THE EFFECTS OF URBANIZATION ON RUNOFF AND DISCHARGE IN THE MILL CREEK WATERSHED, ERIE, PENNSYLVANIA

Mill Creek is a stream that flows northwest through the city of Erie, PA and empties out into Lake Erie. Following a disastrous flood in 1915, the city began construction of a tube 3.74 kilometers long to confine the stream to a concrete channel that directs the stream under the city. This tube acts as a funnel, collecting precipitation and runoff from the surrounding urban area and directing it into the lake. Its purpose is to protect against future flooding in the urban areas of Erie.

One way to understand the contribution of runoff by urban surfaces lies in the comparison of the highly urbanized areas to less urbanized areas. Two locations were selected to compare these broad areas. The first location is at Headwaters Park. Observation of aerial photographs determined approximately 88% of the watershed near Headwaters Park is a combination of grassland and forest. The second location, a more urbanized area, is immediately in front of the beginning of the Mill Creek tube. 52% of the surfaces in this portion of the watershed are impermeable. This is a 41% increase in impermeable surface area in this location since 1939. This increased area of urbanization, in conjunction with the channeling effect of the tube, leads to a potential increase in flood hazards. Consequently, limiting the amount of runoff urbanization contributes to Mill Creek is critical for flood hazard control.

To quantify changes in water level in both areas, two stream gauges were deployed, one at each location. The stream gauges used in this experiment work as pressure transducers, measuring the amount of water flowing over them by a change in pressure. The stream gauges work simultaneously, recording a data point every minute for easy comparison between gauges. In addition to the stream gauges, one tipping bucket rain gauge was placed on the roof of an academic building at Mercyhurst University, between the two stream gauges. Each rainstorm is recorded by the rain gauge, measuring the amount of precipitation. Changes in water levels during these events are recorded by the stream gauges. Additionally, variations in stream flow are further quantified by measuring the velocity of the stream using a propeller flowmeter. When combined with cross-sectional information, total discharge can be calculated. Data are currently being collected via all of the aforementioned methods.