The Mekong thalweg profile exhibits a very irregular system of pools and riffles in the central part of the delta (Fig. 3aI). The deepest pools are up to 45 m deep and are located in meander sectors such as Sà Dec (km 135–140, seeFig. 1for distances) or in narrower sections such as upstream of the Ham Luong (km 125) and Co Chien (km 100) bifurcations. Riffle areas correspond to depths from−15 to−5 m. Further downstream (Fig. 3aI), the thalweg profile of the My Tho shows around −15 and−10 m and riffles around−10 and−5 m. Morphological irregularities are less pronounced than upstream. The Bassac thalweg is less irregular than those of the Mekong and the My Tho (Fig. 3aII). The deepest pools lie between−30 and−25 m (km 90–130, near Can Tho), with the exception of one that descends down to−40 m (km 190) (Fig. 3aII) and which corresponds to a narrow channel sector at the bifurcation through the Vam Nao to the Bassac. As in the My Tho,the bottom of the bed becomes elevated and more regular near themouth (from km 50) (Fig. 3aII)
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