The concept of inflatable rubber dams was developed by French engineers, and the first inflatable rubber dams were designed and installed by American engineers in Los Angeles in the mid 1950's. In the 1960's, a series of large rubber dam projects were completed in the United States, and the technology was licensed to Sumitomo Electric in Japan, which made the technology widely available around the world. Within the next 30 a, Japan became the world's largest manufacturer of rubber dams. Today, Japan accounts for about two-thirds of the world's approximately 6,000 rubber dams, which are used for irrigation, water supply, water storage, flood control, habitat restoration, and power generation. Rubber dams are permanent structures consisting of a rubber-coated fabric that is secured to a reinforced concrete base by means of pressure plates and ground bolts. The rubber body expands by inflation (water) to reach the design height and pressure, and collapses by exhaustion (water). Usually rubber dams are designed for fully automated control, but they can also be designed for manual operation. Due to the advantages of smaller civil engineering works, easy installation, low investment and simple operation, they are usually used in the renovation projects of various types of flood relief buildings. In the hydropower industry, rubber dams are often used as diversion weirs in run-of-river hydroelectric projects, in the same way as automated sluice gate systems, to add extra generating head to a power station, or for other purposes such as sand flushing.

1 Types of rubber dam

          Rubber dams can be categorized into two types: inflatable and water-filled. Inflatable rubber dams are the most cost-effective as they have a smaller cross-section and require a smaller body of rubber. Inflatable rubber dams are lighter in weight and are better able to cope with cold climates and are unaffected by freezing temperatures in colder regions. Another advantage of inflatable rubber dams is that they can be regulated (inflated and deflated) quickly, usually much faster than water-filled rubber dams for the same size. One of the disadvantages is that at high head flooding (head exceeding 20% of the height of the dam), instability may occur, resulting in vibration of the dam bag, and when the bag exhausts and collapses, concentration of the water flow can occur, resulting in a V-shaped notch. In contrast, water-filled rubber dams are able to withstand higher diffuse heads (up to 50% of the height of the dam) because the weight of the water inside the bag makes it more stable. In some specific cases, the upstream water level can be controlled by gradually draining the dam bag and allowing it to collapse.
          Because of their wider base plate, water-filled rubber dams may be less suitable for installation on existing structures, particularly reverse-arc spillways, but they offer some advantages in terms of regulating performance and other features.

 

2 Application of air-filled rubber dam

          Rubber dams are cost-effective alternatives to hydraulic steel gates and are a better choice for small run-of-river hydroelectric plant forebays around the world.
          Rubber dams are also frequently used to upgrade or replace wooden gate systems in the United States and Canada. The dam allows high flows to pass through the spillway by exhausting slumps, and when the flow returns to normal, inflates and expands to hold back the water, adding generating head to the power plant. As a result, rubber dams can optimize power production and generation revenues over a longer period of time than conventional sluice gate systems.
         Rubber dams have the ability to be flexibly adjusted, and power plant operators are better able to implement the frequently changing discharge flow instructions of the environmental authorities. Fully automated inflatable rubber dams greatly improve the safety of dam operators compared to older wooden gate systems. At the push of a button, the dam crest elevation can be raised by 1 to 2 m. Previously, dam operators had to manually raise the slats, which was a dangerous working environment. Rubber dams are also suitable for forebay storage, providing power producers with a simple and efficient way to increase forebay capacity, regulate power production and meet changes in power demand.

 

3 Key Benefits of Inflatable Rubber Dams

         As mentioned earlier, the main features of rubber dams are ease of installation, low maintenance requirements, and the ability to cope with severe weather. Inflatable rubber dam system structure is simple, civil engineering work is small, become many hydroelectric project owners and developers are happy to accept the program, many new hydroelectric projects choose rubber dam program, in the existing building upgrading, rubber dam program also accounted for a large proportion. Inflatable rubber dams are used to upgrade existing buildings, first of all, the spillway needs to be modified to adapt to the collapse of the rubber dam bag exhaust, the need to develop a suitable rubber dam anchoring system and piping system protocols. Hydraulic steel gates have limited spans and require careful balancing and accurate operation, and rubber dams can withstand water pressure loads uniformly over their total length. As a result, rubber dams can have large spans (the longest single rubber dam has a span of 190 m) and can be factory-fabricated into curved shapes for easy installation in existing spillways. Taking into account the conditions of installation, operation and transportation, a span of about 50 m is appropriate. Large span rubber dams are heavier and require larger cranes for lifting. These factors have to be taken into account, mainly because they are directly related to transportation and installation costs. In terms of regulating the upstream water level, the choice of several short-span rubber dams has additional advantages. Inflatable rubber dams are better adapted to cold climates, and there are many inflatable rubber dams in Canada and the northeastern U.S., where they have been documented to have withstood a 100 a flood without any damage. Whether inflatable or water-filled, rubber dams offer excellent containment (minimal leakage), a clean operating environment, and are virtually maintenance-free, reducing investment and operating costs. In addition, unlike hydraulic steel gates, rubber dams do not require the use of lubricating oil and there is no risk of discharging hazardous substances into the river, so owners are not at risk of heavy fines. Due to the better corrosion resistance of the rubber material, rubber dams can be built not only in freshwater environments, but also in saltwater environments. In tidal locations, rubber dam cross sections can be designed in a symmetrical shape (semi-circular) to withstand water loads from upstream and downstream. Anchor assemblies for rubber dams are typically made of ductile iron and hot-dip galvanized, or stainless steel in brackish water environments. The design life of the anchor components is usually 50 a, or even longer. In addition, rubber dams have a low-profile appearance, especially when a small amount of water flows over the dam and the dam is immersed in the water flow, the dam blends in with its surroundings. As a result, many rubber dams have been constructed in urban rivers for recreation, hydroelectric power generation and urban renewal.

