» Properties & Applications
Inflatable rubber dams are variable dam barriers with a number of advantages over traditional constructions. The simple construction design with no movable parts (such as swivel joints) along with a plain shape of the concrete structure ensure low maintenance requirement of the dam. Any forces created are distributed evenly in the concrete foundation easing the reinforcement planning and the mounting on an existing dam structure. Mounting is possible on any vertical, inclined or twisted dam walls or curved or bent dam crests. What is more, due to their low construction height, rubber dams integrate harmoniously into the landscape. Repair and/or exchange of the rubber bladder is generally completed within a few days or weeks. Rubber dams are low-cost, adaptive and reliable barriers offering numerous application options.
Air-filled rubber dam on Lake Britton (USA)
Rubber dams can be used for a variety of purposes. When used for hydropower purposes, rubber dams retain the water for optimal use of the power-generating turbines. In coordination with the turbine’s capacity utilization the rubber dam allows to maintain the retention set point in a large variety of discharge scenarios. In addition, rubber dams are used to extend the storage capacity of existing dams. In this way the turbine capacity may be increased quickly and at low costs.
Precise water level control is very important when the dam is used for navigation (shipping) purposes. Rubber dams ensure that the retention set point is observed with narrow tolerance. For this use the automatic control system developed by Floecksmühle has proved especially effective.
Water-filled rubber dam on river Maas (France)
Rubber dams work as relief dams when used in the context of flood protection, for instance by integration in a dike. Thus polders or flooding areas may be flooded in a controlled manner. Due to their quick and easy operation as well as robust construction type, rubber dams also find application as mobile flood protectors. In the context of coastal protection rubber dams are used as storm tide barriers.
In the agricultural area rubber dams are used for retaining water for ground irrigation. Other applications are water storage for the direct watering of plants. Especially in regions with long dry periods rubber dams can be put to use for extending the water storage capacity so water supply is ensured on a continuous and economic basis.
Rubber dams also allow to separate sea water from fresh water in coastal regions. The bladder may be used with fresh water as well as sea water and brackish water. A special design also permits damming from the downstream side. This is the reason why rubber dams have proved efficient also as a barrier against sea water intrusion in agricultural coastal regions.
Rubber dams are used in sewage systems for water regulation, waste water retention and for rinsing the sewer system.
In combined sewer systems, part of the water from heavy rains must be stored to ensure that the sewage plant’s capacity is not exceeded. By installing an inflatable gate, the sewage duct can be used as an intermediate reservoir.
Requirements such as operational safety, adaptability to the sewer, dirt-proof and corrosion-proof design and remote controllability are all fully met by rubber dams.
Due to their flexibility and high operational safety, rubber dams can be used for a very large variety of purposes. Other possible applications are water sports, ecological water scene structuring, provision of cooling water and urban planning. Rubber dams can be customized to almost any particular application.
Air-filled rubber dam for irrigation purposes
Use of rubber dam in the sewage duct
» Structure & functional principle
Rubber dams are hydrostatic structures provided with a bladder of textile-reinforced rubber screwed to the dam structure which creates a tight inner space.
3D design of a water-filled rubber dam
The dam may be water-filled or air-filled. In either case a balance is created between the internal pressure of, and the water load on the bladder. By varying the filling volume the height of the bladder and thus the retention and discharge sections are adjustable to the relevant retention requirements.
3D design of an air-filled rubber dam
The pumps and valves are controlled from a power house. The appliances required for water-filled systems are located in underground shafts and for air-filled systems in an over ground power house. Using the respective control system the retention set point is adhered to reliably. The duration of Inflating and/or deflating is adjustable.
The filling medium is supplied to the rubber dam by pipes connected with the control system. As soon as the rising water level in the retention zone exceeds the retention set point, the bladder is gradually deflated until complete depletion, thus clearing the full dam opening. Vice-versa, as soon as the water level decreases the bladder is inflated. In this way the upstream water level is kept constant at the specified retention set point.
The choice of the appropriate filling medium depends on the requirements of the individual project. A number of criteria have to be considered at the planning stage.
