Theme for 1995:
1995 Floods — What Happened and Why
Sierra College, Rocklin, CA
Use of Radar-Rainfall Extremes to Model the January 9-10, 1995 Floods in Sacramento
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In terms of potential economic impact and numbers of people threatened, Sacramento has one of the highest levels of flood risk of any city in the nation. The region currently faces a number of very difficult policy decisions regarding flood control and flood plain management.
From the magnitude of the rainfall and resulting flooding, local officials concluded that the region's second flood disaster in nine years could have a significant impact on policies guiding local flood risk management. Investigations were launched immediately to assess the January storm, to evaluate data collected since 1986, and to revisit flood plain policies established in the aftermath of the 1986 disaster.
The Floods of January 1995, in the Dry Creek Watershed, Placer County, California
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The storm and flood of January '95 were remarkable in other ways. The second largest flood, that of February 1986, had occurred just 9 years earlier in approximately the same area, with the same orientation and direction of flow of moist air feeding the system. It has been speculated that the state's topography and typical storm tracks may favor this particular area. If this were the case, it would be important to know in anticipating the potential for flooding over a long term both within and outside the area in question. Unfortunately, however, there is insufficient data to conclude with reasonable assurance that this is the case.
The 1995 Floods
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In conclusion, the 1995 winter storms were unique with respect to the breadth of unusually heavy precipitation statewide. The major flood control works of the Sacramento and San Joaquin Valley handled all the rain and runoff quite well. The main problems occurred on the smaller streams and on the unregulated or partially regulated rivers, especially in the North Bay and Central Coast regions. Intense local convective storms within the broader wet circulation did overload small streams and storm drainage facilities and produced some of the rare recurrence statistics which you have heard about from previous speakers.
The 1995 Water Year
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It was the wettest water year since 1983. The prolonged storminess was still with us in mid-June when Fairfield on June 15 had 3/4 inch hail and 1.63 inches of rain in 24-hours. This is a record one-day storm in June at Fairfield.
I will provide some facts about the water year and some historical perspective.
Overview of the Meteorology of Rain Events in California
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The purpose of this paper is to introduce the reader conceptually and, in cursory fashion, to the major rain-producing storm systems in California as outlined by Weaver (1962); it is not meant to be exhaustive. In fact, it is not even meant to be a summary of the oral presentation given by the author at the Symposium. Instead, the intent here is to gently remind the reader that much was understood about the general controls on flood events in California as early as the 1960's. Weaver's work is not merely an historical artifact; it should be resurrected and examined since operational meteorologists could learn much from it.
- Sierra College Science Center
- Floodplain Management Association