Converting (maize) fields on slopes into grassland or woodland
Grassland and woodland are better than arable land at capturing and slowing down rainwater. This is because the soil on bare arable land becomes compacted after heavy rain. The soil then absorbs very little water. Furthermore, arable land on a slope is susceptible to erosion (mudslides).
Maize fields are particularly vulnerable because they are only covered with vegetation late in the summer. If the bare soil becomes compacted, intense sunshine will ‘bake’ the top layer hard. Rainwater infiltration is then virtually impossible. The steeper the slope, the greater the problem of water and mud flows. But even the gently sloping edges of plateaus are vulnerable and require adaptation, as they are the first to catch the water flowing down from the large plateaus.
Natural solutions
Developing natural grasslands
Natural grassland captures surface and groundwater. It also provides resistance to flowing water. It can be developed on former farmland or former production grasslands.
Developing natural forests
Natural forest captures a great deal of water both above and below ground. It also provides resistance to flowing water. It can be developed on former arable land and former (production) grasslands. Conversion to a natural (or more natural) forest can also take place from production forest.
Food forest
A food forest is a production forest, although here the focus is not on timber production but on the production of edible nuts, berries, fruits, mushrooms, etc. Thanks to its layered structure and water management, the food forest contributes more to the absorption and retention of rainwater than a monotonous timber production forest.
Making space for beaver activity
Beavers feel at home in a forested stream valley. They are water engineers who shape the water cycle to their will. With beaver dams and gnawed trees in the stream, they create delays, backwater and water storage. In nature reserves where there is space for the dynamics of the water, the activities of this engineer are very welcome and help prevent flooding downstream. The stream bed is also better protected.
Making room for natural floodplains
When the stream floods, a wide, natural valley floor (floodplain) can store a great deal of water. If the water can spread out, it rises less. It is also slowed down by friction with the ground. Natural, rough vegetation in the valley floor (scrub, bushes, trees) provides additional delay. This helps to prevent a flood wave downstream.
Making room for meandering
A meandering (winding through the landscape) stream (see photo below) can accommodate more water than a straightened stream, because a meandering stream is much longer and also has side channels and oxbow lakes. The water also flows less rapidly. A meandering stream constantly shifts its course (a natural stream valley process). The space required for this must be set aside in the stream valley.
Raising the stream bed
By raising the stream bed of a deeply incised (side) stream using natural material (gravel), the stream is lifted, allowing it to make use of the wide (natural) valley floor sooner (for water storage and flow regulation).
Lowering banks
If a stream can spread out during high water, this provides water storage, slows the flow, increases infiltration and reduces flooding downstream. However, due to various (human-induced) factors, the difference in level between the stream bed and the valley floor at the Geul and the Gulp has become so great that the water no longer spreads out as quickly, except during extremely high-water levels (such as in 2021). In some locations (at local bottlenecks), it can help if the bank is lowered and, at the site of a silted-up meander, a channel or channel-like depression is dug into which the water can flow. These lowered sections are returned to nature.
Removing drainage systems
By removing drainage systems, rainwater and groundwater flow less quickly into the stream. This reduces the height of flood peaks and alleviates the impact of drought.
Planting scrub hedges and copses
Scrub hedges and copses help to capture rainwater and allow it to infiltrate the soil. In fact, they are miniature forests. Traditionally, the hilly countryside has been rich in hedges, scrub hedges and small copses. These are known as small landscape features or ‘bocages’. Many of these have been lost due to the increase in scale in agriculture. The return of these features to the agricultural landscape, particularly if they are planted in a robust form, helps to slow down water and reduce flood peaks. They are particularly functional on slopes, but also in the valley.
Standard orchard
Trees collect rainwater with their foliage, absorb rainwater through their roots, and contribute to a porous soil with good sponge-like properties thanks to their deep roots, humus and the soil organisms that live in it. In combination with herb-rich or extensively grazed grassland, the soil achieves optimal sponge-like functionality.
Wide infiltration strip
On moderately steep slopes with arable fields and uniform agricultural grasslands, current land use can be sensibly continued if plots are interspersed with 10 to 20-meter-wide infiltration strips, running parallel to the contour lines. These strips are considerably flatter than the slope on which they lie and are covered with dense vegetation. This slows down and captures surface runoff, allowing the water to infiltrate effectively via the vegetation’s root system. The distance between these infiltration strips depends on the steepness of the slope and the infiltration capacity.
Grafts
Cuttings are steep slopes along contour lines. They divide a slope into terraces situated one above the other. Thanks to their stepped structure, the terraces are less steep, and rainwater runs off more slowly. Traditionally, the slopes or the upper edges of the slopes (Grafts) are covered with scrub hedges (often consisting of hawthorn, blackthorn, elder, dogwood, grey willow and blackberry). In the shrub hedges, provided they are wide enough, the water is given the chance to sink into the humus-rich soil. The width of the swaths is an important consideration in this regard.
Swales
Swales collect runoff rainwater, preventing it from flowing straight into the stream valley. They are man-made depressions positioned along the contour lines of the terrain. By intercepting the runoff water, the peak of a flood is reduced. The water is given time to slowly seep into the soil. Swales are covered with vegetation.
Keylines
Keylines are man-made trenches positioned along the contour lines of the terrain.
Wadi
A wadi is a vegetated depression. It collects rainwater and retains it so that it can slowly infiltrate the soil. This also replenishes the groundwater level. The difference from a pond or pool is that a wadi only retains water during heavy rain or water runoff and therefore dries up for part of the year. It has well-drained soil. Furthermore, the water drained into a wadi can infiltrate slowly. In this respect, it differs from a buffer, where the water often has to drain away within 24 hours.
Intercepting runoff on (sunken) roads
Water flowing (far too quickly) down a steeply sloping road can be channelled towards the countryside or the verge. There it can infiltrate. This reduces the likelihood of a high-water peak in the stream.