Mount St. Helens, Washington
Summary of the Flood of February 8, 1996

The 1996 water year realized many periods of high water and flooding throughout Washington in a year of above normal precipitation. Baring, on the west slope of the Cascade Range, received over 150 inches of precipitation during the year, comparable to wetter places on the west side of the Olympic Mountains (National Oceanic and Atmospheric Administration, 1995). The wettest month was November, with some areas along the west slope of the Olympic Mountains and Cascade Range receiving over 30 inches of rain -- Baring received almost 41 inches (National Oceanic and Atmospheric Administration, 1995). November, along with February, also experienced the worst flooding in the State. At some stations, November produced the highest peak, but for most, it was in February. The combination of heavy rainfall and high snowmelt in February produced record-setting peak discharges at many stations in the southern half of the State. The driest months were March, June, and July. ...

Streamflows during November were above average throughout the State except for the northeast quarter, where they were average. Flows approached or exceeded peaks of record for some stations due to very heavy rainfall from three series of storms (November 5-8, 10-11, and 27-30). Several locations on the west side of the Olympic Mountains and Cascade Range received over 30 inches of rain during the month. About 10 inches of rain were recorded in the Puget Sound region. Peak streamflows on November 29-30 approached peaks of record in the Snoqualmie, Sauk, upper Nooksack, and Cowlitz River Basins and exceeded instantaneous peaks of record at some stations in the Skagit, lower Nooksack, and Wenatchee River Basins.

In December and January, rains continued, but precipitation averaged only slightly above normal in the State. Several stations on the west side of the Olympics received over 20 inches of rainfall in December and again in January. Streamflows averaged above the mean throughout the State in December and ranged from normal to above normal in January. Streamflow at several stations in small basins approached or exceeded instantaneous peaks of record in December -- Canyon Creek near Cedar Falls (station 12116100, December 4, 107 ft3/s, peak of record is 131 ft3/s), Boxley Creek near Edgewick (station 12143900, December 3, 260 ft3/s, new record), and Duckabush River near Brinnon (station 12054000, December 12, 9,240 ft3/s, new record). Arctic air moved into the State on January 27, producing some snow on January 27-29, but brought clearer skies and extremely cold temperatures afterward. The air temperature at Davenport, near Spokane reached -28 degrees Fahrenheight (degrees F) on January 31 (National Oceanic and Atmospheric Administration, 1996). Hydrographs for all stations in the State dropped during this period as freezing weather prevented snowmelt and, along with drier weather, reduced streamflows.

The cold weather continued into early February, but was soon replaced by a warmer, very wet series of storms February 5-9 that produced heavy rain, high rates of snowmelt, and record flooding throughout much of the State. Streamflows were above normal throughout Washington except for the northwest corner. Very heavy rains on February 5-9 -- Cougar, 18 inches; Packwood, 12 inches; Baring 15 inches; SeaTac, 6 inches; Plain, 6 inches (National Oceanic and Atmospheric Administration, 1996) on already saturated ground in western Washington, or on frozen ground in eastern Washington accompanied by snowmelt induced by the rain and warmer air (freezing levels above 6,000 feet) produced high flows at most stations in the State. On February 8-9, flows at many stations in the southern half of the State exceeded the peak flow of record. At a number of stations, such as in the Cowlitz Basin, peak February flows were just slightly higher than the near-record peak flows in late November. At many gaging stations in western Washington, the February flooding was the worst since November, 1990, when some stations in the Skagit and Nooksack River Basins in northern Washington recorded their peak discharges of record. At many eastern Washington stations, peak flows were below the peak of record, such as at Tucannon River near Starbuck (station 13344500, 5,580 ft3/s, on February 9, peak of record 7,980 ft3/s on December 22, 1964). At some stations where temperatures remained near freezing, only a little rise in streamflow was noted on February 8-9 (Methow River near Pateros).

