Big Rock and Welch Creeks are located in southwestern Kane County, Illinois. This area
of Kane County is expected to experience development in the coming years; thus an accurate
representation of local flood hazards is important. Regulatory floodplain maps now in effect for
these streams show floodplain boundaries based on observations of flood events that occurred
more than 30 years ago and lack engineering analyses that meet current standards and
expectations. The purpose of this project is to better define flood hazards posed by streams in
the Big Rock and Welch Creek watershed based on hydrologic and hydraulic analyses of existing
conditions. Illinois State Water Survey (ISWS) staff worked with Kane County and community
representatives to identify stream reaches for study and the level of study detail for each reach.
Hydrologic and hydraulic analyses were conducted and used to delineate floodplain boundaries
corresponding to the 1-percent-annual-chance flood, the base flood used by the Federal
Emergency Management Agency (FEMA) for regulatory flood protection. Information was
generated using spatial datasets and field data. Digital floodplain boundaries and attendant data
are stored in the FEMA-prescribed Digital FIRM (DFIRM) database format for ready
incorporation in the regulatory maps upon review and approval by FEMA. This study will
provide information for floodplain management in both urban and rural areas.Kane County Department of Environmental Concernspublished or submitted for publicationis peer reviewe
