Rainwater Harvesting: Ten Things Water Companies Could/Should Explain To Prevent Soil Erosion, Flooding, CSOs & Rainwater Wastage.

Without water there is no life. But as well as giving us life, water can be very destructive. Unless We Implement Rainwater Harvesting.

Your body is around 60% water. Some plants contain much more water. And we live on a planet that is more ocean than dry land. 

So how can we maintain the balance between water being essential and being subject to floods, erosion, tsunamis and more? And with heatwaves, droughts and hosepipe bans becoming more common, how can we store more water for when we need it in gardens & reservoirs and prevent it being destructive?

Though the responsibility for water storage is the responsibility of water companies, many argue that they haven’t kept up with the need to build enough reservoirs to provide water for a growing population and that leaks, from an ageing underinvested infrastructure, are leading to too much wastage. Clearly they need to do more, but what can ordinary people do to help?  

I believe water companies should be explaining the following Rainwater Harvesting techniques to gardeners and consumers.

The Excess Rainwater Problem

Gentle rains are able to percolate permeable soil and other surfaces and eventually enter the aquifers deep in the soil. However, once the soil is waterlogged, excess water flows downhill, sometimes causing erosion, until it enters drains or water courses such as streams or rivers. Some of this water flows into reservoirs, or can be pumped into more distant reservoirs, but most of it finally enters the sea. 

When rain is very heavy, and the ground is sodden, excess water can erode excessive quantities of soil from arable land and even gardens. The soil is then deposited in water courses where it ruins spawning habitat for fish and can lead to flooding. Some of the excess water also enters storm water systems that are connected to sewers and this too frequently leads to Combined Sewage Outfalls (CSOs) releasing sewage into rivers and the sea. 

Are There Plant nutrients in Rainwater? Calculate Your Rainwater Harvesting Potential
Are There Plant Nutrients in Rainwater?

Householders and gardeners can do a great deal to prevent excess rainwater from causing soil erosion, flooding drains, and causing CSO sewage dumping. To do so we need to go back to basics and look at the reasons rainwater can be so problematic.

Water Flows Downhill, Never Uphill! 

We all know that water naturally flows downhill and never uphill. Rainwater falling on a roof will run down the roof, along the gutter and down the downpipe. It’ll enter the drains and carry on flowing downhill until it reaches the sea. 

What isn’t so obvious to some people is that water doesn’t need a slope to flow. Pour a bucket of water on a flat piece of concrete and it doesn’t just sit there in a heap. It spreads out looking for any slope it can find. Even if put on the most perfectly level surface it still spreads into a very thin layer. The reason for this is because of hydrostatic pressure. You can’t stack water in a heap. It needs a container to contain it! 

There is another basic that needs considering. Water is able to soak into many surfaces, such as lawns, flower and vegetable beds etc but isn’t able to soak into impermeable surfaces such as concrete or tarmac. Again it is obvious to most people but often forgotten where we pave over gardens and drives. 

What surprises some people is that soil can sometimes be as hard for rain to soak into as concrete. In very hot weather soil surfaces can dry out to the extent that they repel water as much as concrete. Rain falling on sun backed surfaces soon runs off and away downhill. Or it fills low areas and causes flooding. 

However, when sun baked soil has gentle rain for long enough the rain slowly soaks in, often over days, and it can absorb significant amounts of rainfall without it running downhill to drains and water courses. 

Once we understand the above two basics its not hard to work out how to reduce rainwater run-off, reduce erosion and help prevent CSOs dumping sewage in our precious rivers and into the seas where wildlife, beaches and tourism can be seriously damaged. 

Slowing The Rainwater Flow

Beavers stop the flow of water by building dams. And we can copy what they do, though not necessarily by building dams in the same way as them. But simple things such as a water butt can dam the flow of rainwater and prevent it going downhill. And the great thing about it is that we can then use that water to water our plants when it is hot or dry. It’s a win-win for us and the environment. 

Fitting a flow diverter to a downpipe is a relatively easy and low cost way to divert excess rainfall into a water butt. And we needn’t limit ourselves to one water butt. We can have as many as we want and even divert water from them to other storage tanks, such as IBC tanks, elsewhere in the garden. In my own case I’ve installed recycled pipes from water butts to IBC tanks on the other side of my garden. They fill by siphon and gravity where I use the power of water to flow downhill to move the water to where I want it, right next to my greenhouse. And if we don’t want to use the water in a garden we can fit leaky taps that allow the water to slowly leak away. This delays the time before it enters the drains or ground and thus relieves the pressure on them. The principle is similar to the balancing tanks (or ponds) sometimes seen beside roads and motorways. The idea is that they balance the flow of water leaving, over a period of time, and so take pressure off the natural systems.

