craig333
Riley's Human
As a lifelong resident of Sacramento I've seen some big floods or near floods. The American at 130,000 cfs (15,000cfs over capacity) was a sight to see. How the city and state have dealt with it is very interesting. While the Sacramento area is still very vulnerable it has a long history of flood control.
Scroll down to the timeline for some very interesting reading. Armed men blowing up dams and all.
http://www.water.ca.gov/newsroom/docs/WeirsReliefStructures.pdf
Just imagine if they hadn't built the bypass system when they did. No way you build one now.
The city also has fifteen flood control gates. You know its bad when these are closed.
Sacramento also depends on a network of 15 floodgates to keep the city dry when rivers rise. These seal off roadway openings in levees that allow traffic to flow in dry times.
The floodgates are closed only when rivers rise and begin to threaten low-lying areas. The gates are crucial to protect the city, but when closed they also limit evacuation routes.
The gates are manually operated and somewhat medieval in appearance. They take several hours to shut and require city workers to either close giant steel doors or place heavy boards into steel slots. Both types are then sealed with sandbags and plastic sheeting. These materials are stored with some gates, but in other cases must be transported from storage yards.
City transportation crews hold drills each fall to stay skilled at operating the gates as swiftly as possible.
One has been closed already.
Folsom dam is the other primary flood control structure. From wikipedia.
Folsom Dam was proposed as early as the 1930s under California's State Water Plan, in response to chronic flooding in low-lying Sacramento. The flood risk to the state capital had been exacerbated since the 1850s by hydraulic mining debris and the construction of levees to protect farms and towns, which reduced the channel capacity of the Sacramento and American Rivers.[24] The current dam was originally authorized by Congress in 1944 as a 355,000 acre·ft (438,000 dam3) flood control unit, and was reauthorized in 1949 as a 1,000,000 acre·ft (1,200,000 dam3) multiple-purpose facility.[25][26]
The current Folsom Dam replaced an earlier, smaller dam that had been completed in 1893 by Horatio Gates Livermore. The earlier dam had fed the Folsom Powerhouse, generating electricity that was transmitted to Sacramento over a 22 mi (35 km)-long distribution line, the longest electrical distribution system in the world at the time.[27] The remains of the earlier dam can be seen downstream from the Folsom Lake Crossing.
Construction of the dam began in 1951 with preliminary excavations for the Folsom Power Plant. The primary contract was awarded to Savin Construction Corp. of East Hartford, Connecticut, and Merritt-Chapman & Scott of New York for $29.5 million, with oversight by the U.S. Army Corps of Engineers. On October 29, 1952, the first concrete was poured for the foundation. Flooding washed out the temporary cofferdam three times in 1953, delaying work and causing damage to Nimbus Dam which was also under construction at the time. Water storage in Folsom Lake began in February 1955, and the final concrete in the main dam was poured on May 17, 1955. The first hydroelectric power was generated in September of that year. In order to acquire the necessary land in the future Folsom Lake bed, the government had to relocate families on 142 properties, including the settlements of Mormon Island and Salmon Falls.[24]
Even before the dam was complete, it demonstrated its effectiveness as a flood control facility during the record storms of December 1955, which completely filled Folsom Lake in a matter of weeks, and preventing $20 million of property damage. The dam was officially dedicated on May 5, 1956, and operation was transferred to the Bureau of Reclamation on May 14.[24][28]
Much of the calculations were made considering the American river watershed is relatively small and with little historical data < my own interpertation>.
