Seasonal risk analysis for floodplains in the Delaware River Basin

Overland pollutant transport via surface runoff and flooding is a primary c oncern in the management of agricultural land resources in the Delaware Riv er Basin. The Catskills is home to multiple water reservoirs that supply th e drinking water for New York City. Contamination of this water by pollutan ts emanating from agricultural sources located in floodplain areas necessit ates risk quantification for these locations. This study was performed to a ssess the risk of rivers topping their banks, or flooding, during various t ime periods of the year. Streamflow data for seven stations were analyzed t o produce monthly partial duration and maximum series. A log-Pearson Type I I analysis was performed on the maximum and partial duration series to prod uce monthly probabilities of flooding. Based on the maximum series,on avera ge, March had the highest probability of Rood occurrence at 28%, and April and December had the next highest, at 18 and 12%, respectively. Larger floo d probabilities were calculated using the partial duration series, and this result was attributed to the tendency of some months to have multiple floo ds. Calculated yearly flood probabilities from monthly results agreed well with theoretical values. This study has important ramifications for decisio n making based on hydrologic risk of pollutant transport in floodplain soil s (e.g., this information is needed to determine surface water pollution ri sks from manure-spread agricultural fields and develop schedules to reduce this risk).