Projects & Studies

Clear Creek Second Outlet Channel and Gated Structure

Why They’re Here

Located near S.H. 146, just north of the Clear Lake natural outlet at Kemah/Seabrook, the Clear Creek second outlet channel was built from Clear Lake into Galveston Bay so water levels in the lake would not be increased when a proposed upstream enlargement to Clear Creek occurred. Gates were constructed between Clear Lake and Galveston Bay to minimize changes to the existing environmental and hydraulic conditions between the lake and the bay. These conditions include salinity and sediment transport and the rate of tidal inflows from the bay.

FACT: The gates do not provide tidal or hurricane protection for lakeside or Clear Creek communities.

The Clear Creek Federal Flood Damage Reduction Project is a partnership project between the U.S. Army Corps of Engineers (the Corps), the Harris County Flood Control District (the Flood Control District), Galveston County, and Brazoria Drainage District #4. The Corps is the lead agency for this project.

The project was updated in 2013, and the proposed Clear Creek channel enlargement upstream of Clear Lake to Dixie Farm Road is not included. However, the second outlet gates will be operated by the Harris County Flood Control District in an effort to reduce flood levels produced from rainfall runoff.

Construction and Operation

The second outlet channel and gated structure were constructed by the U.S. Army Corps of Engineers. Gated structure construction began in May 1989 and was completed in March 1991. Construction on the second outlet channel began in August 1996 and was completed in July 1997. It was rehabilitated in 1997.

Operations of the second outlet channel and gated structure were transferred from the Corps to the Harris County Flood Control District on March 11, 1998, and accepted by the Flood Control District on April 21, 1998. In 2003, the Flood Control District built an on-site gate control and generator storage building and currently maintains the facility and makes ongoing improvements.

Storm Operation Plan

The Flood Control District’s Flood Watch staff monitors the conditions in the watershed using rainfall and state gages, as well as information available from other sources. The lake level rise is estimated using actual and predicted rainfall, actual water levels in the lake and upstream, and tide forecasts (see gage locations, top right). Using the operation criteria, the Flood Watch leader assesses the situation and provides instructions directly to the gate operator.

Operation Criteria

THE GATES ARE OPENED

  • When Clear Lake’s elevation is above +3.0 feet and exceeds Galveston Bay’s elevation.
  • When the Clear Lake elevation is higher than the Galveston Bay elevation by any amount, and a rise in the Clear Lake elevation is anticipated above +3.0 feet from rainfall exceeding 3 inches.
  • Once per month to exercise the gates, actuators and generator. This may be cancelled if the gates have been operated within the month for reasons listed above.

THE GATES ARE CLOSED

  • When the Clear Lake elevation is equal to, or lower than, the Galveston Bay elevation.
  • When the Clear Lake elevation is below +3.0 feet.
  • When sustained winds exceed, or are forecast by the National Weather Service (NWS) to exceed, 55 mph.
  • When Clear Lake’s elevation is rising and is anticipated to exceed +8.3 feet.
  • When the Galveston Bay elevation is forecast by the NWS to exceed +6.0 feet.

Facts

SECOND OUTLET CHANNEL

Length: 5,130 feet (about one mile)

Bottom: 15 feet deep, 120-140 feet wide

Top: 200-240 feet wide

Gated Structure

Total Length: 141 feet

Gates: Six roller gates, each 20 feet wide by 21 feet high

Powered By: Electric motors

Power Source: Reliant Energy (generator backup)

OPERATION

Normal Condition:  All six gates closed

Potential Flood:  All six gates open (no partial opening)

Time Need to Open/Close:   1.5 hours for all six gates (opened in pairs)

GATE OPERATORS

Primary: Harris County Flood Control District Staff

Back-up: City of Seabrook Public Words Department Staff

 

Gate Status Check

To check the status of the Clear Creek gates at any time, logon to the Flood Control District’s Flood Warning System at http://www.harriscountyfws.org/ and follow these steps:

1  Click the “+” sign in the upper left corner of the map to zoom in to the Clear Lake area.

2  Mouse over the gage at Hwy. 146 and select “More Information.” On the gage detail page, the “Gate Status” is shown in the upper right corner.