Summary: When it comes down to large scale restoration with native tree species, water availability is truly a key impediment. Without it, tree mortality is huge, and if you have it, the cost of deploying it to individual trees is commonly prohibited given the scale desire.
RainCatcher is one idea being developed to overcome the massive tree mortality we have when planting trees with volunteers. One can easily capitalize on the manpower of volunteers to plant trees, but the needed irrigation after planting remains a critical limitation to unleash the planting potential of people at large.
Lets start with the "Collect" side of the problem. The amount of water that you can collect at any give place is in principle a function of the amount of rainfall and the area over which you collect the rainwater. Using the
rainwater catchment calculator, I estimated that for some of the driest of places in Hawaii, one need to collect rainwater over a 10 square feed area to ensure at least 2 litters of water a week.
While effective at fulfilling the technical requirements of rainwater irrigation, the problem of version 3 was the cost.
For this version, I used a custom made join to ensure one could create an inclination in the canopy as to allow water to be funneled into the reservoir.
Each of these joins cost $25cents, and we needed four of them. So this part alone was one dollar. Add the cost of the PVC pipes (another $2.5 dollar) plus the cost of the actual catchment bag ($5), and the price tag for this version was already $8.5 dollars.
The solution to this problem was to use a reinforcement with a stronger material in each corner.
In order to reduce cost of version 3, I replace the four way join for a readily available 5-way join (it costs only $20 cents in Amazon).
And rather than having four bars to keep the tent up, I used only one pipe in the middle. These design changes reduced cost of PVC pipe to just $1 and the cost of the joins to $20 cents as we only needs one join.
The result is RainCatcher version #4:
It cost $4.5 dollars. The materials have UV light protection and it should last under the elements for up to 15 years.
This version above requires minimum assembly, provides a benefit for weed control and the canopy is designed to collect dew water. Basically, this version will collect water even if it does not rain. The idea here is that the water tank could create enough temperature differential, for water in the air to condense on the canopy of the tank. The gridded structure will allow for the condensed water to precipitate and be funneled to the tank. I explored the mass production of this version with different suppliers and the best we came out with was $18 per unit using Thermoforming. So, this version is technically pretty nice, but unfeasibly economically. I even modified it such that it can be re-used making the cost per tree lower, but even then, it was not economically viable.
The version above requires no assembly at all. Just put it by your seedling and done. This will be very convenient to work with volunteers. The problem again was cost. We reviewed the design with several manufacturers and the best we got was $30 per unit using a technique called Rotomolding.
It turns out that one can make a part much cheaper using injection Molding. But the bigger the part, the bigger the mold and the bigger the price tag. So, in the design above, I broke RainCatcher into two components: one is the tank, which does not need to be too big and the canopy, which needs to be broad to collect water over large of an area. The water tank came be done with injection molding at $6 each and the canopy can be made of plastic carton at $70 cents per unit. The price of the mold is $30,000, auch…. This version will also require some assembly.
This version above is the most promising one. It can be put around the tree to control weeds, it has large of an area to collect water and the tank can store up to 50 litters. It is basically, a kid’s inflatable pool with a canopy. It will cost only $1.5 per unit. More on this soon.