Commentaries: Art. 42

Before an authority authorises the flushing out or emptying of an impoundment, it shall ensure that sediments are removed other than by washing away if this is environmentally compatible and economically acceptable.
When washing away sediments the authorities shall ensure that communities of plants, animals and micro-organisms are harmed as little as possible, in particular by laying down:
1. time and type of flushing out or emptying;
2. the maximum concentration of suspended matter in the water which must be respected during the flushing out or emptying;
3. to what extent washing away must be carried out so that during the flushing out or emptying, fine matter deposited in watercourses is removed.
Paragraphs 1 and 2 do not apply to the abrupt lowering of the water level following an exceptional event (Art. 40 para. 3 WPA).