|Air-filled rubber dams||Water-filled rubber dams|
|Even overtopping when operating at 95%-100% of the maximum bladder height||Even overtopping in every operating mode|
|V-shaped dent is formed when bladder is deflated below 95% to 90% of the maximum bladder height|
|Spans can be controlled individually||Spans can be controlled individually|
|Setting times for inflation and deflation within 5 to 30 minutes (depending on size)||Setting times for inflation and deflation from 1 to 4 hours (depending on size)|
|The filling medium is ambient air||The filling medium is generally river water (measures for improving the water quality might be required)|
|No icing of filling medium in winter||Efficient measures against icing required in the cold season|
|Calculation of discharge is possible for 95% - 100% of the max. bladder height||Calculation of discharge is possible because of the Floecksmühle system for measuring the bladder height (in the range of 25% - 100% of the max. bladder height)|
|Longer service life of the dam in hot regions due to less heating of the membrane|
|Lower loss of filling medium in the case of damage to the bladder|
|Dimension of dam structure|
|Width of depleted bladder: approx. 1.8 x bladder height||Width of depleted bladder: approx. 2.4 x bladder height|
|Small pipe diameters||Larger pipe diameters|
|Control system of compact design requires little space, especially in costly underground structure||Control system must be located in shafts next to the rubber dam|
|Control system not required to be located directly next to the rubber dam|
// Air-filled rubber dams
The bladder of this type of rubber dam is filled with air. The dam is kept erect only by the air pressure inside the bladder. For inflating the dam, the compressor located in the power house on the riverside feeds air into the bladder through a control pipe.
The inflating bladder is completely air-tight, including the side wall sections, impounding the upstream water as the filling proceeds.
The deflation process is carried out by electrically or pneumatically controlled valves. Additionally, all valves can be operated manually. In the case of small dams the entire control system may be housed in a thermally insulated and heated control cabinet.
Functional principle of an air-filled rubber dam
The rubber dam is equipped with a number of sensors ensuring safe operation, precise setting and permanent monitoring of the dam operation. The sensors measure the water level in the retention area and the internal pressure of the bladder. Besides, the interior of the bladder is monitored for possible condensate formation or intrusion of outside water. The internal pressure of the bladder is measured separately for each span. Therefore separate measuring pipes are provided leading to the control house.
Air-filled rubber dam in Los Laureles (Honduras)
Up to a deflation of approx. 95% to 90% of the maximum bladder height, air-filled dams behave in a way similar to water-filled dams. When depleted further, a V-shaped dent forms involving higher overtopping of the dam. As a consequence, air-filled dams are not overtopped as evenly as water-filled dams. This may have advantages as well as disadvantages depending on the site location. The control system developed by Floecksmühle ensures strict observance of the retention set point also for air-filled rubber dams.
As a general rule, rubber dams may be used in locations where the downstream water is retained. When there is no downstream retention, the air-filled bladder is fixed to the dam body with one upstream fixing line. If the retained downstream water reaches up to the non-overtopped dam, a second fixing line may be necessary.
Overtopped air-filled rubber dam in Tolosa (Spain)
// Water-filled rubber dams
In water-filled rubber dams the water pressure in the bladder is created to the principle of communicating vessels as a water column in a regulating shaft connected with the inside of the bladder by a pipeline (inlet/outlet pipe). The height of the water column in the regulating shaft determines the internal pressure and thus the height of the inflated bladder.
Functional principle of water-filled rubber dams
The water bag – and thus also the bladder – are filled by one or more filling pump(s). The water is taken from the supply shaft which is generally connected with the upstream water by one or more pipes. The bladder is inflated by feeding water into the regulating shaft. As soon as the pressure inside the bladder exceeds the sum of external forces (bladder weight and water load), the bladder starts to prop up. The inflated bladder retains the water in the retention area.
Water-filled three-span rubber dam on the Maas river (France)
The crest of water-filled rubber dams is always horizontal, even when filled only in part. Therefore the overtopping water flows very evenly across the dam.
The measured parameters include the water level in the retention area and on the downstream side as well as the bladder height if required. As a consequence, water-filled dams make it possible to calculate the discharge rate in a certain range. In this way the discharge rate may be accounted for in the control system as a control parameter.
// Inflatable gates in sewage water systems
3D-design of an inflatable sewer gate
Inflatable sewer gates are installed in sewage ducts of combined sewage systems.
In combined sewage systems, rain water and wastewater are channeled together to the water treatment plant. As the collector duct and the water treatment plant are designed for a limited capacity, part of the sewage water from heavy rains must be stored temporarily to ensure that the water treatment plant’s capacity is not exceeded.
The installation of inflatable sewer gates allows the use of the existing sewage duct as an intermediate reservoir. The discharge volume passing across the inflatable sewer gates can be regulated in such way that the capacity of the connected sewage treatment plants is not exceeded. Inflatable sewer gates are generally designed as air filled rubber gates. Depending on the design, the complete cross section of the sewage duct can be closed.
Inflatable sewer gates offer several advantages:
- They can easily be installed in existing sewage water systems.
- The simple design of inflatable gates requires low maintenance.
- Electro-mechanical components can be installed in easily accessible operating shafts.
- Existing sewage ducts can be used as buffer reservoirs for sewage water.