So last week we were talking about planning now for future projects (read last week’s blog here), and this week World Wetland Day is here – coincidence? I think not! Wetlands, natural or engineered, have a place at the edge of EVERY body of water, man-made or otherwise. Why? Because Mother Nature has put millions of years of trial and error into creating the most efficient and beneficial filters on the planet, and we ignore Her at our peril.
Wetlands make coastal life possible. They keep sediments from burying coastal seashores in mud, absorb wave and storm energy to eliminate erosion, absorb and sequester heavy metals and toxins, turn excess nutrients into food for millions of organisms – per square foot! (Yes, I’m counting bacteria, the most important organisms on the planet. Who? Us? We’re just bags hosting untold BILLIONS of microorganisms.)
Arguably, the most important function of wetlands is their ability to clean and clear water. This attribute is easily harnessed for our own devices in engineered wetlands, often affectionately referred to as ‘veggie filters’. Originally just shallow gravel beds with plants whose roots helped pull out nitrates, these have evolved into highly efficient bioconverters with sediment traps that are incredibly efficient with little maintenance.
Completely scalable, these mini wetlands punch far above their weight. This little planted bowl filter designed by the ever-innovating Nelson Water Gardens will keep a preformed or small liner pond clear and free of algae, and it’s beautiful to boot.
On the other end of the scale, this gravel bed in Culiacan has managed to remove literally all of the suspended solids from the 80,000 gallons of opaque river water that was pumped into the Victoria Pool a couple of weeks ago – and that’s before planting!
The way these both work is remarkably similar. Sediment laden water from the bottom is pumped into a grid or chamber at the bottom of the gravel bed. The water velocity slows on its way up and out through the gravel. As any moving liquid carrying dissolved solids slows, its sediment carrying capacity drops. In the bowl, the sediments drop out and are trapped in the gravel, where roots metabolize the organics along with any dissolved nitrates, starving out any algae that would green up the water if nitrates were present.
The larger application requires a little more infrastructure, but the results are impressive. In the Victoria Pool there are two settling chambers filled with Eco-Blox water matrix blocks, one at each end, each capped by a 12” layer of gravel. Skimmers fitted with twin TT9000 pumps push about 15000 gallons of sediment-laden river water into each of the Eco-Blox chambers. As the water spreads out and slows in the chambers it drops most of its sediments; whatever remains never makes it through the gravel that caps the blocks. A 4” bottom drain in each chamber will allow the accumulated solids to be flushed out to a shallow gravel pit whenever cleaning, or collection of organics for the garden, is required or desired.
The photos show the opacity of the river water on Day One and the clarity on Day Ten.
This video taken yesterday reveals the bottom a meter below water level perfectly clearly.
Bear in mind, this wetland isn’t even operating properly yet, because there are no plants or fish. It’s just working as a sediment trap until the crew at the Botanical Garden plant it up next month, when it will really come on line and shine, just in time for the balmy 120 degree days of summer in Sinaloa. I promise to keep you posted.
About the Author:
Demi has been in water garden construction since 1986. As Atlantic’s Director of Product Information, if he’s not building water features, he’s writing or talking about them. If you have a design or construction question, he’s the one to ask.