Case Study Example 3:

Background

The scope of the project is to review the rain events near a switching yard, which is located in South Seattle close to Safeco Field. The goal is to determine if excessive amounts of rain occurred on 1-10- and the days leading up to 1-10- and to make a statement concerning the possibility of standing water in the area. We reviewed and analyzed rainfall data from 12-19- to 1-10- from the official weather stations at Seattle Boeing Field and Seattle Tacoma Airport, the two closest stations to the Stacy switching yard. We also reviewed the official climate data from the following US government agencies: NOAA Regional Climate Centers, Applied Climate Information Systems, and Western Regional Climate Center.

Rainfall Totals

The rainfall summaries and totals can be found in the appendix and found in exhibit number 1 through number 4. In summary, the period starting 12-19- and concluding at the end of the day on 1-10- can be defined as a significantly wet period for the Seattle area. Specifically:

Rainfall for Seattle Tacoma Airport, the official weather station for Seattle, was 11.07 inches for this period while the normal is 4.04 inches. Seattle Boeing Field had 11.45 inches of rain during the period. Thus the rainfall for this period exceeded the average rainfall by a factor of 2.75

At Seattle Tacoma Airport, 20 of the 23 days leading up to 1-10- had rainfall that equaled or exceeded the daily average rainfall.

For the two days on 1-9- and 1-10-, there was a combined rainfall of 2.09 inches of rain at Seattle Tacoma Airport and 2.38 inches at Seattle Boeing Field. The probability of this amount of rainfall occurring over a two day period is 1.5%

Steady rain occurred at Seattle Boeing Field on 1-9- from 7 pm till midnight a total of 0.52 inches fell in this short 5 hour period.

Due to the steady and above average rainfall on, during and before 1-10- the soil across the Seattle was so saturated that stormwater contributed significantly to the total flow into South Wastewater Treatment plant. This extreme additional stormwater flow into the King County sewer collection system during the first 14 days of January raised treated wastewater at South Plant to record levels.

Conclusions

The rainfall that occurred on 1-10- in the South Seattle area and the days prior was constant and exceeded the normal rainfall by a factor of 2.75. Thus given this and the moderate to heavy rainfall that occurred on 1-9- and on 1-10- it seems to be a fair assumption the ground would be saturated and that there would be standing water in many locations of South Seattle.

Rainfall totals in inches