During a severe storm in December 1964, the inflow into Folsom Lake reached a record high of 280,000 cu ft (7,900 m3) per second, with a river release of 115,000 cu ft (3,300 m3) per second.[32]
In February 1986, nearly 500,000 people faced the possibility of flooding when engineers at Folsom Dam were forced to open the spillway gates after heavy rains.[29] The flooding was made worse by the failure of the Auburn Dam cofferdam upstream which released an extra 100,000 acre feet (120,000,000 m3) into the American River. A peak flow of 250,000 cubic feet per second (7,100 m3/s) entered Folsom Lake, forcing operators at Folsom Dam to open all the spillway gates, releasing 130,000 cubic feet per second (3,700 m3/s) into the American River. This was 15,000 cubic feet per second (420 m3/s) above the safe capacity of downstream levees. Although the dam and the Sacramento levee system held without major damages, the requisite winter flood control space was increased 50%, from 400,000 to 600,000 acre feet, to protect against future floods. In addition, about 33,000 acre feet (41,000,000 m3) of sediment carried down from the mountains was deposited in Folsom Lake, considerably reducing its capacity. The consequence was a reduced capacity to store winter rainfall for summer use. Folsom Dam may have prevented as much as $4.7 billion in damages in 1986 alone.[33]
The New Year's Day storm of 1997 was the most severe in recent history, with a total inflow of 1 million acre feet (equal to the entire capacity of Folsom Lake) over a 5-day period. However, this time the Bureau of Reclamation was able to limit releases to less than 110,000 cubic feet per second (3,100 m3/s).[34] The 1997 storm was a classic example of a "rain on snow" event, during which a warm tropical storm melted existing snowpack at lower and middle elevations, effectively doubling the volume of runoff. Prior to the New Year's storm, the winter of December 1996 had also been one of the wettest ever recorded, saturating the ground and depositing a considerable amount of snow.[35][36]
The Bureau of Reclamation's Safety of Dams Program determined the risk of flooding in the Sacramento area made it one of the most at-risk communities in the United States.[37]
Two projects to increase flood protection are currently underway. The first will raise the surrounding dikes by 7 feet (2.1 m) to increase flood protection. The second, a new spillway, is designed to handle the runoff from large storms and snowmelt floods that might cause damage in the region. The new spillway is built with gates 50 ft (15 m) lower than the existing spillway, allowing for more efficient evacuation of reservoir storage before flooding events.[38][39]
The new spillway is complete or nearly so and it will be interesting to see if its put to use. Many of the small creeks have been channelized and concreted to help prevent local flooding. Seems to work fairly well until you get down to where they all come together.
Scroll down to the timeline for some very interesting reading. Armed men blowing up dams and all.
http://www.water.ca.gov/newsroom/docs/WeirsReliefStructures.pdf
Just imagine if they hadn't built the bypass system when they did. No way you build one now.
The city also has fifteen flood control gates. You know its bad when these are closed.
Sacramento also depends on a network of 15 floodgates to keep the city dry when rivers rise. These seal off roadway openings in levees that allow traffic to flow in dry times.
The floodgates are closed only when rivers rise and begin to threaten low-lying areas. The gates are crucial to protect the city, but when closed they also limit evacuation routes.
The gates are manually operated and somewhat medieval in appearance. They take several hours to shut and require city workers to either close giant steel doors or place heavy boards into steel slots. Both types are then sealed with sandbags and plastic sheeting. These materials are stored with some gates, but in other cases must be transported from storage yards.
City transportation crews hold drills each fall to stay skilled at operating the gates as swiftly as possible.
One has been closed already.
Folsom dam is the other primary flood control structure. From wikipedia.
Folsom Dam was proposed as early as the 1930s under California's State Water Plan, in response to chronic flooding in low-lying Sacramento. The flood risk to the state capital had been exacerbated since the 1850s by hydraulic mining debris and the construction of levees to protect farms and towns, which reduced the channel capacity of the Sacramento and American Rivers.[24] The current dam was originally authorized by Congress in 1944 as a 355,000 acre·ft (438,000 dam3) flood control unit, and was reauthorized in 1949 as a 1,000,000 acre·ft (1,200,000 dam3) multiple-purpose facility.[25][26]
The current Folsom Dam replaced an earlier, smaller dam that had been completed in 1893 by Horatio Gates Livermore. The earlier dam had fed the Folsom Powerhouse, generating electricity that was transmitted to Sacramento over a 22 mi (35 km)-long distribution line, the longest electrical distribution system in the world at the time.[27] The remains of the earlier dam can be seen downstream from the Folsom Lake Crossing.
