much water you are getting in an average month, multiply the amount of rain that falls in that month (R) with the area it is running off of (A) and the runoff coefficient (C), or

W=R*A*C

Now take this number and divide it by the area of your basin. This will give you how many inches of water you are collecting in your basin for that month. Compare that with the numbers from your water budget.

To determine how quickly your water absorbs into the soil, you need to know a little about your soil. The bigger the particle size, the quicker it will absorb. Water flows through sand very quickly, while it flows through clay very slowly. The best way to test this is to do a perc (short for percolation) test. A basic perc test can be done pretty easily. Dig a hole at least 1' deep and as big around as you care to dig. Fill it with water and let it drain. Then fill it again and time how long it takes to drain. If it drains within a few minutes, you can make your basin as big as you want. If it takes a few hours, the basin should probably be a foot or two deep. If it takes over 24 hours, make a shallow basin, say 6" to a foot deep, unless you live in an arid environment.

Now for the tricky part: adjusting your system. Unless you hire an engineer to really calculate this exactly, or you are particularly good at this sort of calculation yourself, it is going to be difficult to size it exactly just by doing the math. Let's just say that I left out a lot of details to simplify the calculation. The fine tuning can be done pretty easily in the field. As I mentioned previously, you will want an overflow in your berm. By adjusting this overflow up or down, you can adjust how much water your basin will collect. If it is too soggy, lower your overflow. If it is too dry and too much water is running off, raise the overflow and/or the entire berm.

Finally, a little disclaimer: Always check with your local municipality before doing something like this. Different areas have different laws regulating this sort of activity. Also remember never to change the direction that water flows across your property. The place where water enters your property and leaves your property must remain unchanged throughout this process, or you may open yourself up to liability. Good luck!