Rainwater retention to reduce flooding
There are a number of small ways in which we as householders, and more especially those of us with gardens, can increase the amount of rainwater our domain can retains. This can reduce the risk of flooding in two ways.
- By keeping water out of, or by delaying the water entering into, the storm water drains we can help prevent them from overflowing – a common cause of flooding in urban areas.
- By increasing the water absorbency of our grounds, we can delay the time and speed with which rainwater enters local streams and/ or the water table. This will reduce the pressure on the capacity of local streams and rivers, so reducing the risk of flooding.
How can we do this?
- Install water butts. These collect water before it enters either the ground of storm water drains. If, advance of heavy rainfall, the butts are empty, then corresponding volumes of water can be held back from entering the ground or drains. Whilst one single butt may not make difference, a 1000 water butts each with a capacity of 200litres can hold back 200,000 litres – 200 cubic meters – of water. This does require some focus by the householder on rain forecasts. A less precise solution would be to leave the water butt tap half open or it to a leaky hose. Either way it is important that you ensure the empty butt is weighted down to stop it blowing over – either leave some water in the bottom or put in some bricks or out a heavy lid on top.
- The RHS suggests using rainwater from butts to wash cars and paths in the winter and plants in the summer.
- Avoid areas of bare earth. Ground that is covered with plants will slow the passage of rainwater into the water table. Rainfall will be interrupted by leaves and rainwater will absorbed by roots and by any mulch covering the ground.
- Compacted soil is less able to absorb rainwater – where the ground is regularly trafficked create a path that uses porous materials – eg gravel, bark, stepping stones.
- Ensure a range of planting so that there are always some plants covering the ground and some plants with leaves.
- Cover areas of bare earth – eg before planting begins or in the autumn after harvesting – with a mulch or with a quick growing green crop – otherwise known as green manure – such as alfalfa, clover, mustard. https://www.rhs.org.uk/soil-composts-mulches/green-manures
- Avoid hard surfaces if possible. Where a hard surface is needed (as a patio, for car parking etc) you can opt for a porous hard surface such as gravel or paving stones spaced out with gaps for drainage. You could also incorporate a soak-away to catch and collect water that runs off the area.
- If you have a pond, keep it filled up with rain water. Run a hosepipe from a water butt so that when it rains the pond benefits from rain gathered over a larger area.