City Expansion due to human migration for better civic amenities changing original land use posing flood risk in the cities located near river. Present study was conducted to investigate flood risk of Big Blue River/ Wildcat Creek due to expansion of Manhattan city, Riley County, Kansas State, USA. Hydrographs and peak runoff were determined for three different scenarios current zoning, future zoning, and adding 20% impervious surfaces onto current zoning. Stage discharge relationship was developed for all three land use characters for 5 and 25 years storm events. Assumption was made that, if the water exceeded 6 meter depth, the area it could submerge was considered prone to flooding. Results of the study revealed that, there was no increase in depth of water (stream stage) in Wildcat Creek before and after planned rezoning of Manhattan. However, by increasing the impervious areas by 20%, stream stage in the Wildcat creek exceeds 6m threshold level posing potential of flooding.
