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6.8 Soil Dykes

6.8 Soil Dykes. DIVERSION DYKE. GUIDE DYKE. SOIL DYKES: MOST COMMON WAY OF DIVERTING WATER. Diversion cum guide dykes: In upper part of river, where slope is higher, water force is higher and there are mainly gravel and coarse sand deposits Crossdykes cum guide dykes :

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6.8 Soil Dykes

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  1. 6.8 Soil Dykes

  2. DIVERSION DYKE

  3. GUIDE DYKE

  4. SOIL DYKES: MOST COMMON WAY OF DIVERTING WATER • Diversion cum guide dykes: • In upper part of river, where slope is higher, water force is higher and there are mainly gravel and coarse sand deposits Crossdykes cum guide dykes: • In lower part of the river, more gentle slopes, sandy-loamy deposits, water velocity is less, can breach during high floods

  5. SOIL DYKES: DIMENSIONS OF SAD/GANDIS IN DI KHAN IMPORTANT TO INCLUDE THE GUIDEDYKE ALONG THE FLOOD CHANNEL TOO!! Source: Khan and Marwat, 2004

  6. Construction soil dykes: using bulldozers or..

  7. Using bullocks with scraperboards Local organisation

  8. Constructing soil dykes • Location: • Determined by lay of the land • Manage water levels and avoid overflow/ flooding • In case of cross dyke - preferably at angle, try to dissipate energy • In case of cross dyke -may have upstream offtakes too • Construction • Look for good loamy soil – avoid gravel and sand • Avoid saline soil and do rat control – to prevent piping • Develop layer by layer • Compaction with bulldozer driving across the dyke • Protect against animal tresspassing • Protect with some vegetation and brushwood • Generally crest 0.6-0.9 meter above the level of the flood channel • Special issue • Often flood channels are not well maintained and silted up causing pressure on the soil dykes – that may break too soon

  9. Soil dykes break: • In case of high floods or: • If the flood channels cannot remove all flood water in time • Or on purpose if the entire area is served and/or water has to be passed downstream

  10. SOIL DYKES: MAINTENANCE

  11. SOIL DYKES: MAINTENANCE Source: Khan and Marwat, 2004

  12. Reinforcing earthen dykes: Gabions

  13. Reinforcing earthen dykes:plastic sheeting Material Black polyethelene plastic 150-250 micron Cost 0.35 USD/m2 Construction Avoid puncture Use steps to contruct to Avoid slippage Anchor at toe and head Cover with 50 cm soil

  14. Reinforcing with wooden pegs

  15. DISCUSSION: SCOPE FOR SUCH SYSTEMS IN LOWLANDS OF ETHIOPIA?

  16. POTENTIAL TO BE EXPLORED.....

  17. POTENTIAL TO BE EXPLORED..... Convert natural drains in flood channels Pre-irrigate and store moisture Protect vegetation on river banks Use diversion cum guide soil dykes

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