harvesting

TABLE 2.3 Recommended practices for road-drainage systems and water harvesting

OBJECTIVE

Systematically collect and divert runoff

APPLICABLE DRAINAGE PRACTICE

The road-drainage system is a mechanism for effectively collecting and diverting all water that is gathered around the road. If adequately designed, it can help “harvest” a large part of the runoff from the catchment uphill of the road and avoid waterlogging upstream of the road. The road-drainage system should generally have sufficient capacity to remove the peak runoff volume quickly enough to facilitate transit.

Dispose of runoff in areas where it can be used beneficially

Have an adequate number of outlets from the drainage system

Reduce the hydrological connectivity of the road network Road-drainage water should not be disposed of in areas where it creates damage or where it serves no useful purpose; rather, it should be led to agricultural areas, tree plantings, rangeland, recharge areas, or ponds. It is also important that road-drainage water (including the sediment and other particles it carries) not be directly discharged into streams where it will create turbidity and cause stream sedimentation. It is important to have adequate outlets from the road-drainage system; these outlets should distribute the water over a wide area rather than accumulating water flows too voluminous to be handled from a limited number of outlet points. In a few cases, however, on steeper and erodible slopes where gullies develop below each cross-drainage structure, runoff should be concentrated at fewer points that lead to well-reinforced waterways. This approach helps optimize resources invested in waterway stabilization on steeper terrain. To minimize the road’s contribution to hydrological connectivity, runoff collected from road drainage should be diverted or distributed to vegetative bunds, pasture, or farmland and should not be allowed to quickly discharge into local streams and drains. This recommendation prevents the rapid buildup of flood peaks after rainfall in the watershed.

Harvest sediment from road-drainage systems Road-drainage systems can also be used to collect sediment. This objective requires the side-drain slope to be broken with drop structures such as scour checks. Sediment will be deposited in the flat sections and can then be collected and used as building material, particularly if collected near towns. Sand harvesting from road drains can be an important job opportunity.

Source: MetaMeta, (www.roadsforwater.org).

water management in watersheds: that roads should not contribute to hydrological connectivity.

Culverts are important elements in road-water management. Culverts that discharge water in an uncontrolled manner can be a major source of damage, but culverts can also guide the runoff from the catchment to places where it is used beneficially. Culvert design, including bed sill and some of the ancillary structures, can also help control erosion. There are a number of important recommended practices:

• Culverts should be placed on drainage lines. As obvious as it sounds, culverts are often incorrectly located during the road design and construction process. • An adequate number of culverts should be built. distorting natural drainage patterns by reducing the number of cross-drainage points is likely to create highly erosive runoff, flooding, or both. • Culverts should be installed close to productive land, storage ponds, and recharge areas. When necessary, they should be equipped with diversion canals that direct runoff water to benefit areas and structures such as ponds or infiltration trenches. • The upstream side of culverts must be designed properly and include any protection measures (Berhe 2018) to guide water through the culvert at a controlled velocity. These measures may comprise the following: – Widened intake channels to slow the runoff passing through the culvert – Protection of the intake channels with riprap or vegetation to prevent erosion