Cowlitz River at Castle Rock

[Graphic,13K,GIF]
Flood of November-December 1995
-- stage adjusted to feet above sea level (NAVD88)

[Graphic,11K,GIF]
Flood of February 1996
-- stage adjusted to feet above sea level (NAVD88)

[Graphic,13K,GIF]
Flood of November-December 1995
-- stage in feet above gage

[Graphic,12K,GIF]
Flood of February 1996
-- stage in feet above gage

From: Dallas Childers, February 20, 1996
CVO FLOOD SUMMARY - Flood of February 8, 1996

Heavy snows accumulated in the Cascade Mountains in northwest Oregon and southwest Washington throughout late January and early February, 1996. During the storm, the snows extended to the lower elevations and were followed by freezing temperatures which were subsequently followed by freezing rain. The warm storm of February 5-8 dropped heavy rains on the frozen ground and snowpack resulting in very high rates of runoff causing severe flooding.

In the Toutle, Lewis and lower Cowlitz River basins, 5 gaging stations had the highest flows of record and 2 gages were destroyed by high flow.

Access to much of the CVO field area north of Vancouver was blocked by landslides in I-5 and other highways. Access to the Muddy River gage, which has lost its orifice line, is now only by helicopter. The S.F. Toutle River near Camp 12 gage house and cableway anchor were completely smashed and carried away by the flood. Two members of the flood crew slept in their truck Thursday night because of road blockages and full motels. A flood measurement could not be made at E.F. Lewis River near Heisson gage because the cable car was partially submerged by the flow. At Lewis River at Ariel, the gage was overtopped by the flood but recorded data was retrieved from the submersible recorder.

Telemetry from all gages functioned properly during the flood, except for the two lost gages, and data were provided to users through USGS/CVO WWW server, through normal satellite telemetry downlinks and through other pathways.

Exhausted field crews returned to the office Tuesday to compute measurements, process data and refurbish field equipment before returning to the field later in the day.

Two gages and one cableway need to be rebuilt.

Hazard Monitoring Network    Telemetry and Instrumentation
                                                                              
Station                      Type of instrumentation


14240304 Spirit Lake         lake level, precipitation    functioned ok
  at Tunnel                                               rain gage ok

14240307 Loowit Channel      acoustic flow monitor        functioned ok
 at Mount St. Helens                                      

 N.F. Toutle River           acoustic flow monitor        functioned ok
  at Maratta Creek

 N.F. Toutle River           acoustic flow monitor        functioned ok
  at Hoala

14240350 Coldwater Lake      lake level, precipitation    functioned ok
                                                          rain gage ok

14240446 Castle Lake East    lake level, precipitation    functioned ok
                                                          rain gage ok          

Streamflow Network
                                                                              
Gaging Station            Q meas.    Peak Q      Peak Stage    Comments
                          (cfs)      (cfs)       (feet)
                                                                              

14216500 Muddy River       2,260     42,000 est   32 est    lost gage orifice;
 below Clear Creek,                                         new peak of record.
 near Cougar, WA.                                        

14219800 Speelyai Creek    1,330      3,900 est    8.14     new peak of record.
 near Cougar, WA.                                         

14220500 Lewis River      56,700         *          *       peak overtopped
 at Ariel, WA.                                              gage.

14222500 East Fork                       *          *       new peak of record;
 Lewis River                                                lost gage house.
 near Heisson, WA.                                        

14240525 N.F. Toutle       7,740     13,500       62.13     new peak of record.
 River blw Sediment
 Retention Structure,
 Near Kid Valley, WA.

14240800 Green River                 12,000 est   15 est    gage discontinued;
 above Beaver Creek,                                        exceeds peak of
 near Kid Valley, WA.                                       record.

14241100 N.F. Toutle                                        gage discontinued;
 River at Kid Valley, WA.                                   exceeds peak of
                                                            record; research
                                                            platform destroyed.
                                                            
14241490 S.F. Toutle                     *          *       new peak of record;
 River at Camp 12,                                          lost gage house and
 near Toutle, WA.                                           cableway.

14242580 Toutle River     48,900     60,000 est   22.97     new peak of record
 at Tower Road,                                             at this site;
 near Silver Lake, WA.                                      new peak of record
                                                            mainstem Toutle 
                                                            (since 1919).
 
14243000 Cowlitz River    85,200    112,000       32.1      second 100-year 
 at Castle Rock, WA.      60,600                            flood during WY1996.


footnote:

*  not yet determined