Roughness (or heterogeneity) of hard surfaces creates turbulences, that can dissipate incoming wave energy, reducing small scale wave impact. Unlike interlocking blocks and solid seawalls that are sturdy and inflexible, randomly placed crushed rock or similar weathering resistant materials can experience re-settlement and adjustment by the displaced wave energy, although only up to a point (anon., 2013). On hard, man-made structures surface heterogeneity can create microhabitats and shelters, influencing biodiversity and abundance of species that could settle there. Surface roughness can be examined at micro-scale (mm to cm) and also in macro-scale (cm to dm, or m).
Macro scale surface roughness can be increased by creating irregularities in the coastal defense structures and adding different structural elements, such as geometric concrete blocks or small, water retaining intertidal pools. It must be noted, that in general macro scale roughness is not as common in designs of the subtidal part of the sea defenses, especially concerning riprap. One possible way for greater heterogeneity of foreshore rubble could be varying its structure with the addition of relatively small patches of larger boulders.
Micro scale surface roughness has a positive effect on the settlement rates of sessile invertebrates and algae, and has the additional effect of decreasing grazing and foraging efficiency of their predators. Substrate roughness is depended of the type of material used, for instance, various cracks and pores in vesicular (cavity filled) volcanic rock (such as basalt), coarse concrete surfaces (dependent on the type of concrete), or crystalline texture of rocks such as granite that are rich in silica. In most riprap design guidelines angular stones are the preferred choice instead of rounded stones, as they are able to interlock with each other creating a stable layer of stones. Rough angular stones also have a greater surface area and overall roughness (Lagasse et al., 2006; Murray et al., 2002; Roff and Zacharias, 2013).
Referenties
- Riprap Design Criteria, Recommended Specifications, and Quality Control, Lagasse, Peter F., P. E. Clopper, L. W. Zevenbergen, and J. F. Ruff., 1 januari 2006.
- Methods for Performing Monitoring, Impact, and Ecological Studies on Rocky Shores, Murray, Steven N., Ambrose, Richard F. and Dethier, Megan N., 2002.
- Marine Conservation Ecology, Roff, John, and Zacharias, Mark, 5 september 2013.
- Design of Coastal Revetments, Seawalls, and Bulkheads, anon., 13 februari 2013.
Zie ook
- The colonization by seaweed and fauna of different revetment types at Sint-Annaland, Tholen; RAAK-PRO Building for Nature final report
- Properties revetments
- Building with Nature; from concepts to practice
- Ecological potential of mastic asphalt for rich revetments
- On the relationship between dike revetments and ecology: lessons learned for design and follow-up monitoring for asphalt covered locations
- Early colonization of algal communities on polyurethane bonded aggregate: a field and laboratory study
- Ecosystem recovery after hypoxia: what can foraminifera indicate?
- Oesterdam sand nourishment - ecological and morphological development of a local sand nourishment
- The Benthic Ecosystem Quality Index (BEQI), intercalibration and assessment of Dutch coastal and transitional waters for the Water Framework Directive. Final report
