Modeling Energy Loss with Reef Balls


Home -- Project Objectives and Motivations -- What are Reef Balls? -- Background -- Approach -- Results -- References	What are Reef Balls^TM Figure 1: Reef Balls being installed at a location (Reef Ball) Description Reef Balls^TM create shoreline stabilization through wave attenuation, which is a decrease in wave energy. The energy that does not pass through is termed wave transmission. To achieve this wave attenuation, reef balls are formed in rows in a shallow area of water. Generally, a clearance of 2.0 meters between the structure and the water-air interface is required for effective wave attenuation. When designing a structure, it is important to meet a certain wave transmission value to ensure the waves will decrease enough to allow sediments to settle out of the waves. As the structure breaks the wave's energy, it allows the sediments to drop out of suspension in the area between the shoreline and the structure, called the lee. The end result is accretion, which is sand building up along the shore. Reef Balls are engineered to sustain oceanic forces, both physical and chemical, and sustain marine life through material and shape (ReefBall). To ensure they cannot be overturned by wave impacts, reef balls are tested in a wave tank in a lab. Reef Balls cannot withstand the wave impacts by themselves; therefore, an anchoring system is needed to ensure stability. Such systems consist of fiberglass reinforced rods driven into the ground or chains placed in the reef ball (ReefBall). The design incorporates a hollow interior allowing it to be habitable for marine life. The holes are sporadically placed all over the Reef Ball, creating a whirlpool effect on the water passing through it. As a result, nutrients are transported inside to help marine life flourish. Furthermore, since the holes allow waves to pass through, the chance of the wave height increasing is lessened (ReefBall). Decreasing the chance of the wave height increasing can reduce the overtopping of waves and reduce the amount of scouring that could occur near the reef ball. Material A material with a high success rate for artificial reefs is concrete. Concrete used in artificial reefs can last up to 500 years, providing a long term solution. Concrete also has a high resistance to sulfates and other chemicals that can break down the composition of a structure in saltwater. Furthermore, if concrete is mixed with a low concrete to water ratio, the permeability is reduced once it hardens. This helps the concrete reduce its susceptibility to chemical effects because the chemicals cannot filter into the material. Cost Transporting reefs to their intended location can have high equipment costs and a long installation time. However, reef balls have a hollow interior, which allows an inflatable object, called an ion bladder, to be placed inside (Figure 2). By using this, the artificial reef can be floated out to the intended site and lowered into the water. To reduce transportation costs, reef balls can even be built on site. Only molds need to be transported to the location, and the concrete can be poured into the mold at the site. Figure 2: A Reef Ball Mold System, the red shape inside of the reef ball is the bladder used to float a reef ball out to its intended location for installment (ReefBall)

What are Reef Balls^TM

Figure 1: Reef Balls being installed at a location (Reef Ball)

Description
Reef Balls^TM create shoreline stabilization through wave attenuation, which is a decrease in wave energy. The energy that does not pass through is termed wave transmission. To achieve this wave attenuation, reef balls are formed in rows in a shallow area of water. Generally, a clearance of 2.0 meters between the structure and the water-air interface is required for effective wave attenuation. When designing a structure, it is important to meet a certain wave transmission value to ensure the waves will decrease enough to allow sediments to settle out of the waves. As the structure breaks the wave's energy, it allows the sediments to drop out of suspension in the area between the shoreline and the structure, called the lee. The end result is accretion, which is sand building up along the shore.

Reef Balls are engineered to sustain oceanic forces, both physical and chemical, and sustain marine life through material and shape (ReefBall). To ensure they cannot be overturned by wave impacts, reef balls are tested in a wave tank in a lab. Reef Balls cannot withstand the wave impacts by themselves; therefore, an anchoring system is needed to ensure stability. Such systems consist of fiberglass reinforced rods driven into the ground or chains placed in the reef ball (ReefBall).

The design incorporates a hollow interior allowing it to be habitable for marine life. The holes are sporadically placed all over the Reef Ball, creating a whirlpool effect on the water passing through it. As a result, nutrients are transported inside to help marine life flourish. Furthermore, since the holes allow waves to pass through, the chance of the wave height increasing is lessened (ReefBall). Decreasing the chance of the wave height increasing can reduce the overtopping of waves and reduce the amount of scouring that could occur near the reef ball.

Material

A material with a high success rate for artificial reefs is concrete. Concrete used in artificial reefs can last up to 500 years, providing a long term solution. Concrete also has a high resistance to sulfates and other chemicals that can break down the composition of a structure in saltwater. Furthermore, if concrete is mixed with a low concrete to water ratio, the permeability is reduced once it hardens. This helps the concrete reduce its susceptibility to chemical effects because the chemicals cannot filter into the material.

Cost
Transporting reefs to their intended location can have high equipment costs and a long installation time. However, reef balls have a hollow interior, which allows an inflatable object, called an ion bladder, to be placed inside (Figure 2). By using this, the artificial reef can be floated out to the intended site and lowered into the water. To reduce transportation costs, reef balls can even be built on site. Only molds need to be transported to the location, and the concrete can be poured into the mold at the site.

Figure 2: A Reef Ball Mold System, the red
shape inside of the reef ball is the bladder used
to float a reef ball out to its intended location for
installment (ReefBall)