Kinney Run and Tributary No. 10 Stormwater Analysis Abstract Kinney Run, an 8.288 square kilometer (3.20 square mile) watershed, and an Unnamed Tributary No. 10 Scott Township, a 5.698 square kilometer (2.20 square mile) watershed, are tributaries to the Susquehanna River within the Act 167 Study for Susquehanna River Tributaries, Columbia County, Pennsylvania. Originating in Scott Township, their headwaters are in moderate to steeply sloping uplands and then follow their paths through a joint flood plain to their outlets at the Susquehanna River. The analysis of the stormwater problems for these watersheds presented unique problems for modeling purposes. Natural and manmade conditions within the watershed have created impacts on downstream peak discharges. Analysis of the stormwater problems was performed using a combination of the NRCS TR-20 watershed model and the Army Corp HEC-RAS Hydraulic model. Trial and error was required to determine the discharge at several points within each watershed. This required first using TR-20 and its divert and reservoir storage routines to determine peak flows at various locations. These values were then used to perform HEC-RAS analysis. The discharge quantity and the elevations were compared at critical points in the two models. Adjustments were then made in each model until the peak discharges and discharge elevations in both models coincided. Once the existing condition models were calibrated in this manner, additional conditions evaluations were performed to determine their effects on downstream peak discharge. They include: (1) effects of future development within the watershed with no stormwater controls, (2) reduction in flood plain storage by filling the areas within the limits permitted by flood plain regulation; and (3) a combination of flood plain fill and future development without stormwater controls. Watershed analysis has identified a number of areas where stormwater is presently stored and results in reduction of downstream peak discharges. Many of these areas are in areas subject to intensive pressure for development. The analyses have also resulted in considerable discussion as to the types of stormwater Best Management Practices (BMPs) that may be needed to control impacts of future development on downstream stormwater discharges. In addition to the standard infiltration and detention or retention Best Management Practices, a need to preserve the natural and unintentionally man-made storage areas at their present capacity exists. Preservation of these stormwater storage areas will affect the value of these areas for their owners and depending upon the method used could be considered a taking of landowners’ rights. Introduction Kinney Run and Tributary No. 10 to the Susquehanna River in Scott Township are only two of forty-one watersheds being studied as part of an Act 167 Watershed Phase II Plan preparation for the Susquehanna River Tributaries, Columbia County, Pennsylvania. Kinney Run flows to its outlet at Bloomsburg through a very flat gradient (0.002 m/m) stream channel in the Susquehanna River flood plain. The stream channel flows parallel to the river through the common flood plain for 3230 meters (10,600 feet) and has tributary areas within the flood plain as well as additional upland areas. During major flood events, Kinney Run usually experiences flooding in its flood plain due to stormwater runoff from its drainage area. Kinney Run then returns its stormwater discharge to within channel area, before the river floods into it again. Page 1 Tributary No. 10 also flows to its outlet with the river in Scott Township through the joint Susquehanna River flood plain for a distance of 1931-meters (6336 feet). During major flood events Tributary No. 10 follows the same flooding pattern as Kinney Run. The problem of managing stormwater for both streams has been recognized for a number of years. Several proposals have been developed to divert them directly to the river at different locations. The description of the problems and the unique challenges for analyzing their peak discharges are as follow: Eroded soil from upland areas has silted in some of the stream channels at the upland- flood plain interface. In some cases the channels are non-existent. There are a number of stormwater detention areas within the flow paths of Kinney Run and Tributary No. 10. These areas consist of both natural wetlands and stormwater storage areas created by railroad and highway fills within the watersheds. Many of these stormwater storage areas are not recognized as such and are located in areas under extensive pressure for development. Some of the areas along U.S. Route 11 are considered so valuable for commercial development that developers are looking for wetland mitigation sites in order to develop them. Many of the stormwater detention areas are within the designated FEMA Flood Insurance Plans. Several large ones that were created by roadways have not been identified in the FEMA Flood Insurance Plans as being located within the 100-year flood plain. In the watershed there are two