The National Weather Service outlook for the winter of calls for average precipitation and warmer than normal temperatures in the western United States. The Pineapple Express pattern can bring one to two weeks of stormy wet weather, followed by extended periods dominated by high pressure with generally dry conditions. This wet-dry pattern repeats itself every 45 to 60 days. Such neutral conditions were in play in January when a barrage of sub-tropical storms generated the worst flooding in history for California and Nevada.
A analysis by Jan Null, a Consulting Meteorologist and owner of Golden Gate Weather Services, reveals that in the past 30 years, San Francisco has had 18 severe storms that have dumped two inches or more of rain in hours.
Indicative of the increased chances for torrential rain this winter, twelve of these 18 storm events occurred during neutral years. Floods are common on the volatile Truckee River which has had 20 major floods in the last years, giving a statistical chance of a serious flood every 10 years or so. Since a handful of reservoirs have been built in the Truckee River watershed, which have boosted flood protection for downstream communities, but the system is still not foolproof.
Fifty-five years ago, Boca Reservoir stood alone as flood protector on the Truckee River. In , record setting rains before Thanksgiving overwhelmed the small solitary dam.
Torrents of water poured over Boca's spillway and added to the destructive flow rushing downstream. Damage in Floriston, Reno, and Sparks was extensive. Storms came unusually early in During September and October, precipitation in the northern Sierra exceeded percent of normal. By November the soil was saturated and snow lay four feet deep in the upper elevations.
On November 13, a moisture-laden, monster storm plowed in from the Pacific Ocean. A strong jet stream energized this potent weather system and forced the saturated air mass over the Sierra. Heavy snow fell in the mountains, but that soon turned to rain as the tropical nature of the storm grew more dominant. When this weather pattern stalled over Northern California, the stage was set for disaster. For nine consecutive days, heavy rain drenched the Sierra.
The tropic-like downpours quickly melted the high elevation snow pack in what hydrologists call a "wet mantle" flood event, where rain and melting snow combine to generate exceptional runoff. On the Sierra west slope, nearly 27 inches of rain fell at Blue Canyon. The normally peaceful, Yolo River, exploded into a raging torrent.
Floodwaters four feet deep flowing over Highway 40 closed the road at Cisco, 25 miles west of Truckee. About feet of Highway 50 was washed out near Twin Bridges. Both of these vital, trans-Sierra highways were shut down for 10 days.
Donner Lake soon hit flood stage and washed out the bridge over Donner Creek on southbound Highway 89, while Truckee's school closed when high water flooded the furnace. A massive mudslide near Emigrant Gap and a washout at Floriston forced Southern Pacific to cancel all trains over the Sierra. The luxury streamliner, City of San Francisco, was caught between the blockades and spent the night parked at Norden on Donner Pass.
Two years later this upscale passenger train would be trapped in snow for three days near Yuba Gap. Only United Airlines could offer transport from Reno to California. More than 10 inches of rain fell in Tahoe City in one week. Alex Cushing, a founder of the Palisades Tahoe ski area, and about 30 workers were trapped in the valley when Squaw Creek washed out both bridges into the valley.
Just as she edged out onto the bridge, the whole span collapsed into the muddy torrent. Fortunately for Mrs. Miller, the front bumper hooked on some debris and held the car until a tow truck arrived in time to pull her to safety.
Down river the floodwaters washed out feet of Highway At Verdi, the Highland ditch was dynamited to release floodwaters into nearby fields. Everyone could see that the Truckee River flood-control system had over-loaded. Reno residents and business owners were now vulnerable to the unchecked onslaught of the rampaging Truckee.
Floodwaters poured over the Virginia Street Bridge and washed out the Rock Street Bridge; soon all spans across the river were closed for safety. National Guard Troops joined emergency workers sandbagging the beleaguered city.
When emergency pumps in the basement of the Reno Evening Gazette failed, water poured in and flooded the presses. They managed to produce a single sheet, printed on both sides. Despite the flood, tourists still found their way into downtown casinos. Adventurous gamblers at the Mapes and Riverside casinos were seen playing slots dressed in rubber hip boots. Finally on Nov. Downtown Reno streets were piled high with muddy office furniture, equipment and Christmas goods that had been stored in the flooded basements.
There had been no warning to move supplies to higher ground. Deep water still covered the rich farmlands of the Carson Valley, but it was subsiding. Flood protectionSince additional reservoirs have been built in the Truckee River watershed, which have boosted flood protection for downstream communities, but the system is still not foolproof. Remember the devastating floods in Feb.
The observations from a Truckee Meadows farmer should be well-heeded. It comes in floods. Mark, a Carnelian Bay resident, can be reached at mark thestormking. Your financial contribution supports our efforts to deliver quality, locally relevant journalism. Now more than ever, your support is critical to help us keep our community informed about the evolving coronavirus pandemic and the impact it is having locally.
Every contribution, however large or small, will make a difference. Start a dialogue, stay on topic and be civil. Click around to see why:. Policies dictate how water is moved through the Truckee River reservoir system to downstream users. Separated from their natural enemies, non-native species—both flora and fauna, in water and on land—upset the natural balance of nature. Help identify and eradicate invasive flora. A healthy watershed is the best defense against severe weather. It holds water in a drought, reducing fire danger and providing wildlife habitat.
And it soaks up excess water during heavy rains, preventing erosion and run-off.
0コメント