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Beyond the drought - Designing For Water Scarcity
By Anno Torr
3. CAPTURE RAINWATER ALSO REFER TO POINT 1 - RAIN GARDENS AND SWALES
Rainwater capture is best handled close to the source as a large volume is easier to control before being given a chance to speed up and join other fast-moving sources.
Water tanks and containers:
Storing water in the ground is the first choice but double up with water tanks, barrels and other containers to catch overflow or surplus water that would otherwise flow off-site and slow down the water before directing it into the garden. These above-ground containers also provide irrigation during dry spells for struggling plants and those with high water-needs like vegetables. A 304 m2 roof gives you 2346.96 litres of water for every 2.54 cm of rain that falls! Without a soil storage facility, you’ll need enough water tanks to collect it all. Make sure to direct the overflow away from the foundations into the garden. Redirecting the downspout into a series of rain gardens is another option. Again, plan for overflow.
Turn rooftops into green infrastructure:
Green roofs can absorb between 40 – 60 % of water falling on it. These designs direct water into storage systems at ground level but must be installed by a professional.
Pavement, driveway edging: Raised edging directs rainfall to a single exit area gathering speed as it washes along the hard, impervious material. Landscape architects are now designing edges with voids that allow stormwater to empty into adjacent rain gardens or swales at various intervals along its length. This design spreads the solution along the line rather than having to deal with the problem at a single point. Watch how water flows over the paving or driveway - can you add a few exit places before it reaches the only exit point?
According to a report from the Sustainable Business Network of Greater Philadelphia, 2,54 cm of rainwater falling on a 102 m2 of paving over an hour yields 27 000 gallons/ 102 200 litres of water; an irresponsible waste should it all wash down the storm drain.
Make paved or cement-based patios and pathways more permeable by replacing grout with a porous medium like sand or lime, or cutting grooves through to ground level in cement surfaces. All of these measures enable infiltration at intervals across the surface, reducing the volume and speed of water across a solid surface.
A point about gravel: while allowing water to soak in this stone material absorbs the suns’ heat increasing evaporation and raising the ground temperature to levels dangerous to soil life. Keep this cover to small areas of compacted ground like pathways, firepits and driveways.
Nature: Did you know that trees use up a lot of water? Canopies can intercept up to 35% of the water that falls over them.
Hydro-zone & contour the garden
Rain chain & permeable paving
4. DESIGNATE PLANTING HYDRO ZONES
Every garden has its own microclimates, slopes and hills, soils and aspect. Having shaped the ground, built absorbent soils, and put systems in place to capture and direct rainfall and runoff, you now know where water will pool, spread out and soak in.
Designate hydro zones – high, moderate, low, and a no water usage zone - to ensure you correctly match a plant’s water needs to soil moisture levels. For example place plants with lower water needs in the areas that will have more extended sun exposure and no supplemental irrigation.
Driest areas: tops of slopes, steep banks, full sun, and hot west- and north-facing beds.
Moister areas: bottom of slopes, slight depressions, shady areas, south-side of buildings.
Seasonally wet soils: rain gardens, where water runs off paving and driveways. If you’ve built a berm or two, you’ll find water collects where the existing ground and raised mound meet. This is often the right spot for wetland edge plants that grow in moving water, where land changes from dry to wet, or wet to dry. Use them in areas where directed stormwater temporarily pools.
5. CHOOSE CLIMATE APPROPRIATE PLANTS
Adding your garden’s light conditions – sun, shade, partial – to the hydro zone plan, you’re now ready to plant. Not all indigenous plants have low-water needs, but those that belong in your immediate area are climate and soil adapted with a timetable of water, nutrient and temperature needs that match your local weather patterns and geology. Locally indigenous species should be our starting point.
According to soil specialists, plants play a role in developing the soil profile and so are adapted to growing in these soil types. Unfortunately, gardeners world-wide grow similar plant palettes, so we’re advised to amend our soils to a default rich, moist loam! Instead, work with what you have and plant local species already adapted to local soils.
