Alternative road option in floodplains: Submersible roads

PHOTO 7.5

Water in canal controlled by gates on the culvert, Uganda

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ALTERNATIVE ROAD OPTION IN FLOODPLAINS: SUBMERSIBLE ROADS

The preceding part of this chapter discusses roads on embankments in floodplains. These all-weather roadways are closed for a limited number of days during the year. There is an alternative concept for roads in floodplains: roads that are submerged for a large part of the year during the flooding season.

To provide downstream protection of a horizontal submersible track, an opening of 10–15 centimeters wide is set every 3–4 meters to drain the road (Bender 2009). These roads are inundated during the flooding season but facilitate transport during the dry period when they reemerge. They can be reused, usually after some small repairs. These submersible roads do not interfere negatively or positively with the flood regime in the floodplain.

The following requirements apply for submersible roads (figure 7.1):

• They should be based on stable bed material capable of coping with waterlogging conditions, preferably free-draining and solid material; coarse sand is preferred. • The road must be slightly elevated and may be anchored at the side. • The slope gradient should be 0 percent.

To avoid prolonged flooded conditions after a flood, it is possible to make one or two parts of the road 5–20 centimeters below the lower level of the ground.