Rainfall totals approaching 9 inches

Heavy Upstream Rainfall Now Working Its Way Down

While no flooding in the Lake Houston Area is predicted at this time, the East and West Forks of the San Jacinto are swelling because of 5-9 inches of upstream rainfall–mostly to the north and northwest. As that stormwater works its way downstream, residents should be prepared to take action.

Cumulative rainfall totals including last three days. Note band of heavy rainfall up to almost 9 inches that will funnel down into the East and West Forks of the San Jacinto.

Meteorologists warned us that rainfall totals for Wednesday through Friday could creep upwards of 8-inches where cells started to train. And that is exactly what happened.

Since Wednesday, 7-9 inches of rain fell across southeast Grimes County and western Montgomery County into central Walker County. This caused significant rises on the upper and middle Spring Creek tributaries in northern Waller and southeast Montgomery Counties and Lake Creek. Rises are also ongoing along the West/East Forks of the San Jacinto River (see below).

The threat for additional heavy rainfall will shift south and east today.

Overall the trend in the Lake Houston Area for this afternoon, tonight, and Saturday will be for slowly decreasing rain chances and amounts.

Mainly San Jacinto Watershed Impacted

Because of frequent breaks and manageable rates in the rain, most watersheds have responded well. Getting 8 inches in three days is not as bad as getting 8 inches in three hours…especially when the grounds were so dry.

However totals have eventually piled up across northern Waller, western Montgomery, and central Walker Counties impacting mainly the San Jacinto River watershed. 

Spring Creek: 

Rises are ongoing along Spring Creek and its tributaries such as Mill, Walnut and Threemile Creeks. They are all producing high flows into Spring Creek from northern Waller, SE Grimes, and SW Montgomery Counties. While Spring Creek will rise today with these inflows, no significant flooding is expected. The channel capacity of the main creek is much larger and should be able to handle incoming inflows.

West Fork of the San Jacinto River: 

Inflows will be moving down Lake Creek which has recorded 7-9 inches of rainfall across the upper headwaters of the basin in western Montgomery County as well as local inflow below Lake Conroe Dam and ongoing minor releases from Lake Conroe (around 6,000 cfs this morning). The river is expected to rise to near 48.0 ft over the weekend as upstream run-off moves downstream. This is currently about 1 ft below flood stage at Humble (US 59).

From Harris County Flood Control Flood Warning System
East Fork of the San Jacinto River: 

Upstream run-off from Walker and San Jacinto Counites will move downstream toward New Caney (FM 1485) and Plum Grove over the next few days. The river is currently forecasted to rise above flood stage late this weekend and potentially approach moderate flood levels late Sunday into Monday.

The upstream rainfall could impact FM 1485 and low lying areas near the river downstream of the SH 99/FM 1485 bridge crossing.

Jeff Lindner, Harris County Meteorologist
Lake Conroe Report

Lake Conroe released water all day yesterday at more than 6000 cubic feet per second (CFS). Today, the rate has slowed slightly to just under 6000 CFS. The lake level is holding steady at 202.54 feet as of 4/7/23 at 10:40 AM. That’s about a foot and a half above its normal level.

The San Jacinto River Authority adopted a compromise lake lowering policy. In April, May, September and October, they are lowering Lake Conroe a half foot WHEN the City of Houston requests it. The releases are not as great, nor are they automatic as in previous years.

Lake Houston

Lake Houston opened all its floodgates on Tuesday and has released water steadily throughout this event. The lake level was at 41.7 feet at 9:30 AM. Normal is 42.4. So the precautions seem to have paid off. But a test still lies ahead.

Posted by Bob Rehak on 4/7/23

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