krah tm logo

This website uses cookies. If you continue to use the website, you agree to the use of cookies.

This website uses cookies. If you continue to use the website, you agree to the use of cookies. Learn more

I understand

Storm water retention

Storm water retention

Draw of storm water retentionDraw of storm water retention

Not only global warming but also population growth lead to a change of the usual conditions in many areas, which require a reaction to the “new”, but also necessary and current building measures lead to changes.
One sector of these changes are building measures which are realized in gaps between buildings or on open spaces (e.g. through sealing) and therefore lead to increasing water quantities which have to be drained, which in cases of average and heavy rainfalls the existing sewerage network cannot absorb. Underground buffers are a widespread solution here, because they don’t overload the sewerage system due to a delay of derivation.
In most cases the network operator determines the conditions for the opening, he defines who, when and how much can be fed to the network, since an overload can lead to widespread damage, e.g. through overflowing.
For such changes the installation of underground restraint systems, especially of storm water retention from PE-HD, has proved, since discharge systems can be realized in a simple, fast and effective way and is therefore a benefit to the whole network , as well as a relief to sewage treatment plants.

In principle the storm water retention consist of a gully, the actual storage and a control chamber, which limits the inflow. Furthermore an overflow option has to be planned, which prevents an overload of the storm water retention and can drain the rain water into a dry well without any damage.
The ATV worksheet A 128 is decisive for measuring and designing rainwater drainage systems in the catchment area of water treatment plants. Storm water retentions (SK) in a rainwater / mixed water system are discharge facilities with overflow in waters. These special buildings are built in rainwater and combination sewers due to economic reasons. If the discharge systems aren’t measured and designed according to the technical policies, high dirt loads can get into the waters during rainfalls and put a heavy strain on them. The objective of mixed water treatments is the best possible reduction of total emissions from the sewer system and treatment plant. Sewer system and treatment plant are connected and have to be coordinated.
To design a storm water retention effectively and sustainably the decisive evaluation parameters have to be defined:

hna - long-time average height of rainfall
The long-time average height of rainfall is a location-dependent factor and has a considerable influence on the exonerative effect of the rainwater reservoirs. With increasing height of rainfall more mixes water gets into the waters. Details of the annual height of rainfall hna can be seen from the  German Metrological Service or similar.

Au - impermeable total area (fixed/unpaved)
The fixed or impermeable areas have to be carefully determined since they have a considerable influence on the size of the storage volume of the storm water retentions. This applies particularly during the forecast calculations for prospective construction or industrial areas. It has to be critically tested if the estimated areas are appropriate for prospective construction or  industrial areas. An area increase of more than 20% should be calculated in any case.

Qm - Combined sewage flow
The combined sewage flow Qm is the parameter who has the most influence on the volume determination of the storm water retention. It is often unnoticed that the parameter Qm has to be drawn from the sewer system calculation, not from the sewage treatment plant dimensioning. If a new sewage treatment plant is planned or an existing plant has to be renovated and extended, and therefore has to be measured with a Qm, which is to contain reserves for a longer period of time (15 – 25 years), this Qm has to be used in the dimensioning of the rainwater drainage system.

Qt24 - Middle dry weather flow
The actual water consumption figures are to be used. The sum of the dry weather flow from the sewer system usually has to correspond to the annual dry weather inflow of the sewage treatment plant. Within the planning the consumption figures have to correspond to the sewage treatment plant inflow.


Storm water retention - Lifted Pipes at construction site
Lifted Pipes at construction site
Storm water retention - Jointing pipes at construction site
Jointing pipes at construction site
Storm water retention - Retention pipes onsoil
Retention pipes onsoil

By calculating the crucial parameters the required buffer volume results, from which the individual assemblies can be measured and constructed. Under consideration of the local conditions the storm water retentioh from PE-HD can be manufactured custom-fit, whereby the maximum possible execution is chosen instead of the required execution due to reasons of sustainability. The costs of an immediate volume increase are in no commensurate to extensions works which have to be carried out 25 years later.
The most important formula is QZ ≤ QA + QÜ, to exclude a collapse of the restraint system.
The version of the storm water retention always conforms to the local requirements and installation conditions:

  • Type of restraint (above, middle or on the ground)
  • Type of restraint of dirt loads
  • Type of throttling
  • Type of overflow 

The thermoplastic material PE-HD has established itself as material for big volume storage sewer systems since multiple constructive and creative possibilities can be combined with optimum workability, long operating life and tightness of welded systems. The “dissolved” cross section which acts raw material saving, as well as the almost unlimited recyclability, even after decades of installation, complement the excellent features.

Steffen Lampe
Henze GmbH

Unique storm water solution

Unique storm water solution

Our English pipe producer Polypipe Civils in Loughborough, UK has provided a stormwater attenuation solution for a luxury residential development in the heart of the idyllic Bedfordshire countryside in eastern England.

