Answer:
Alaska; Yukon River
California; Salton Sea
Arizona; Gila River
New Mexico & Texas; Pecos River
Step-by-step explanation:
Leaving aside the Hudson River in N.Y. and the Susquehanna River in Pennsylvania (a relatively low frequency of floods) the 4 states that would benefit enormly from building dams etc. because of their high frequency of flood events) are California, Arizona, New Mexico and Texas.