Marion County is drained by numerous rivers, creeks, brooks, runs and ditches, the majority of which eventually flow into the White River. The White River flows predominantly from north to south through the County and downtown Indianapolis. The two largest tributaries of the White River are Eagle Creek and Fall Creek. Eagle Creek flows from the north-west of the County, through the Town of Speedway, and then drains into the White River downstream of downtown Indianapolis. Fall Creek flows from the northeast, along the northern boundary of the City of Lawrence, and joins White River upstream of downtown Indianapolis. The Eagle Creek Dam, located in the northwest corner of the County and Geist Reservoir, located on the northeast corner, regulate water levels for Eagle Creek and Fall Creek respectively.
Although there are a number of waterways in Marion County that could flood, the majority of flooding problems are along the White River. Approximately 18% or 46,234 acres of the County are in the 100-year and 500-year floodplains, 31.3% of which is along the White River. The river valley of the White River is flat and wide with a significant floodplain area equal to approximately 6% or 14,450 acres of the land area in the County. With the exception of where flood control structures narrow the floodplain, the 100-year floodplain can be as great as 1 to 2 miles wide. Much of this floodplain area has been developed, and subsequently floods.
Click map for larger version
Approximately 18% of the land area in the City of Indianapolis is considered 100-year floodplain (blue) or 500-year floodplain (pink). The majority of the floodplain is along the White River. Please note this map is intended for illustrative purposes and is not intended to be used in place of the most recent FIRM map.