Wadi's and (bulb)bplanting

Better use of rainwater in urban areas: wet gardens and wet public spaces

What is a wadi?

A completely new form of specially designed wet locations are so-called wadis. A wadi ('Water Drainage and Infiltration') actually works just like a floodplain or a riverbed. It is a specially designed place that can store and infiltrate water, thereby slowing down surface water discharge to groundwater. This way, it relieves the sewer system. A well-designed wadi system limits overflow, improves surface water quality, and reduces drought. A wadi has a planted top layer with a permeable soil.

A wadi system is designed for a certain volume of water to be captured. The wadi is typically calculated for a maximum water depth of a few tens of centimeters and is then underwater for a short period, usually no more than a day. Outside of this flooding period, the wadi often remains dry for an extended period.

A rain garden is a depressed planted area with a flat bottom, planted with a variety of plants and shrubs. It is intended to temporarily capture water after heavy rainfall and allow it to slowly percolate into the ground. The vegetation serves to retain the water, improve infiltration into the soil, and promote evaporation. Like a wadi, a rain garden remains dry for most of the time.

Dry wadi

A wadi when it is dry. This will occur less frequently because the infiltration slows down the drainage of rainwater to groundwater.

WET wadi

A wadi when it is submerged. The rainwater is purified by the top layer of the wadi and slowly seeps back into the soil. If too much water enters the wadi, the excess water will be stored via the overflow pipe and drained away through the drain.

(NATUral) WADI planting

A naturally planted wadi is not only beautiful but also has many additional benefits: the infiltration capacity of the wadi increases because not only does the infiltration crate do its job, but the plants also store water in their hollow stems. A nature-friendly wadi requires less maintenance than one covered with lawn, where the grass needs to be mowed much more often. Additionally, the tall, flowering vegetation of a natural wadi contributes to urban biodiversity: many insects, birds, and mammals such as hedgehogs find their habitat there. Varied planting also ensures a better-rooted, airy soil with healthy soil life that remains permeable to water in the long term.

Suitable asSORTMENT

Plants suitable for a wadi are not always marsh plants but must be able to withstand dynamic or changing situations: often dry and sometimes (very) wet. Lawn grass is not suitable for wadis: turf grasses are poorly adapted to oxygen deficiency. A (perennial) herbaceous vegetation, with or without trees, is ideal. A limited assortment of flower bulbs can also be used in a wadi. Flower bulbs tolerate drought during their dormant period, and some species can be very well adapted to wet to moist locations. In all cases, drainage must be optimal. A reasonable level of soil fertility is also a requirement. For optimal naturalization, mowing management should be adjusted to allow the foliage enough time to die back so the bulb can store nutrients for the next growing season.