Subterranean retention pond and method for producing same

Abstract

The invention relates to an underground retention pond comprising: • a natural sealing layer lining the pond, • a porous and load-bearing fill material arranged on the sealing layer, and • a water-permeable cover lying on the fill material, wherein the natural sealing layer seals the bottom and side walls of the pond, the fill material enables the storage and controlled release of water, and the water-permeable cover allows the infiltration of surface water into the retention pond.

Description

[0001] The invention relates to an underground retention pond and a method for producing the same.

[0002] In light of climate change, rainwater storage and harvesting are becoming increasingly important. Extreme weather events such as droughts and heavy rainfall are becoming more frequent and endangering ecosystems.

[0003] Due to climate change, extreme weather events such as heavy rain and flooding are becoming more frequent in many regions.

[0004] The current approach of draining rainwater as quickly as possible through various stormwater systems, ultimately rendering it unusable for human consumption in the salt water of the oceans, is not sustainable. Yet this is the current state of planning. Cities generally encounter too little space for real change. Commercial and climate-friendly areas are in strong competition here. Efficient stormwater management plays a key role in minimizing the consequences and risks of such events. Sponge cities, among other things, are intended to remedy this. Accumulating rainwater is to be collected locally, utilized, and additionally stored. Using various measures, the sponge city is intended to absorb water in various places like a sponge.

[0005] Water storage is an important method for meeting the water needs of humans, animals, and plants and for regulating water resources in regions prone to heavy rainfall. As a result of global warming, long dry periods and more frequent heavy rainfall events will occur.

[0006] There are various ways to store these amounts of water efficiently: On a large scale, dams are used to dam up water from rivers and store the water in a reservoir, artificially created surface lakes and ponds, underground aquifers are used to store water in deep rock layers as groundwater, rainwater storage systems are used to collect rainwater from roofs or streets and store it in tanks or underground metal or plastic cisterns.

[0007] Rainwater storage systems, such as underground metal or plastic cisterns and tanks, are an effective way to store rainwater for future use, reducing tap water consumption and, consequently, lowering costs.

[0008] Given the aforementioned challenges, the task is to develop an innovative rainwater management system.

[0009] This object is achieved by an underground retention pond having the features of claim 1 and by a method for producing a retention pond having the features of claim 14. Further developments and advantageous embodiments of the invention emerge from the respective subclaims.

[0010] The underground retention pond according to the invention comprises a waterproofing layer lining the pond, a porous and load-bearing filling material placed on top of the waterproofing layer and a water-permeable cover placed on top of the filling material, The sealing layer seals the bottom and side walls of the pond, the filling material enables the storage and controlled release of water, and the water-permeable cover allows the infiltration of surface water into the retention pond.

[0011] The underground retention pond according to the invention offers a wide range of possibilities for sustainable rainwater management.

[0012] Such a retention pond can retain water during extreme rainfall, but also store it for use during droughts. Rainwater collected on roof surfaces during rainfall can be channeled into the retention pond. The waterproofing layer prevents the rainwater collected in the retention pond from seeping into the ground.

[0013] The main purpose of the underground retention pond according to the invention is the storage and use of rainwater. The water can be used in a variety of ways. The stored rainwater can be used to irrigate plants during dry periods. Furthermore, filtered retention pond water can also be used in households, thereby reducing tap water consumption. Rainwater can be used for flushing toilets and also for washing machines, as well as for brewing water.

[0014] By using the underground retention pond according to the invention, the stormwater fees are reduced, since the roof area on which the rainwater is collected is no longer counted as a sealed area.

[0015] The advantage over conventional water storage tanks, such as underground metal or plastic cisterns, lies primarily in the manufacturable size, the use of natural raw materials, and the longevity of the underground retention pond according to the invention, which is particularly protected by the cover. Furthermore, the retention pond is relatively inexpensive to construct.

[0016] The cover contributes to virtually loss-free underground water storage. The evaporation rate is minimal because the underground retention pond according to the invention is covered.

