Water

Use pavement only where necessary. Reducing pavement and adding greenery also contributes to a cooler environment.

Water that runs off paved surfaces, such as roads, facades and roofs, also carries away any contaminants (e.g. precipitated soot, particulate matter, heavy metals and organic contaminants). If run-off water ends up in natural water courses, this can lead to a deterioration of the water quality.

Where paving may be necessary, for example on squares and parking lots, water-permeable pavement is a possible solution. There are also products to which the mineral olivine has been added, and this creates a water-permeable semi-hard surface that also binds CO2.

Open joints and paving patterns – The method of laying the pavement may also affect water permeability. An open paving pattern can be achieved with (porous) clinkers or grass-spaced concrete blocks that are laid with an open joint or in an open pattern.

Integrate trees and green areas in parking areas to collect, temporarily store, filter and infiltrate runoff water into the soil.

There are all kinds of attractive alternatives that allow rainwater to infiltrate. Consider, for example, grids in combination with planting, semi-paving and lighting.

Many municipalities now have a policy to disconnect rainwater pipes to prevent flooding of overwhelmed drainage systems. Disconnecting the downspout combines well with local reuse of rainwater in gardens and public spaces.

During a heavy rainstorm, curbs can keep the water on the street or steer it towards a green zone

Using height differences, rainwater can be encouraged to flow effortlessly from one place to another. Areas where it is desirable that no water remains are elevated. The water can flow to unpaved areas, such as a lower green strip, via a slope, where it can infiltrate into the soil.

By creating height differences, different areas are created with more wet or dry habitats for plants and animals.

Green sunken lawns and parts of (play) parks can serve as infiltration areas to retain rainwater and replenish the groundwater supply.

Where there is sufficient space, gutters or ditches (wadis) can be constructed to temporarily collect rainwater or drain it into a pond or ditch. A gutter can both transport and store water. The advantage of a swale is that it can transport, store and infiltrate water on site. Bioswales are particularly suitable for areas with a low groundwater level.

Bioswales are often provided with grass. Planting with a richer vegetation than just grass improves infiltration capacity and water purification capacity, and eliminates the need for frequent mowing.

This planting also supports biodiversity. The experiential value also increases.

Plants for bioswales must be able to withstand temporary (very) wet and dry growing conditions. There are plenty of options to adjust the selection accordingly. A landscaping professional or horticultural specialist will be able to provide advice.

If there is enough space, above-ground facilities are often the least expensive and the easiest to implement. In areas with limited space due to dense buildings, a combination of greenery with engineered measures underground (such as infiltration crates, systems and storage reservoirs) offers opportunities for storage of surplus water.

Green banks and phytoremediation ponds can be used in the city to improve water quality in a natural way. A planted filter with specially selected plants (such as yellow cattails, calamus, reeds and matt rush) can be used to naturally filter wastewater to a quality that is harmless to the environment. For the treatment of domestic wastewater, approximately 2.5 to 5 m2 of plant-based filter is required per inhabitant.

Water that has been purified by phytoremediation is not drinkable, but can be used, for example, for flushing the toilet or watering plants. It may also be used in natural swimming ponds.

Shade from tree canopies limits the warming of watercourses in urban areas. This contributes to increasing the amount of oxygen in the water and limits growth of undesirable algae.

Floating aquatic plants such as water lilies also have a cooling effect on hot summer days due to surface-covering leaves. They also make surface water less sensitive to blue-green algae.

Greenery stimulates the infiltration of rainwater because vegetated and well-rooted soil absorbs water much better than bare soil. Bare soil also tends to dry out faster.

A planted soil warms up slower in the summer than a bare soil. Ground covers can retain precipitation on and within their leaves, which later can evaporate. This allows 5 to 34% of the precipitation to evaporate naturally.

Plants retain rainwater on the leaves, the trunk and the branches. This precipitation evaporates again after the shower. Deciduous trees can absorb as much as 5 to 20% of annual precipitation, and conifers up to 50%. Tall and deep-rooted trees and shrubs in particular have a positive influence on the absorption capacity of precipitation of the plants themselves and of the soil. The absorption capacity of a planted soil is a factor of three greater than bare soil.

On average, it can be assumed that a leafy tree crown will retain the first 2 to 4 mm of precipitation. With more light showers at intervals, a much larger portion is intercepted and retained than when the same amount falls in one (downpour) shower. An average mature tree in an urban environment can hold 200 to 400 gallons of water in the crown.

Trees with rough sturdy foliage and conifers retain more water, even rough bark contributes to this. In addition, the density of leaves and the leaf position are strongly decisive: many small, closely spaced leaves retain more water than a few large, scattered leaves.

The volume of precipitation collected is highly dependent on the leaf mass. Therefore, where possible, combine trees with a broad crown and large leaf mass with a second layer of smaller trees and/or shrubs. An underlayer of perennials and a litter layer also help to retain water.

Tree roots, litter and vegetation act as a filter that can remove contaminants, sediment and fertilisers from runoff water before they enter surface or groundwater.

Make the growing space for a tree (and the vegetation underneath) as large as possible and make sure that the soil is suitable for absorbing larger amounts of water, so that water that runs off along the trunk can sink into the soil and not run off superficially.

A varied planting of trees, shrubs and a layer of herbs is most effective and at the same time prevents soil erosion.

Native plants may better adapted to the local situation. Native animals are commonly more attuned to native flora. Climate change can impact the local flora and fauna diversity.

So-called prairie planting is more resistant to longer periods of drought. Prairie planting consists of deep-rooted plants; The soil is covered with volcanic material, which ensures better buffering of rainwater. As a result, watering these plants in case of drought is less required.

Combine water storage measures as described above with: reducing temperature, increasing biodiversity, experience and relaxation, playing, reducing noise pollution and education

Green roofs, especially on large buildings, contribute positively to the temporary retention of water and the delayed discharge to the sewer system.

• Joondalup, Australia