All floods are local
This is a fine report by Dennis Wyatt, managing editor of the Manteca Bulletin, on flooding in his vicinity, complete with a brief history of floods there. We can expect pronuncimientos from state, federal and agribusiness sources on the present weather impacts, but Wyatt's focus is the only one that really counts, because all floods are local. It remains to be seen if any paper in a northern California flood area produces a better report of what its readers need to know, now. If there is one thing you can say about journalism in San Joaquin County, it is that there are always a few reporters and editors on duty there that know water.
Badlands Journal editorial board
3-24-11
Manteca Bulletin
Flood releases swell rivers
Big runoff expected for New Melones
By Dennis Wyatt
Managing Editor
dwyatt@mantecabulletin.com
209-249-3532
http://www.mantecabulletin.com/news/article/22041/
Steady rain and continuing snow accumulation in the Sierra has prompted the Bureau of Reclamation to spill from all of their Central Valley Project reservoirs for flood control.
New Melones on the Stanislaus River was the last Bureau dam to impose flood releases. Spilling was scheduled to have started Tuesday. Rain is expected for the next four days with a high wind advisory through 5 p.m. today.
The Bureau had been holding back on New Melones releases due to releases coming from state and federal dams farther south along the San Joaquin River’s watershed. The strategy effectively prevents a repeat of the January 1997 episode when heavy releases from elsewhere on the San Joaquin River tributary system and the Stanislaus River releases hit at their confluence almost at the same time where the two rivers combine 11 miles south of Manteca triggering nine levee breaks and subsequently 80 square miles of flooding.
Conditions are also different this time. In 1996, a heavy December snowpack unexpectedly started melting when unseasonably warm weather occurred at the end of the month and on into early 1997 to rapidly fill New Melones. There were concerns the dam could be breached. It also was not raining in the valley but was dry and sunny.
New Melons as of Wednesday had only 567,000 acres feet of storage left in the 2.4-million acre-foot reservoir with increasing inflows. On top of that, the Department of Water Resources reported Tuesday that the projected runoff into New Melones between April and July will be between 630,000 and 1,120,000 acre feet.
Water level at Vernalis south of Manteca near the confluence of the Stanislaus and San Joaquin rivers was at 20.69 feet Wednesday at 11 p.m. Flood stage is 24.5 feet. The highest recorded level was 34.9 feet on Jan. 5, 1997.
The state started emergency levee repairs in January along the San Joaquin River near Durham Ferry in anticipation of a big spring run-off. Crews worked 24/7 to strengthen the levee that has failed a number of times since 1929.
The same stretch of levee also was stressed significantly in May of 2006. The levees were strengthened back then as well. No flooding occurred, though.
It is one of nine spots south of Manteca that failed during January of 1997 along the Stanislaus and San Joaquin rivers triggering the flooding of 80 square miles. There was $100 million in property damages, 2,000 people were evacuated, 20,000 head of cattle were relocated, and 800 homes and other structures sustained some form of water damage.
The northern Sierra that feeds the Sacramento River that has a much wider channel plus a series of bypasses is at 115 percent of normal in terms of the snowpack. The southern Sierra that runs off into the San Joaquin River, though, is at 140 percent of normal. The San Joaquin River channel lacks bypasses, has a narrower channel, and has more levees under stress.
The weakest part on the entire San Joaquin River section is just south of Manteca.
The area south of Manteca has flooded 11 times since 1929.
The biggest recorded flood in modern South County history started in 1950. It caused flooding west of present-day Interstate 5 in Lathrop. Flood waters threatened San Joaquin County Hospital and came within four miles of downtown Manteca. There were 2,000 people evacuated. Today, if the same flooding occurred, it would force 20,000 people to flee.