The observation of climate changes, as a consequence of global warming, reveals the aggravation of extreme situations, including alternating torrential rain periods with drought situations. Therefore, it’s important to ensure that road drainage systems are calculated for extraordinary phenomenon (both precipitation and flow) associated with a predetermined return period, which includes an allowance for the worsening of weather conditions. Designing to historic weather patterns is likely to mean that there will be an increase in the frequency when elements of the drainage system will not have adequate capacity, with inevitable consequences for the safety of users and, eventually, for the survival of the infrastructure itself.
Today’s road drainage elements should be monitored to allow measurement of the return period for which they are designed, adopting in latter life of the drainage system a solution for increasing the capacity in face of the reality found on site. One should also ensure that inside this observation phase (which could take some years), efficient cleaning and maintenance plans are implemented with adequate frequency, so that the drainage elements are in perfect functioning order. For example, after drought seasons the tendency to become clogged with sand is higher.
Future infrastructures should be dimensioned by adopting the revised values and parameters collected through information recovered in rainfall and/or water flow monitoring stations placed near the locations of the particular road scheme.
A safe and comfortable road requires a great investment in scheme planning, careful design, quality construction and ongoing maintenance. At each stage of the road’s life, the hydraulic, geotechnical and pavement performance must be considered alongside the environmental response of the road and its “corridor”.
Drainage standards exist to aid design, performance and maintenance, but they are not to be followed as laws, but as a reference and recommendation for a project. As important as the standards are for many facets of a highway’s design (including the safety aspects), it is the engineer’s experience and good sense that must determine the road scheme planning and its detailed execution at a project level. Greater rigor by consultants and owners concerning the choice of drainage solutions is important, yet they should be given greater flexibility in the project’s execution schedule and in construction of the work’s drainage system. It is also the consultant and owner who are best placed to determine the appropriate safety implementation.
The wide variety of solutions available to ease the road through the hydraulic environment will necessitate careful study and selection in order that the most economically, socially and environmentally beneficial solution is found. A similar attention will need to be paid to the selection of materials and components. This is partly because of the wide range of geosynthetic materials and composites with properties specifically “tuned” to drainage applications that are now readily available and partly because of the ever-increasing pressure to use marginal, waste and by-product construction materials in place of the conventional aggregates with which designers may be more familiar.
This chapter has, albeit briefly, sought to indicate something of the breadth of solutions and the considerations. It will be apparent that much more could be written and much more detailed design advice and sample calculations could have been presented. However this chapter is already the longest in the book and the book longer than intended! It will suffice for now to advise readers of the wealth of information available in the references listed below and at the end of the previous chapters.
Water is often considered the chief enemy of the pavement engineer. It is one of the materials to which the environmental expert gives prime attention. It is the very basis of the hydrogeologist who seeks to protect it so as to ensure continued pure water supplies. It is right, therefore to make it the subject of this book which, one hopes, will help to ensure that it is treated appropriately by everyone who has a role to play in providing and maintaining roads in our precious environment.