Rain channels down the slope

Rain gardens – planning ahead

Continuing high temperatures are forecast for the Algarve, so now is the time to plan ahead. We are past the summer solstice and the days will soon feel shorter and, we hope, cooler nights might bring some welcome humidity.

For those of us with no automatic irrigation systems (and no automatic high water bills!), efficient use of free rain water is a subject of great interest. The challenge is to make the best of the intermittent and sometimes violent winter showers by planning to capture, store and use the water in our gardens, land and urban areas.

Many houses in the Algarve are not built with gutters or with tanks in which to store run off water – this is an enormous waste of a very precious resource. There are many water-saving strategies that are cheap and easy to build into a new house, including using a settling tank and overflow for the water which falls onto hard surfaces. For houses far away from any mains water, a cisterna fed by runoff rainwater is essential but may need topping up in the long hot summer months by buying in water.

If we concentrate on saving rainwater for irrigation, rather than using water treated for human consumption, then life becomes much simpler. Gutters and downpipes directed into a closed holding tank or cisterna can provide weeks of water for a fruit and vegetable patch, and good quality water it is too. This can be especially valuable for anyone pulling salt contaminated water out of a coastal borehole as it can be mixed with stored rainwater and used on the garden.

Bioretention is a simple way of retaining water and can stop harmful erosion and flooding by storm water runoff. Looking at the areas where water gathers naturally is the first step. Shallow depressions of differing shapes can be enlarged or created. The soil is opened up by ploughing or rotavating and water absorbed. This will infiltrate into soils slowly and naturally, thus helping to establish nearby trees and shrubs.

After many months of total drought, the hard ground does not absorb water easily. Excess water will drain into the soil rather than running off, taking upper fertile soil layers with it, and causing damaging erosion on slopes.

Just slowing down the runoff during rainy days will aid penetration into the soils and a lovely garden feature can be made with large rocks to simulate a ‘dry’ riverbed. You may have seen some lines of ploughed land running along contour lines; this is to retain water which would otherwise run straight down the slope. In permaculture, creation of swales to retain water serves the same function.

In urban areas where land is at a premium, the use of green roofs also captures rain and greatly reduces runoff. Specially selected plants will take advantage of water when it is available and will survive long months with no water at all.

A long-term project in Italy has shown which plants can be used to create green roof structures in hot dry climates. Other advantages are the insulating qualities of the plants for the building. A way of reducing needless use of energy for air conditioning or heating as the building does not reach excessive high or low temperatures. Urban spaces are shown to have higher temperatures, so rain gardens make a green contribution to the built environment.

In the Algarve, there is a green roof on the hotel rooms at the Estoi Palace Pousada, but there are other examples. A Portuguese specialist company has built these structures on domestic, commercial and industrial buildings, and they look stunning!

The new trend towards vertical gardens with living plants providing complete wall cover shows what can be done with imagination in new projects in urban settings. The Dolce Vita shopping centre in Lisbon is well worth a look.

Large tourist complexes and urban developments can save money and create beautiful features by recycling wastewater in reed beds as well as capturing rainwater. The aim of bioretention is twofold, it allows the reduction of impervious surface areas (so often a contentious part of planning applications) and it allows soils to naturally store and filter storm water and avoid erosion.

Managing rainwater can also significantly increase the visual beauty of any site – creating green spaces and shady corners where we can imagine the sound of gentle rainfall cooling the landscape …

For further information on how to make a rain garden, go to: https://www.chicagobotanic.org/downloads/wed/WI_DNR_homeowners.pdf

Mediterranean green roof study from Calabria, Italy: https://www.mdpi.com/2073-4441/11/7/1378/htm

Algarve projects using green roof constructions: http://www.josecavacolda.pt/en

Neoturf Green Spaces & Green Roof construction: www.neoturf.pt

Website of Botanist and original maker of vertical gardens: https://www.verticalgardenpatrickblanc.com/

By Rosie Peddle
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289 791 869 | [email protected]

Building a dry river bed
Car park planting
Moraine view
Rain channels down the slope
Rain garden California