Water levels on the San Joaquin River at the Mossdale Crossing in Lathrop will be increasing in the next few days.

And its not from the usual culprits which are releases from New Melones on the Stanislaus River and Don Pedro on the Tuolumne River.

Instead, it is Friant Dam on the San Joaquin River.

Water releases from the three dams on Friday were:

*18 cubic feet per second (cfs) from New Melones.

*532.99 cfs from Don Pedro.

*4,240 cfs from Friant.

The lingo “4,240 cfs”  means the water passing a given point in a second’s time from Friant is the equivalent of what roughly 4,240 basketball balls could hold.

The Bureau of Reclamation that operates both Friant and New Melones significantly increased water releases on Friday from Friant and plans to keep them near the 4,500 cfs level as more storms batter California. Turlock Irrigation District operates Don Pedro.

Water releases from upstream dams during heavy storms plays a pivotal role on the ability of levees along the San Joaquin River to protect areas in southwest Manteca and south of town, Lathrop, as well as Weston Ranch in Stockton.

And nowhere is that more critical than the stretch between the confluence of the Stanislaus and San Joaquin rivers at Vernalis some 11 miles southwest of Manteca and just south of the Airport Way bridge and Mossdale Crossing.

The timing of the releases can make matters worse.

In 1997, critics of the Bureau of Reclamation as well as state water officials say the slow response to increase water releases from New Melones and Don Pedro from unexpected steady warm rain in the higher elevation that  prematurely melted a much more robust than normal Sierra snowpack that accumulated in December was what caused levee failures that ended up flooded 70 square miles between Manteca and Tracy.

The levees — saturated with rainfall — failed on a sunny and warn early January day.

Due to the rapidly filling reservoirs that created the potential for the dams to be breached which would have led to a catastrophic situation, there were significant releases that took place almost concurrently with the flow ramped up in a fairly fast manner.

Even though heavy rainfall that could bring as much as 3 inches of rain to the Northern San Joaquin Valley and portions of the foothills is expected  Monday and Tuesday with rain in the forecast daily through at least Thursday, the situation is not the same as in 1997.

That’s because the drought has depleted capacity on New Melones and Don Pedro much more severely than the dry conditions that started off the 1996-1997 water year.

Friant — a 520,500 acre foot reservoir —was at 79 percent capacity Friday with 5,969 cfs of water flowing in and 4,240 cfs of water flowing out.

By contrast, the 2.4 million acre foot New Melones which is the most depleted of the state’s seven major reservoirs, was releasing only 18 cfs on Friday for the exclusive purpose of generating electricity.

At the same time, 7,320 cfs of water was flowing into New Melones that now has 753,860 acre feet of water. That put New Melones at 31 percent of capacity with storage 56 percent of normal for the date of Jan. 5.

The surge from Friant’s ramped up releases won’t start to mingle with that from Don Pedro on the Tuolumne until sometime this weekend,. The flood monitoring gauge at United States Geological Survey gauge at Vernalis where the Stanislaus joins the San Joaquin was at 14.5 feet and rising on Friday.

It had been as high as 17.7 feet on Jan. 3.

When the water level reaches 24.5 feet it triggers stepped up levee monitoring. Minor flood stage is at 29 feet, moderate flood stage is at 32 feet and major flood stage is at 37.3 feet.

To contact Dennis Wyatt, email dwyatt@mantecabulletin.com