[0017] The water storage method of the underground retention pond according to the invention offers versatile application possibilities. The core function of the underground retention pond is the storage and utilization of rainwater. Due to climate change, extreme weather events such as droughts, heavy rainfall, and floods are becoming increasingly frequent. Through the efficient use and storage of water resources, adaptation to these climate events can be achieved and risks reduced. It also saves valuable drinking water and enables more flexible land use in urban areas.

[0018] Compared to conventional water storage methods, the underground retention pond according to the invention has the advantage that sustainable resources, such as clay as the main component, can be used to form the sealing layer of the retention pond. Furthermore, the underground arrangement of the retention pond and the accessible and saltable surface as a cover on the retention pond advantageously save a lot of space, which can be used for green spaces, parking lots, or roads, for example. The underground retention pond is also relatively inexpensive, costing only approximately 32 cents per liter. This makes an underground retention pond more cost-effective than stainless steel tanks, which cost approximately 40–67 cents per liter. While plastic tanks are in the mid-range of 27–43 cents per liter, they are not made from sustainable raw materials.

[0019] Depending on the scale, the underground retention pond offers different applications. In a small-scale configuration, the model can reduce water consumption by private households, while in a large-scale configuration, cities and municipalities can use it as a water retention method to prevent flooding.

[0020] In summary, this type of water storage and use offers many possibilities.

[0021] It can be advantageous if the waterproofing layer is natural and contains natural clay, preferably made of natural clay, with the natural clay preferably being pure natural pit clay. The advantage over conventional water storage systems, especially underground metal or plastic cisterns, lies in the use of natural, pollutant-free, and sustainable raw materials.

[0022] It can be advantageous if the natural clay is vacuum-compacted without chemical additives into sealing segments or plates, which are then tightly laid on the floor and side walls of the retention pond.

[0023] Sealing segments or panels, known under the brand name "DIA Natural Pond Made of Clay ®<", have proven particularly suitable in this context. Vacuum compaction makes the sealing particularly secure. The sealing segments or panels can be conveniently manufactured directly on-site during the construction of the retention pond. While plastic film is generally suitable as a sealing layer, the advantage of this type of natural sealing is that no plastic film needs to be installed in the ground, thus eliminating the risk of health risks from plasticizers or similar substances. Another advantage is that modifications and extensions to the underground retention pond can be implemented flexibly at any time. The natural sealing layer is extremely durable, highly resilient, and even suitable for traffic.

[0024] It may be advantageous if the sealing layer is up to 20 cm, preferably up to 15 cm, particularly preferably up to 10 cm, in particular between 8 and 10 cm, thick.

[0025] It may be advantageous if the infiltration rate through the natural sealing layer is a maximum of 3 l / year m 2< , preferably a maximum of 2.5 l / year m 2< , particularly preferably a maximum of 2.0 l / year m 2<.

[0026] The waterproofing layer therefore contributes to almost loss-free underground water storage.

[0027] It may be advantageous if the porous and load-bearing filling material and the covering on top of it are such that the covering can be walked on and / or driven over.

[0028] The cover thus forms the walkable and / or driveable area above the retention pond. This area can be advantageously used as a parking lot, sidewalk, or green space, which is particularly suitable in urban areas where space is limited.

[0029] It may be beneficial if the cover includes topsoil.

[0030] In this context, the material-specific properties of the porous and load-bearing fill material, especially expanded clay, of the underground retention pond can be utilized. The capillary effect, particularly of expanded clay granules, is used to automatically transport water vertically into the cover. Here, water can pass directly into the topsoil, allowing passive irrigation of vegetation above the porous and load-bearing fill material, especially the expanded clay layer, without requiring significant personnel effort. This enables the growth of a wide variety of plant species with diverse needs.

