BASIC SEDIMENT TRANSPORT AND RIVER MORPHOLOGY 6.2 BASIC SEDIMENT TRANSPORT AND RIVER MORPHOLOGY

STATEMENT: IN SPATE IRRIGATION MANAGING SEDIMENTATION IS AS IMPORTANT AS MANAGING WATER

THE WIDE FLOOD CHANNEL IN THE UPPER SECTION TYPICALLY CONTAINS A NUMBER OF LOW FLOOD CHANNELS – THAT ARE FORMED BY THE PRECEEDING HIGH FLOWS AND THE RECESSION FLOWS IN THIS SECTION EPHEMERAL RIVERS CAN BE QUITE UNSTABLE AND EVEN CHANGE DIRECTION IN A HIGH FLOODS UNLESS THEY ARE CONTAINED – IN THESE AREAS EMBANKMENTS AND GUIDE BUNDS ARE IMPORTANT

BECAUSE OF SEEPAGE, CHANNEL STORAGE AND IRRIGATION ABSTRACTIONS, FLOODS FLOW REDUCE AS THEY PASS DOWN AND THE EPHEMERAL RIVER OFTEN REDUCES IN DEPTH IN THE LOWER SECTIONS

NEW BED LEVEL OLD BED LEVEL YANDOFERO RIVER, KONSO, ETHIOPIA RIVER MORPHOLOGY GONE WRONG:AFTER THE CUTTING OF A RIVERAINE FOREST THE YANDOFERO RIVER CHANGE ITS DOWNSTREAM COURSE AND BED LEVELS DROPPED 1-3 METERS

SEDIMENT TRANSPORT

SEDIMENT LOADS OF 5% OF WEIGHT ARE COMMON IN FLOODS HIGH FLOODS MAY CARRY AS MUCH AS 10%

WITHIN THE EPHEMERAL RIVER SYSTEM A MIX INCLUDING COARSE MATERIAL IS USUALLY FOUND IN THE UPPER SECTIONS

CLAYS AND FINE MATERIAL SETTLE MORE IN THE TAIL

The fine sediment in one irrigation may reach 15 cm height!