Si los escurrimientos son de plástico, entonces sería 'yieldings' en lugar de 'trickles'. Pero sin más contexto no lo sé...

¡Suerte!

It's runoffs of things which are drained off for whatever reason; - probably because they have a negative impact. They may well flow in a trickle, but I think it's a case of run-offs here, in the sense of ' escorrentía';

this is the way I would say it.
The meaning in Spanish is that run-off should work and it should do it the way it was originally intended to.

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Note added at 1 hora (2013-11-11 15:19:02 GMT)
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http://www.esru.strath.ac.uk/Documents/MSc.../Carroll.pdf‎

....its rainwater runoff performance with that of a perspex sheet (to replicate a ... that green roofs have the capability to offset the 'poorer' runoff performance of PV...

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Note added at 1 hora (2013-11-11 15:20:01 GMT)
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http://www.google.com.cu/url?sa=t&rct=j&q=&esrc=s&source=web...