Excavation: Trials and tribulations
After starting the actual excavation process, an underground creek bed was found to be the reason for the massive amount of water seeping through the ground; therefore, to prevent any future issues, the higher filtration pond was divided from the lower swim zone to stabilize the area. This was done using Type 1 concrete masonry units (CMUs) to avoid erosion and withstand any ground movement with the water flow. The design also included an underwater cave at the waterfall area; therefore, to support the giant rocks on top of the NSP membrane, a concrete slab was poured for stability.
After some well-organized work, within a few weeks the entire pond was excavated and ready for the thick, specialized NSP membrane to be installed, along with the protective felt for both the underside and topside of the liner. The membrane, which is sourced from Europe, arrives in 1.5-m (5-ft) wide and 23-m (75-ft) long rolls and was installed by a group of experts. Each job is unique in its design and, therefore, each liner is also created for this certain size and shape. That said, the liner is not an off-the-shelf product, but rather specifically cut and seamed for each NSP.
Skilfully installing the membrane
Within a few days, construction was ready to begin on the rock structure that was being built on top of the felt-protected membrane. Before this process can occur, however, special safety and performance quality rules are performed to ensure the liner is installed properly to eliminate the potential for any future problems from occurring.
For example, the installer on the heat gun seaming machine is not permitted to be the only person double-checking the seams; a different team member who was not involved in the seaming process checks the entire membrane for any spots that may have been missed as well as potential areas for leakage, product malfunction, or damage. Every team member is also specifically trained on how to work on top of the liner membrane to minimize any possible damage from occurring.
It seems logical for anyone working with a liner that certain precautions must be taken; however, if one has not worked on top of a membrane before, it involves some thinking outside the box as it can be a challenge. This is where job-specific training comes into place. For example, simple precautions such as making sure the bottoms of work boots do not have sharp rocks embedded in them is a simple, yet effective, way to eliminate possible punctures from taking place when a crew member is walking and/or working on top of the membrane.
Bring in the gravel and sand
After installing the protection felt, the distribution layer at the bottom of the filtration field was next on the list for installation. The design for this pond required three separate, and different, layers of a gravel and sand mixture.
Due to the property’s limited accessibility, a specialized excavator had to be used. This machine is capable of going where other excavators cannot; it can also be used on top of a membrane without causing any damage as it uses four ‘legs’ to walk into a construction site. This allows freedom of movement and agility, which was extremely important on this particular site. These legs provide several pressure points, thus spreading out the machine’s weight, while also evenly distributing the load it is carrying.
With the entire team’s hard work and determination, three layers of gravel and sand were installed within a week, and pockets for the filtration plants were created. The filtration pond was then filled slowly with water and ‘dry fitting’ started for the layout and location of the filtration plants.
Planting the seeds
The first priority was ensuring these plants were arranged properly so their roots were situated in the ideal water depth for the summer, when the pond is being used for swimming, and for the winter, when the pumps are stopped and the water level slightly decreases. The second priority was taking care during the planting process to ensure they were not only vitally functional, but also esthetically appealing.
Within 10 days, the filtration pond was complete and the plants’ roots started to settle down for future growth and development. It is of special note, in the first two years of a pond’s life, plant growth will be slower and somewhat minor, and in some cases, appear a little sparse than perhaps one would see in a mature pond; this is no different than in any landscape situation when a garden is new and freshly planted. In a filtration pond, usually by the third year, a big growth spurt can be seen, plant multiplication starts, and the foliage begins to fill-in. At this point, the maximum biological filtration capacity is typically achieved and the pond is in a situation of ideal balance.
The plant life, combined with the three layers of sand and gravel, act like a giant mechanical fine filter to purify the water, providing perfect water quality. The plant roots will provide bio filtration action and will begin to balance the phosphate (PO43−), nitrates (NO3−), and sulfate (SO42−) in the water to perform their main function, aside from being visually pleasing. To create a biologically balanced filtration pond, local underwater plants were introduced as the best form of oxygenators. Plants such as large grasses and water lilies were also used to help keep the photosynthesis to a minimum, which in turn equals less algae and sediments for the filtration pond.
