Rubber dam
A rubber weir is a simple and inexpensive construction method for a weir in smaller watercourses . The use of a hose filled with water or air to hinder the flow of water and to adjust the water level eliminates the need for a complex foundation construction and numerous expensive mechanical parts, as are required for other types of weirs. Hose weirs are particularly suitable for use in small and medium-sized rivers and are increasingly used to replace old systems for regulating water levels.
technology
A flexible hose is attached to a concrete foundation on the river bed and the side walls, which is filled with water, air or a heterogeneous mixture of both media. When the hose is filled and the resulting increase in volume, the upper edge of the hose rises and hinders the flow of water. This increases the level of the headwater . The hose material mainly consists of an elastomer membrane with an inlaid fabric (e.g. made of polyester or polyamide ) for stabilization. The elastomer membrane is attached to the weir body using clamping rails which, depending on the manufacturer, can be located either inside or outside the hose. When empty, the hose folds up and lies almost flat on the weir body. In this way, damage to the weir in the event of a flood can be largely avoided. Vent valves, vent lines and, if necessary, the use of pumps ensure that the hose can be completely emptied and folded up in any environmental condition.
Hose weirs are now successfully used up to water widths (dust widths) of several hundred and heights of up to ten meters (e.g. hose dam near Ramspol , the Netherlands). In addition, the technology is used to increase the storage space of dams and as an emergency facility for flood protection.
Advantages and disadvantages
The advantage of hose weirs compared to conventional height-adjustable weirs lies in their comparatively simple design and low maintenance requirements. This is due to the fact that a rubber dam does not require complex drive technology (e.g. hydraulic cylinders or chain drives) or bearings . A complex foundation for sinking the weir is not necessary.
The disadvantage of such weirs is
- the lack of passability for boats from the headwater
- the insurmountability for fish from underwater
- the comparatively short lifespan due to disruption by UV light
- the only roughly possible regulation of the water level
Regulation of the water level
The headwater level of the weir can be adjusted by filling or emptying the hose. Here, the pressure inside the hose in water-filled weirs is around 20 to 60 percent above the pressure level of the headwater. In the case of water-filled weirs, the desired pressure is usually set using a control shaft, which is filled with water with the aid of a pump. The control shaft is hydraulically connected to the interior of the hose. The effect of the water column in the control shaft is therefore the internal pressure in the rubber dam. In air-filled weirs, the internal pressure is built up and regulated by a compressor .
Filling medium
In addition to the area of application, a distinction is made between hose weirs with regard to their filling medium. Some special features of the respective medium are listed below.
water
- Elliptical tube shape due to the high weight of the filling medium. This results in an increased material requirement to achieve a certain storage height compared to the filling medium air.
- High inertia of the filled hose, therefore less tendency to vibrate
- Low compressibility of the filling medium, thereby increased dimensional stability of the hose and more even flow over it
- Possible damage from freezing at temperatures below freezing. This risk can be counteracted by continuously overflowing the weir as well as by circulating and, if necessary, heating the filling medium.
- More complex construction of the foundation, due to the control shaft
- Danger of contamination of the filling line
air
- Circle-like tube shape due to the low weight of the filling medium. This results in a lower material requirement to achieve a certain storage height compared to the filling medium water. This leads to a reduction in material costs.
- Increased susceptibility to vibrations
- The compressibility of the filling medium results in deformations of the hose with changes in the inflow and overflow up to the point where the weir buckles.
- Maintenance of the weir possible by walking through the hose
- Shorter filling and emptying times
Air Water
- When using air and water within a rubber dam, the advantages and disadvantages of both media result.
history
The first water-filled rubber dam was built in the USA in the mid-1950s. The inventor of the technology is considered to be engineer Norman Imbertson , who works at the Los Angeles Department of Water and Power . In 1956 the first weir on the Los Angeles River went into operation. In 1978 Bridgestone introduced an air-filled rubber dam. Today more than 2,500 plants are in operation, including over 2,000 in Japan .
literature
- Standard DIN 4048-2, edition: 1994-07, hydraulic engineering; Terms; Part 2: hydropower plants.
- Michael Gebhardt: Hydraulic and static dimensioning of hose weirs. In: Communications from the Institute for Water and Water Development - Department of Water Management and Cultural Engineering - of the University of Karlsruhe (TH). Dissertation, No. 235, 2006 ( PDF; 14.7 MB ).
- Michael Gebhardt: Status of the rubber dam technology, application examples and operational experience. In: Bulletin of the Federal Institute for Hydraulic Engineering. No. 91, 2007 ( PDF; 2.2 MB ).
Web links
- Photo gallery and models on the website of the Verden Waterways and Shipping Office