Storm Water solution - Construction siteStorm Water solution - Construction site

Renowned developers, Taylor Wimpey, called upon Polypipe to provide an engineered drainage solution, designed to work with a sloping gradient found on site. Set in the countryside town of Houghton Regis, the Regent’s Place large-scale residential development comprises of a mix of 180 two, three and four bedroom houses nestled in a tranquil area that offers stunning views of the landscape. The landscape surrounding the Regent’s Place development features a large public open space with limited footprint for drainage design and sloping gradients. Taking on the challenge, Polypipe worked closely with Taylor Wimpey and Consultant Engineers JPP Consulting, to design a KRAH storm water solution, incorporating staggered legs to take requirements and adopted elements laid out under Section 104 agreement for approving site conditions into account that also met site water company, Anglian Water. 

Read more ...

Retirement yes, but not retired

Retirement yes, but not retired

Wolfgang SchneiderWolfgang Schneider

For 42 years he has been loyal to the company Krah. Now the passionate design engineer Wolfgang Schneider has gone into retirement. We interviewed him about his time at the Krah company.

Clear brew, a thundering Corvette and a “Mahlzeit” (German salutation for every day situations; literally translated “meal”) any time of day. If you mention these words every employee of Krah knows we’re talking about Wolfgang. For the past 4 dcades there has always been a loud roaring when Wolfgang drove onto the car park of Krah. One of his passions are cars, preferably old and special…or especially loud.

However,since February it has been more silent in front of the company building. On January 31st at 5 p.m. Wolfgang clicked “shut down” for the last time ever on his computer. A last soup from the automat in the kitchen, a last chat with colleagues and Wolfgang ends 42 years of working at Krah.

“I’m feeling good”, he says while walking over the car park which he has crossed thousands of times. “I’m looking forward to what comes next.”
He was very delighted about the farewell party which had been organized by his colleagues, with lots of presents some days before. “A personal highlight was a treasure chest from aluminium, made in the tool manufacture, with brass inserts to slide it open. Engraved were some figures which represented my 42 years at Krah. When I opened the chest there was a Krugerrand anniversary edition from 2017 from fine gold, a troy ounce. That was a successful surprise for my goodbye into retirement.“

Wolfgang Schneider and his CorvetteWolfgang Schneider and his Corvette

Wolfgang Schneider is a primary rock of Krah. When Karl-Heinz Krah wanted to get him for his company “Werkzeug-&Vorrichtungsbau” in 1975 Wolfgang didn’t hesitate and accepted a job as tool manufacturer.

“A decision I have never regretted”, says 63-year-old Wolfgang. “Since I can think I liked to build things and felt gravitated to technical things. In my childhood I had always wished for an electric motor.” No wonder he describes the tasks in the company more as ‘hobby’ than work.

Karl-Heinz Krah spotted this excitement for technical things and offered him a job as design engineer only a few years later. Initially he was responsible for drawing Bihler tools. His tasks changed when Krah pursued increasingly to special machine construction and finally sold the complete Bihler area.
A highlight in his career was the decisive contribution to the development of the first gravity pipe machine in 2003/2004.

Back then there was lots to fiddle. For a tinkerer like him this was a great challenge.

He described his work as “goal-oriented”. “When the things you constructed worked in the end you were happy”, says Wolfgang. “As design engineer you work for goals, not tasks.” These results are known to many Krah customers all over the world. However, Wolfgang himself is only known by very few customers. His “territory” was always the engineering office in the Westerwald. According to Wolfgang he feels way more comfortable in his office with drawing board and measurement chart than being on a business trip abroad. Still today he remembers one of the few business trips with beads of sweat on his forehead. He had almost missed his flight back then. “I almost got stuck in Russia. That was nothing for me”.  He always felt very homey at Krah. “Otherwise I wouldn’t have stayed for that long. I turned my hobby into a career. A great time!”, so Wolfgang.

Wolfgang likes to fiddle on his audio system or watch one of his many films - especially with a bottle of local beer.From now on it will be even cosier in the home theatre. Wolfgang likes to fiddle on his audio system or watch one of his many films - especially with a bottle of local beer.

He now is one of almost 21 Mio. pensioners in Germany. But he surely isn’t afraid of boredom. His answer to the question what he will miss most he smiles and says “Actually nothing. I have worked for 47.5 years now and have never been ill for a long time. I now have more time for my other hobbies.” He will continue crafting and building, especially on his home theatre audio system. But what he is most looking forward to are long trips with his Corvette and meetings with other car-fans. And if he’ll drive past KRAH during one of his tours, he will be happy to stop by and have a chat with his old colleagues.

Intake pipeline DN/ID 800mm

Intake pipeline DN/ID800mm with submerged chamber of DN/ID2000mm

96 meter of ID800 intake pipeline + ID2000 submerged chamber. Installed partly into a trench to a depth of approximately 3 meters.

One of our customers from Finland approached us with a request for 96m of SN8 pipes for a project. After the initial price quotations we were asked more technical questions and we actually found out that the pipes were meant for a intake pipeline. After convincing the customer that the regular SN8 pipes might not be the correct choice for such a project, we were asked to provide a technical solution for this exact task.