 

4 Design limitations and influencing factors of rubber dams

       The world's tallest rubber dam in the Netherlands, with a height of 8.35 m when the bags are fully inflated, is used as a tide gate and was completed in 2001. The design is unique in that it consists of three spans, each 80 m long. Typically, the height of rubber dams is only about 6.5 m at maximum, and the dimensions are limited by the material properties (mainly tensile strength), the size and capacity of the production equipment (autoclave, plate vulcanizers, etc.), and the ability to handle, transport, and install the large-scale rubber fabrics. In some typical engineering cases, the rubber fabric weighs several tons, requiring large equipment to lift and install to the concrete base, the design stage will need to consider the above factors, and therefore sometimes choose a multi-span rather than a single-span scheme. Similarly, the circumference of the rubber dam body also has an impact on transportation methods, and if the rubber sheeting can be packed into standard-sized containers, transportation costs can be greatly reduced. Large areas of rubberized fabric need to be manufactured using special supports, which also adds to the cost. In addition, factors such as loading, unloading and unfolding of rubber sheets need to be fully considered at the design stage.

 

5 Recent rubber dam projects in Canada

         Dyrhoff recently supplied seven rubber dams in Canada, four of which were installed by Algonquin Power at the Donnacona hydroelectric plant in Quebec, while work on the de la leme steeple-chute rubber dam on the province's Mistassini River was completed in early 2017. Meanwhile, installation of two rubber dams at the Yellow Falls hydroelectric project near Ontario was completed in 2017.

5.1 Donnacona Project, Quebec

         The project is located on the Jacques Cartier River, a short distance from the town of Donnacona and Guessant, Quebec. The Donnacona Rubber Dam replaced an old wooden sluice gate dam, built in 1918 and severely damaged in May 2014, with a rubber dam at the original site. After careful consideration, the owner of the dam, Algonquin Power Company, and its consultant, WSP, decided to install an inflatable rubber dam at the dam's original location because it was the most cost-effective alternative to the original site's flow control facilities. The new Donnacona Rubber Dam consists of four spans, each 1.95 m high, with a single span of 23 m. The new inflatable rubber dam is located near the hydroelectric power plant and will enhance the water level management capabilities of Donnacona Dam. The rubber dam will operate fully inflated when the upstream water level is at normal level, and once the forebay water level reaches a predetermined upstream level, the dam bag will begin to vent and collapse, releasing flood water below and avoiding upstream inundation. Alternatively, a large amount of runoff from heavy rainfall can be discharged by sequentially exhausting and collapsing one or more spans of the rubber dam body, relieving the threat of flooding until the upstream reservoir level drops to a safe level. In order to cope with the high water level upstream, the dam can be operated frequently, with an average of 5 to 10 exhaust collapses per span per year. The design slump time for this inflatable rubber dam is less than 45 min. after the civil contractor Pomerleau completed the civil construction, the installation of the rubber dam was completed within 20 d under the direction of Dell'Ovre. initial commissioning began in November 2016, and it was formally commissioned in early 2017, shortly after which the run-of-river hydroelectric power plant, with an installed capacity of 4.8 MW, resumed power production.

5.2 Mistasini River Project

         The Mistassini River project is being developed by Lac St-Jean Energy on behalf of its partner, the Mistassini River Hydroelectric Company. The project has already launched the operation of a small hydroelectric plant with an installed capacity of 18.3 MW, which will be able to satisfy the electricity needs of 3,000 households. The new inflatable rubber is 2. 7 m high and has a span of 30 m. A two-wire anchoring system is used to increase the stability of the dam. The rubber dam regulates the upstream water level for the spillway and hydropower plant when managing the minimum flow requirements of the Mistasini River. When upstream water levels need to be controlled, the dam bag is typically fully inflated and swollen, and when the need to increase downstream flow arises, the dam bag will exhaust and collapse, discharging floodwaters. One of the technical reasons for choosing the rubber dam option in this project is that its operating level can be adjusted in response to changes in the inflow of water from the Mistasini River. The entire installation of the rubber dam took 12 d and was completed in early 2017.

5.3 Yello Falls, Ontario Project

         The Yello Falls Hydroelectric Project in Ontario, Canada is located on the Mistasini River, south of Smooth Rock Falls. The hydroelectric power plant relies on two rubber dams to control water flow, one of which is 4.2 m high and spans 45 m, and the other is 4.2 m high and spans 25 m. Under the supervision of Dell'Ovre and the leadership of its partners, contractor Neilson completed construction of the two rubber dams in the fourth quarter of 2017.

 

6 Conclusion

         With these examples of rubber dams in Canada, most homeowners are even more enthusiastic about choosing a rubber dam solution because they are well aware of the benefits of rubber dam engineering. In these retrofit or new construction projects, Dell'Orford
is confident that owners will continue to choose rubber dams because they are less expensive and simpler to operate and maintain than steel gates.