Have you ever noticed how plants appear greener and brighter after a good rain? It’s not just because the dust and dirt get washed off. Rainwater is a clean, salt-free source of water that contains many beneficial ingredients for plants.
Rain can contain sulfur, potash, several other minerals and even microorganisms, all of which provide a boost to plant growth. During summer thundershowers there can even be an added bonus when lightening converts atmospheric nitrogen into a nitrogen solution for plants.
But water harvesting has another surprising benefit.
Storm drains in our urban neighborhoods can collect all kinds of pollutants during a storm event. Microscopic particles of heavy metals like zinc and copper are commonly found. There’s also oil and petroleum-based hydrocarbons, fertilizers and pesticides that wash off lawns and landscapes, and even pet excrement contributes a significant amount of bacteria to urban streams and rivers. The more water we can collect onsite to be filtered by soil and plant roots, the better.
Why Harvest Water?
• Reduces waste of a valuable resource
• Reduces pollutants to area streams and rivers by keeping water on site
• Collect water for later use on landscape plants (check local and state water ordinances)
• Stormwater contaminants can be broken down in the soil
Methods of rainwater harvesting
• Bioswales
By carefully grading a subtle channel throughout your landscape, you can direct the flow of water to a rain garden or drain. As the water runs through the landscape, it\’s filtered by plant roots and soil to remove toxins, such as from an asphalt-shingled roof. With a bioswale, the water is directed through the landscape, but may not always be reused.
• Above ground barrels
Bushman and other brands sell kits and tanks for storing rainwater above ground. You simply hook up a pipe to your downspout and connect it to the storage tank. If gravity isn\’t on your side, you may need to use a pump, which can be purchased with the tank. The water from these tanks can be used with a hose or with your drip irrigation system.
• Below ground tanks and cisterns
These heavy duty tanks are meant to be buried beneath your landscaping, so you don\’t need to have room for storage in order to successfully harvest a large quantity of rainwater. While these can be pricy to install because your landscaper will need to dig them into the ground, it\’s the least obtrusive option, and like an aboveground barrel, can be hooked up to your drip irrigation system and used with a minimum of fuss.
• Rainwater Harvesting from pathways
In the recent past, rapid growth in the urban areas has led to asphalted roads and stone slabs or pavers for footpaths. This accounts for nearly 10% of the total area of Bangalore. Consequent to this, the rainwater run-off has increased and ground water recharge has declined.
As the roads are built sloped towards the sides, rainwater falling on the road is guided to the side drains. When it rains, water flows from the apex to the sides and collects in the sidewalk area and subsequently flows to the storm water drains.
As the rainwater from the road flows into the infiltration trench, water percolates into the ground. During heavy rainfall, excess water spills over to the storm water drains. The infiltration trenches store water temporarily during rainfall and later for infiltration. These infiltration trenches may be exposed as walk ways or paved with inter-locking pavers, specially designed with gaps in between for water to flow into the infiltration trenches.
• Parks and Open Spaces
Water harvesting methods in parks and open spaces involve micro-watershed management methods that allow rainwater infiltration and percolation into the ground. The runoff has to be minimized by providing adequate number of percolation pits and dispersion trenches.
In large parks, storage of rainwater in small ponds is also possible since the ponds can be integrated with the landscape of the park. Mapping of the contours, planning for rainwater outflow in consonance with natural drainage patterns, identifying appropriate areas for percolation pits / dispersion trenches will be required.