Read more ...

Potable water plant

Potable water plant of municipal utilities

2x 150 m³ pipe containers made of PE100 pipe by FRANK FTW - as storage tanks for the new waterworks “Vogelhölzle”

Planning view of the waterworks with pipe container from abovePlanning view of the waterworks with pipe container from above

The municipal utilities in Dillingen-Lauingen (DSDL) started to replace the old waterworks “Vogelhölzle”, originated in 1962, by a new construction in autumn 2015. The old waterworks were situated in the setting range (ground water protection zone), which is, under current regulations, not permitted anymore. Since October 2016 up to 30.000 people are provided with drinking water from the new waterworks.
The planning engineering company PfK Ansbach GmbH planned a reinforced concrete building with a pent roof for the waterworks. In this building the complete piping, water treatment (oxidation) and the pumps are stored. The natural water is pumped to the waterworks from two 12m deep wells. If needed, up to 40 l can be conveyed per second. In the new waterworks the water flows through the oxidation and is then stored in two storage tanks. From there the potable water is pumped into an elevated tank and then reaches the consumer.

Planning draw of the waterworksPlanning draw of the waterworks

The two storage tanks, each with 150 m³ capacity, were planned as pipe containers completely made from PE100. The connection of the two pipe containers was already made during the shell construction into the outer wall of the waterworks.

Extract from workplan - View of pressurized doorExtract from workplan - View of pressurized door

In order to do so, do so, a ground water tight and tensile cross-wall junction of the system FRANK Kunststofftechnik was used. Due to the pliable material behaviour of PE, pipelines or tanks of this material can be connected to concrete buildings without articulation pieces. The following advantages of pipe containers from PE were decisive for the planning:

  • Fabrication only with materials that are approved for the contact with potable water
  • Easy geometry
  • High level of prefabrication; short installation time
  • Long operating life
  • Smooth surface;easy cleaning
  • Easy connection / combination with cast-in-place concrete structure

Extracts from the workplan - view and profile with pressure door, overflow, stairs and podest etc. Extracts from the workplan - view and profile with pressure door, overflow, stairs and podest etc.

After public tendering, the order for the construction of the new waterworks was awarded to the company Carl Heuchel GmbH & Co. KG from Nördlingen.

After ordering the two pipe containers from the Frank GmbH the FRANK Kunststofftechnik GmbH in Wölfersheim started the construction documentation. For the technical equipment of the containers there were exact specifications, which were implemented by a production drawing and released by the planner. Significant equipment features of the two containers were:

Spiral pipe made from PE100 with co-extruded blue inner layer – raw material with approval
Inner diameter DN 3000 - 150 m³ effective volume
Construction length approx. 23.6 m
End cover and functional wall
Completely factory-made prefabricated and delivered to the construction site in one piece
Pressurized door stainless steel DN 1000 for underwater entry
Stairs with platform from stainless steel 1.4571
Complete piping of the container from the inside with connection flanges of the functional wall – in detail:

  • Bottom outlet
  • Extraction with strainer
  • Filling pipe
  • Air tube and vent line
  • from stainless steel            
  • Inspection glass
  • LED lights

After approval of the construction documentation the two pipe containers were fabricated in one piece in the factory. After performed factory approval test by the planner and the client the two pipe containers were delivered with special transport. The containers had an outer diameter of 3,3 m and a length of 24 m.
On site the company Heuchel had already completed the shell construction in such a way that the two pipe containers could be unloaded and transferred with a mobile crane. As support for the pipes a gravel base layer with sand bedding below was made. During the transfer the pipes were placed correctly into the respective block-outs in the building. These block-outs were concreted later on.


Integration of the two functional walls in the outer wall of the waterworks Integration of the two functional walls in the outer wall of the waterworksView through inspection hole on water surfaceView through inspection hole on water surfaceFinished waterworks “Vogelhölzle” with building and pipe containers under embankmentFinished waterworks “Vogelhölzle” with building and pipe containers under embankment
Functional walls integrated into the plant engineering in the waterworks
Functional walls integrated into the plant engineering in the waterworks

During the installation the containers were covered with the high-load fabric ‘Kortex’ by FRANK GmbH. By doing so the buoyancy safety can be assured during the production of the embankment.
This was necessary since the construction site was in a flood area.

After finishing the ground and structural works the expansion of the waterworks started with plant engineering and piping. The two functional walls of the pipe containers were integrated into the plant engineering through grids, so that an excellent operability could be achieved. Due to the short construction time, avoidance of budgetary overruns and the quality of the construction, the client and planner were completely satisfied.


Placement of the pipe containers on previously prepared soilPlacement of the pipe containers on previously prepared soil
Delivery of the two pipe containers with special transport
Delivery of the two pipe containers with special transport

Planner: Engineering office PfK Ansbach GmbH
Construction company:  Carl Heuchel GmbH & Co. KG, Nördlingen
Settlement partner: Richter + Frenzel TBU GmbH

For further information on this subject please contact : This email address is being protected from spambots. You need JavaScript enabled to view it.