1. Unpolluted raw water with 3gO2/m3 and a temperature of 8C is passed over a straight weir of a height of 0.55m. Estimate the downstream oxygen content. 2. Determine the number of steps of a cascade to achieve maximum oxygenation, assuming an available head of 1.0m, an efficiency coefficient K depending on the weir height h as stated by figure given below (Cs=12g/m3,C0=3g/m3). 3. There are three stages in a cascade. Each step raises the oxygen concentration from 0 to 25% of the saturation value. If the inlet water temperature is 15C and the oxygen concentration is 20% of the saturation value, what will the effluent concentration be