Description of Reef Architecture

The objective is to provide marine plant and animal life with the features of hard substrates, a range of ecological habitats that are as large and diversified as possible (dimen sions of cavities between a few decimeters and a few millimeters) to provide food sources and shelter to all stages of biological cycles of the different species (Tables 1 and 2).

Biological effectiveness is provided by the system known as "chaotic piles," which has proven to be valuable in the Mediterranean. But the legal obligation to plan for the eventual possibility of reef removal (due to the temporary nature of territory acquisition in the public maritime domain) has led to significant constraints. As well, studies have been done on the design of large-volume units (58-306 m3) that are solid and stable on the bottom, and that are easy to manufacture and immerse (as well as to remove).

Ecological optimization of these structures, which are organized on land, essentially focuses on the interior three-

Table 1 Number and volume of the different models used

Percentage (%)

Type of reef

Number Total volume (m3) Number Volume

Piles:

- Concrete cubes

- Quarry rocks (ABR) Units:

- Metal basket reef

- Fakir basket reef

- Chicane reef (RC) Floating ropes:

245 2C2

43 142 21

10,000 3,100

6,9CC 8,300 4,725

1,575

100 2,000

337 9,000

14 3,500

730 27,300

34 28

14 46 44 2 100

37 11

25 30 17

33 20 13 100

Table 2 Data on the weight and volume of the reefs

Unit or pile

Weight (t)

Volume and total weight

Piles of 6 Concrete cubes (ACB) + low floating ropes (FB) Piles of quarry rocks (ABR) Metal basket reef (RPA) + low floating ropes (FB)

Fakir basket reef (RPF) Chicane reef (RC) + low floating ropes (FB) High floating ropes (FH)

TOTAL

Volume of one cube = 1.7 m3 Pile of 6 cubes ± FB = 25 m3

1 element = 45 m3 RPA = all 3 elements piled up + FB = 266 m3 75 m3 50 m3

43 ABR = 6,900 m3 for 21,500 t 21 RPA = 5,600 m3 for 1,000 t

21 RPF = 1,575 m3 for 1,000 t 100 RC = 5,000 m3 for 1,500 t

Unintentional Artificcall Reefs Forms
Fig. 1 The different types of artificial reefs used in the PRADO REEFS OPERATION in Marseille

dimensional complexity and uniformity obtained with the materials used in their fabrication (concrete, steel, synthetic cords for guard lines) and the interior packing using units of different sizes and functions (1.7 m3 concrete cubes, blocks, oyster shell nets, octopus pots).

Project studies have led to three overall types of reefs being retained:

- Large volume "basket" models

- Piles of concrete cubes

- Quarry rocksand two types of guard lines:

- "High" floating ropes, which are independent units of two floors

- "Low" floating ropes, which are always combined in groups of four; there are three specific models: the metal basket reef, the chicane reef, and the piles of concrete cubes (Fig. 1).

Continue reading here: Plan for Implantation

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