![]() The drift should have a curvature toward the center of the river to ensure that the water concentrates in the middle of the river, minimizing erosion along the riverbank.At the foundation of the drift on the downstream side, gabions should be installed to prevent the foundation from being undermined by the overflow of floodwater.The height of the drift above the existing riverbed should be a maximum of 1 m to ensure sufficient depth for the accumulation of sand and water upstream.The width of the roadway slab should vary between 3 m and 5 m, depending on the anticipated type and volume of traffic.The foundations, walls, and slab should be rigidly tied together to give the drift great resistance to being washed away by floodwaters.The drift should be filled with hardcore material and compacted to a maximum depth of 1 m on sandy riverbeds and 0.6 m on rock riverbeds.The top slab, on which traffic passes, should have a constructed thickness of at least 150 mm to 200 mm, depending on traffic volume and load.Foundations should have a minimum width of 500 mm and a construction depth of 250 mm.In sandy riverbeds, anchor the structure at 1.5 m below the existing riverbed level in rocky riverbeds, the foundations should be laid on the bedrock.Extend the approach above the experienced flood level to prevent damage when floods are high.Expand the drifts by 5 m to 10 m on either riverbank, depending on the width of the river.However, the main points with respect to the design of the non-vented drifts are presented below: Annex 2 provides a detailed description of the design of a non-vented drift. The design of a non-vented road drift consists of several elements: the body of the drift, the approach road, the upstream protection of the stream, and the downstream apron. Road drift on a small river near Kitui town, Kenya Sample Supplement Terms of Reference Road Programs Dimensions and spacing of eyebrow terraces and stone strips Bio-engineering measures for road side-slope stabilization Making it work: governance for green roads for water.Combining water harvesting and tree planting.Controlling upstream water levels with cross-drainage structures.Adequate cross drainage and subsurface flow capacity.Location and height of road embankments and controlled overflow sections. ![]() Use infiltration bunds to control erosion and enhance recharge.Planning road alignments for adequate drainage and water management.Water harvesting and drainage from unpaved roads.River crossings as sand dams and bed stabilizers.Ensuring the safety of the converted borrow pit.Road water harvesting for surface storage.Road water harvesting for groundwater recharge.Using springs opened by road construction.Roads as temporary flood shelters and evacuation routes. ![]()
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