A Natural History of Millbrook Marsh,
A Wetland In An Urbanizing Setting
Wetlands associated with streams and rivers often provide a flood control function by dissipating and temporarily storing natural and stormwater flows. This stormwater, if not managed carefully however, can also cause significant damage to wetlands and riparian corridors. This results in a reduced flood control function. Substantial disturbance has occurred in Millbrook Marsh, as evidenced by the observations of adjacent property owners and long-time residents (N. Deno, B. Niebel, pers. comm.) and by examining the stream characteristics. The stream surveys conducted in reaches of Slab Cabin Run and Thompson Run within Millbrook Marsh during 1997 yielded evidence that high stream flows attributable to stormwater runoff have negatively influenced the morphology of both streams (Brooks et al. 1998).
In a more natural or less degraded system there would be few or no point source entries of stormwater. Instead there would be overland sheet flow and an overall, and in most cases, relatively gradual rise and fall in stream flow. This is not the situation at Millbrook Marsh where there are multiple stormwater outlets discharging throughout the site and flowing into the streams offsite (Map 7). There are stormwater outfall pipes located outside the bounds of the Millbrook Marsh Nature Center, but still within Millbrook Marsh. Others are outside the marsh but still affect the site. A major input of stormwater flows into Thompson Run before it crosses to the north side of East College Avenue. This has been the primary cause of scouring and bank erosion observed in Thompson Run. One of the detrimental aspects of stream bed scouring is the lowering of the water table. Further downstream the result is an increase in silt deposited on the stream beds of Thompson Run and Slab Cabin Run. The majority of stormwater originates in both the Borough of State College and the Pennsylvania State University campus. It flows first into a ditch on the east side of the University Waste Water Treatment Plant (Figure 3-2) and then joins with part of Thompson Run above the Duck Pond. The Penn State campus drainage area is approximately 172 ha (426 ac).
Figure 3-2 Stormwater drainage ditch above the Duck Pond. The height of the person is 160cm.
(Photo by J. Pierce)
The estimated discharge in 1994 for a 10-year storm was 14.2 cms to 19.8 cms (500 to 700 cfs). The portion of stormwater contributed by drainage areas outside of the University was estimated to be between 5.7 cms and 8.5 cms (200 and 300 cfs) (Gaudlip, pers. comm). The Borough has two main drainage areas totaling about 99 ha (245 ac) that drain (with the University stormwater) into the ditch above the Duck Pond. One, the Calder Way system, drains approximately 89 ha (220 ac), and the other, the Holly Alley system, drains approximately 51 ha (125 ac). Estimates of discharge were made in 1988 to 1990. The expected discharge of the Holly Alley system for a 10-year storm was 4.8 cms (170 cfs) (Wagner, pers. comm.). The combined Borough and University area is 312 ha and the combined 10-year storm discharge estimate is 27 to 33 cms. In addition to the stormwater entering Thompson Run from above the Duck Pond, there is also stormwater draining into Walnut Spring Run, which then enters Thompson Run just before it crosses under East College Avenue and into Millbrook Marsh. Thompson Run also has two stormwater outlets just after East College Avenue, the point at which it enters the south western corner of the Marsh.
Two more stormwater entry points are located at the southeastern corner of Millbrook Marsh. One is located at the entrance to the upper parking lot of the State College Township Building, and one is at the lower level parking area, and includes the sheet drainage from the parking lot (Figure 3-3 and 3-4). This flows through a swale into the floodplain. These two stormwater outlets drain into the marsh itself, not into the associated streams.
At the south eastern corner of Millbrook Marsh one stormwater outlet drains into Slab Cabin Run at the crossing of East College Avenue. Approximately 60 m from East College Avenue is another stormwater outlet flowing into Slab Cabin Run.
Another stormwater outfall is located along the boundary adjacent to the Mt. Nittany Expressway about half way between Puddintown Road and East College Avenue. It is on the west side of the paved footpath, and drains into a short swale.
Figure 3-3 Parking lot drainage entry into southeast corner of Millbrook Marsh behind College Township Building.
Figure 3-4 Swath left in emergent wetland vegetation within 100-yr floodplain from parking lot drainage, southeast corner of Millbrook Marsh, College Township Building parking area drainage.
On to Water Quality