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Gardens and flooding: what can we do to help?
When rain hits the ground it has to go somewhere. If the ground is hard and impermeable it will flow away quickly. If the ground is permeable it will filter more slowly into the ground. In cities and suburbs a lot of ground is taken up with impermeable surfaces: roofs, roads, paths and car parks. In rural areas many smaller towns and villages have areas of light industrial units, garages and leisure facilities, all with big expanses of hard surfaces. When taken collectively, gardens and buildings in urban or suburban areas take up a big proportion of the land.
A pond near the house can act as a reservoir for rainwater run-off, acting as a valuable buffer for streams and rivers.
In big towns and cities, gardens and domestic parking places play a huge part in the general ecosystem. With people increasingly opting for low maintenance options, permeable ground is disappearing at an alarming rate. This means that in periods of sustained or heavy rainfall water reaches rivers and streams faster than it would have before. This leads to them reaching over capacity and bursting their banks. As many of our towns and cities are by the sea, this can combine with high tides to mean that the water has nowhere to go - except into our homes. Therefore, pushing the water off our own property quickly and efficiently isn't always the answer as the water ultimately backs up and causes more trouble. Read more...
As individuals and garden owners we can keep this is mind when choosing materials for our gardens - and indeed the roofs of our homes and outbuildings. The most efficient surfaces for absorbing and percolating water have a combination of plants, including trees, shrubs and smaller plants. This is much as nature would have things if left to its own devices, and Ireland in its natural state would be a combination of forest and scrubland. In our own gardens we manipulate this by choosing the plants we want. The second best for percolation is soil with a single crop on it such as grass or wheat, which is what most of agriculatural Ireland is comprised of. On a domestic scale, this translates into a patch of lawn and some flowerbeds punctuated by trees or shrubs. Not only is this model better for our country - it looks attractive and provides us with a pleasant environment in which to live.
As families have more cars they need more parking space. Gravel is the easiest and most economical parking surface and it is permeable to water. New developments mean that you can use a honeycomb-like grid under the gravel which keeps it firmly in place, reducing the need for raking and making it suitable for slopes. Panels of this honeycomb material are laid on the ground and gravel is brushed over it, making it invisible and keeping the gravel firmly in place. Another advantage of gravel is that it can be locally sourced. It's importanat to choose gravel correctly and to lay it to the right depth. Too deep and it can be difficult to walk in; too small and it can get caught in the grips of shoes and come into the house where it can damage floors. But chosen and laid correctly it can look very smart and function extremely well.
Another surface - and one that is rarely used in Ireland - is 'permeable paving'. This is similar to cobble-lock but includes holes or gaps filled with soil. The paviors are normally made from concrete and are laid over sand to make a very solid surface. This makes it a firm surface suitable for vehicles but also a green and permeable one. It can be mown like grass if necessary but withstand vehicular traffic. Other solutions include having strips of paving through soil, so that the car wheels park on a hard surface but the rest of the garden remains untouched.
Two parking areas in Dublin city centre: the first with strips of paving, the other with permeable paving blocks.
A green roof on your house or outbuildings acts as a small reservoir and when used in cities can drastically reduce flooding. Correctly installed, it includes a bottom layer which can fill with water. During dry spells, plant roots access this water. In wet periods, rainwater is intercepted by this 'reservoir' system, slowing down the speed at which it runs off. Green roofs have the additional benefit of providing excellent insulation, reduce heat deflection (which is important in cities) and making an ideal environment for wildlife.
Even a humble water butt attached to a downpipe can help to intercept rain from suddenly entering the system, and many houses in built up areas are now required by law to have a rainwater recycling tank installed in their gardens. With a huge capacity, these tanks can provide a household with water for baths and toilets whilst also keeping it out of stormwater systems. For anyone with space, a garden pond can act in much the same way. It can be easily connected to the house, and if the pond has a slow leak it will drain slowly in drier periods and then, when heavy rain occurs, have the ability to absorb sudden inflows. Not only is a pond useful in this regard: it can be a beautiful addition to a garden and add a new habitat for plants and animals.