Adequate environmental flows are needed to maintain the ecological integrity of the estuaries. The environmental flows from a watershed are influenced by changes in land use/land cover, variability in climate, and water regulations. San Antonio, TX, the 8^th largest city in the US, is likely to affect environmental flows to the San Antonio Bay/Guadalupe Estuary, in the San Antonio River basin. Rapid urbanization has changed the land use and land cover in this river basin. Changes in land use can change the flow regime by altering timing, magnitude, and frequency of freshwater inflows. This study used satellite remote sensing techniques to assess the effect that this change has in the regional hydrology. LANDSAT satellite data for the years 1987, 1994, and 2003 were used in an unsupervised ISODATA classification to quantify changes in land use/land cover. In order to quantify the effect of land use/land cover change on environmental flow (flow volume in  the San Antonio river in particular), the model was calibrated using the remotely sensed data from 1987; and then, only land use/land cover data for the year 1994, and 2003 were changed in subsequent simulations. The predicted daily time series for flow was then aggregated for seasonal flow analysis. This study also used wavelet techniques on model output to assess the changes in scale and frequency of flow due to urbanization. Present study will help water resources managers and regulators assess the effect that urbanization potentially has on environmental flows.