Forthcoming Research Paper

Habitat Accessibility in the Design of Nature-Inclusive Void Features in Marine Structures

by Samuel John Stephen Hickling, Kyle Dearson, and Ferrante Grasselli

Abstract

Nature-inclusive design aims to enhance the ecological performance of human-made marine structures with positive habitat features, like internal void spaces. Currently, interstitial space metrics are inadequate in quantifying the volume of void spaces whilst considering their geometric properties. We propose a new method to inform nature-inclusive design called accessible space analysis, and two new accessibility metrics to be quantified from digital habitat models: Accessible Volume (AV) and Accessible Refuge Volume (ARV). We calculated AV and ARV with a numerical modelling program, from digital models of structures, comparing them to a conventional metric: total interstitial volume (VInt). ARV was calculated considering access classes with a minimum to maximum size ratio of 1:5, to assess refugia provision for fishes from predation. Our experiment included four ordered structural layouts, with known geometric properties, and a nature-inclusive design scenario, comparing two designs of hypothetical berm structures, one with conventional graded rocks and a second with Reef cubes®, incorporating void features. The visualization of accessible space and accessibility metrics distinguished the ordered layouts, for which VInt remained constant. When comparing the berm designs, both the conventional VInt and accessibility metrics were greater in the Reef cube® design. VInt was 66% higher, mean difference of AV was 369% higher and mean difference of ARV 172% higher across 10 access classes. The results indicate that the integrated void features increased the availability of accessible space and refugia, especially for accessing diameters below the maximum void entry diameter in the Reef cube® units, suggesting that accessible space positively describes void geometry on a per unit design basis in such combined structures. Accessible space analysis provides a robust methodology for generating size-sensitive information from structured habitats, capable of differentiating marine structural designs based on functional habitat accessibility and providing expansive insight to complement existing methods.