Construction of the dam began in 1951 with preliminary excavations for the Folsom Power Plant. The primary contract was awarded to Savin Construction Corp. of East Hartford, Connecticut, and Merritt-Chapman & Scott of New York for $29.5 million, with oversight by the U.S. Army Corps of Engineers. On October 29, 1952, the first concrete was poured for the foundation. Flooding washed out the temporary cofferdam three times in 1953, delaying work and causing damage to Nimbus Dam which was also under construction at the time. Water storage in Folsom Lake began in February 1955, and the final concrete in the main dam was poured on May 17, 1955. The first hydroelectric power was generated in September of that year. In order to acquire the necessary land in the future Folsom Lake bed, the government had to relocate families on 142 properties, including the settlements of Mormon Island and Salmon Falls.[24]
Even before the dam was complete, it demonstrated its effectiveness as a flood control facility during the record storms of December 1955, which completely filled Folsom Lake in a matter of weeks, and preventing $20 million of property damage. The dam was officially dedicated on May 5, 1956, and operation was transferred to the Bureau of Reclamation on May 14.[24][28]
Much of the calculations were made considering the American river watershed is relatively small and with little historical data < my own interpertation>.
During a severe storm in December 1964, the inflow into Folsom Lake reached a record high of 280,000 cu ft (7,900 m3) per second, with a river release of 115,000 cu ft (3,300 m3) per second.[32]
In February 1986, nearly 500,000 people faced the possibility of flooding when engineers at Folsom Dam were forced to open the spillway gates after heavy rains.[29] The flooding was made worse by the failure of the Auburn Dam cofferdam upstream which released an extra 100,000 acre feet (120,000,000 m3) into the American River. A peak flow of 250,000 cubic feet per second (7,100 m3/s) entered Folsom Lake, forcing operators at Folsom Dam to open all the spillway gates, releasing 130,000 cubic feet per second (3,700 m3/s) into the American River. This was 15,000 cubic feet per second (420 m3/s) above the safe capacity of downstream levees. Although the dam and the Sacramento levee system held without major damages, the requisite winter flood control space was increased 50%, from 400,000 to 600,000 acre feet, to protect against future floods. In addition, about 33,000 acre feet (41,000,000 m3) of sediment carried down from the mountains was deposited in Folsom Lake, considerably reducing its capacity. The consequence was a reduced capacity to store winter rainfall for summer use. Folsom Dam may have prevented as much as $4.7 billion in damages in 1986 alone.[33]
The New Year's Day storm of 1997 was the most severe in recent history, with a total inflow of 1 million acre feet (equal to the entire capacity of Folsom Lake) over a 5-day period. However, this time the Bureau of Reclamation was able to limit releases to less than 110,000 cubic feet per second (3,100 m3/s).[34] The 1997 storm was a classic example of a "rain on snow" event, during which a warm tropical storm melted existing snowpack at lower and middle elevations, effectively doubling the volume of runoff. Prior to the New Year's storm, the winter of December 1996 had also been one of the wettest ever recorded, saturating the ground and depositing a considerable amount of snow.[35][36]
The Bureau of Reclamation's Safety of Dams Program determined the risk of flooding in the Sacramento area made it one of the most at-risk communities in the United States.[37]
Two projects to increase flood protection are currently underway. The first will raise the surrounding dikes by 7 feet (2.1 m) to increase flood protection. The second, a new spillway, is designed to handle the runoff from large storms and snowmelt floods that might cause damage in the region. The new spillway is built with gates 50 ft (15 m) lower than the existing spillway, allowing for more efficient evacuation of reservoir storage before flooding events.[38][39]
The new spillway is complete or nearly so and it will be interesting to see if its put to use. Many of the small creeks have been channelized and concreted to help prevent local flooding. Seems to work fairly well until you get down to where they all come together.
