Narrow stream is not flowing in ditch (8)
I believe the answer is:
jettison
'ditch' is the definition.
(to jettison is to ditch or discard)
'narrow stream is not flowing' is the wordplay.
'narrow stream' becomes 'jet' (I am not sure about the 'narrow' bit.).
'flowing' indicates anagramming the letters.
'is'+'not'='isnot'
'isnot' with letters rearranged gives 'tison'.
'jet'+'tison'='JETTISON'
'in' is the link.
Can you help me to learn more?
(Other definitions for jettison that I've seen before include "Throw overboard or discard unwanted material" , "Form of motor racing" , "Throw away (from ship or aeroplane?)" , "Get rid of" , "Throw (into the sea)" .)