Opinion: We must be careful not to plant up most of the garden with a limited palette of succulents and dry-region plants as it reduces your regions diversity and, should most of the plants be out-of-area, limits available wildlife food impacting local plant/ animal relationships. Plus, most dry-region plants won’t handle prolonged damp, humid conditions of summer rainfall gardens, and may not thrive where the rainfall and temperature timetables are out of sync with their needs. Restrict these beauties to the toughest spots if you’re unable to find local plants that work there. They are also well suited to growing in containers.
6. ESTABLISH RESILIENT PLANTS
Establish new plants during the rainy season as they need frequent and generous watering for the first few weeks. Often though, days can pass between rainfalls, so, to be safe, plant to plant up the size of the area to match the amount of irrigation water you have available. This means it will take longer to establish the garden you envisage, but plants, if given enough water during the establishment, phase grow stronger, deeper roots to withstand dry periods or seasonally wet soils. Even drought-tolerant plants need watering when newly planted.
How to water: Water plants as soon as you get them in the ground. Allow the water to soak in, then water again until the soil is thoroughly moistened. For the first week or so after planting: Plants need watering daily or every other day as the roots cannot access soil moisture from a wide area until they begin to grow. Supplement with stored water when rainfall is insufficient. After the first week, two or three times per week is sufficient unless you're battling scorching heat. Hand water during intermittent rain and test soil moisture around roots with a moisture meter (available at hardware stores for around R100). After a month, plants should cope with seasonal rainfall.
Know your soils absorption rate: Soil type affects watering frequency and duration. Don’t apply the water faster than the soil can absorb it. Add a thick mulch layer to absorb the water.
Get water to the roots: Direct water onto the soil around the plant, not over the foliage from above.
Don’t over-water: Deeper, less frequent watering will grow plants with healthier and more extensive roots that stand up better to drought stress. If you are planting a few plants in an existing planting bed, hand water the new plants while not overwatering the rest of the bed.
Buy young plants in 2 and 3-litre bags: The smaller root systems need less water to establish and adapt quickly to your garden’s soils, resulting in more resilient plants.
Space plants according to final size, so they don’t compete with each other for scarce water and nutrient resources.
Plant in suitable conditions: Don’t plant in high heat, windy days as both evaporation and transpiration will be high. Early morning is best, or late afternoon once the day has cooled down.
Don’t amend the planting hole with rich compost and fertiliser; plants are already nursery pampered, and the different textures between garden and nursery soils cause water to wick away from the roots into the existing soil.
Keep weeds down with a dense mulch layer as these opportunists rob the soils of nutrients and moisture. Cut those that are growing off at root level; pulling them out disturbs the soil bringing new seeds up to the light where they’ll germinate and grow as fast as Jack’s beanstalk.
Reduce evaporation: build living screens to block drying winds that strip soils and plant leaves of moisture increasing transpiration. If necessary, create temporary screen until the shelterbelt has grown in. Try to shade new plants – cut small, leafy twigs off large shrubs and pop into the soil around them.
Lawn: Reduce the size to just what you need for children and pets, and replace with easy-care local species. Don’t be tempted to cover the area with gravel or permeable paving; while they do allow infiltration, they increase the ambient air and ground temperature, increase evaporation, and reduce animal habitat. Aerate the lawn with a hollow tined fork to improve compaction and air and water movement. There are a few intriguing aerator shoes available too! Mow long to shade grass roots and keep soil temperatures cool, reduce surface evaporation, and provide longer blades to capture the early morning dew. Finally, do not fertilise during dry periods.
We have such an opportunity to design beautiful, creatively self-sustaining landscapes. It may take a bit of back-breaking work but it’s essential that we take time to prepare our gardens to absorb and hold the precious rain, for they play a vital role in supporting the fragmented patches of nature by offering wildlife food and shelter. They, in turn, provide valuable goods and services without which we’ll battle to survive – clean air and water, regulation of air and ground temperature, rainwater management, carbon sequestration, and the pollination services that help grow our food. And they bring us joy.
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