Yes well designed dams can ...

Yes well designed dams can control floods to some extent. Down stream people can still get flooded when the dam operators open the spillways to avoid dam damage. If the dam height is not properly designed to take care of prolonged transpiration, operators often have no choice but open the spillways. 

Drought management will also depend on the balance the designers considered in terms of water for irrigation, people and the health of the dammed river. A lot depends on how accurate the data used are the data used in dam design. The integrity of the data used in design is critical.