EVALUATION OF FLOOD RECURRENCE IN THE CHEMUNG RIVER WATERSHED, NEW YORK

The Chemung River watershed comprises approximately 6490 km² in Steuben and Chemung Counties, NY and portions of surrounding counties in the southern tier of New York and northern Pennsylvania. The Chemung is a major tributary to the upper Susquehanna River. The USGS maintains 12 gauging stations within the watershed, some with records exceeding 100 years. An analysis of these records was completed to ascertain changes in flood recurrence and the magnitude of events in an effort to evaluate the impact of changes in watershed management in light of changing climate. Analysis of the record at Chemung, NY, the furthest downstream gauging station with records starting in 1904, shows peak annual flows ranging from 393 to 5352 m³ s^-1, and most commonly occurring in March and April. The three largest flows were found to be outliers with the next highest peak flow being 2656 m³ s^-1. Discharge values for a 25-year event are 2603 m³ s^-1 including outliers, and 2375 m³ s^-1 excluding outliers. A plot of peak annual flow versus year show a positive slope with an r² of 0.32 that is significant, indicating an increase in the magnitude of peak annual flows over time. An analysis of discharge for 10-year events using decadal data show a similar increase to peak flows with an r² of 0.66 that is significant. Using daily average flow data, monthly recurrence values were obtained for comparison. Discharge values for 10-year events range from a low value of 490 m³ s^-1 in August to a high of 1768 m³ s^-1 in March. The pattern shows the highest discharge values in the winter and early spring months, decreasing through the summer, increasing through the fall. With changing climate, a continued increase in peak discharges due to more rapid snow melt in the late winter and early spring is probable.