[0031] It may be advantageous to provide wicks between the cover, especially the topsoil, and the porous and load-bearing fill material to channel stored water from the porous and load-bearing fill material into the cover. The wicks thus serve to irrigate the topsoil using the water stored in the porous and load-bearing fill material.

[0032] Depending on the season, the cover, i.e., the green area covering the topsoil, can also be irrigated from above. Additional irrigation has the advantage that unused water flows back down into the underground retention pond, is stored in the porous and stable fill material, and is thus available for further use elsewhere or at a later date.

[0033] It may be advantageous if the porous and load-bearing filling material comprises gravel, chippings, lava, gravel or the like and / or preferably expanded clay, preferably expanded clay and / or gravel.

[0034] Expanded clay is an environmentally friendly, sustainable, and modern material that, in addition to its advantageous properties, offers a wide range of application potential. Expanded clay is known as clay granules, planting clay, Lias clay, Liapor, and Leca, among other names, and belongs to the non-cohesive, cohesive soil type.

[0035] Expanded clay can be produced as closed or open-pore granules. Clay with a low lime content and finely and homogeneously distributed organic components is cleaned, ground, and fired at 1200°C with limestone as a separating agent in a rotating kiln. The so-called rotary kiln consists of a rotating tube several meters long in which the crushed clay expands into a spherical shape. The organic substances inside the spheres burn, and the resulting carbon dioxide creates small cavities, causing the clay to expand to four to five times its original volume. The surface of the spheres fuses together to form a ceramic shell, which gives the expanded clay its high compressive strength. The ceramic shell of expanded clay can be mechanically broken to produce smaller grain sizes. The porous fired clay is spherical with diameters of 2–20 mm.

[0036] Expanded clay has diverse material properties. Among its most important qualities are its low weight, high load-bearing capacity, durability, and reusability. Other properties include resistance to fungi and mold, fire resistance, weather resistance, and sound and thermal insulation.

[0037] Expanded clay balls have a core with closed pores and a porous surface.

[0038] One of the material properties of these surface pores is their ability to absorb and hold water. Capillary forces within the pores act on the water. The capillary effect is a physical phenomenon in which liquids can rise and fall in narrow tubes or channels. This effect is caused by a combination of surface tension and adhesion forces within the liquid. A prerequisite for the capillary effect is capillary pores with a size of 10 -7 < - 10 -3 < m. The smaller the pores, the greater their capillary suction force.

[0039] Further material properties are listed in the following table. Thermal conductivity 0,1 - 0,18; 0,1 - 0,23 W / mK Bulk density 60 - 160 kg / m 3 Soundproofing effect 68 db Price Approx. 0.36 EUR / l Bulk density 235 - 800 kg / m 3 PH value 7 Compressive strength 0,45 - 15 N / mm 2

[0040] Expanded clay can be used as a raw material for construction, plant cultivation and water management.

[0041] It is known that expanded clay can be used with a cement mixture to produce lightweight concrete. A concrete brick with expanded clay as an additive can be up to four times lighter than a conventional brick. The use of lightweight building materials simplifies operation, particularly in construction. In construction, especially in wall systems, expanded clay is also suitable as a filler material to improve sound insulation, heat protection, and moisture regulation in walls.

[0042] Expanded clay is known to excel in plant cultivation due to its low density, structural stability, water retention capacity, and reusability. It can be used particularly for hydroponics and as a drainage material.

[0043] Given the increasing frequency of extreme weather events due to climate change, such as heavy rainfall and flooding, expanded clay can be used for stormwater management. Rainwater retention and accumulation are the primary objectives. Expanded clay is suitable as a fill material for stormwater retention basins and infiltration systems, as well as a substrate for greening.

[0044] In various loading cases investigated, including a person, a car, and a truck, and the resulting stress distribution in the soil, it was found that the expanded clay spheres are subjected to very low stresses. The highest static load from a truck exhibits a stress of 0.079 N / mm². This is still 5.5 times lower than the lowest known compressive strength of expanded clay. Therefore, an expanded clay layer in underground retention ponds is safe for static loads from people, cars, and trucks.

