Drainage systems in roads and railways include perimeter ditches, retention ponds, culverts, and other transversal structures. Ensuring standards for water evacuation and road safety through drainage systems can be combined with enhancing biodiversity by providing habitats for wildlife. Ponds and ditches can host invertebrates and fish, attract amphibians to breed and provide shelter and food for insects, reptiles, mammals and birds. Two basic principles apply when enhancing aquatic habitats for wildlife:
- Legal obligations for wildlife conservation such as European Directives of Habitats and Bird, require that maintenance tasks do not injure, kill or disturb the breeding sites of endangered species (see Appendix 1. Environmental regulations and strategies).
- Conflicts with traffic safety and the creation of ‘ecological traps’, attracting animals to areas with high mortality risk, must be avoided with expert help to carefully select the areas where biodiversity could be enhanced.
Drainage transversal structures such as culverts, open-span bridges and viaducts can also play a key role in ecological connectivity, providing links for wetlands, channels, rivers, and other aquatic elements of the Green Infrastructure. Drainage elements that can play a role as habitats for wildlife should be identified and specifications for management must be provided.
Maps of aquatic habitats in retention ponds, ditches and other elements of the drainage systems to be inspected and maintained, should be included in a GIS database. Management should be planned primarily to maintain the function of drainage and areas managed to enhance biodiversity should have particular specifications including standards to be met for all features in ponds and drainage elements (including water level variation, water quality, vegetation conditions, etc.).
Water, road and wildlife experts must work together to design successful drainage system maintenance practice.
Main aspects to be considered for drainage systems biodiversity-friendly maintenance best practice are listed below:
- Drainage plays a basic role in water evacuation and road safety which is always the priority factor.
- Modifying features of ponds or ditches to provide habitats for endangered aquatic and semi-aquatic species depends on the ability to provide adapted management which avoids any incidental damage or killing of protected species among invertebrates, fish, amphibians, reptiles and mammals such as otters and the critically endangered European mink (see Habitats Directive article 12.4).
- Avoid creating ‘ecological traps’ where animals are attracted to places where they could become trapped with no possibility of exit, get injured, poisoned or die.
- Define procedures to detect and record threatened fauna and flora during the maintenance tasks.
- Apply early awareness measures to detect and eradicate invasive alien species. Do not introduce any invasive species in ponds.
- Define procedures for ponds and drains cleaning adapted to target species requirements and planning fauna rescues beforehand if required.
- When ponds don’t provide safe habitats for aquatic organisms due to pollutants, steep edges or very frequent cleaning requirements, prevent access for amphibians or other semiaquatic animals by installing appropriate fencing.
The following descriptive maintenance task sheets are provided in Section 7.4 – Maintenance tasks sheets.