Allah – The Exalted- says:

أَنزَلَ مِنَ ٱلسَّمَآءِ مَآءً فَسَالَتْ أَوْدِيَةٌۢ بِقَدَرِهَا فَٱحْتَمَلَ ٱلسَّيْلُ زَبَدًا رَّابِيًا وَمِمَّا يُوقِدُونَ عَلَيْهِ فِى ٱلنَّارِ ٱبْتِغَآءَ حِلْيَةٍ أَوْ مَتَٰعٍ زَبَدٌ مِّثْلُهُۥ كَذَٰلِكَ يَضْرِبُ ٱللَّهُ ٱلْحَقَّ وَٱلْبَٰطِلَ فَأَمَّا ٱلزَّبَدُ فَيَذْهَبُ جُفَآءً وَأَمَّا مَا يَنفَعُ ٱلنَّاسَ فَيَمْكُثُ فِى ٱلْأَرْضِ كَذَٰلِكَ يَضْرِبُ ٱللَّهُ ٱلْأَمْثَالَ

He (Allah) sends down water (rain) from the sky, and the valleys flow according to their measure, but the deluge bears away the foam that mounts up to the surface, and (also) from that (ore) which they heat in the fire to make ornaments or utensils, rises a foam like unto it, thus does Allah (by parables) show forth truth and falsehood. Then, as for the foam it passes away as scum upon the banks, while that which is for the good of mankind remains in the earth. Thus Allah sets forth parables. Ar-Ra’d 17]

PDF

deluges_valleys_and_benefits