DISASTER RELIEF APPLICATION AND GEOLOGIC DATA FOR RECORD PRECIPITATION AND LANDSLIDE ACTIVITY IN PITTSBURGH, PA., FEBRUARY TO APRIL 2018

Record precipitation of 7.04” in February, 2018 set a rainfall record for what is usually the driest month of the year in the Greater Pittsburgh Area. This began a series of landslides and more wet weather that led to over 200 documented landslides from February through April, 2018. Storms in late March and April brought more rainfall and more landslides.

A State Disaster declaration was issued for Allegheny and Westmoreland Counties, and application made to FEMA for a federal declaration, which requires a higher level of economic loss. This was initially rejected, at least partially because the February and March-April rainfall clusters were considered separate events for purposes of disaster determination.

To appeal the initial denial, new data was required. A current Pennsylvania Geologic Survey project includes a GIS database of historic and modern landslide cases. Lists of landslide reports from several sources were combined in the GIS database, which allowed efficient elimination of duplicates, and sorting by date of occurrence or report.

Soil moisture monitoring data from a USGS / Pennsylvania Geological Survey project provided information on the relationship between soil moisture and precipitation events. Although soil moisture rose and fell with each precipitation event, the lower limit of each cycle increased through the spring. This supported the argument that the whole series be considered a single event, as the February storms provided a boost to soil moisture prior to the March-April storm sequence. The later storms seemed to require a lower threshold of rainfall to initiate landslides than the February series, suggesting that the continuing elevated base level of soil moisture was a contributing factor for initiation.

Most of the initial group of landslides in February were shallow soil and debris slides and flows. Several deep-seated slides destroyed houses and caused the well-publicized closure of the Lincoln Highway (US Route 30), a major commuter route, for approximately 3 months.

Much of the data were supplied by Francis Ashland of USGS, the Allegheny County Emergency Management office and the Pennsylvania Emergency Management Agency. These data were essential in the preparation of an appeal of the declined application to FEMA for disaster relief. Results are not known by the abstract deadline.