Optimizing the thermal production of electricity in the short term in an integrated system when a thermal unit commitment has been decided means coordinationg hydro and thermal generation costs over the time period under study. Fundamental constraints to be satisfied are the covering of each hourly load and satisfaction os spinning reserve requeriments and transmission capacity limits. A nonlinear network flow model with side constraints whit no decomposition into hysro and thermal subproblems was used to solve the hydrothermal scheduling. A novel thermal generation and transmission network is replicated with line outaged in order to obtain a secure multi-interval shot-term power flow. Computational results are reported.