We couldn’t have asked for a more beautiful day. It had rained earlier in the week but this morning it was cool and crisp, with a bright sun coming up behind the trees. The snack table was being set, signs were going up, materials were being unloaded. There was the excitement of breaking ground in the air. As an instructor from G3, Green Gardens Group, this morning I would guide the group in the process of building a rain garden.
Getting rid of the grass
The first participants arrived: members of the Hollywood Beautification Team who joined with Water LA to assist residents with the installation of various rainwater capturing methods. (See WaterLA.Org for more info on how this project evolved). Four fellows piled out with tools in hand and energy in their step. Definitely what we were going to need for the job at hand.
At 9:00 am the residents from the neighborhood arrived – boots and gloves and hats. They had been forewarned this was a ‘hands-on’ workshop. They would learn by doing, working hard, getting dirty.
One could ask, ‘Why do we need a rain garden? How is a rain garden different than any other kind of garden?’ And, that is a very good question. As we stood in a circle and looked at the semi dead grass and lone lemon tree in a barren patch of dirt – the answer became evident.
Front yard – before
The concept is simple enough. Currently, rain falls onto a property and hits any number of surfaces – mostly impermeable. From there, the water runs off the property and into the street where is it flushed thru our flood control system – billions of gallons of water are lost this way with each rain incident. What we are doing instead is capturing the rain and keeping it on the property so that it can infiltrate into the garden and water table or be stored for future use. Looking to nature and watersheds as the inspiration and model – we began.
At the top of a natural watershed are the mountains. In our built environment it is the roof; one of the most significant impermeable surfaces on the property. To be able to capture even a portion of the water that comes off that surface would make quite a dent. For every 1” of rain on a 1,000 sf of roof, we could capture some 600 gallons of water. In an average rainy season – that is more than 6,000 gallons of water per year.
Roof for rainwater capture
In our case, the portion of roof we were working with created about 300 gallons. The next step was to figure out what to do with those 300 gallons. Left to its own device they would most likely hit the yard and flow right off. So what we needed to do was create a swale or bowl in the garden that would hold the water long enough for it to sink into the ground. Feeling like we were all back in 5th grade math class, we calculated that 300 gallons needed about 40 cubic yards to hold it (300/7.48).
Once we had the size we needed, we could get creative in both depth and dimensions: the shallower the bowl, the larger the size. Conversely, the deeper the bowl, the smaller the size. We opted for a circle that was about 6” deep x 10’ wide.
Now it was time to get to work. Over the next few hours every one did what they could, taking turns with the shovels, the rakes or their hands as we began by grubbing out the grass in the area of our rain garden. This was probably the most tedious but important thing to be done. It is quite the bow to Mother Nature to see how tenacious the grass can be and if we did not get rid of it as thoroughly as possible, it would be right back with the next rains.
Working with a bunyip
From there, we began to shape our swale. Starting with the deepest point, we expanded and graded until we had a gentle bowl. Excess soil was bermed and smoothed along the perimeter, though primarily to the sides. We wanted to be able to capture any water flowing upstream of the new garden in addition to the roof. We also added a gentle depression that would guide the water from the downspout to our new garden. At one point, I found myself sitting in the bowl, swishing that soil around, moving it, smoothing it, until it was just the right shape; my hands and arms giving me so much more control than a rake.
The last thing to build was a trench between the rain garden and the rest of the yard that would create a barrier, a literal moat, to keep the invasive grass out of our newly cleared area. When we were done, our circle had evolved into more of an oval horseshoe – quite a lovely shape for a rain garden.
The day was coming to an end, and it was time to clean up and celebrate. A few moans as folks stretched and discovered they had muscles they didn’t know about. And though not finished, we could already see the amazing transformation. I hosed down the bowl and could see how easily those droplets of water were already being absorbed into the soil. Next week we would be back, bringing in plants, mulch and irrigation to put the final touches on the garden. In no time at all, the microbes in the soil would flourish with the water, oxygen and compost. And with the winter rains just around the corner, there would be an explosion of color and life come spring.
Rain garden – after
As we stood in a circle looking at what was the foundation of our rain garden, drinking the coffee and eating the hearty pupusas – I would say the feeling was one of gratitude. Gratitude for those in the circle who had joined us, gratitude for the hostess who had opened her home and heart to us, and gratitude that we could be a part of making a difference.