Small retention consists in collecting water in natural (ponds, oxbow lakes) and artificial (ponds, streams, small dam reservoirs) with a capacity of up to several thousand cubic meters, as well as in river networks and drainage ditches. By increasing the humidity of habitats and raising the level of groundwater, small retention allows you to create a microclimate that is more friendly to fauna and flora. Traditionally, wood, concrete, stone or steel were used to build such hydrotechnical structures. A more durable, ecological and cost-efficient alternative to conventional solutions are products made of thermoplastics, e.g. vinyl sheet piles and small retention sluices.

Water retention comes down to construction of new water reservoirs or erecting  damming structures on the existing ones in order to slow down the water run-off and increase the retention capacity. The ability to locally store water in the ground can also be increased by restoring the network of watercourses and protecting the ecosystems of swamps and peat bogs against drainage.

Small damming structures help maintain the water level difference. The part of the reservoir with the water raised as a result of the damming barrier is referred to as the upper water or the upper station, while the part located below the barrier are called the lower water or the lower station. Damming structures perform additionally the following functions: they stabilize the bottom, silt up deep watercourses and level the slope of the watercourse bottom.

When designing small damming structures such as, inter alia, water thresholds, water barrages and penstocks, it is worth reaching for alternative solutions that, in addition to durability and attractive price, are environmentally friendly solutions, thanks to a low carbon footprint and full neutrality to drinking water. In addition, structures made of vinyl sheet piles can be easily combined with other ecological materials, e.g. wood to increase their stiffness.

The use of vinyl sheet piles in the construction of small damming structures

The choice of the appropriate type of structure depends primarily on the damming height we want to achieve and on the hydraulic flow conditions in the channel.

Water Barrages

A water barrage is a structure protruding above the bottom of the watercourse [1], with the same elevation on both sides of the structure. Barrages not only raise the low water table, but they usually block the movement of sediment dragged along the bottom. The height of the overflow should not exceed 0.3 m so that the barrages do not interfere with the migration and flow of fish. The threshold is a structure with a fixed crown, without the possibility of adjusting the level of the damming. Water barrages made of vinyl sheet piles which are highly resistant to environmental conditions, are extremely durable and do not require any maintenance. The raw material used for their production is resistant to corrosion and UV radiation. The certificate issued by the National Institute of Hygiene confirms that the sheet pile material does not affect the parameters of drinking water.

Fig. 1 Threshold in a forest ecosystem made of a vinyl sheet piling topped with a vinyl cap - under construction.

Water Thresholds

Water thresholds create the bottom casing at the fault [1]. Unlike barrages, thresholds are created where there is difference in bottom level below and above the damming structure and their task is to reduce the longitudinal slope of the watercourse and to stabilize the bottom. Taking into account the environmental conditions, in order not to interfere with fish migration, as in the case of barrages, the difference between the upper and lower water level should not be greater than 0.3 m. Water thresholds also do not allow for the regulation of the level of damming. By using vinyl sheet pile profiles with thicker walls, such structures are stable, erosion resistant and long-lasting.

Fig. 2 A wide water threshold built on a shallow watercourse made of vinyl sheet pile and wooden beams.

Retention sluices

Penstocks or retention sluices are damming hydrotechnical objects located in watercourse beds, equipped with closures that allow water level regulation. Retention sluices allow water to be damming up to the level required at a given moment. Such hydrotechnical structures consist of a wall separating the watercourse bed, in which there is an opening limited by closure guides. Closures, most often in the form of horizontal beams, are movable parts of the structure, enabling the regulation of the water level in the watercourse from the upper water side. The Pietrucha Group has developed and introduced to the market a comprehensive vinyl system of small retention.

Fig. 3 Comparison of a wooden small retention valve with a modern vinyl valve.

Small retention sluices made of PVC are highly resistant to external conditions, user-friendly  and require no maintenance. The certificate issued by the National Institute of Hygiene confirms that the material of the sheet piles does not affect the parameters of drinking water. Thanks to the use of recycled PVC components that can be recycled, the solution is environmentally friendly, and due to its low weight, no heavy equipment and a large technical team are required to assemble the vinyl gate. Small retention sluices harmoniously and aesthetically blend in with the surroundings.

PVC is a durable material, which eliminates the need to replace after five or ten years, as in the case of wooden counterparts, which additionally require regular maintenance.

The material used to make pvc piling is resistant to extreme temperatures and the freezing water, which can be proved on the basis of the photos below, which document the project carried out in a forest ecosystem in Northern Poland.

Fig. 4 EcoLock vinyl retention sluice installed in 2017 in Podanin.

The small retention sluice gate system is made of tubular profiles in the shape of a honeycomb – Dhex. This profile design guarantees high strength and at the same time lightweight transport and easy assembly in hard access spots. The profiles are connected with locks equipped with valves which guarantee 100% water-tightness of the construction. The walls smooth surface of the walls may be  extruded in the form of a tree ring pattern to perfectly melt with the surrounding environment. When the water level rises, the PVC tubular profiles assembled diagonally fill in with water. The weight of the water inside the profiles makes the locks fit tightly to create water-resistant sluice. The water retaining system based on Dhex profiles is part of vinyl mobile flood protection systems.

Fig. 5 Design of a vinyl small retention sluice.


  1. Budowle wodne z naturalnych materiałów. Ewa Jędryka. Instytut Melioracji i Użytków Zielonych w Falentach, Falenty 2007r.
  2. The Pietrucha Group archive materials

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