Yes, DAMs help if due ...

Yes, DAMs help if due attention is given to their  designing  which considers the # of months in  a year evaporation exceeds transpiration in an area where  storage is foreseen as Kevin L. noted , obviously taking into account also issues  associated with the soil- such as the problem of  percolation. But beyond it, expensive though, it is also  good to look into  activities like 'Rivers Training'  I.e. taking structural measures to improve rivers and their banks along  River lines, as potential River bank areas (arable or those suited for grazing)  are on being continuously trimmed of by either over flows or Rivers that deviate from their natural course.