[0045] A fundamental strength of the underground retention pond according to the invention, preferably sealed with "DIA pond construction elements made of clay ®<", is its longevity and freedom from pollutants, which has a beneficial effect on water quality, particularly with regard to water abstraction.

[0046] The water storage capacity of expanded clay depends on the type of expanded clay. To ensure a high water storage capacity, it is advantageous to use crushed expanded clay. Due to its porosity in the internal pore space, this material can absorb water well. However, even crushed expanded clay contains a large proportion of closed, air-filled pores that cannot absorb water. In contrast to crushed expanded clay, uncrushed expanded clay has a ceramic shell that allows significantly less water to enter the interior of the sphere.

[0047] The water storage capacity of individual expanded clay spheres varies depending on their size and mass. The smaller the expanded clay spheres, the greater their average water absorption capacity. One explanation for this is that smaller spheres have a higher number of open pores on their surface. Expanded clay spheres with a larger volume have more closed pores and can therefore absorb less water. Due to the numerous cracks and edges, broken expanded clay can absorb far more water than closed expanded clay with a ceramic shell.

[0048] Expanded clay spheres with a ceramic shell have a water content of only approximately 26% after water absorption. Expanded clay spheres with a rugged surface, numerous cracks, and open pores, in comparison, can have a water content of approximately 37% and are therefore more suitable for water storage.

[0049] Expanded clay spheres measuring 2-4 mm have very high water absorption capacities and can retain approximately 60% water. Larger expanded clay classes only achieve a water content of approximately 44% and 35%.

[0050] As previously described, it can be advantageous if the expanded clay is broken expanded clay.

[0051] It may be advantageous if a pump is provided by which the water stored in the porous and load-bearing filling material can be conveyed to the surface for further use, wherein preferably several water collection pipes are laid on the bottom on the sealing layer of the retention pond, wherein the water collection pipes are preferably provided with small openings in order to collect the water, if necessary, also in a water collection shaft and to direct it to the pump.

[0052] The water pumped to the surface can be used in a variety of ways.

[0053] It may be advantageous to provide a pumping shaft into which the water collecting pipes or, if applicable, the water collecting shaft open, with the pump being arranged inside or above the pumping shaft.

[0054] It may be advantageous to provide a zone near the upper edge of the retention pond or an emergency overflow at the highest filling level of the retention pond, whereby excess water that can no longer be stored in the retention pond can be discharged into the sewer system, into the groundwater or, in a throttled form, into rivers.

[0055] If the retention pond is full and demand is met, it is possible to channel the excess rainwater through one or more infiltration areas or zones into the groundwater, thereby supplying it to drinking water, or to discharge it into rivers at a reduced rate. This can be used to bridge droughts in a resource-efficient manner, and to mitigate periods of rain and the threat of flooding.

[0056] The invention also relates to a method for producing an underground retention pond, comprising the steps: a) Dimensioning the retention pond according to the specific requirements for storage and drainage capacity, b) Excavation of the pit, preferably by dredging, and removal of the soil in the area of ​​the intended retention pond, c) Creation of a natural sealing layer on the bottom and side walls of the excavation pit, preferably by laying out a plastic sheet or particularly preferably by densely laying out sealing segments, in particular slabs, made of natural clay, particularly preferably to form a homogeneous, approximately 10 cm thick natural sealing layer, d) If necessary, insertion of a thermally consolidated geotextile above and below the sealing layer, e) Filling the excavation pit prepared in this way with a porous and load-bearing filling material, preferably with expanded clay and / or gravel, to form the underground retention pond, f) If necessary, insertion of a thermally consolidated geotextile above the porous and load-bearing filling material and / or if necessaryPlacing a frost protection layer above the porous and load-bearing filling material, g) covering the porous and load-bearing filling material with a water-permeable cover, preferably comprising. a. a gravel base layer, sub-base chippings and concrete block to form a parking area or b. a fleece and a layer of topsoil to form a lawn.

