page_title: Arwadito
section_title: Flash floods and flood buffering
hierarchical_section_title: Arwadito / Flash floods and flood buffering
caption_attribution_description: English: Log Dam May Qoqah
context_page_description: Arwadito is a torrent of the Nile basin. Rising on the Ts’ats’en plateau of Dogu’a Tembien in northern Ethiopia, it flows northward to empty finally in Giba and Tekezé River.
context_section_description: Runoff mostly happens in the form of high runoff discharge events that occur in a very short period (called flash floods). These are related to the steep topography, often little vegetation cover and intense convective rainfall. The peaks of such flash floods have often a 50 to 100 times larger discharge than the preceding baseflow.
  The magnitude of floods in this river has however been decreased due to interventions in the catchment. 
  Physical conservation structures such as stone bunds and check dams also intercept runoff. 
  Observing that, in rivers with coarse bedload, gabion check dams were destroyed by abrasion, boulder-faced  log dams were installed transversally across this torrent. They were embedded in the banks of torrent, 0.5–1 m above the bed, and their upstream sides were faced with large rocks. Such dams lead to temporary water ponding, spreading of peak flow over the entire channel width, and sediment deposition. After testing under extreme flow conditions (including two heavy storms) it appeared that 60% of the dams resisted strong floods, particularly in the upper segment of the river. Neighbouring farmers appreciate such structures to control first-order torrents with coarse bed load because the technique is cheap and can be easily installed.
caption: Log dam in Arwadito River
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