Once all my tanks are full I divert excess water into my pond. Without rainwater it would eventually evaporate and my water lilies, dragonflies and frogs would all suffer. Once my pond is full the surplus seeps over the edge and can slowly soak into the soil until it becomes saturated. At that time I have other strategies that can be adopted.

Rain gardens are areas of garden where we encourage surplus water to gather. Rain gardens aka bio-retention facilities can be permanent or temporary in nature. The temporary ones get surplus water when it is available but dry up in dry weather. This is what happens to lots of fields and used to be the basis of water meadows. Wet in winter and dry in summer. 

Permanent rain gardens can be fed by rainwater from a roof or natural seepage. They tend to remain wet all year, though much wetter in winter. They may have a pond at their heart but are essentially wet areas, akin to marshland, and the plants in them are wetland species such as kingcup, hemp agrimony, ragged robin, sedges and rushes. They are richly biodiverse and a delight to many gardeners. 

Swales and berms are another method of retaining water or slowing its flow into the natural systems or drains. Swales are water retaining trenches dug along the contour of the land. The soil removed from them is heaped along the lower edge to form a slightly raised barrier to prevent rainwater from flowing down a slope. The rainwater that is held back slowly percolates into the soil and aquifer and is available to nearby plants for a considerable time. 

Swales and berms, when properly constructed in a formal garden are barely discernible. The “trench” is very shallow and the “berm” quite low. They look like a slight ripple in the surface of a lawn but still have the capacity to hold back significant amounts of water for short periods. That period might only be an hour or two, but it can make a significant difference when there is a heavy downpour. The water retained in the soil means that much less watering is needed in gardens that use this system. In some cases there is not just one swale system. There are several in succession across a gentle slope that seems to gently ripple across a hillside!

Where land is steeper the swale can be much deeper, perhaps hidden from sight in a flower bed or along a hedge. It becomes a deep drain that holds back a lot of water when needed. 

Plants to Slow The Flow … For Rainwater Harvesting

All the above techniques hold back rainwater once it has left your roof. But if we use a living roof we can slow the rain down before it leaves the roof. A roof that contains plants, such as sedums or similar species, can slow the flow before the water enters the downpipe. Every little helps and some councils now fit a living roof to bus shelters and public buildings.

And at ground level we can use plants to reduce flow rates in a similar way. Long grass holds back the flow of rainwater as does a hedge, trees, shrubs and other vegetation. 

The worst runoff occurs when there is no vegetation to quell the deluge and slow its progress. Bare land, especially arable fields after crops such as maize, is easily eroded by heavy rain. The result is roads covered in mud, mud, silt and stone deposits in water courses and hedges being swept away. 

Though less likely in gardens with fences and hedges this is not uncommon on allotments with inadequate vegetation cover in winter. Crops not only prevent the soil being battered by heavy rainfall, plant roots help bind the soil and make it less liable to erosion. Sheeting down allotments isn’t going to help flood and erosion prevention. Plastic sheets and tarpaulins just shed water onto someone else’s space. Green manures are a good alternative to sheeting down. 

That brings the discussion back to using concrete to cover the soil. Concrete, tarmac, resin surfaces and paving are all impermeable and shed water to other sites. That might be a neigbours land, the local stream or, in extreme cases, into your own home. It happens! 

Where a drive or path is necessary, and we all need access to our properties, then the use of SUDS (Sustainable Urban Drainage) is an option. The covered area is constructed with built in drainage to a soak away, or similar system, that prevents severe flooding elsewhere. Other options are to use permeable concrete that allows rainwater to penetrate into the soil below. 

More Permeable Surfaces …. For Rainwater Harvesting

The most permeable natural surfaces are often found under the tree canopy where soil has had years of autumn leaves that feed the soil and make it very water permeable. 

We can recreate these natural surfaces in our gardens by covering our soil surface with woodchip or other natural materials that act as a barrier to rapid run-off and feed the soil. It’s noticeable how, in our community food forest, the woodchip covered areas are now weed free and soak up plenty of rainwater when it rains. Surprisingly being water retentive doesn’t mean they get boggy. Due to improved soil structure they also drain very well, Its another win-win. Soil that retains water and drains well .. it seems impossible until you see it in action. 

For me the ultimate gardener-produced permeable surface in the garden is the No Dig bed. The addition of organic matter to the surface stimulates worms, bacteria and fungi. It gives soil life and grows incredibly good crops. 

Tag: Rainwater Harvesting

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