pression . ▁The ▁Log one ▁r ises ▁west ▁of ▁the ▁territory ▁and ▁flows ▁north ▁to ▁form ▁most ▁of ▁the ▁border ▁between ▁the ▁Far ▁North ▁and ▁Ch ad . ▁It ▁eventually ▁meets ▁the ▁Ch ari , ▁which ▁also ▁r ises ▁in ▁Ch ad . ▁The ▁Ch ari ▁forms ▁the ▁remainder ▁of ▁the ▁Ch ad - Cam ero on ▁border ▁beginning ▁at ▁K ouss éri ▁before ▁empty ing ▁into ▁Lake ▁Ch ad . ▁ ▁These ▁rivers ▁all ▁follow ▁a ▁tropical ▁regime , ▁fl uct u ating ▁between ▁high ▁water ▁in ▁the ▁wet ▁season ▁( May ▁to ▁September ) ▁and ▁low ▁water ▁in ▁the ▁dry ▁season ▁( Oct ober ▁to ▁April ). ▁At ▁the ▁height ▁of ▁the ▁dry ▁season , ▁many ▁of ▁the ▁water ways ▁disappear ▁completely ▁or ▁else ▁dimin ish ▁to ▁a ▁mere ▁trick le . ▁The ▁Log one ▁all ▁but ▁disapp ears ▁during ▁the ▁wet ▁season . ▁The ▁low ▁elev ation ▁of ▁the ▁Ch ad ▁bas in ▁( 2 0 0 – 5 0 0 ▁metres ) ▁causes ▁flo oding ▁during ▁the ▁wet ▁season ; ▁the ▁Log one ▁is ▁especially ▁pr one ▁to ▁this , ▁and ▁much ▁of ▁its ▁bas in ▁is ▁mar sh like ▁conditions ▁along ▁its ▁length ▁during ▁the ▁wet ▁season . ▁Even ▁during ▁the ▁dry ▁season , ▁some ▁of ▁these ▁remain , ▁called ▁Ya éré ▁in ▁Ful ful de . ▁The ▁El ▁Be ï d ▁and ▁Ser bew el ▁R ivers ▁d rain ▁these ▁mar sh y ▁areas ▁into ▁Lake ▁Ch ad . ▁The ▁Diam ar é ▁P lain , ▁part