Watershed Description

The Flatfork Creek-Fall Creek Watershed is a 17,798 acre watershed that drains land in Madison County, Hancock County, Town of Fishers, and City of Indianapolis into Fall Creek upstream of Geist Reservoir. A small portion (10%) of this watershed is within the Town of Fishers planning area. Very little of this watershed (4%) is within the Town’s corporate limits. Major waterways in the Town of Fishers planning area include Fall Creek and Flatfork Creek and 1 regulated drain (Flatfork Creek Drain).

This watershed remains predominantly undeveloped in agricultural land use (70%). Pockets of low density residential development are scattered throughout. 

Existing Conditions and Concerns

Existing condition and concerns were gathered using a variety of data sources. All resources are referenced in Chapter 7 of this Master Plan.  Supporting documentation on water quantity data listed below can be found in Appendix 2 and water quality in Appendix 3.

• Detailed floodplain studies (Zone AE) have been completed for Flatfork Creek and portions of Fall Creek. Approximate (Zone A) delineations exist for portions of Fall Creek.
• The Zone A delineation along Fall Creek near the Madison County line appears to miss some floodplain area. It is therefore possible that development would be improperly allowed in the actual floodplain.
• Hydrologic modeling of the Flatfork Creek watershed was done as part of the neighboring Hancock County FIS.
• There are 2 USGS stream gauges monitoring flow and stage level within the larger Fall Creek watershed. One gage is located at 71st Street in Indianapolis. Readings of 76 different parameters have been taken monthly since 1991. The other gauge is located near Fortville on Fall Creek. That gauge has been operating continuously since 1941 providing flow and stage data.
• Based on the hydrologic modeling of Flatfork Creek done for the Hancock County FIS, the pre-development 1% annual chance and 10% annual chance peak runoff rates are lower than the default 11-100 year and 0-10 year allowable release rates, respectively. Therefore, current ordinance allowable release rates are allowing post-development discharges to be higher than predevelopment discharges. No existing modeling was located that could be used to evaluate the release rates required by the Ordinance for Fall Creek.
• Flatfork Creek at the County line is sparsely wooded but has good setbacks (150 or more feet) between homes and stream. Density and width of cover grows as Flatfork travels north to confluence with Fall Creek. Along Fall Creek between Lick Creek and Flatfork Creek the riparian corridor is dense and approximately 300 feet on either side.
• There are 37 acres of notable palustrine forested, broad leaved deciduous temporarily flooded wetlands along Fall Creek east of Atlantic Ave. (27 acres) and along Flatfork Creek south of 101st Street (10 acres).
• This watershed is predominantly an undeveloped, agricultural watershed with low density single family residential land use.
• Based on available land use date, imperviousness is estimated to be 47% which is typically indicative of moderate to poor water quality.
• Water quality monitoring conducted in 2009 at Flatfork Creek and 101st Street for this Master Plan indicates:
• Chemical – Nitrogen concentrations were highest at this location throughout the sampling period while phosphorus concentrations were below water quality targets. E. coli concentrations were highest in April and May, but declined throughout the remainder of the sampling period with exceedances in 57% of the samples.
• Biological – The average PTI score for this site resulted in the 2nd lowest average PTI score of 20 (Good).
• Physical –Overall QHEI score (65.5/100) was 4th highest of 10 with good individual metric scores associated with substrate, in-stream cover, and channel morphology.
• Other water quality studies?
• IDEM has completed fish tissue and fish community sampling at 2 locations; 1 upstream of the planning area and 1 located at Flatfork Creek and CR 400.
• IDEM has a fixed water quality monitoring station located at Fall Creek and SR238. (attempting to get data)
• 1 USGS Stream gage monitors flow and stage level on a continual basis at Fall Creek and SR 238.
• Marion County Health Department has completed general water quality sampling between 1995 and 1997 at Fall Creek and SR 238. E. coli levels were not monitored and nutrient and metal concentrations were either below detection limits or present in concentrations below water quality targets.
• Fall Creek to the confluence with Lick Creek is the only waterway in this watershed that is listed on the State of Indiana 303(d) List of Impaired Streams.
• Based on available land use for this watershed, it is anticipated that water quality in some or all water bodies is likely impacted by elevated nutrient, bacteria, and total suspended solids loads.
• Dry weather screening conducted by the Town of Fishers identified 0 outfalls (observed dry weather flow at 0 outfalls).