RainAmp S1 in growing in Las Vegas Desert?

Question From Laura on Facebook Group Gardening Tips, Ideas & Resources

I don’t think it rains enough to capture enough water to last…in Vegas, anyways. I guess you could add water to the barrels. I like the idea of monitoring the moisture in the soil. I wouldn’t want cement. The rock mulching layer is fine to get water down into the soil but the heat will evaporate it from the dirt also and rocks absorb and hold heat. Maybe this would work on high desert areas.

I have used the similar small system for my house plants. I used aquarium sand for my top layer. It sinks in fast and adds a layer over the soil to help it stay moistened.

Response:

RainAmp is great for the high desert but Ideal for Low Desert

RainAmp does indeed work very well in the high desert and on islands with eroded freshwater lenses but it was designed or the low desert’s where we have long growing seasons. The problem with low deserts is they have increasingly scarce water and government regulators are being forced to further restrict pumping ground water. In many low desert locations local cities are placing sever restrictions on using what water they have available for gardening or landscaping. So how do you grow food producing trees and bushes when you don’t have legal access to irrigation water to support those plants? RainAmp is designed to solve these problems. Even in the most harsh deserts the size of the bio-sponge, capture bowls and water storage can be adapted to allowed continued agriculture when the only other option is to let the land sit idle. It is true that RainAmp can be cheaper and easier to install in areas with more rain since the bowls and storage can be smaller the huge benefit comes from areas with long growing seasons but these are also often areas where lack of water prevents or will soon prevent agriculture. When you drive out of deserts like those that surround Las Vegas you see a lot of Baren land. and RainAmp can help convert at least some of this land to productive agriculture. For home owners who are forbidden by local watering laws from planting landscaping RainAmp can increase your options for what can be grown on your land.

RainAmp is ideal for Las Vegas but there are caveats

RainAmp is better for areas where delivering the water on a regular basis would be too difficult or expensive. RainAmp is also ideal for areas where you do not have legal access to water or you do not have wells installed or where you can not legally pump enough water. In our area we are restricted to pumping only enough water for 1/4 acre or less of water but we wanted to grow several acres of food producing trees and bushes. RainAmp allows us to stay within the legal limits and still grow the trees we wanted. This kind of condition is where we designed RainAmp to be used. RainAmp is also great in locations where it is too difficult or expensive to drag out a hose or deliver water via tanker which means that growing property perimeter wind break trees is an ideal use

Is there Enough Rain in Las Vegas:

Well it kind of depends. I personally have been to Las Vegas several times when enough water fell from one storm that there was water everywhere, filling areas under overpasses, flooding roads, causing flash floods, etc. That means that while the total rainfall of 5″ is relatively low the way it arrives tends to favor large bio-sponges and large storage capacity.

A 7′ by 7′ RainAmp bowl with 1/4″ of rain will yield 2304 cubic inches of water. If we use a 14″ wide by 27″ deep bio sponge that area and we expect to saturate the soil at 35% holding capacity (since it has been heavily augmented with bio-matter) it will require 1323 cubic inches of water to fully saturate the bio-sponge. That means a 1/4″ of runoff provides 1.7 times the water we need to fully saturate our bio-sponge. Is this enough, it depends on the plant. You can increase the size of the bio-sponge and increase the size of the capture bowl and it will work for many plants.

The RainAmp core design maximizes water capture from what rain does fall. The 5″ annual rainfall in Las Vegas with rain with a 7′ X 7′ capture bowl will yield a total of 26,460 cubic inches or of run off or 114.5 gallons of water for the plant in the center. This would allow the system to drip feed an average of 0.31 gallons per day which is more than adequate for many plants but would probably not be adequate for a huge willow tree. If you increase the capture bowl size to 10′ X 10′ the water capture rises to 311 gallons which is enough to drip feed 1 gallon per day. The size of the capture bowl and the size of storage can be customized to meet local needs. The RainAmp S1 system only drip feeds the water based on target soil moisture levels so during the winter it may only deliver 0.05 gallons per day while in the summer it may need to deliver 1 gallon per day.

Benefits of Concrete Bowls

The goal with RainAmp capture bowls is to deliver as much water as possible to the central area where it can be used to re-hydrate the bio-sponge and where we can capture any excess so we can use it to drip feed the tree latter. To deliver this capability then any mostly impermeable surface will work with the most common being rocks, plastic, clay and concrete. Remember that we don’t water soaking to the main bowl area because it evaporates quickly from surface soil and is lost. We want maximum water delivered to the central area where it can be absorbed into deeper soil where less is lost to evaporation. We don’t really care what you use for the impermeable surface but if you do use plastic then you should cover it with something that protects it from the sun. Plastic that is protected from sun exposure will last 20 years or more but if you leave it exposed to the sun it may age out in just a few years. Since we want to be eco-sensitive lets make our plastic last as long as possible.

We form the concrete from local soil and simple Portland cement. We only use about 1/6th of a 60 pound bag of cement to form the bowl which is less expensive than 6 mil plastic.