[0057] The frost protection layer ensures that the porous and load-bearing filling material is not exposed to weather conditions.

[0058] It may be advantageous if, prior to process step f), a pumping shaft, preferably made of concrete, is constructed at the preferably deepest point of the retention pond and several water collecting pipes, preferably provided with small openings, are laid at the bottom of the retention pond in order to collect water and direct it into the pumping shaft.

[0059] It may be advantageous to install a zone at the upper edge of the retention pond or an emergency overflow at the preferably highest filling level of the retention pond in order to drain excess water that can no longer be stored in the retention pond into the sewer system, into the groundwater or, in a throttled form, into rivers.

[0060] It can be advantageous if the sealing segments, especially sealing plates, made of natural clay, which are laid out closely next to one another, are kneaded mechanically to create a homogeneous sealing layer.

[0061] An underground retention pond according to the invention can also be referred to as an underground pond cistern.

[0062] The invention will be explained below with reference to exemplary embodiments shown in the drawings. Fig. 1 shows a schematic cross-section through an underground retention pond according to the invention, showing the essential components and their arrangement in the retention pond, and Fig. 2 shows a schematic representation of a rainwater cycle management system with an underground retention pond according to the invention.

[0063] To avoid repetition, it is noted that in the various figures, the same reference symbols designate the same or similar components.

[0064] Fig. 1 shows a schematic cross-section of an underground retention pond 10 according to the invention, wherein the essential components and their arrangement are identified by reference numerals.

[0065] Rainwater 36 is channeled into the retention pond 10 via a rainwater inlet 38, with the rainwater 36 preferably originating from roof surfaces 40 or other suitable collection points. After being introduced, the water is stored in the porous and load-bearing fill material 14 of the underground retention pond 10 and can be pumped out again as needed by a water extraction device in the form of a pump 18 and conveyed to the surface 42, for example for irrigation.

[0066] To prevent flooding of the retention pond 10, an emergency overflow 30 is provided, which drains excess water as soon as the maximum fill level of the retention pond 10 is reached. The excess water can be directed either into the sewer system or into specially provided infiltration zones.

[0067] At the deepest point of retention pond 10 is a pumping shaft 24 that collects the collected water. The pumping shaft 24 is constructed of concrete to ensure stability and durability. Pump 18 is installed in the pumping shaft 24, which pumps the water for withdrawal.

[0068] Water collection pipes 20 are also arranged at the bottom of the retention pond 10. The water collection pipes 20 are provided with small openings 22 through which water from the porous and load-bearing fill material 14 enters. These water collection pipes 20 allow the water from the porous and load-bearing fill material 14 to be directed into a collection shaft, from where it is forwarded to the pump shaft 24.

[0069] The floor and side walls of the retention pond 10 are provided with a sealing layer 12 consisting of a mineral natural clay layer. This sealing layer 12 can be protected by geotextile layers arranged above and / or below the natural clay layer. The sealing layer prevents the water in the pond from seeping into the surrounding soil and simultaneously guarantees a long service life of the entire structure of the retention pond 10.

[0070] The retention pond 10 itself is preferably filled with expanded clay as a porous and load-bearing filling material 14, which serves to store and controllably release water and at the same time contributes to the structural stability of the retention pond 10.

[0071] Finally, the retention pond 10 is provided with a water-permeable cover 16 on its upper side. "Water-permeable" can also simply mean that rainwater 36 is channeled through the cover 16 into the retention pond 10 via a rainwater inlet 38. In other words, the cover 16 can be water-permeable at one point, at several points, or over its entire surface. The latter is the case, for example, if the cover 10 comprises topsoil. In the case of a concrete cover, water permeability is more likely to be provided at one or a few points. After being introduced, the water is stored in the porous and load-bearing fill material 14. The cover 10 allows rainwater to penetrate the retention pond 10, protects the underlying system, and permits the use of the area above the retention pond 10, for example, as a parking lot or green space.

