URBAN HYDROLOGY: A GIS STUDY OF FLOODING THAT OCCURRED ON JULY 26, 1988 IN THE SWEETBROOK DRAINAGE BASIN IN STATEN ISLAND, NY

Extensive flooding occurred as a result of an intense rainstorm in the 7.56km² Sweetbrook drainage Basin on the afternoon of July 26, 1988. Newspaper accounts of the storm indicate that the total rainfall for the 24hr period was 66.04mm with 50.8mm of rain falling between 1PM and 5PM. Effects of this urban flooding included eighteen parked cars in an apartment complex's parking lot that were swept up by the flood and piled in the front parking lot on top of one another. Using a GIS this author integrated topographic map data from 1899, 1955, 1966 and 1981 topographic maps to study the evolution of this drainage basin in order to determine the causes of this extreme flooding event. A comparison of these GIS topographic maps show increased urbanization in the drainage basin. They also reveal that the apartment complex described above was built directly on a second order tributary of the Sweetbrook sometime between 1955 and 1981. Between 1966 and 1981 there was further urbanization. Recently, the NYCDEP has mitigated future flooding in this basin with BMP's(Best Management Practices) of their bluebelt programs. However, this study clearly illustrates that urbanization of a drainage basin is the main cause of this extreme flooding.