The white colored cement when mixed with local soil is lighter in color than surrounding soil so it reflects more light away before it can be converted to sensible heat. In areas with extreme heat it is better to reflect the energy way and back into the sky than it is to convert to heat.
Reflects for solar energy back into the sky using black body radiant cooling which keeps the sensible heat near the plant lower.
Light reflected from surface can actually be used by the plant. Most of the reflected light goes back to the sky but some of it will hit the plants where it can be used for photosynthesis. Since we have ensure the plant has adequate water it can actually use that energy. In contrast light hitting native soil and getting converted to sensible heat ends up heating the air which the plant can not use at least during summer conditions.
Sheds much of absorbed solar heat back to the sky. It is shaped so it generally is not at a 90 degree angle to the sun which means it normally has a clear view of the sky which allows us to use radiant chilling to direct a portion of the solar energy absorbed back to space. During the spring in the high desert this can be undesirable as it can delay blooming but during the summer it can help keep soil temperatures lower.
It helps radically reduce evaporation losses to the soil. We mix the cement with local sandy soil using a high water mix so our concrete mix is slightly breathable and slightly porous so we do loose a small amount of water via evaporation and the surface absorbs a very small amount before producing runoff but It still delivers allows far less evaporation than native soils with saturated surfaces while still out performing plastic that has wrinkles which ours always seems to have at least a few.
Avoid the use of plastic for forming the impermeable bowl skin.
When formed from local soil it is less expensive than 6 mil plastic
It is easy to avoid wrinkles which helps water flow down into the central area quicker. This is important in areas where they may only get 1/10″ of rain from any single storm.
It doesn’t absorb much water so it delivers maximum water to the central area where we want it.
It is easy to shape like a sculpture with simple tools like a hand shovel so it can be worked into semi-art shapes.
When it breaks down or needs to be replaced it is easy to break up and use to cover over bowls
Easier than gathering racks to cover plastic which must be done to extend life of the plastic sheet.
Easy to repair. These are not structural elements so the bowls are 1 to 2 inches thick when we get cracks it is easy to roughen the surface and repair.
It never blows away, never shreds and seldom degrades due to sun exposure.

Don’t the rocks absorb and Hold Heat

It depends on the rock but all high mass material will absorb and hold heat but there are a lot of variables. Very white rocks perform a lot like our white colored concrete which helps reflect solar energy away before it is absorbed. Since most of the solar energy absorbed into the rocks is eventually converted to sensible heat and shed to the local air it means that light colored rocks will produce less heating. The rocks nicely randomize the light reflected but that means more of that light will end up hitting other rocks and being absorbed. The rocks when properly shaped can provide a low surface areas in contact with the ground and a higher surface area with air exposure which maximizes convective heat exchange especially when sized from 2-fist to head size. Since we know that warmer air will always rise and create a convective plume this can be a way to remove heat from the area while keeping the soil beneath the rocks cooler. Darker rocks, smaller rocks and sand do not perform as well in this regard. We use a lot of rocks over plastic sheeting because they are cheap and if we cover the sheet with at least 3 layers of rocks then the plastic life can exceed 20 years. Under very harsh summer conditions the rocks will generally under perform compared sculpted concrete:

Sculpted Concrete maximizes reflection of solar energy back to the sky before it can be absorbed and converted to sensible heat. Rocks are more likely to reflect light into other objects where it is absorbed and converted to sensible heat.
Sculpted Concrete sheds more heat to the sky via blackbody radiant chilling keeping a lower sensible heat load. The randomized surface of racks means heat they radiate tends to hit other local objects and get absorbed so less heat is shed to the sky.
Sculpted Concrete delivers more water from small rainstorms to the center where in plastic a little bit gets caught in wrinkles.

Aquarium sand is a good idea

It is a bit expensive but it allow rapid infiltration and helps protect the surface soil from air exposure which should slow down evaporation. Just like a bunch of mini rocks but easier to apply. The downside is that a portion of the water that falls will end up trapped in the sand and be lost to evaporation more quickly. It may be better to use a plastic under layer for the bowl with the opening in the center then cover the plastic with the sand. That way any water that falls will go towards the central root mass and soak into the ground bio-sponge in the center. Remember out goal is to take what may only be a 1/10″ of rain and concentrate it where it can provide sustaining hydration for a much longer period between storms. Net, Net the Aquarium sand could be a great solution for larger storms that produce more runoff but may reduce the amount of water delivered to the core bio-sponge for storms that drop less rain.

Manually Adding Water to Barrells:

That is a good idea. RainAmp with the capture bowls and S1 system will probably mean that you seldom need to add water to the barrels but it is always nice to have options. One thing you may consider is that if you already have a hose and it is not too difficult to drag it out to fill the barrel then just uses just use the barrel plus drip feed. We do this with some plants we installed before we had the RainAmp system and it works OK. .

Nevada Legal Caveat:

Nevada has some strict rain capture laws. Those lows clearly limit rooftop rain capture to only 1 drum of water. We are pretty sure it is legal to use the RainAmp bowls and bio-sponge. It is less clear if it is legal to capture excess water from the bowl to pump to storage for latter use drip feeding the tree. We are pretty sure it is OK if you only have 1 drum of water but for parcels like ours we could have 100 drums buried near the trees which is where Nevada residents should check with legal experts to ensure they don’t violate local law. If you find that storing the water is not legal at your location then we suggest that you increase the size of your bio sponge and use bio-matter that can absorb a lot of water. This means the central root mass area you can hold at least 4 times more water compared to native sand soils which your trees can leverage between storms. In this instance you do not need our S1 system but feel free to use the rest of the system design. We are not legal experts so please talk to people who understand your local laws and regulations before installing RainAmp.