[0072] Fig. 2shows a schematic representation of a rainwater cycle management with an underground retention pond according to the invention.

[0073] The retention pond 10 according to the invention comprises a natural sealing layer 12 made of natural clay, which lines the retention pond 10, a porous and load-bearing filling material 14, preferably expanded clay, which is arranged on the sealing layer 12 and fills the retention pond 10, a water-permeable cover 16, which lies on the filling material 14.

[0074] The sealing layer 12 seals the bottom and side walls of the retention pond 10, the filling material 14 enables the storage and controlled release of water, and the water-permeable cover 16 allows the infiltration of surface water or rainwater into the retention pond 10. The infiltration rate through the natural sealing layer 12 is minimal.

[0075] The porous and load-bearing fill material 14 and the covering 16 lying thereon are designed such that the covering 16 can be walked on and / or driven over. In this case, the covering 16 comprises topsoil in sections and forms a green area. In other locations, the covering 16 comprises a gravel base layer, substructure chippings, and concrete block and forms a parking area.

[0076] It is clearly visible that the rainwater 36 falling onto the roof surface 40 of the house shown is channeled through an inlet 36 through the cover 16 into the porous and load-bearing fill material 14. The longer it rains, the more the retention pond 10 fills with rainwater. In this case, it is indicated that the retention pond is approximately half full of rainwater, which is stored in the fill material 14.

[0077] The water stored in the porous and load-bearing filling material 14 can be transported to the surface 42 for further use, for example for irrigation, for drinking water production or as process water.

[0078] The material-specific properties of the porous and load-bearing fill material 14, particularly expanded clay, of the underground retention pond 10 can be utilized for irrigation. The capillary effect, particularly of expanded clay granules, is used to automatically transport water vertically into the cover 16. Here, water can pass directly into the topsoil, allowing passive irrigation of vegetation above the porous and load-bearing fill material 14, particularly the expanded clay layer, without requiring significant personnel effort. This enables the growth of a wide variety of plant species with diverse needs.

[0079] To support irrigation, wicks 26 can also be provided between the cover 16, in particular the topsoil, and the porous and load-bearing filling material 14 to guide stored water from the porous and load-bearing filling material 14 into the cover 16. There, it is then available to the plants of the greened area.

[0080] If the retention pond continues to fill, a zone 28 is provided in the area of ​​the upper edge of the retention pond 10, as described above, or an emergency overflow is provided at the highest filling level of the retention pond 10, whereby excess water that can no longer be stored in the retention pond 10 can be discharged into the sewer system, into the groundwater or, in a throttled form, into rivers. List of reference symbols (is part of the description)

[0081] 10 Underground retention pond 12 Sealing layer 14 Porous and load-bearing filling material 16 Cover 18 Pump 20 Water collection pipe 22 Opening 24 Pump shaft 26 Wick 28 Zone 30 Emergency overflow 32 Geotextile 34 Geotextile 36 Rainwater 38 Rainwater inlet 40 Roof area 42 Surface

Claims

1. Underground retention pond (10), comprising • a sealing layer (12) lining the retention pond (10), • a porous and load-bearing filling material (14) arranged on the sealing layer (12) and • a water-permeable cover (16) lying on the filling material (14), wherein the sealing layer (12) seals the floor and side walls of the retention pond (10), the filling material (14) enables the storage and controlled release of water and the water-permeable cover (16) allows the infiltration of surface water into the retention pond (10).

2. Underground retention pond (10) according to claim 1, characterized in that the sealing layer (12) is natural and preferably comprises natural clay, preferably consists of natural clay, wherein the natural clay is preferably a naturally pure pit clay.

3. Underground retention pond (10) according to claim 2, characterized in thatthe natural clay is vacuum-compacted without chemical additives to form sealing segments or plates, which are tightly laid on the bottom and side walls of the retention pond (10).

