Page 175 - RoadCem Manual - PCT BV

6.3 External Drainage 6.3.1 Introduction
External drainage involves methods of crossing of watercourses, measures to divert water away from the road and prevention of damage caused by erosion. In the construction of roads there is often wide scope for the use of various measures to improve external drainage, such as low-level structures, drifts etc. where 100% passability to traffic throughout the year may not be required.
It is not within the scope of this Section to provide a detailed description of all the various measures that make up a good drainage system. Conditions on site will vary tremendously in respect of in-situ soils, topography, vegetation, climate, human settlement patterns, environmental concerns, etc. The skills of site personnel and knowledge about local conditions are critical for successful installation of drains, catch-water drains, side drains, berms, channels, cut-off drains and crossings along the road .
Figure 6.10 Ground movement. Figure 6.11 Flooding.
6.4 Hydrology and Hydraulic Calculations 6.4.1 Introduction
The use of sophisticated methods to estimate run-off and for the calculation of the size of waterway structures is not always appropriate for road construction. In many of the developing countries because either the data and/or the resources required are not available. Thus, alternative methods, which also rely on visual observations and historical evidence from consultations with the local populations are often more appropriate. Furthermore, financial constraints also means that a compromise is often required between structures that provide all-weather access and those that can be constructed with the available resources.
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