It is almost a mantra in Phoenix to hear news commentators speak of the "normally dry Salt River." The Gila/Salt River system drains most of southern Arizona. The Gila River is 649 miles long and has several major tributaries, including the Salt and Verde Rivers, the Agua Fria and the San Pedro. The reason they are normally dry by the time the rivers reach the desert is due to huge storage reservoirs in the mountains to the east of the Salt River Valley. Normally dry does not tell even part of the story however. In wet years, like 2010, the reservoirs fill completely with water and then any additional runoff goes down the dry river beds.
With a stellar lack of planning, the cities and towns in the Salt River Valley build their roads in the dry river bed, only to have them washed away every few years. The picture above is looking roughly north at the Salt River crossing at Gilbert Road in the east valley. The road was washed out about a year ago, but had been in service for several years before that. The bridge to the west is a replacement for other bridges that had washed away. It is handling the river flow, at the moment, with the river running at about 5500 cfs (cubic feet per second). If the river increases its flow to any greater extent (which is highly likely this year), the river will wash out both ends of the bridge and could, wash out the entire bridge.
In the picture, you can see where the water, in a much drier year, ran across the road where I was standing to take the picture. If the rains stop this year, and the weather stays cool, the run off from record snow falls may not flood. But if the weather warms up suddenly and it continues to rain, the runoff will have no place to go but down the Salt and Gila Rivers. Arizona is unique in that the dry river beds are called "rivers" but when there is water they are referred to as flooding. One difficulty in gauging the severity of the floods is the fact that various measures of water flow are used by different authorities. The Salt River Project uses cubic feet per second, but scientific journals talking about historic water levels use cubic meters per second roughly 27 times greater. It appears that the greatest floods ever recorded ran at about 4600 cubic meters per second or over 124,000 cubic feet per second.
Given the built up condition of the river bottom in the Salt River Valley, a flood of historic proportions would be interesting to say the least.
With a stellar lack of planning, the cities and towns in the Salt River Valley build their roads in the dry river bed, only to have them washed away every few years. The picture above is looking roughly north at the Salt River crossing at Gilbert Road in the east valley. The road was washed out about a year ago, but had been in service for several years before that. The bridge to the west is a replacement for other bridges that had washed away. It is handling the river flow, at the moment, with the river running at about 5500 cfs (cubic feet per second). If the river increases its flow to any greater extent (which is highly likely this year), the river will wash out both ends of the bridge and could, wash out the entire bridge.
In the picture, you can see where the water, in a much drier year, ran across the road where I was standing to take the picture. If the rains stop this year, and the weather stays cool, the run off from record snow falls may not flood. But if the weather warms up suddenly and it continues to rain, the runoff will have no place to go but down the Salt and Gila Rivers. Arizona is unique in that the dry river beds are called "rivers" but when there is water they are referred to as flooding. One difficulty in gauging the severity of the floods is the fact that various measures of water flow are used by different authorities. The Salt River Project uses cubic feet per second, but scientific journals talking about historic water levels use cubic meters per second roughly 27 times greater. It appears that the greatest floods ever recorded ran at about 4600 cubic meters per second or over 124,000 cubic feet per second.
Given the built up condition of the river bottom in the Salt River Valley, a flood of historic proportions would be interesting to say the least.
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