Debris used to be there following evacuation (5)
I believe the answer is:
waste
'debris' is the definition.
(thesaurus)
'used to be there following evacuation' is the wordplay.
'used to be' becomes 'was' (eg 'he was...' means 'he used to be...').
'there following evacuation' becomes 'te' (I can't justify this - if you can you should give a lot more credence to this answer).
'was'+'te'='WASTE'
Can you help me to learn more?
(Other definitions for waste that I've seen before include "Use carelessly" , "Useless leftovers" , "Not use effectively" , "unused" , "Use to no purpose" .)