Thesis Defense: Joshua Simpson!

Originally from Illinois, Joshua Simpson served in the Illinois Army National Guard from 1999 to 2005, including a 12-month tour in Iraq. He was awarded the Purple Heart and an Army Commendation Medal. He then studied GIS and environmental science at Northern Illinois University and graduated in 2007. He moved to Seattle immediately after and, before enrolling at UW to study applied economics and GIS, he built hiking trails, mapped hiking trails and restored environments in the Puget Sound area.

For the past couple years, Simpson has been completing his graduate study at SEFS, and the public is invited to see him present his thesis tomorrow, May 30, at 2:30 p.m. in Anderson 22: “An Econometric Analysis of Sewer Backup Claims in Seattle.”

Joshua SimpsonAbout Simpson’s Research:
Seattle is known for its high occurrence of rainfall events, and most of them are low-intensity events. When it rains heavily, sewer backups occur and, by all accounts, that’s bad news. Damage claims are filed and, in some cases, the city will cover the amount of damage. Sewer backups caused $8 million of damage from August 2004 to March 2011. Most of the damage claims were due to three major storms that occurred within that timeline.

For his thesis, Simpson examined factors that explain the damage caused by those three storms using a rare events logistic regression model. Sewer backups are rare events in Seattle, as the highest claim-producing storm in the city produced 147 claims, while there are more than 180,000 parcels in Seattle. Simpson used the claims from the three storms and a random stratified sample of parcels throughout Seattle to explain the causes of the backups.

Rainfall and soil saturation variables explain most of the damage that occurred, but other factors such as demographic and sewer system variables explain the cause of backups. Simpson used a spatial econometric model to measure the causes of various levels of sewer backup damage. Rainfall, soil saturation, demographic and sewer system variables, as well as tree density, explain the various levels of damage that occurred within the stated time line.

The results of both models were combined together to produce an expected sewer backup damage amount for the sample parcels. This data, along with the separate results of both models, were used to create three maps that represent probabilities of backups (given the results of a particular storm), potential damage and Expected Sewer Backup Damage.

These maps and data can be used to prioritize preventative maintenance before a storm season. There are many other risks that face utility customers in Seattle, but focusing on this risk allows for the application of two econometric models. Such an approach has not been utilized to analyze the occurrence of sewer backups to date. With the results of Salathe et al. (2010) and Zhu (2012) that suggest that higher frequency and higher intensity storms will affect the Puget Sound area, the accumulation of data and the use of the best information can mitigate future damage caused by these storms.

Simpson’s committee chair is Professor Sergey Rabotyagov, and the other members are John Perez-Garcia, Robert Halvorsen and Terry Martin. So come out and support him tomorrow at 2:30 p.m. as he completes his latest chapter in life!

Map graphic © Joshua Simpson.

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