Check MCDD’s Story Map above, an interactive web feature with text, photos, and maps. It commemorates the 20-year anniversary of the 1996 flooding and covers flooding in the Districts from MCDD’s perspective. You can check it out in a bigger, separate window by clicking here.
The Districts have experienced four “100-year events” and two “500-year events” since 1894, the highest flood on record for the Columbia River at the Vancouver Gage. The names for these events can be misleading as history shows. Technically, a 100-year event has a 1-percent chance of occurring within any given year and a 500-year event has a 0.2-percent chance of occurring in any given year.
June 1894 Flood Event
Heavy precipitation throughout the Columbia River basin during the 1893-94 winter led to heavy snowpack. This was followed by a dry, warm spring resulting in a massive snowmelt. There was still heavy rainfall in the lower basin, contributing to the flooding. Water levels remained at major flood levels (31.3+ NAVD88) for 38 days. The Districts were not formed at this time.
May 1948 Flood Event
Heavy precipitation in the Columbia River basin throughout the winter led to heavy snowpack. Early spring had little precipitation and few warm days. May brought heavy rainfall and warm temperatures, which created heavy snowmelt in late May causing flooding throughout the entire basin. Water levels remained at major flood levels for 26 days. Levees/embankments breached in PEN 1, PEN 2, and MCDD.
June 1956 Flood Event
Persistent heavy precipitation in the Columbia River basin started in October of 1955 through February of 1956. Heavy rainfall in the northern Columbia basin continued in March. Snowpack in higher elevations started by the end of October, and by springtime snowpack was much higher than usual. Warm temperatures in late spring augmented the snowmelt. Water levels remained at major flood levels for 12 days. The Districts’ system performed well.
December 1964 Flood Event
Unusual cold weather in early December was followed by heavy snowfall. Subsequently there was warm, persistent, heavy rains later in the month. December rainfall that year was more than 3.5” above average in the Portland area. Water levels remained at major flood levels for 2 days. The Districts’ system performed well.
February 1996 Flood Event
The season had heavy snowfall, ice, and warmer temperatures earlier in the season. Floodwaters were fed by heavy rains and melting snow. The Portland Airport area received about 7 inches of rain in a four day period. The Willamette River reached 28.6 feet (WRD) in height and crested the downtown Portland seawall (33.8 NAVD88). The Districts’ system performed well, erosion and seepage were main concerns.