4. Underground retention pond (10) according to one of the preceding claims, characterized in that the sealing layer (12) is up to 20 cm, preferably up to 15 cm, particularly preferably up to 10 cm, in particular between 8 and 10 cm, thick.

5. Underground retention pond (10) according to one of the preceding claims, characterized in that the infiltration rate through the natural sealing layer (12) maximum 3 l / year m 2 , preferably a maximum of 2.5 l / year m 2 , particularly preferably a maximum of 2.0 l / year m 2 amounts.

6. Underground retention pond (10) according to one of the preceding claims, characterized in that the porous and load-bearing filling material (14) and the cover (16) lying thereon are such that the cover (16) can be walked on and / or driven over.

7. Underground retention pond (10) according to one of the preceding claims, characterized in that the cover (16) comprises topsoil.

8. Underground retention pond (10) according to one of the preceding claims, characterized in that the porous and load-bearing filling material (14) comprises lava, chippings, gravel, and / or preferably expanded clay, preferably expanded clay and / or gravel.

9. Underground retention pond (10) according to claim 8, characterized in that the expanded clay is broken expanded clay.

10. Underground retention pond (10) according to one of the preceding claims, characterized in thata pump (18) is provided, via which the water stored in the porous and load-bearing filling material (14) can be conveyed to the surface for further use, for example for irrigation, for drinking water production or as process water, wherein preferably several water collecting pipes (20) are laid on the bottom on the sealing layer (12) of the retention pond (10), wherein the water collecting pipes (20) are preferably provided with small openings (22) in order to collect the water and direct it to the pump (18).

11. Underground retention pond (10) according to claim 10, characterized in that a pump shaft (24) is provided into which the water collecting pipes (20) open, wherein the pump (18) is arranged inside or above the pump shaft (24).

12. Underground retention pond (10) according to one of the preceding claims, characterized in thatWicks (26) are provided between the cover (16), in particular the topsoil, and the porous and load-bearing filling material (14) in order to guide stored water from the porous and load-bearing filling material (14) into the cover.

13. Underground retention pond (10) according to one of the preceding claims, characterized in that in the area of ​​the upper edge of the retention pond (10) a zone (28) or at the highest filling level of the retention pond (10) an emergency overflow (30) is provided, whereby excess water that can no longer be stored in the retention pond (10) can be discharged into the sewerage system, into the groundwater or, in a throttled form, into rivers.

14. A method for producing an underground retention pond (10), comprising the steps of: a) dimensioning the retention pond (10) according to the specific requirements for storage and drainage capacity, b) excavation and removal of the soil in the area of ​​the intended retention pond (10), c) creation of a sealing layer (12) on the bottom and the side walls of the excavation pit, preferably by densely laying out sealing segments, in particular plates, made of natural clay to form a natural sealing layer (12), particularly preferably to form a homogeneous, approximately 10 cm thick sealing layer (12), d) optionally inserting a thermally consolidated geotextile (34) above and / or below the sealing layer (12), e) filling the thus prepared excavation pit with a porous and load-bearing filling material (14), preferably with expanded clay and / or gravel, to form the underground retention pond (10), f) if necessaryInserting a thermally consolidated geotextile above the porous and load-bearing filling material (14) and / or optionally inserting a frost protection layer above the porous and load-bearing filling material (14), g) covering the porous and load-bearing filling material (14) with a water-permeable cover (16), preferably comprising a. a gravel base layer, substructure chippings and concrete block for the formation of a parking area or b. a fleece and a layer of topsoil for the formation of a green area.

15. Method according to claim 14, characterized in that before process step f) a pumping shaft (24), preferably made of concrete, is constructed at the preferably deepest point of the retention pond (10) and a plurality of water collecting pipes (20), preferably provided with small openings (22), are laid at the bottom of the retention pond (10) in order to collect water and direct it into the pumping shaft (24).

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