Site visits conducted to the project area and satellite images showed that there is one existing culvert under the road south of the project area. This culvert exists to pass the flow of the stream (A) mentioned in the hydrological study. Table 1 shows the characteristics of the existing culvert and table 2 shows the summary of the hydraulic analysis of the culvert.
The culvert should be capable to convey the flow which means that the water level upstream the culverts and at its inlet should be lower than the existing road level so that no damages is caused to the road body and adjacent properties. Accordingly, the culverts were checked for the 50 years return period floods to ensure that its inlet water levels are lower than the road levels. The 50 years return period is generally the adopted design storm for culverts under roads and according to Ministry of Transport (MOT) recommendations. Moreover, the checking was made on the velocity of flow at its outlet which should be lower than 6m/s as per design criteria of culverts.
Table 2 shows that the culvert cannot convey the flow and the road will be subject to overtopping during extreme rainfall events. The traces of water are clearly seen at the top of the existing culverts revealing the extreme conditions these culverts were subject to. Figure 1 shows the hydraulic analysis of the culverts which is done using CulvertMaster software.