locations where stormwater flow is diverted from the Kinney Run channel to either Tributary No. 10 or the Susquehanna River. Major differences in the 100-year frequency peak discharges were noted between the Town of Bloomsburg and the Scott Township FEMA studies for Kinney Run. The Town of Bloomsburg study indicates a 100-year discharge of 8.41 cubic meters/second (297 cfs) at the mouth, while the Scott Township study indicates a 100-year discharge of 38.51 cubic meters/second (1360 cfs) upstream from the mouth at the Scott Township boundary with Bloomsburg. Kinney Run Watershed and Problem Description The Kinney Run watershed with 8.299 square kilometer (3.20 square mile) drainage area is presented as Figure 1. The Kinney Run watershed originates in rolling upland topography with numerous small steep gradient tributaries (grades range from 0.02 to 0.08 meters/meter) that intersect the main flat gradient channel (0.002 meters/meter) throughout its length. The main channel transverses 1931-meters (6336 feet) in the joint floodplain with the river. During the last thirty-five years, there has been extensive residential and commercial development within the watershed. The upland land use has shifted from agricultural production having extensive land conservation treatment to residential developments and a few commercial enterprises, many of which have no stormwater detention and/or retention systems. The flatter sloped land areas of the watershed have also experienced extensive growth, with a high percentage of that development being commercial enterprises. Since the portion of the watershed within the Town of Bloomsburg was extensively developed, most of the new growth is occurring in Scott Township. Kinney Run stormwater problems have created considerable controversy between Bloomsburg and Scott Township. Both municipalities have independently addressed stormwater concerns by developing and implementing their own municipal stormwater ordinance within the last 10-years. Until the Act 167 study, Kinney Run was not looked upon as a complete watershed in order to determine the effects of the stormwater ordinances. Page 2 Development with the increase in impervious areas and installation of the stormwater drainage pipes and channel systems has not only increased the discharges from subwatershed areas, but has accelerated the movement of stormwater downstream. Due to these changes in discharge, many of the upslope channels are eroding at an accelerated rate. The sediment is carried downstream to the valley interface where it is deposited as the channel grade flattens out. The sediment deposition results in reduced channel conveyance capacity and in some cases, the sediment has completely filled the channels. A portion of Kinney Run, east of Central Road, is one of the areas where the channel has been silted in. Not only has this occurred but also the formerly farmed area has reverted to a wetland. At this location, (Diversion-1 on Figure 1), some of Kinney Run’s stormwater flow diverts to Tributary No. 10 through the wetland area. After the June 1972 Agnes Flood, in order to relieve flooding problems in Bloomsburg along Kinney Run, a structure, (Diversion-2 on Figure 1) was constructed to divert a portion of the flood flows directly to the Susquehanna River via a channel and large diameter pipe (2100 millimeter) under the airport runway. Several past studies have recommended other diversions of Kinney Run to the Susquehanna at several locations within Scott Township and just east of Catherine Street in Bloomsburg. These diversions were recommended to relieve flooding of potentially developable land in Scott Township and to reduce flooding from Kinney Run in Bloomsburg. Within Kinney Run’s joint flood plain with the river there are a number of obstructions and natural wetlands that detain stormwater runoff and reduce peak discharges. The North Shore railroad bed and U.S. Route 11 were constructed parallel to the river, and in many places, through areas of wetlands or hydric soils. The wetlands and obstructions that affect the stormwater peak discharge locations are noted on Figure 1 and a description is included in Table 1. Beavers create additional stormwater level problems, as they build dams and block culverts. The result of the beavers’ labor raises stormwater levels and increases the area inundated. It also reduces the available stormwater detention volume within those areas. The area identified as Stormwater Storage #2 on Figure 1 has been zoned as Flood Overlay District by Scott Township. However, other than not developing within the actual floodway, the major requirement of the zoning regulations is that the first floor of any building within this area must be constructed 0.4572 meters (1.5 feet) above the designated 100-year flood level in the FEMA Flood Insurance Plan. Historically, serious floods along Kinney Run have been accompanied by major flooding on the Susquehanna River. During the Agnes and January 1996 floods, Kinney Run first experienced flood plain flooding from stormwater discharges from within its watershed.